Download The Microbial Ecology of Dental Caries - Co

REVIEW ARTICLE
The Microbial Ecology of Dental Caries
G. H. W. Bowden
From the Department of Oral Biology, Faculty of Dentistry, University of Manitoba, 780 Bannatyne Avenue,
Winnipeg, Manitoba, Canada R3E 0W2
Correspondence to: George Bowden, Department of Oral Biology, Faculty of Dentistry, 780 Bannatyne Avenue,
Winnipeg, Manitoba, Canada R3E 0W2. Tel: + 1 204 789 3595; E-mail: george – [email protected]
Microbial Ecology in Health and Disease 2000; 12: 138–148
The microbial ecology of caries is complex and incorporates mechanisms common to the natural colonization of the host and to plaque
accumulation at sites that do not develop caries lesions. It is not simply accumulation of plaque in the oral cavity but also the ecology
of oral bacteria among the host population and the ecology of organisms in the lesion. In these three habitats odontopathogens and other
oral bacteria can undergo genotypic change, which may produce phenotypes more virulent or better able to survive specific evironments.
Adaptation and response to stress will also enhance bacterial survival and selection. Therefore, in these habitats diversity is generated and
this, coupled with adaptation, provides strains that are selected to be best suited to specific environments, including cariogenic
environments. In this way odontopathogens may be selected and become more numerous among hosts in a population. The most
common ecological mechanism associated with caries is bacterial succession, and dominance of the plaque community by mutans
streptococci. However caries is the outcome of interactions within the plaque community, host physiology, diet, fluoride, pH and the
nature of the tooth enamel, and dominance by mutans streptococci does not always produce a lesion. Caries can be reduced by bacteria
that degrade lactate or produce base from urea and salivary peptides, while other bacteria, including a group of ‘low pH’ streptococci
could lower the pH of plaque, and produce enamel demineralization. In addition, the plaque biofilm not only serves as a habitat but
includes in its structure a fluid phase (plaque fluid) and a matrix that have a direct influence on the physiology of plaque bacteria and
the formation of a lesion. Given the complexity of the microbial ecology of caries even with the elimination of mutans streptococci caries
would most likely persist, albeit at a significantly reduced level. Key words: biofilms, caries, microbial ecology, mutans streptococci,
plaque fluid.
INTRODUCTION
Microbial ecology describes the interaction between microorganisms and the structural, physical and biological
components of their habitats and infectious diseases
provide examples of the impact of ecology of specific
organisms on their host populations of plants or humans
and other animals. Moreover, disease promotes responses
from the host, changing the ecology between the host and
the bacteria, influencing the well-being and activities of the
host population (1). Examples of the responses of host
populations that affect microbial ecology include vaccination, to reduce the ability of bacteria to colonize the host
and delivery of fluoride in water and dental products that
modifies bacterial metabolism and reduces the incidence of
caries. Considering microbial ecology and its outcomes, at
the level of infectious disease with a specific pathogen
(2–5) makes it clear that complex mechanisms are involved and assessing their function in nature is a difficult
task. This problem is made more complex when, as is the
case with dental caries, odontopathogens are usually components of the resident flora of the host, unlike many other
overtly pathogenic bacteria.
Analysis of microbial ecology has been simplified to
some extent by limiting studies to a selected stage or
© Taylor & Francis 2000. ISSN 0891-060X
sequence of stages in the ‘life cycle’ of a specific bacterial
strain, a species, or a bacterial community. This approach
has been taken with oral microbial ecology, where study is
usually made of the stages of plaque accumulation, the
biology of specific bacteria or selected microhabitats, and
plaque physiology. However, studies of the ecology of oral
bacteria in caries have not been limited to their activities in
the mouth. A role for the human host population as a
reservoir for mutans streptococci (6) has been considered
in relation to transmission among hosts (7 – 9) and in
approaches to prevent caries in humans (10, 11). Also,
studies of antibiotic resistance and specific genes of individual strains of oral bacteria have revealed evidence for
transfer of genetic characters that enhances their diversity
(12 – 15). Furthermore, the ecology of caries includes not
only the processes that cause destruction of enamel but
also those that promote bacterial invasion of dentine.
Clearly, the microbial ecology of caries involves at least
three easily recognizable areas, 1. Bacterial ecology among
the host population, 2. The ecology of the plaque community, 3. The ecology of the community within the lesion.
Figure 1 shows the relationships between areas 1 and 2,
which determine the composition and contribute to the
microbial diversity of the oral flora of an individual host.
Microbial Ecology in Health and Disease
The microbial ecology of dental caries
There are several reviews and book chapters that discuss
the microbial ecology of caries (16–20). Consequently, this
review will try to emphasize and discuss areas that are
problematic and those that require more study.
THE COMPLEXITY OF ORAL MICROBIAL
ECOLOGY AND CARIES
A problem in understanding microbial ecology of caries is
that many of the events that lead to the development of a
caries lesion are common to those associated with healthy
enamel. In human nursing caries S. mutans can predominate at sites that develop a white spot and those that do
not. This can occur even at adjacent susceptible sites in the
same individual (21). Similarly, van Ruyen et al. (22) have
shown no significant difference between the numbers of
‘low pH isolates’ from white spot lesions and normal
enamel in subjects with caries. Explanations for such observations include suggestions for local environmental differences and ecological mechanisms that could modify the
microflora to reduce its cariogenic potential (17, 19, 20,
23). The significance of the presence of mutans streptococci, diet and dietary sucrose, fluoride, poor oral hygiene
and host antibodies on caries in 6i6o is well accepted.
However, some other factors that may be involved such as
1. Complex interactions among cells within the dental
plaque biofilm (24), 2. Novel expression of genes during
biofilm formation (25, 26), 3. Stress responses by oral
bacteria (27), and 4. The ability of bacteria to modify local
environments (23, 28) may often be supported predominately by findings in 6itro. Confirmation of their roles in
caries in animals or preferably in humans, is an important
topic for research in oral microbiology. In 6itro study of
mechanisms is essential to aid in developing strategies for
prevention and control of caries however, the true value of
139
any strategy has to be confirmed in 6i6o and preferably in
humans.
A second significant point is that although many aspects
of the caries process are common among hosts they may
be influenced by factors that reflect the individuality of a
person and their microflora. The common processes include adhesion, co-aggregation, growth and survival,
which are basic to bacterial colonization of the mouth
(29 – 32). However, genetic variation among hosts, their
habits and immunological history (e.g. disease, vaccination), together with the variety of habitats in a given
mouth, and the diversity among strains of species of oral
bacteria that colonize a host are unique to a person.
Therefore, while general observations can be made of
microbial ecology and the development of a carious lesion
it has to be recognized that host specific factors also
influence the process.
SIGNIFICANT FACTORS IN THE MICROBIAL
ECOLOGY OF CARIES
Before discussing microbial ecology and caries some of the
components and factors shown in Figures 1 and 2 should
be discussed. The final outcome of the interaction among
these different factors and processes at a specific site on
the dentition determines the formation, or not, of a caries
lesion.
The habitat
The oral cavity provides an excellent environment for the
growth and survival of bacteria. Although saliva is not a
complete nutrient for all oral bacteria some species or
consortia of species utilize it as a substrate (30, 33 – 36).
Other oral nutrients arise from gingival crevicular fluid
and desquamated mucosal cells. Also, in addition to these
Fig. 1. The stages involved in colonization of infants by oral bacteria from the host population and the factors that contribute to the
diversity among the bacterial populations within the oral cavity and the plaque biofilm.
140
G. H. W. Bowden
Fig. 2. Stages in the accumulation of dental plaque, including the factors that contribute towards the metabolic activities of the plaque
biofilm that determine the outcomes of oral microbial ecology in caries.
physiologically based nutrients, oral bacteria receive an
erratic input of variable substrate from the hosts’ diet, an
important factor in caries risk (37). Apart from the nutritional components of saliva there are molecules that enhance colonization and those that have an adverse effect
on oral bacteria (38–43). Saliva also acts as a buffer,
modifying plaque pH and reduced salivary flow, xerostomia and the variation in salivary flow over different tooth
surfaces can influence the formation of a caries lesion
(44–46). In addition fluoride, which can dramatically influence the carbohydrate metabolism of bacteria is a significant component of both saliva and plaque. Fluoride
delivery has proved to be one of the most important
anticariogenic strategies available, and its action is based
on modification of the ecology of bacteria and interaction
with enamel and tooth root (47).
The hard (enamel and tooth root) and soft (mucosal)
tissue surfaces in the mouth provide a variety of microhabitats with distinctly different structural and environmental
parameters. In particular, the non-shedding surface of
enamel allows the accumulation of a biofilm that provides
a protected habitat with a variety of niches that support a
wide range of bacterial genera and species (48, 49). The
plaque biofilm is an essential factor in the aetiology of
caries. The interactions among the bacteria in dental
plaque together with the variations in nutrient, buffer,
fluoride, concentrations of various ions and pH in the
biofilm determine the formation of a caries lesion.
In addition to forming the substratum for dental plaque
accumulation enamel and tooth root are the tissues that
are destroyed during the formation of a caries lesion. The
composition of enamel varies among teeth and even over
the surfaces of a single tooth. These variations include the
degree of mineralization and also the fluoride content (50,
51). Significantly, the composition of enamel is a determinant in its susceptibility to demineralization and consequently variation in enamel at a site can influence the
development of caries lesions (52).
Bacteria associated with caries in humans
These bacteria are opportunistic pathogens, found commonly as members of the resident flora of persons without
caries and expressing their pathogenicity only under specific environmental conditions. Streptococcus mutans and
Streptococcus sobrinus, two species of the ‘mutans streptococci’ are the most significant in human caries (16, 19, 53)
and studies of the microbial ecology of caries have been
directed principally at these species (21, 54 – 56). There is
The microbial ecology of dental caries
also a strong association between Lactobacillus spp. and
caries but little is known of the relative significance of the
different species.
It has been apparent for years that other genera and
species of oral bacteria can either be associated with caries
in humans, or cause caries in experimental animals (17, 22,
57–59). In particular, although S. mutans and S. sobrinus
are the principal agents of enamel caries, a wider range of
organisms is proposed as opportunist pathogens in root
surface caries. Generally the organisms other than mutans
streptococci and Lactobacillus associated with caries fall
into Streptococcus and Actinomyces.
Actinomyces odontolyticus, originally isolated from
caries lesions (60), colonizes infants before eruption of
teeth (61). An association between this species and progressing incipient interproximal caries lesions in humans
has also been shown (62). Some root caries lesions are
dominated by Actinomyces naeslundii and it has been
suggested that strains of this species could play a pathogenic role in this disease (63–66) and recently, A. israelii
and A. gerencseriae have also been shown to be present in
high numbers in root caries lesions (67). Schüpbach et al.,
(65) demonstrated the complexity of the bacterial community associated with root caries and most importantly, they
correlated the microflora to the state of lesions in extracted
teeth (66).
The other significant Streptococcus species involved in
caries includes Streptococcus mitis (58, 63) and a group of
‘low pH’ aciduric streptococci (68). Recently, these, and
other ‘low pH’ isolates (possibly Bifidobacterium and Actinomyces) have been isolated from white spot lesions in
humans (22).
In contrast to bacteria that lower plaque pH there are
others including Veillonella and Actinomyces that degrade
lactic acid, thereby increasing plaque pH and reducing its
cariogenicity. This proposed anti-caries mechanism has
been shown to be effective with Veillonella both in 6itro
and in an animal model (69–71). A second bacterial
process promoting an increase in plaque pH is the production of base from urea and the arginine containing peptides in saliva (31, 72). Oral streptococci and actinomyces
can be protected in low pH environments by expression of
urease (26, 73, 74). Recently, studies with recombinant
strains of S. mutans in experimental animals have shown
that urease production by strains contributed to reduction
of caries (75). Also, support for this ‘anticariogenic’ effect
comes from studies of plaque pH in 6itro and in 6i6o (76,
77) and from patients with chronic renal failure, who have
high levels of salivary urea and show a reduction in caries
(78).
Di6ersity among strains of species of oral bacteria
Although bacterial populations in oral microbial ecology
are often studied at the level of species, it is well accepted
that phenotypic characteristics among strains of bacterial
141
species can vary. Differences in phenotype may be important in caries if specific variants within the plaque community at localized sites on the dentition were ‘more
cariogenic’ or, in contrast, strains had increased capacities
to degrade lactate or produce base from urea and salivary
peptides, reducing the cariogenicity of plaque. In addition,
changes in the phenotypes in plaque could influence bacterial selection and survival (31, 79) and the overall (communal) activities of the plaque community (see below). In the
past variations among strains of a species were identified
by biochemical, physiological and antigenic differences.
Analysis of variation in their enzyme profiles or their
genomic DNA (31) has identified more recently individual
strains (clones). The DNA typing methods have been
valuable in showing the transmission and persistence of
clones of oral species within and among their host population and the diversity among clones of a species in a
habitat (8, 79, 80).
Variations in the genome of daughter compared to
parent cells can originate from mutation, transposition and
recombination and also integration of DNA from other
bacteria (79, 81). Therefore, the genome of strains within
oral species may differ, resulting in a species population
composed of clonal variants (31, 80, 82, 83). Commensal
bacteria, including oral opportunistic pathogens usually,
but not always, show more genetic diversity than overt
pathogens and very often several different clonal variants
will colonize a single host (31, 79). Interestingly, from the
aspect of colonization of a host population clones of oral
species can have a specific association with a limited group
of hosts (84, 85). Although there are data on clonal
diversity within oral species there is relatively little on any
relationship between such variation and the phenotype or
virulence of strains of oral opportunistic odontopathogens
(31).
In addition to generation of diversity through changes in
their genomic DNA strains of species of oral bacteria
colonizing a mouth may be influenced by ‘clonal replacement’. In ‘clonal replacement’ new clones replace the existing clones in a habitat and contribute to strain diversity
(79). ‘Clonal replacement’ may be more common on mucosal surfaces where cells are shed, compared to the dental
plaque biofilm, which provides a retentive and protected
habitat.
Adaptation by oral bacteria to en6ironmental parameters
Apart from ecological advantages provided to oral bacteria arising through changes in their genome they will also
adapt (phenotypic adaptation) and respond to environmental stress in order to survive. Generally, adaptive and
stress response mechanisms such as tolerance of acid,
starvation, oxygen, fluoride and expression of urease (26,
27, 31, 72, 73) that are common among strains of a species
can be regarded as having evolved to assist bacteria to
survive stresses common to their habitats (86). Phenotypic
142
G. H. W. Bowden
adaptation is usually transient and expressed only during
stress (31). However, stable adaptation to tolerate xylitol
by S. mutans has been shown in 6i6o and although xylitol
will normally inhibit the growth of S. mutans, xylitol
tolerant strains are selected when S. mutans is grown in
6itro on another carbohydrate (glucose) in the presence of
xylitol (87).
An important feature of adaptation and survival of
bacterial cells in sub-optimal growth environments (e.g.
low pH, heat, starvation), is expression of a range of
‘stress proteins’ (88–90). These proteins that promote the
survival of the cells in adverse conditions are the subjects
of extensive research. Relatively little is known of stress
proteins in oral bacteria, although information is accumulating (27). Significant to the current discussion is that
adaptation or response to stresses varies among different
oral species and among strains of a species, including
odontopathogens (91).
Responses by bacteria will also include the production
of different signaling molecules that influence the activities
of the cells within the population (92). Signaling molecules
include peptide pheromones that promote competence and
cell density dependent peptides in Gram positive and
N-acyl homoserine lactones in Gram negative cells (24).
These latter density dependent molecules are responsible
for ‘quorum sensing’ in bacterial populations, promoting
expression of genes when the population has reached a
specific cell density. In one case a molecule that seems to
act in a ‘quorum sensing’ manner has been demonstrated
in an in situ model of dental plaque (93).
The biofilm mode of growth
Dental plaque is a complex biofilm community where
bacterial populations exist as separated micro-colonies in
physiologically diverse environments. Biofilm cells exhibit
different characteristics from the same cells growing in
suspended culture (24). Together with demonstration of
the unique characteristics of biofilm cells has come the
recognition that bacteria in a biofilm can form a community where the spatially distributed populations may interact (24). Caldwell and his colleagues have described the
concept and implications of bacteria growing as communities (94). The activities of a community (communality) are
distinct from those of a simple mixture of the same bacterial populations and the community life style provides
advantages compared to those of the component populations. The range of habitats for colonization can be extended, resistance to stress and host defenses will increase,
and cooperative degradation of complex substrates can
take place (24). However, it is important to recognize that
the presence of an organism in a biofilm does not necessarily mean that it is part of a community. Some bacterial
populations could be present in their defined area of the
biofilm, physiologically isolated from other populations,
without interaction.
The composition of the plaque biofilm community is
directly related to the process of formation of a caries
lesion. Also, the presence of a biofilm is important in
governing the physical changes seen in enamel (95) during
the formation of a lesion. Gelatine gels and biofilms of
Streptococcus spp. have been used in 6itro to show the
importance of such coatings in caries lesion formation and
also, their interaction with different ions (96 – 99).
Biofilms consist of three physical components, cells,
extracellular matrix and a fluid that bathes both cells and
matrix. Although the knowledge of the bacterial populations in plaque is far from complete over 300 taxa have
been described. Relatively little is known of the composition of the extracellular matrix of plaque in 6i6o (100) but
given its relationship to the formation of lesions, the
composition of the matrix and factors controlling its composition and production would seem to be an important
area for research. However, there are in 6itro studies of the
structure and impact of bacterial polysaccharides on diffusion and demineralization (101 – 104). The fluid component
of plaque, plaque fluid, plays a significant role in caries
and microbial ecology. This fluid can be regarded as the
‘planktonic phase’ of dental plaque and as such its composition reflects not only the outcome of the physiological
and metabolic activities of the plaque microflora but also
the result of the dynamic interaction between these activities and tooth enamel. Importantly, differences in composition have been shown between plaque fluid from samples
of plaque from caries free and caries active persons after
sucrose rinses. Margolis & Moreno (105) discuss various
aspects of plaque fluid, including variation in composition
and the relationships between plaque fluid and demineralization and remineralization of enamel. Although methods
are available to analyze the composition of plaque fluid
from single tooth surfaces (106 – 108) relatively few studies
(97, 98) have been made of plaque fluid from mixed or
single culture in 6itro biofilms. Information on the influence that the composition of this fluid has on the physiology of biofilm cells and vice versa, would be very valuable.
In particular, the potassium levels in plaque fluid are
higher than those in saliva and extracellular potassium
levels influence bacterial metabolism (109 – 113). Plaque
fluid also probably acts as a ‘carrier’ for substrates, the
endproducts of bacterial metabolism and the signal
molecules that mediate interaction between bacterial cells.
It seems most likely that the channels that run through the
plaque biofilm (114) are conduits for plaque fluid.
The foregoing has emphasized some of the aspects of
microbial ecology that contribute to the complexity of the
biology of dental plaque and factors that can influence its
cariogenicity. Despite this potential complexity, caries remains a common problem in humans, suggesting that the
occurrence of one or more combinations of factors necessary to produce a lesion is also common. It is possible that
among these factors are those that may play a greater role
The microbial ecology of dental caries
than others. Given a normal resident flora, which would
include odontopathogens, one can consider diet to be one
such dominant factor (37). However, even under dietary
conditions that favour caries identical bacterial succession
may only produce a lesion on one of two adjacent susceptible sites in the same person (21).
MICROBIAL EVENTS LEADING TO THE
FORMATION OF A CARIES LESION
Plaque accumulation is a dynamic process and central to
the microbiology of caries is the concept that the plaque
community responds to autogenic (internal) and allogenic
(external) stimuli that modify the parameters of the niches
available for bacterial populations (16, 48). The changing
niches and interactions (24) result in sequential selection of
component populations (succession) within the community
of bacteria that develops to be in balance with its environment (climax community). Figure 2 shows the stages of
accumulation of dental plaque together with the factors
described above that can influence the ecology of the
microflora during the formation of a climax community,
and also the possible outcomes of such accumulation.
Two processes that are not mutually exclusive and may
be perhaps two stages of the same process can describe the
microbial ecology of caries. The most obvious, well described and easily understood is bacterial succession in an
environment (e.g. high carbohydrate, low salivary flow)
leading to local dominance by mutans streptococci, followed by enamel demineralization and cavitation, that
often involves Lactobacillus (16–20). This process probably accounts for the majority of caries lesions in humans.
The second process involves different species of bacteria
(22, 58, 59, 65, 66) and perhaps, the communal activities of
plaque. It is more speculative, with less evidence to support it, compared to dominance by mutans streptococci.
Both of these processes are illustrated in Figure 2 and
discussed below.
Dominance by mutans streptococci
The risk of caries in children is influenced by the oral
health status and attitudes of their care-givers (115), although isolation frequencies of odontopathogens in children may be independent of their socio-economic
background (116). The ease of transmission and colonization of infants and children by mutans streptococci could
be regarded as the earliest stage in the process leading to
dominance of plaque by these bacteria. Factors influencing
the transmission, oral colonization, caries risk and survival
of S. mutans among its hosts have been described (6, 7, 10,
11, 117, 118). Clones of S. mutans vary in virulence (119)
and selection or generation of more virulent clones of S.
mutans within the host population could also influence the
process of dominance by this species.
143
Adhesion and coaggregation
A wide variety of oral bacteria will have colonized the
mucosal surfaces of the oral cavity of infants prior to their
acquisition of S. mutans and S. sobrinus. Therefore, mutans streptococci adhering to the newly erupted non-shedding surfaces of teeth do so in competition with a wide
variety of established oral bacteria (29). Bacteriocin production is one mechanism that promotes colonization of S.
mutans in the presence of other bacteria (117) and detailed
analyses of these molecules has been made (120).
A second mechanism for adhesion of bacteria to the
dentition is by interaction with previously adherent bacteria, through a process described as co-aggregation (32).
Co-aggregation of S. mutans with Actinomyces has been
shown in 6itro (121) and Veillonella and S. mutans coaggregate in 6i6o (122).
Growth and response to the en6ironment
Although co-aggregation is significant it is only one of the
mechanisms that determines the composition of dental
plaque. Two other factors, the growth of bacterial cells in
plaque (30), and the survival of strains that cannot grow
(31, 79), also play important roles. There is a close association between diet and caries that identifies carbohydrate
and acid production by plaque as significant risk factors
for caries (19, 22, 37, 123). Dominance by S. mutans or S.
sobrinus in areas of the plaque biofilm indicates that a
strain or strains of these species occupy a favourable niche
with available carbohydrate and a low pH (16, 23). It is
the latter parameter that has featured predominantly in
explaining the etiology of caries. The relationship between
the ‘resting pH’ of plaque, the characteristics of the
Stephan Curve including the lowest pH level reached and
the time of recovery to the resting pH, are all related to
caries risk (123). Selection of aciduric bacteria in plaque
environments of low pH remains the central and fundamental concept in the microbial ecology of caries.
An unanswered question is whether S. mutans is always
responsible for the reduction in pH that gives it an ecological advantage in plaque. Other organisms such as the ‘low
pH’ group (22, 124) may initially lower the pH of the local
plaque environment and thereby promote dominance by
mutans streptococci. Some in 6itro data support a role for
other organisms in lowering the pH of communities of oral
bacteria sufficiently to decalcify enamel or promote dominance by mutans streptococci (121). Studies in humans
using a banding model also suggested that early enamel
decalcification, presumably resulting from low pH could
occur in the absence of S. mutans (57). However, in this
study colonization by mutans streptococci was more common as the bands were left on the teeth for longer periods,
suggesting that the early non-mutans organisms produced
an environment conducive to colonization by mutans
streptococci (125). Recently Van Ruyven et al. (22) have
144
G. H. W. Bowden
proposed a model for succession in caries that takes into
account carbohydrate intake, ‘low pH’ groups of bacteria
and mutans streptococci. In any event, there is substantial
evidence that succession in a suitable environment leads to
local dominance by mutans streptococci that is associated
with formation of a caries lesion.
As stated above, it is less easy to explain why under
apparently identical conditions, even in a child at high
caries risk, S. mutans dominance at an adjacent susceptible
site does not always lead to caries (21). In this case,
although the environment promoted dominance by the
organism, demineralization did not occur. As we have seen
above and in Figure 2 a variety of complex factors may be
involved in determining the formation of a lesion and
more data are available on some than others: 1. The time
of exposure to a ‘cariogenic’ plaque may be too short,
2. Salivary flow and fluoride levels at each site might be
different, 3. The composition and fluoride content of the
enamel at the sites may vary, 4. The local community or
individual bacterial populations may increase the plaque
pH at the ‘resistant’ site, 5. Strains of mutans streptococci
at the two sites may vary in virulence, 6. The plaque fluid
within the biofilm at the resistant site can provide a
different environment for the biofilm community and influence demineralization, 7. The sites may receive differing
levels of carbohydrate, 8. The populations of mutans streptococci may be in different spatial relationships to the
enamel surface, 9. Unknown chemical mediators that modify the physiology of S. mutans may be present in plaque at
the ‘resistant’ site.
Although there is a plethora of factors and interactions
that can influence dominance by S. mutans leading to the
formation of a caries lesion it is possible that at some
point this organism may be released from any constraints
of the community. A dominant microcolony might become
independent of the other populations in the community
and ‘control’ its own environment (126). This would mean
that essentially in a limited area the population could be
acting in a manner similar to cells in a biofilm in mono-associated gnotobiotic animals. The release of such a microcolony from any ‘community control’ may encourage
lesion formation.
Finally, a point worth noting is that mutans streptococci, like other oral bacteria can, in all probability,
survive in the plaque biofilm in the absence of an immediately available niche (31). These cells could take advantage
of any change in the environment that provided a suitable
niche and then move to dominance in the community.
THE INVOLVEMENT OF BACTERIA OTHER THAN
MUTANS STREPTOCOCCI IN CARIES
The results from several studies (see above) suggest that
other bacteria can also become dominant in plaque community and be associated with demineralization and for-
mation of a caries lesion. The common finding of a
predominant species in lesions suggests that the process of
selection, succession and dominance is independent of the
species involved. Again it is assumed that such succession
to dominance is based on selection in an environment of
low pH. However, there is some evidence that the pH
associated with root surface lesions may not necessarily be
any lower than that of plaque on normal enamel (127).
Also, early lesions of root caries seem to favour Actinomyces (65), which are generally less acid tolerant compared
to mutans streptococci (125, 128). Consequently, although
acid selection may operate, it may be less stringent in some
cases and favour bacteria that while being less aciduric
than mutans streptococci are still able to destroy tissue.
Also, it is known that other species and strains may be as
aciduric as mutans streptococci (22).
We lack evidence for caries being the result of the
collaborative activities of a community (communality), as
we usually tend to find dominance by a particular strain.
However it could be argued that communality is responsible for all caries lesions. The formation of a lesion is the
end result of a temporal process involving the bacterial
community and also the physiology of the host. Certainly,
other organisms and interactions (i.e. communality) are
invoked for reducing the cariogenicity of plaque. However,
as mentioned previously, the failure of these anti-cariogenic interactions and the loss of ‘communality’, which
promotes isolated activity by a specific odontopathogen
could promote caries.
The microbial ecology of the lesion
Bacteria decalcify enamel and tooth root and may follow
protein in the enamel, and invade dentine via the tubules
(95). It is well accepted that the microflora of lesions in
teeth and tooth roots is extremely complex and may vary
at different sites (65, 125, 129). Although decalcification is
a major factor involved in the initiation of enamel and
root caries, degradation of dentine probably involves proteolysis (130). Also, specific receptors allow Lactobacillus
to localize to exposed dentine, via collagen receptors (131)
and similar molecules may be present on other bacteria.
The results of Schüpbach et al. (66) are particularly significant when the possibility of succession in caries lesions is
addressed. These authors found different species to be
predominant in the flora of lesions of different severity,
suggesting that succession could occur during lesion formation. They present a detailed and logical discussion of
the microbiology of caries lesions based on their careful
sampling and extensive analysis of the microflora.
The populations in the lesion community may also be
spatially distributed in a manner similar to those in a
biofilm. Therefore, one could suggest that a range of
niches and microhabitats could equally well exist within a
lesion. Spatial distribution could be one explanation of the
finding of the same patterns of distribution of ribotypes of
The microbial ecology of dental caries
A. naeslundii, in samples from enamel, root and caries
lesions of individuals (80), although in one case they have
been shown to have different phenotypes (79). The emphasis that has been placed on the mechanisms involved in the
initiation of caries lesions in enamel is easily understood in
terms of designing strategies to prevent caries. However,
the microbial ecology of the stages of dentine destruction
presents an equally fascinating area for study.
CONCLUSIONS
The microbial ecology of caries includes the biology of
oral bacteria within three related habitats 1. The host
population, 2. The oral cavity of individuals and 3. The
caries lesion. The distribution of odontopathogens among
the host population influences the colonization of infants
and children. Caries in an individual is characterized by a
series of interactions and succession within the plaque
biofilm as the populations respond to environmental
changes and succession probably also occurs in the lesion.
The population interactions are complex and apart from
the commonly known mutualism, competition etc. involve
stress responses, adaptation, variation in gene expression,
genetic variation and probably ‘quorum sensing’. All of
these can result in selection of bacteria, including odontopathogens best suited to the environment, which in some
cases is conducive to caries. Modulation of the microbial
ecology of caries using relatively simple approaches such
as oral hygiene, diet control and fluoride are very effective.
Perhaps that is because they modulate the oral bacterial
community so that the bacteria cannot adapt, (oral hygiene), or control a significant parameter (diet) or adaptation reduces the cariogenicity of odontopathogens
(fluoride). Other approaches to modulate the flora and
control caries e.g. antibacterials (132), immune mechanisms (133), replacement therapy (134) are attractive and
more sophisticated in concept and delivery. However, in
general these approaches are directed at mutans streptococci and although their use would make significant reductions in caries, they may not eliminate the disease. As we
have seen, oral microbial ecology is complex and other,
somewhat forgotten bacteria, could assume the role of
mutans streptococci in caries.
REFERENCES
1. Locker D, Clarke M, Payne B. Self-perceived oral health
status, psychological well-being and life satisfaction in an
older population. J Dent Res 2000; 79: 970–5.
2. Finlay BB, Falkow S. Common themes in microbial pathogenicity revisited. Microbiol Mol Biol Rev 1997; 61: 136 – 69.
3. Brumell JH, Steele-Mortimer O, Finlay BB. Bacterial invasion. Force feeding by Salmonella. Curr Biol 1999; 9: R277 –
80.
4. Meyer TF. Pathogenic neisseriae: complexity of pathogenhost cell interplay. Clin Inf Dis 1999; 28: 433–41.
5. Rosenberg R, ed. Microbial Ecology and Infectious Disease.
Washington:
American
Society
for
Microbiology,
Washington, DC, 1999.
145
6. Keene HJ, Folsom KS, Basel DA, Puente ES. Primary
reservoirs of Streptococcus mutans and their relationship to
caries experience in adults with good oral health. Oral
Microbiol Immunol 1990; 5: 19 – 23.
7. Caufield PW, Cutter GR, Dasanayake AP. Initial acquisition
of mutans streptococci by infants: evidence for a discrete
window of infectivity. J Dent Res 1993; 72: 37 – 45.
8. Redmo Emanuelsson I, Wang X. Demonstration of identical
strains of mutans streptococci within Chinese families by
genotyping. Eur J Oral Sci 1998; 106: 788 – 94.
9. Redmo Emanuelsson I, Thorhqvist E. Genotypes of mutans
streptococci tend to persist in their host for several years.
Caries Res 2000; 34: 133 – 9.
10. Köhler B, Andreen I, Jonsson B. The effect of caries preventive measures in mothers on dental caries and the oral
presence of the bacteria Streptococcus mutans and lactobacilli in their children. Arch Oral Biol 1984; 29: 879 – 83.
11. Köhler B, Andreen I, Jonsson B. The earlier the colonization
by mutans streptococci, the higher the caries prevalence at 4
years of age. Oral Microbiol Immunol 1988; 3: 14 – 7.
12. Reichmann P, König A, Liñares J, Alcaide F, Tenover FC,
McDougal L, Swidsinski S, Hakenbeck R. A global gene
pool for high-level cephalosporin resistance in commensal
Streptococcus species and Streptococcus pneumoniae. J Infect
Dis 1997; 176: 1001 – 12.
13. Hackenback R, König A, Kern I, van der Linden M, Keck
W, Billot-Klein D, Legrand R, Scoot B, Gutman L. Acquisition of five high Mr penicillin-binding protein variants of
high-level b-lactam resistance from Streptococcus mitis to
Streptococcus pneumoniae. J Bacteriol 1998; 180: 1831 – 40.
14. Poulsen K, Reinholdt J, Jespergaard C, Boye K, Brown TA,
Hauge M, Kilian M. A comprehensive genetic study of
streptococcal immunoglobulin A 1 proteases: evidence for
recombination within and between species. Infect Immun
1998; 66: 181 – 90.
15. Hanley SA, Aduse-Opoku J, Curtis M. A 55-Kilodalton
immunodominant antigen of Porphyromonas gingi6alis has
arisen via horizontal gene transfer. Infect Immun 1999; 67:
1157 – 71.
16. Bowden GHW. Which bacteria are cariogenic in humans?
In: Johnson NW, ed. Risk Markers for Oral Diseases, Vol 1
Dental Caries. Cambridge: Cambridge University Press,
1991: 266 – 86.
17. Bowden GHW, Edwardsson S. Oral ecology and dental
caries. In: Thylstrup A, Fejerskov O, eds. Textbook of
Clinical Cariology, 2nd Ed. Copenhagen: Munksgaard,
1996: 45 – 69.
18. Marsh PD. Microbiology of dental plaque and its significance in health and disease. Adv Dent Res 1994; 8: 263 –71.
19. Van Houte J. Role of microorganisms in caries etiology. J
Dent Res 1994; 73: 672 – 81.
20. Hamilton IR. Ecological basis for dental caries. In: Ellen R,
Kuramitsu H, eds. Oral Bacterial Ecology: The Molecular
Basis. Wymondham: Horizon Scientific Press, 2000: 219 –74.
21. Milnes AR, Bowden GH. The microflora associated with the
developing lesions of nursing caries. Caries Res 1985; 19:
289 – 97.
22. van Ruyven FOJ, Lingström P, van Houte J, Kent R.
Relationship among mutans streptococci, ‘low pH’ bacteria
and iodophilic polysaccharide-producing bacteria in dental
plaque and early enamel caries in humans. J Dent Res 2000;
79: 778 – 84.
23. Burne RA. Oral streptococci… products of their environment. J Dent Res 1998; 77: 445 – 52.
24. Marsh PD, Bowden GHW. Microbial community interactions in biofilms. In: Lappin-Scott H, Gilbert P, Wilson M,
146
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
G. H. W. Bowden
Allison D. eds, Community Structure and Co-operation in
Biofilms. Society for General Microbiology Symposium series. Cambridge:Cambridge University Press, 2000: in press.
Burne RA, Chen y-TM, Penders JEC. Analysis of gene
expression in Streptococcus mutans biofilms in 6itro. Adv
Dent Res 1997;11:100-9.
Li Y-H, Chen Y-YM, Burne RA. Regulation of urease gene
expression by Streptococcus sali6arius growing in biofilms.
Environ Microbiol 2000; 2: 169–77.
Svensäter G, Sjögreen B, Hamilton IR. Multiple stress responses in Streptococcus mutans and the induction of general
and stress-specific proteins. Microbiology 2000; 146: 107 – 17.
Marsh PD, Bradshaw DJ. Physiological approaches to the
control of oral biofilms. Adv Dent Res 1997; 11: 176 – 85.
Ofek I, Doyle RJ. Adhesion of bacteria to oral tissues. In:
Bacterial Adhesion to Cells and Tissues. London: Chapman
and Hall, London, 1994:195-238.
Bowden GHW, Li Y-H. Nutritional influences on biofilm
development. Adv Dent Res 1997; 11: 81–99.
Bowden GHW, Hamilton IR. Survival of oral bacteria. Crit
Rev Oral Biol Med 1998; 9: 54–85.
Kolenbrander PE, Anderson RN, Clemans DL, Whittaker
CJ, Klier CM. Potential role of functionally similar coaggregation mediators in bacterial succession. In: Newman HN,
Wilson M, eds. Dental Plaque Revisited Oral Biofilms in
Health and Disease. Cardiff: Bioline, 1999: 171–86.
Van der Hoeven JS, de Jong MH, van Nieuw Amerongen A.
Growth of oral microflora on saliva from different glands.
Microb Ecol Hlth Dis 1989; 2: 171–80.
Van der Hoeven JS, Camp PJ. Synergistic degradation of
mucin by Streptococcus oralis and Streptococcus sanguis in
mixed chemostat cultures. J Dent Res 1991; 70: 1041 – 4.
Bradshaw DJ, Homer KA, Marsh PD, Beighton D.
Metabolic cooperation in oral microbial communities during
growth on mucin. Microbiology 1994; 140: 3407–12.
Byers HL, Tarelli E, Homer KA, Beighton D. Isolation and
characterisation of sialidase from a strain of Streptococcus
oralis. J Med Microbiol 2000; 49: 235–44.
van Palenstein Helderman WH, Matee MI, van der Hoeven
JS, Mikx FH. Cariogenicity depends more on diet than the
prevailing streptococcus species. J Dent Res 1996; 75: 535 –
45.
Scannapieco FA. Saliva-bacterium interactions in oral microbial ecology. Crit Rev Oral Biol Med 1994; 5: 203 – 48.
Rudney JD. Does variability in salivary protein concentrations influence oral microbial ecology and oral health? Crit
Rev Oral Biol Med 1995; 6: 343–67.
Marcotte H, Lavoie MC. Oral microbial ecology and the
role of salivary immunoglobulin A. Microbiol Mol Biol Rev
1998; 62: 71 – 109.
Tenovuo J. Antimicrobial function of human saliva-how
important is it for oral health? Acta Odontol Scand 1998; 56:
250 – 6.
Helmerhorst EJ, Hodgson R, van’t Hof W, Veerman ECI,
Allison C, van Nieuw Amerongen A. The effects of histatinderived basic antimicrobial peptides on oral biofilms. J Dent
Res 1999; 78: 1245–50.
Ayad M, van Wuyckhuyse BC, Minaguchi K, Raubertas
RF, Bedi GS, Billings RJ, Bowen WH, Tabak LA. The
association of basic proline-rich peptides in saliva from the
human parotid gland with caries experience. J Dent Res
2000; 79: 976 – 82.
Dawes C, Watanabe S, Biglow-Lecomte P, Dibdin GH.
Estimation of the velocity of the salivary film at some
different locations in the mouth. J Dent Res 1989; 68:
1479 – 82.
45. Macpherson LMD, Dawes C. Effects of salivary film velocity on pH changes in artificial plaque containing Streptococcus oralis, after exposure to sucrose. J Dent Res 1991; 70:
1230 – 4.
46. Dawes C, Macpherson LMD. The distribution of saliva and
sucrose around the mouth during use of chewing gum and
the implications for the site-specificty of caries and calculus
deposition. J Dent Res 1993; 72: 852 – 7.
47. Fejerskov O, Ekstrand J, Burt BA. eds. Fluoride in dentistry. Copenhagen: Munksgaard, Copenhagen 1996.
48. Bowden GHW, Ellwood DC, Hamilton IR. Microbial ecology of the oral cavity. In: Alexander M, ed. Advances in
Microbial Ecology, vol 3. New York: Plenum Press, 1979:
135 – 217.
49. Theilade E. Factors controlling the microflora of the healthy
mouth. In: Hill MJ, Marsh PD, eds. Human Microbial
Ecology. Boca Raton: CRC Press Inc., 1990: 2 – 48.
50. Weatherell JA, Robinson C, Hallsworth AS. Variations in
the chemical composition of human enamel. J Dent Res
1974; 53: 180 – 92.
51. Li J, Nakagaki H, Tsuboi S, Kato S, Huang S, Mukai M,
Robinson C, Strong M. Fluoride profiles in different surfaces of human permanent molar enamels from a naturally
fluoridated and a non-fluoridated area. Archs Oral Biol
1994; 39: 727 – 31.
52. Tucker K, Adams M, Shaw L, Smith AJ. Human enamel as
a substrate for in 6itro acid dissolution studies: influence of
tooth surface and morphology. Caries Res 1998; 32: 135 –40.
53. Loesche WJ. Role of Streptococcus mutans in human dental
decay. Microbiol Rev 1986; 50: 353 – 80.
54. Lang KP, Hotz PR, Gusberti F, Joss A. Longitudinal,
clinical and microbiological study on the relationship between infection with Streptococcus mutans and the development of caries in humans. Oral Microbiol Immunol 1987; 2:
39 – 47.
55. Radford JR, Ballantyne HM, Nugent Z, Beighton D,
Robertson M, Longbottom C, Pitts NB. Caries-associated
micro-organisms in infants from different socio-economic
backgrounds in Scotland. J Dent 2000; 28: 307 – 12.
56. Sigurjóns H, Magnúsdóttir MO, Holbrook WP. Cariogenic
bacteria in a longitudinal study of approximal caries. Caries
Res 1995; 29: 42 – 5.
57. Boyar RM, Thylstrup A, Holmen L, Bowden GHW. The
microflora associated with the development of initial enamel
decalcification below orthodontic bands in 6i6o in children
living in a water-fluoridated area. J Dent Res 1989; 68:
1734 – 8.
58. Nyvad B, Kilian M. Microflora associated with experimental
root surface caries in humans. Infect Immun 1990; 58:
1628 – 33.
59. Marsh PD, Featherstone A, McKee AS, Hallsworth AS,
Robinson C, Weatherell JA, Newman HN, Pitter AFV. A
microbiologcal study of early caries of approximal surfaces
in schoolchildren. J Dent Res 1989; 68: 1151 – 4.
60. Batty I. Actinomyces odontolyticus, a new species of actinomycete regularly isolated from deep carious dentine. J Pathol
Bacteriol 1958; 75: 455 – 9.
61. Sarkonen N, Könönen E, Summanen P, Kanervo A, Takala
A, Jousimies-Somer H. Oral colonization with Actinomyces
species by two years of age. J Dent Res 2000; 79: 864 –7.
62. Boyar R, Bowden GHW. The microflora associated with the
progression of incipient caries lesions in teeth of children
living in a water-fluoridated area. Caries Res 1985; 19:
298 – 306.
63. Bowden GH, Ekstrand J, McNaughton B, Challacombe SJ.
The association of selected bacteria with the lesions of root
surface caries. Oral Microbiol Immunol 1990; 5: 346 – 51.
The microbial ecology of dental caries
64. Bowden GHW. Microbiology of root surface caries in humans. J Dent Res 1990; 96: 1205–10.
65. Schüpbach P, Osterwalder V, Guggenheim B. Human root
caries:microbiota in plaque covering sound, carious and
arrested carious root caries. Caries Res 1995; 29: 382 – 95.
66. Schüpbach P, Osterwalder V, Guggenheim B. Human root
caries: microbiota of a limited number of root caries lesions.
Caries Res 1996; 30: 52–64.
67. Brailsford SR, Lynch E, Beighton D. The isolation of Actinomyces naeslundii from sound root surfaces and root carious lesions. Caries Res 1998; 32: 100–6.
68. Sansone C, Van Houte J, Joshipura K, Kent R, Margolis
HC. The association of mutans streptococci and non-mutans
streptococci capable of acidogenesis at low pH with dental
caries on enamel and root caries. J Dent Res 1993; 72:
508 – 16.
69. Mikx FMH, van der Hoeven JS, König KG, Plasschaert
AJM, Guggenheim B. Establishment of defined microbial
ecosystems in germ-free rats. Caries Res 1972; 6: 211 – 23.
70. Mikx FHM, van der Hoeven JS, Walker GJ. Microbial
symbiosis in dental plaque studied in gnotobiotic rats and in
the chemostat. In: Stiles HM, Loesche WJ, O’Brien TC, eds.
Microbial Aspects of Dental Caries. Sp.Supplement Microbiology Abstracts Vol III. Washington: Information retrieval
Inc., Washington 1976:763–71.
71. van der Hoeven JS, Toorop AI, Mikx FHM. Symbiotic
relationship of Veillonella alcalescens and Streptococcus mutans in dental plaque in gnotobiotic rats. Caries Res 1978;
12: 142 – 7.
72. Marquis RE. Oxygen metabolism, oxidative stress and acidbase physiology of dental plaque biofilms. J Ind Microbiol
1995; 15: 198 – 207.
73. Sissons CH, Hancock EM. Urease activity in Streptococcus
sali6arius at low pH. Archs Oral Biol 1993; 38: 507– 16.
74. Morou-Bermudez E, Burne RA. Genetic and physiologic
characterization of urease of Actinomyces naeslundii. Infect
Immun 1999; 67: 504–12.
75. Clancy KA, Pearson S, Bowen WH, Burne RA. Characterization of recombinant, ureolytic Streptococcus mutans
demonstrates an inverse relationship between dental plaque
ureolytic capacity and cariogenicity. Infect Immun 2000; 68:
2621 – 9.
76. Sissons CH, Wong L, Shu M. Factors affecting the resting
pH of in 6itro human microcosm dental plaque and Streptococcus mutans biofilms. Archs Oral Biol 1998; 43: 93 – 102.
77. Imfeld I, Birkhed D, Lingström P. Effect of urea in sugarfree chewing gums on pH recovery in human dental plaque
evaluated with three different methods. Caries Res 1995; 29:
172 – 80.
78. Peterson S, Woodhead J, Crall J. Caries resistance in children with chronic renal failure; plaque pH, salivary pH and
salivary composition. Pediatr Res 1985; 19: 796–9.
79. Bowden GHW. Oral biofilm an archive of past events? In:
Newman HN, Wilson M, eds. Dental Plaque Revisited Oral
Biofilms in Health and Disease. Cardiff: Bioline, 1999: 211 –
35.
80. Bowden GHW, Nolette N, Ryding H, Cleghorn BM. The
diversity and distribution of the predominant ribotypes of
Actinomyces naeslundii genospecies 1 and 2 in samples from
enamel and from healthy and carious root surfaces of teeth.
J Dent Res 1999; 78: 1800–9.
81. Arber W. Genetic variation: molecular mechanisms and
impact on microbial evolution. FEMS Microbiol Rev 2000;
26: 1 – 7.
82. Westegren G, Krasse B, Birkhed D, Edwardsson S. Genetic
transfer of markers for sorbitol (D-glucitol) metabolism in
oral streptococci. Arch Oral Biol 1981; 26: 403–7.
147
83. Colby SM, Harrington DJ, Russell RRB. Identification and
genetic characterisation of melibiose-negative isolates of
Streptococcus mutans. Caries Res 1995; 29: 407 – 12.
84. Haubek D, Dirienzo JM, Tinoco EM, Westergaard J, López
NJ, Chung C-P, et al. Racial tropism of a highly toxic clone
of Actinobacillus actinomycetemcomitans associated with juvenile periodontitis. J Clin Microbiol 1997; 35: 3037 – 42.
85. Acton RT, Dasanayake AP, Harrison RA, Li Y, Roseman
JM, Go RC, Wiener H, Caufield PW. Associations of MHC
genes with levels of caries-inducing organisms and caries
severity in African-American women. Hum Immunol 1999;
60: 984 – 9.
86. Rainey PB, Moxon ER, Thompson IP. Intraclonal polymorphism in bacteria. In: Gwynfryn Jones J, ed. Advances in
Microbial Ecology, Vol 13. New York: Plenum Press, 1993:
263 – 300.
87. Trahan L. Xylitol: a review of its action on mutans streptococci and dental plaque-its clinical significance. Int Dent J
1995; 45: 77 – 92.
88. Bearson S, Bearson B, Foster JW. Acid stress responses in
enterobacteria. FEMS Microbiol Lett 1997; 147: 173 – 80.
89. Hecker M, Volker U. Non-specific, general and multiple
stress resistance of growth-restricted Bacillus subtilis cells by
the expression of the sigma B regulon. Mol Microbiol 1998;
29: 1129 – 36.
90. Segal G, Ron EZ. Regulation of heat shock response in
bacteria. Ann N Y Acad Sci 1998; 851: 147 – 51.
91. Hamilton IR, Svensäter G. Acid-regulated proteins induced
by Streptococcus mutans and other oral bacteria during acid
shock. Oral Microbiol Immunol 1998; 13: 292 – 300.
92. Dunny GM, Winans SC. eds, Cell-cell Signaling in Bacteria.
Washington:American Society for Microbiology Press,
Washington, DC, 1999.
93. Liljemark WF, Bloomquist CG, Reilly BE, Bernards CJ,
Townsend DW, Pennock AT, LeMoine JL. Growth dynamics in a natural biofilm and its impact on oral disease
management. Adv Dent Res 1997; 11: 14 – 23.
94. Caldwell DE, Atuku E, Wilkie DC, Wivcharuk KP,
Karthikeyan S, Korber DR, Schmid DF, Wolfaardt GM.
Germ theory vs community theory in understanding and
controlling the proliferation of biofilms. Adv Dent Res 1997;
11: 4 – 13.
95. Thylstrup A, Fejerskov O. Clinical and pathological features
of dental caries. In: Thylstrup A, Fejerskov O, eds. Textbook of Clinical Cariology, 2nd. Ed. Copenhagen: Munksgaard, Copenhagen. 1996: 111 – 48.
96. Ingram GS, Silverstone LM. A chemical and histological
study of artificial caries in human dental enamel in 6itro.
Caries Res 1981; 15: 393 – 8.
97. Bowden GH, Spiers RL, Nash R. Modification of the release
of calcium and phosphate from enamel by deposits of dextran-producing streptococci. Caries Res 1972; 6: 81 – 2.
98. Rose RK, Turner SJ, Dibdin GH. Effect of pH and calcium
concentration on calcium diffusion in streptococcal model
plaque biofilms. Archs Oral Biol 1997; 42: 795 – 800.
99. Assinder SJ, Dibdin GH, Marshall M, Shellis P. An in vitro
system for the analysis of changes in depth distribution of
diffusates in bacterial films. Caries Res 1998; 32: 255 – 61.
100. Guggenheim B, Schroeder HE. Biochemical and morphological aspects of extracellular polysaccharides produced by
cariogenic streptococci. Helv Odont Acta 1967; 11: 131 –51.
101. Cury JA, Rebello MAB, Del Bel Cury AA. In situ relationship between sucrose exposure and the composition of dental
plaque. Caries Res 1997; 31: 356 – 60.
102. Zero DT, van Houte J, Russo J. The intra-oral effect on
enamel demineralization of extracellular matrix material syn-
148
103.
104.
105.
106.
107.
108.
109.
110.
111.
112.
113.
114.
115.
116.
117.
G. H. W. Bowden
thesized from sucrose by Streptococcus mutans. J Dent Res
1986; 65: 918 – 23.
Dibdin GH, Shellis RP. Physical and biochemical studies of
Streptococcus mutans sediments suggest a new factor linking
cariogenicity of plaque with its extracellular polysaccharide
content. J Dent Res 1988; 67: 890–5.
Van Houte J, Russo J, Prostak KS. Increased pH-lowering
ability of Streptococcus mutans cell masses associated with
extracellular glucan-rich matrix material and the mechanisms
involved. J Dent Res 1989; 68: 451–9.
Margolis HC, Moreno EC. Composition and cariogenic
potential of dental plaque fluid. Crit Rev Oral Biol Med
1994; 5: 1 – 25.
Carey CM, Chow LC, Tatevossian A, Vogel GL. Extracellular potassium concentrations in human dental plaque fluid
recovered from single sites. Archs Oral Biol 1988a; 33:
493 – 8.
Carey CM, Gregory TM, Tatevossian A, Vogel GL. The
buffer capacity of single-site resting, human dental-plaque
fluid. Archs Oral Biol 1988b; 33: 487–92.
Vogel GL, Carey CM, Chow LC, Tatevossian A. Microanalysis of plaque fluid from single-site fasted plaque. J Dent
Res 1990; 69: 1316–23.
Keevil CW, West AA, Bourne N, Marsh PD. Inhibition of
the synthesis and secretion of extracellular glucosyl- and
fructosyltransferase in Streptococcus sanguis by sodium ions.
J Gen Microbiol 1984; 130: 77–82.
Wang YB, Germaine GR. Effects of pH, potassium, magnesium, and bacterial growth phase on lysozyme inhibition of
glucose fermentation by Streptococcus mutans 10449. J Dent
Res 1993; 72: 907–11.
Iwami Y, Guha-Chowhury N, Yamada T. Effect of sodium
and potassium ions on intracellular pH and proton excretion
in glycolyzing cells of Streptococcus mutans NCTC 10449
under strictly anaerobic conditions. Oral Microbiol Immunol
1997; 12: 77 – 81.
Russell JB, Diez-Gonzalez F. The effects of fermentation
acids on bacterial growth. Adv Micro Physiol 1998; 39:
205 – 34.
Barnard JP, Stinson MW. Influence of environmental conditions on hydrogen peroxide formation by Streptococcus gordonii. Infect Immun 1999; 67: 6558–64.
Wood SR, Kirkham J, Marsh PD, Shore RC, Nattress B,
Robinson C. Architecture of intact natural human plaque
biofilms studied by confocal laser scanning microscopy. J
Dent Res 2000; 79: 21–7.
Mattila ML, Rautava P, Silanpää M, Paunio P. Caries in
five-year-old children and associations with family-related
factors. J Dent Res 2000; 79: 875–81.
Radford JR, Ballantyne HM, Nugent Z, Beighton D,
Robertson M, Longbottom C, Pitts NB. Caries-associated
microorganisms in infants from different socio-economic
backgrounds in Scotland. J Dent 2000; 28: 307–12.
Gronroos L, Saarela M, Matto J, Tanner-Salo U, Vuorela
A, Alaluusua S. Mutacin production by Streptococcus mutans may promote transmission of bacteria from mother to
child. Infect immun 1998; 66: 2595–600.
.
118. Li Y, Wang W, Caufield PW. The fidelity of mutans streptococci transmission and caries status correlate with breastfeeding experience among Chinese families. Caries Res 2000;
34: 123 – 32.
119. Köhler B, Krasse B. Human strains of mutans streptococci
show different cariogenic potential in the hamster model.
Oral Microbiol Immunol 1990; 5: 177 – 80.
120. Krull RE, Chen P, Novak J, Kirk M, Barnes S, Baker J,
Krishna NR, Caufield PW. Biochemical structural analysis
of the lantibiotic mutacin II. J Biol Chem 2000; 275: 15845–
50.
121. Crowley PJ, Fischlschweiger W, Coleman SE, Bleiweis AS.
Intergeneric bacterial coaggregations involving mutans streptoccci and oral actinomyces. Infect Immun 1987; 55: 2695–
700.
122. McBride BC, van der Hoeven JS. Role of bacterial adherence in colonization of the oral cavities of gnotobiotic rats
infected with Streptococcus mutans and Veillonella alcalescens. Infect Immun 1981; 33: 467 – 72.
123. Johansson I, Birkhed D. Diet and the caries process. In:
Thylstrup A, Fejerskov O, eds. Textbook of Clinical Cariology, 2nd Ed. Copenhagen: Munksgaard, 1996: 283 – 99.
124. Lingström P, van Ruyven FOJ, van Houte J, Kent R. The
pH of dental plaque in its relation to early enamel caries and
dental plaque flora in humans. J Dent Res 2000; 79: 770–7.
125. Bradshaw DJ, Marsh PD. Analysis of pH-driven disruption
of oral microbial communities in 6itro. Caries Res 1998; 32:
456 – 62.
126. Shapiro JA, Dworkin M. eds. Bacteria as Multicellular
Organisms. New York: Oxford University Press, New York,
1997.
127. Scheie A, Luan W-M, Dahlén G, Fejerskov O. Plaque pH
and microflora of dental plaque on sound and carious root
surfaces. J Dent Res 1996; 75: 1901 – 8.
128. Svensäter G, Larsson U-B, Grief ECG, Cvitkovitch DG,
Hamilton IR. Acid tolerance response and survival by oral
bacteria. Oral Microbiol Immunol 1997; 12: 266 – 73.
129. Edwardsson S. Bacteriological studies on deep areas of
carious dentine. Odont Revy 1974; 25 (Suppl.32): 1 – 143.
130. Tjäderhane L, Larjava H, Sorsa T, Uitto V-J, Larmas M,
Salo T. The activation and function of host matrix metalloproteinases in dentine matrix breakdown in caries lesions. J
Dent Res 1998; 77: 1622 – 9.
131. McGrady JA, Butcher WG, Beighton D, Switalski LM.
Specific and charge interactions mediate collagen recognition
by oral lactobacilli. J Dent Res 1995; 74: 649 – 57.
132. Scheie A. Chemoprophylaxis of dental caries. In: Thylstrup
A, Fejerskov O, eds. Textbook of Clinical Cariology, 2nd.
Ed. Copenhagen: Munksgaard, 1996: 311 – 24.
133. Hajishengallis G, Michalek SM. Current status of a mucosal
vaccine against dental caries. Oral Microbiol Immunol 1999;
14: 1 – 20.
134. Hillman JD, Brooks TA, Michalek SM, Harmon CC, Snoep
JL, Der Weijden CC. Construction and characterization of
an effector strain of Streptococcus mutans for replacement
therapy of dental caries. Infect Immun 2000; 68: 543 – 9.