Download Pathogenic enteric Gram

Chair of Microbiology, Virology, and Immunology
PATHOGENIC AND
CONDITIONALLYPATHOGENIC ENTERIC
GRAM-NEGATIVE BACTERIA.
ESCHERICHIA. SALMONELLA.
Lecturer Prof. S.I. Klymnyuk
The Enterobacteriaceae contain gram negative
rodswhich, if motile, are peritrichously flagellated. Because
members of this family are morphologically and
metabolically similar, much effort has been expended to
develop techniques for their rapid identification. In general,
biochemical properties are used to define a genus, and
further subdivision frequently is based on sugar fermentation
and antigenic differences. Yet, many paradoxes exist, for
example, more than 2200 species of Salmonella have been
named, whereas the equally complex species Escherichia
coli is divided into more than 1000 serotypes. Over the
years, many taxonomists with different ideas have been
involved in the classification of these bacteria, and
disagreement still exists concerning family and generic
names.
Classification of the Enterobacteriaceae
Genera
Escherichia
Edwardsiella
Shigella
Salmonella
Citrobacter
Enterobacter
Serratia
Providencia
Yersinia
Klebsiella
Hafnia
Proteus
Morganella
Erwinia
Biochemical Properties Used for Classification
Early taxonomic schemes relied heavily on the organism's
ability to ferment lactose, and numerous differential and
selective media have been devised to allow one to recognize
a lactose fermenting colony on a solid medium. The
effectiveness of such differential media is based on the fact
that organisms fermenting the lactose form acid, whereas
nonlactose fermenters use the peptones present and do not
form acids m these media. The incorporation of an acid base
indicator into the agar medium thus causes a color change
around a lactose fermenting colony. Thus has been a valuable
technique for selecting the major non lactose fermenting
pathogens that cause salmonellosis or shigellosis, under
special conditions, however, many lactose fermenters also
cause a variety of infectious diseases.
Furthermore, many enterics ferment lactose only slowly,
requiring several days before sufficient acid is formed to
change the indicator. They all synthesize beta galactosidase,
(the enzyme that splits lactose into glucose and galactose)
but lack the specific permease necessary for the transport of
lactose into the cell One can easily determine whether an
organism is a slow lactose or nonlactose fermenter by
mixing a loopful of bacteria with orthonitrophenol beta
galactoside (ONPG) dissolved in a detergent. The linkage of
the galactose in ONPG is the same as its linkage m lactose,
inasmuch as the ONPG can enter the cell in the absence of a
permease, an organism possessing beta galactosidase will
hydrolyze ONPG to yield galactose and the bright yellow
compound, orthonitrophenol. Thus, only the absence of a
specific lactose permease differentiates the slow lactose
fermenters from the normal lactose fermenters.
In addition, a number of selective media have been devised that
contain bile salts, dyes such as brilliant green and methylene blue,
and chemicals such as selenite and bismuth. The incorporation of
such compounds into the growth of medium has allowed for the
selective growth of the enterics while inhibiting the growth of
gram positive organisms.
Some other biochemical properties used to classify members of the
Enterobacteriaceae include the ability to form H2S; decarboxylate
the ammo acids lysine, ornithine,or phenylalanine, hydrolyze urea
into CO2 and NH3, form indole from tryptophan; grow with citrate
as a sole source of carbon; liquefy gelatin; and ferment a large
variety of sugars.
Serologic Properties Used for Classification
No other group of organisms has been so extensively classified on
the basis of cell surface antigens as the Enterobacteriaceae. These
antigens can be divided into three types, designated O, K, and H
antigens.
O ANTIGENS. All gram-negative bacteria possess a
lipopolysaccharide (LPS) as a component of their outer
membrane. This toxic LPS (also called endotoxin) is
composed of three regions, lipid A, core, and are peating
sequence of carbohydrates called the O antigen. Based on
different sugars, alpha- or beta-glycosidic linkages, and the
presence or absence of substituted acetyl groups, Escherichia
coil can be shown to possess at least 173 different O antigens,
and 64 have been described in the genus Salmonella.
Sometimes, after continuous laboratory growth, strains will,
through mutation, lose the ability to synthesize or attach this
oligosaccharide O antigen to the core region of the LPS. This
loss results in a change from a smooth colony to a rough
colony type, and it is referred to as an S to R transformation
Interestingly, the R mutants have lost the ability to produce
disease.
K ANTIGENS. K antigens exist as capsule or envelope
polysaccharides and cover the O antigens when present,
inhibiting agglutination by specific O antiserum. Most K
antigens can be removed by boiling the organisms in water.
H ANTIGENS. Only organisms that are motile possess H
antigens because these determinants are in the proteins that
makeup the flagella. However, to complicate matters,
members of the genus Salmonella alternate back and forth to
form different H antigens. The more specific antigens are
called phase 1 antigens and are designated by lower-case
letters (a, b, c, and so on), whereas the less-specific phase 2 H
antigens are given numbers. The mechanism of this phase
variation reveals an interesting way in which a cell
canregulate the expression of its genes. In short, Salmonella
possesses two genes. H1 encoding for phase 1 flagellar
antigens, and H2 encoding for phase 2 flagellar antigens.The
transcription of H2 results in the co-ordinate expression of
gene rhl, which codes for a repressor that preventsthe
expression of H 1.
About every 103 to 10s generations, a 900-base-pair region,
containing the promoter for the H2 gene, undergoes a sitespecific inversion, stopping the transcription of both H2 and
rhl. In the absence of the rhl gene product, the H1 gene is
then transcribed until the 900-base pair region in the H2
promoter is again inverted, resulting in the expression ofH2
and rhl.
After obtaining the serologic data, an antigenic formula can
be written, such as E.coli O111:K-58:H6, meaning this E.
coli possesses O antigen 111, K antigen 58, and H antigen 6.
The formula Salmonella to go 4,12:1,w:1,6 indicates this
serotype of Salmonella possesses O antigens 4 and 12, phase
1 H antigens 1 and w, and phase 2 H antigens 1 and 6.
Escherichia coli.
The organism was isolated from faeces in 1885 by T.
Escherich. E. coli is a common inhabitant of the large
intestine of humans and mammals. It is also found in the guts
of birds, reptiles, amphibians, and insects. The bacteria are
excreted in great numbers with the faeces and are always
present in the external environment (soil, water, foodstuffs,
and other objects).
Morphology. E coli are straight rods measuring 0.4-0.7 in
breadth and 1-3 in length. They occur as individual
organisms or in pairs and are marked by polymorphism.
There are motile and non-motile types. The G+C content in
DNA is 50-51 per cent. The cell surface has pili on which
certain phages are adsorbed. The microcapsule is not always
clearly defined.
Cultivation. E. coli is a facultative anaerobe. The optimum
temperature for growth is 30-37 °C and the optimum pH
value of medium up 7.2-7.5. The organism also grows
readily on ordinary media at room temperature and at 10 and
45 °C, growth becomes visible in the first two days. E. coli
from cold-blooded animals grows at 22-37° C but not at 4243° C.
On meat-peptone agar E. coli produces slightly
convex semitransparent, greyish colonies, and in meat broth
it forms diffuse turbidity and a precipitate. The organism
produces colonies which are red on Ploskirev's medium, red
with a metallic hue on Endo's medium, and dark-blue on
Levin's medium.
Fermentative properties. E. coli does not liquefy gelatin. It
produces indole and hydrogen sulphide, and reduces nitrates
to nitrites; ferments glucose, levulose, lactose, maltose,
mannitol, arabinose, galactose, xylose, rhamnose, and
occasionally saccharose, raffinose, dulcitol, salycin, and
glycerin, with acid and gas formation. It also coagulates
milk. There are varieties of the bacteria which ferment
saccharose, do not produce indole, have no flagella, and do
not ferment lactose.
Toxin production. Certain strains of E. coli are
conditionally pathogenic They contain a gluco-lipo-protein
complex with which their toxic, antigenic, and immunogenic
properties are associated. Some strains possess haemolytic
properties (O124 and others) determined by plasmids.
Pathogenic cultures possess endotoxins and thermolabile
neurotropic exotoxins. The latter accumulate in broth
cultures on the second-fourth day of cultivation, while the
endotoxins appear only after the twentieth day. Haemotoxins
and pyrogenic substances, proteinases, deoxyribonucleases,
urease,
phosphatase,
hyaluronidase,
amino
acid
decarboxylases have been obtained from pathogenic strains.
Antigenic structure. The antigenic structure of E. coli is characterized
by variability and marked individuality. Along with the H- and Oantigens, the presence of other antigens has been shown m some strains,
i.e. the surface somatic (membranous, capsular) K-antigens which
contain the thermolabile L- and B-antigens and the thermostable A- and
M-antigens.
Each antigen group in its turn is composed of a number of antigens
designated by Arabic numbers, e.g. the O-group has 173 antigens, the Ksubgroup 90, the H-subgroup 50, etc. On the basis of antigenic structure
an antigenic formula is derived which fully reflects the antigenic
properties of the strain For example, one of the most widely spread
serotypes is designated 0111 : K58 : H2. Under the effect of
transformation, lysogenic conversion, transduction, and conjugation E.
coli may change its antigenic properties.
Numerous varieties of the organism are produced on cultivation under
artificial conditions. Such varieties are not only of theoretical interest,
but also of great practical importance in laboratory diagnosis of enteric
infections.
Classification. Genus Escherichia includes one E. coli
species consisting of several biotypes and serotypes. They
are differentiated according to cultural, biochemical, and
serological properties. The genus Escherichia includes E.
coli, E. freundi, E. vulneris, and others. E. coli comprises
several varieties which are differentiated by their cultural
and biochemical properties. F. Kauffmann has detected 25
O-groups responsible for various diseases in humans.
About 50 phage variants have been revealed among E. coli
organisms. They are used in laboratory diagnosis as
confirmatory characteristics of the isolated serotypes.
Resistance. E. coli survives in the external environment for
months. It is more resistant to physical and chemical factors
of the external environment than the typhoid and dysentery
bacteria. E. coli is killed comparatively rapidly by all
methods and preparations used for disinfection. At 55° C the
organism perishes in 1 hour, and at 60° C in 15 minutes. E.
coli is sensitive to brilliant green.
E. coli is used as a test microbe in the assay of disinfectants
and methods of disinfection and also in titration of certain
antibiotics.
Pathogenicity for animals. The pathogenic serovars of E.
coli cause severe infections in calf sucklings giving rise to an
extremely high mortality. A parenteral injection of the culture
into rabbits, guinea pigs, and white mice results in a fatal
toxico-septical condition.
Pathogenesis and diseases in man. Definite E. coli
serogroups are capable of causing various acute intestinal
diseases in humans: (1) the causative agents of colienteritis
in children are O-groups-25, -26, -44, -55, -86, -91, -111, 114, -119, -125, -126, -127, -128, -141, -146, and others
(they cause diseases in infants of the first months of life and
in older infants); (2) the causative agents of dysentery-like
diseases are E. coli of the O-groups-23, -32, -115, -124, 136, -143, -144, -151, and others; (3) the causative agents of
cholera-like diarrhoea are the O-groups-6, -15, -78, -148,
and others, they produce thermolabile and thermoresistant
enterotoxins.
Colienteritis begins acutely with high temperature (38-39
°C), and frequently with severe meteorism, vomiting,
diarrhoea, and general toxicosis. The disease usually occurs
in infants of the first year of life.
The infection is acquired from sick children or carriers.
Pathogenic E. coli serovars are found on various objects. It is
assumed that colienteritis is transmitted not only by the
normal route for enteric infections but also through the
respiratory tract by the droplets and dust.
The pathogenesis of colienteritis depends entirely on the
organism's condition. In prematurely born infants and in
infants during the first months of life the bactericidal activity
of blood is considerably lower in respect to the pathogenic E.
coli serovars in comparison to the nonpathogenic types. The
reactivity of the child's body at the time of infection plays an
important role in the mechanism of resistance to the
pathogenic strains.
The pathological process develops mainly in the small
intestine. Most probably, the mucous membrane of the small
intestine in particular is exposed to the action of
thermolabile toxic substances. Serovars O-124, O-151 and
others cause diseases which are similar to dysentery.
E. coli may cause colibacillosis in adults (peritonitis,
meningitis, enteritis, toxinfections, cystitis, pyelitis,
pyelonephntis,
angiocholitis,
salpingooophontis,
appendicitis, otitis, puerperal sepsis, etc.). Over-strain,
exhaustion, and conditions following infectious diseases
facilitate the onset of various E. coli infections. In a number
of cases the organism is responsible for food poisoning.
Immunity. In individuals who had suffered from diseases
caused by pathogenic E. coli serovars, cross immunity is not
produced owing to which re-infection may occur. Over 85
per cent of E. coli strains contain inhibiting substances,
colicins, marked by antagonistic properties in relation to
pathogenic microbes of the enteric group, they are used as
therapeutic and preventive agents, e.g. colibacterin (E. coli M
17, etc.).
Besides this, E colt as well as other common inhabitants of
the intestine are capable of synthesizing various vitamins
(K2, E, and group B) which are indispensable to the human
organism. The ability of various E. coli serovars to suppress
the growth of Mycobacterium tuberculosis has also been
observed. The suppression of E. coli and other members of
the biocoenosis may result in a chronic disease known as
dysbacteriosis.
Laboratory diagnosis. The patients' faeces, throat and nasal
discharges, material obtained at autopsy (blood, bile, liver,
spleen, lungs, contents of the small and large intestine, pus),
water, foodstuffs, and samples of washings from objects and
hands of staff of maternity hospitals, hospitals, and dairy
kitchens are all used for laboratory examination during
colienteritis. If possible, faecal material should be seeded
immediately after it has been collected. The throat and nasal
discharges are collected with a sterile swab. Specimens of
organs obtained at autopsy are placed in separate sterile jars.
The tested material is inoculated onto solid nutrient media
(Endo's, Levin's) and, simultaneously, onto Ploskirev's media
and bismuth-sulphite agar for isolation of bacteria of the
typhoid-paratyphoid and dysentery group. BIood is first
inoculated into broth and then subcultured on solid media
when development of a septic process is suspected. Pus is
collected for examination in suppurative lesions. It is placed
into a dry sterile vessel and then inoculated onto the
differential media of Endo or Levin. The pure culture isolate
is identified by its morphological, cultural, biochemical,
serological, and biological properties.
The corresponding O-group to which an enteropathogenicserovars belong is determined by means of the agglutination
reaction after the K-antigen of the culture that is being
studied has been destroyed by boiling.
Besides, the immunofluorescence method employing type
specific labelled sera is also used. It yields a preliminary
answer in one to two hours.
In serological diagnosis of colienteritis beginning with the
third to fifth day of the disease the indirect
haemagglutination reaction is used which excels the
agglutination reaction in sensitivity. It is positive when the
antibody titre grows in the course of the diseased.
Treatment. Patients with colienteritis are prescribed antibiotics
(tetracycline with vitamins C, B1 and B2) and biopreparations (coli
autovaccine, coli bacteriophage, colicin, bacterin, lactobacterin,
bificol, bifidumbacterin). Physiological solutions with glucose are
injected for controlling toxicosis.
Prophylaxis. To prevent diseases caused by pathogenic serovars
of E. coli, special attention is given to early identification of
individuals suffering from colienteritis, and also to their
hospitalization and effective treatment. Regular examination of
personnel is necessary in children's institutions as well as of
mothers whose children are suffering from dyspepsia.
Considerable importance is assigned to observation of sanitary
regulations in children's institutions, infant-feeding centres,
maternity hospitals, and children's nurseries. Protection of water
and foodstuff's from contamination with faeces, the control of
flies, and gradual improvement of standards of hygiene of the
population are also particularly important.
Sanitary significance of E. coli. This organism is widely
spread in nature. It occurs in soil, water, foodstuff's, and on
various objects. For this reason E. coli serves as an indicator
of faecal contamination of the external environment.
Detection of E. coli is of great importance in estimating the
sanitary index of faecal contamination of water, foodstuff's,
soil, beverages, objects, and hand-washings. The degree of
contamination of water, soil and foodstuff's is determined by
the coli titre or coli index (these terms have been discussed in
the chapter concerning the spread of microbes in nature).
Faecal contamination of articles of use is estimated by
qualitative determination of the presence of E. coli.
Additional materials
Pathogenicity of Escherichia coil. Although E. coli is part of the normal
flora of the intestinal tract, it is also the most common gram-negative
pathogen responsible for nosocomially acquired septic shock, meningitis
in neonates, cystitis and pyelonephritis in women, and for several distinct
forms of diarrheal disease and dysentery affecting populations throughout
the world. Strains of E coli capable of causing such diseases possess one
or more virulence factors that are not found in E. coli strains comprising
the normal flora. Such virulence factors can be characterized as follows,
the capacity to adhere to specific mammalian cells; the ability to invade
and grow intracellularly in intestinal epithelial cells; the secretion of one
or more enterotoxins that cause fluid loss, resulting diarrhea; the
formation of a cytotoxin that blocks protein synthesis, causing a
hemorrhagic colitis; and the possession of an antiphagocytic capsule that
is responsible, at least in part, for the bacteremia and meningitis caused
by E. coli. In addition, the ability to obtain iron from transferrin or
lactoferrin by the synthesis of iron-binding siderophores markedly
enhances the virulence of such strains through their ability to grow in
host tissues.
Diarrheal Diseases. It is estimated that during the American
Revolutionary War there were more deaths from diarrhea than from
English bullets, and during the American War between the states, over
25% of all deaths were because of diarrhea and dysentery. Diarrhea
kills more people worldwide than AIDS and cancer, with about five
million diarrheal deaths occurring annually primarily because of
dehydration. Most of these occur in neonates and young children,
anda large number are caused by pathogenic E. coli. The disease in
adults, known by many names such as traveller’s diarrhea or
Montezuma's revenge, may vary from a milddisease with several days
of loose stools to a severe and fatal cholera-like disease. Such lifethreatening E. coli infections occur throughout the world but are most
common in developing nations.
The virulence factors responsible for diarrheal disease are frequently
encoded in plasmids, which may be spread from one strain to another
either through transduction: or by recombination. As a result, various
combinations of virulence factors have occurred, which has been used
to place the diarrhea-producing strains of E. coli into various groups
based on the mechanism of disease production
Enterotoxigenic Escherichia coli. Enterotoxin-producing E
coli, called enterotoxigenic E.coli (ETEC), produce one or
both of two different toxins – a heat labile toxin called LT
and a heat-stable toxin called ST. The genetic ability to
produce both LT and ST is controlled by DNA residing in
transmissible plasmids called ent plasmids. Both genes have
been cloned, and the ST gene has been shown to possess the
characteristics of a transposon.
HEAT-LABILE TOXIN. The heat-labile toxin LT, which
is destroyed by heating at 65 °C for 30 minutes, has been
extensively purified, and its mode of action is identical to
that described for cholera toxin (CT). LT has a molecular
weight of about 86,000 daltons and is composed of two
subunits, A and B Subunit A consists of one molecule of Ai
(24,000 daltons) and one molecule of A2 (5000daltons)
linked by a disulfide bridge. Each A unit is joined
noncovalently to five B subunits.
Like CT, LT causes diarrhea by stimulating the activity of a
membrane-bound adenylate cyclase.This results in the
conversion of ATP to cyclic AMP (cAMP): ATP  cAMP
+ PPi
Minute amounts of cAMIP induce the active secretion of Cl–
and inhibit the absorption of NaCI, creating an electrolyte
imbalance across the intestinal mucosa, resulting in the loss of
copious quantities of fluid and electrolytes from the intestine.
The mechanism by which LT stimulates the activity of the
adenylate cyclase is as follows: (1) The B subunit of the toxin
binds to a specific cell receptor, GM1 ganglioside, (2) the A1
subunit is released from the toxin and enters the cell; and (3)
the A1 subunit cleaves nicotinamide-adenic dinucleonde (NAD)
into nicotinamide and ADP-ribose and, together with a cellular
ADP-ribosylating factor, transfers the ADP-ribose to aGTPbinding protein. The ADP-ribosylation of the GTP-binding
protein inhibits a GTPase activity of the binding protein,
leading to increased stability of the catalytic cornplex
responsible for adenylate cyclase activity. This results in an
amplified activity of the cyclase and a corresponding increase
in the amount of cAMP produced.
Two antigenically distinct heat labile toxins are produced by
various strains of E. coli. LT-I is structurally and
antigenically related to CT to an extent that anti-CT will
neutralize LT I LT-II has, on rare occasions, been isolated
from the faeces of humans with diarrhea, but it is most
frequently isolated from feces of water buftalos and cows
LT-II is biologically similar to LT-I, but it is not neutralized
by either anti-LT-I or anti-CT.
LT will bind to many types of mammalian cells, and its
ability to stimulate adenylate cyclase can be assayed in cell
cultures.
A report has also shown that CT stimulated an increase in
prostaglandin E (PGE), and that PGE1 and PGE2 caused a
marked fluid accumulation in the ligated lumen of rabbit
intestinal segments. The mechanism whereby CT induces
PGE release is unknown.
HEAT-STABLE TOXIN The heat-stable toxin STa consists
of a family of small, heterogeneous polypeptides of 1500 to
2000 daltons that are not destroyed by heating at 100 °Cfor
30 minutes. STa has no effect on the concentration of cAMP,
but it does cause a marked increase m thecellular levels of
cyclic GMP (cGMP). cGMP causes an inhibition of the
cotransport of NaCI across the intestinal wall, suggesting that
the action of STa may be primarily antiabsorptive compared
with that of LT, which is both antiabsorptive and secretory.
STa stimulates guanylate cyclase only in intestinal cells,
indicating that such cells possess a unique receptor for STa.
The cell receptor for STa is known to be either tightly
coupled to, or a part of, a particulate form of guanylate
cyclase located in the brush border membranes of intestinal
mucosal cells. Also, intimately associated with this complex
is a cGMP-dependent protein kinase that phosphorylates a
25,000 dalton protein in the brush border. It has been
proposed that this phosphorylated protein might be the actual
mediator for the toxin-induced ion transport alterations that
lead to fluid loss. The usual assay for STa is to inject the
toxin intragastrically into a 1 – to 4-day old suckling mouse
and measure intestinal fluid accumulation (as a ratio of
intestinal/remaining body weight) after 4 hours. STa may
also be assayed directly by measuring its effect on the
increase in guanylate cyclasein homogenized intestinal
epithelial cells.
A second heat stable toxin that is produced by somestrains of
E. coli has been termed STb. This toxin is inactivein suckling
mice but will produce diarrhea in weaned piglets. STb
producers have not been isolated from humans. It does not
seem to increase the level of adenylate or guanylate cyclase
in intestinal mucosal cells, but maystimulate the synthesis of
prostaglandin E2. The end resuit is to enhance net
bicarbonate ion secretion.
COLONIZATION FACTORS. Animals also are subject to
infections by their own strains of ETEC, and such infections
in newborn animals may result in death from the loss of
fluids and electrolytes. Extensive studies of strains infecting
newborn calves and piglets (as well as humans) have
revealed that, in addition to producing an enterotoxin, such
strains possess one of several fimbriate surface structures that
specifically adhere to the epithelial cells lining the small
intestine. These antigens (K-88 for swine strains, and K-99
for cattle) usually are fimbriate structures that cause the
toxin-producing organisms to adhere to and colonize the
small intestine. The need for this colonizing ability is
supported by the fact that antibodies directed against the
colonizing fimbriae are protective.
Analogous human ETEC strains also possess fimbriate
structures that have been designated as colonizationfactors
(CFA). At least five such serologically different factors,
CFA/I, CFA/II, CFA/III, E8775, and CFA/V, have been
described. Interestingly, these colonization factors also are
plasmid mediated, and single plasmids have been described
that carry genes for both CFA/I and STa.
Interestingly, during the Gulf War in 1990, there were about
100 cases of diarrhea per week per 1000 personnel. Of these,
55% resulted from ETEC.
Enterohemorrhagic
Escherichia
coli.
The
enterohemorrhagic E. coli (EHEC) were first described in
1982 when they were shown to be the etiologic agent of
hemorrhagic colitis, a disease characterized bysevere
abdominal cramps and a copious, bloody diarrhea. These
organisms are also known to cause a condition termed
hemolytic-uremic syndrome (HUS), which is manifested by a
hemolytic anemia, thrombocytopenia (decrease in the
number of blood platelets), and acute renal failure. HUS
occurs most frequently in children.
Although most initially recognized EHEC belong to
serotype O157:H7, other EHEC serotypes such as O26,
O111, O128, and O143 have been recognized. These
organisms are not invasive, but they do possess a 60megadalton plasmid that encodes for a fimbrial antigen that
adheres to intestinal epithelium. In addition, the EHEC are
lysogenic for one or more bacteriophages that encode for the
production of one or both of two antigenically distinct
toxins. These toxins are biologically identical and
antigenically similar to the toxins formed by Shigella
dysenteriae (Shiga's bacillus), and are designated as Shigalike toxin I (SLT-I) and Shiga-like toxin II (SLT II). Because
the Shiga-like toxins initially were characterized by their
ability to kill Vero cells, a cell line developed from African
green monkey kidney cells, they also arecalled Verotoxin I
and Verotoxin II.
SLT I consists of an A subunit and five B subunits. The
sequence of the B subunit from S. dysenteriae type 1 is
identical to that of the B subunit of SLT I. The B subunit
binds specifically to a glycolipid in microvillus membranes,
and the released A subunit stops protein synthesis by
inactivating the 60S ribosomal subunit. This inactivation
results from the N-glycosidase activity of the toxin, which
cleaves off an adenine molecule (A-4324) from the 28S
ribosomal RNA, causing a structural modification of the 60S
subunit, resulting in a reduced affinity for EF-1 and, thus, an
inhibition of aminoacyl- tRNA binding. The consequence of
toxin action is a cessation of protein synthesis, the sloughing
off of dead cells, anda bloody diarrhea. Notice that SLT 1
carries out the same reaction as the plant toxins ricin and
abrin.
SLT II is biologically similar to SLT I, but because only a 50%
to 60% homology exists between the two toxins, it is not
surprising that they are antigenically distinct. Interestingly, both
STL I and STL-II can be transferred to nontoxin producing
strains of E. coli by transduction.
Outbreaks of hemorrhagic colitis have been traced to
contaminated food as well as to person to person transmission in
nursing homes and day care centres. Contaminated,
undercooked hamburger meat seems to be the most frequently
implicated source of food borne illnesses followed by
contaminated milk and water, indicating thatcattle are a common
reservoir for EHEC. Of note is that E. coli 0157:H7 has been
shown to survive up to 9 months at -20°C in ground beef.
Thus, the EHEC are able to cause hemorrhagic colitis as a
result of their ability to adhere to the intestinal mucosa, and
they presumably destroy the intestinal epithelial lining
through their secretion of Shiga like toxins. The mechanism
whereby the EHEC cause HUS is unclear but seems to
follow bloodstream carriage of SLT II to the kidney.
Experimental results have shown that humanrenal
endothelial cells contain high levels of receptor for SLT-2.
Moreover, in the presence of interleukin (IL)1/, the amount
of receptor increases, enhancing the internalization of the
toxin and the death of the cell.
The section, "A Closer Look," describes several epidemics
of hemorrhagic colitis that have occurred in the United
States and techniques that are used for the identification of
this serotype
Enteroinvasive Escherichia coli
The disease produced by the enteroinvasive E. coli (EIEC)
is indistinguishable from the dysentery produced by
members of the genus Shigella, although the shigellae seem
to be more virulent because considerably fewer shigellae
are required than EIEC to cause diarrhea. The key virulence
factor required by the EIEC is the ability to invade the
epithelial cells.EIEC INVASION. The specific property that
provides these organisms with their invasive potential is far
from understood. It is known, however, that this ability is
encoded in a plasmid and that the loss of the plasmid results
m aloss of invasive ability and a loss of virulence.
Moreover, the shigellae seem to possess the same plasmid,
because Western blots show that shigellae and EIEC
plasmids express polypeptides that are similar in molecular
weight and antigenicity.
EIEC TOXINS. Although the primary virulence factor of
EIEC strains is the ability to invade intestinal epithelial cells,
they also synthesize varying amounts of SIT I and SLT II.
Based on the severity of the disease, however, it could
assumed that the amount of toxin produced is considerably
less than that formed by the highly virulent shigellae or the
EHEC. Other enterotoxic products produced by the EIEC are
under study.
EIEC can be distinguished from other E. coli by their ability
to cause an inflammatory conjunctivitis in guinea pigs, an
assay termed a Sereny test. A DNA probe that hybridizes
with colony blots of EIEC and all species of Shigella also has
been used to identify organisms producing Shiga-like toxins.
Enteropathogenic Escherichia coli. The enteropathogenic E. coli
(EPEC) are diffusely adherent organisms that are particularly
important in infantdiarrhea occurring in developing countries,
where they may cause a mortality rate as high as a 50%. They
comprise a mixture of organisms that seem to produce diarrhea by
a two step process. The classic EPEC exist among a dozen or so
different serotypes, all of which are characterizedby the possession
of a 55 to 65-megadalton plasmid that encodes for an adhesin
termed EPEC adherence factor (EAF). EAF causes a localized
adherence of the bacteria to enterocytes of the small bowel,
resulting m distinct microcolonies. This is followed by the
formation ofunique pedestal-like structures bearing the adherent
bacteria. These structures have been termed attaching and effacing
lesions. The ability to form the effacing lesion resides in an
attaching and effacing gene (eae). The lesions are characterized by
a loss of microvilli and a rearrangement of the cytoskeleton, with a
proliferation of filamentous actin beneath are as of bacterial
attachment.
Thus, the ability of the EPEC to cause diarrhea involves two
distinct genes, EAF and eae. The end result is an elevated
intracellular Ca+2 level in the intestinal epithelial cells and
the initiation of signal transduction, leading to protein
tyrosine phosphorylation of at least two eucaryotic proteins.
EPEC strains routinely have been considered noninvasive,
but data have indicated that such strains can invade epithelial
cells in culture. However, EPEC strains do not typically
cause a bloody diarrhea, and the significance of cell invasion
during infection remains uncertain.
Other Diairhea-Producing Escherichia coli. All possible
combinations, deletions, or additions of the various
virulence factors responsible for intestinal fluid loss result in
diarrhea producing strains that do not fitthe categories
already described. Such has been found tobe the case.
The most recent of these has been termed the
enteroaggregative E. coli. These strains seem to cause
diarrhea through their ability to adhere to the intestinal
mucosa and possibly by yet a new type of enterotoxin. It
seems possible that the acquisition of other virulence factors
may result in the discovery of additional pathogenic strains
of E. coli.
E. coli Urinary Tract Infections. Escherichia coli is the most
common cause of urinary tract infections of the bladder
(cystitis) and, less frequently, of the kidney (pyelonephritis). In
either case, infections usually are of an ascending type (enter
the bladder fromthe urethra and enter the kidneys from the
bladder). Many infections occur in young female patients, in
persons with urinary tract obstructions, and in persons requiring
urinary catheters, and they occur frequently in otherwise
healthy women. Interestingly, good data support the postulation
that certain serotypes of E. coli are more likely to cause
pyelonephritis than others. Thus, the ability to produce Pfimbriae (so called because of their ability to bind to P blood
group antigen) has been correlated with the ability to produce
urinary tract infections, seemingly by mediating the adherence
of the organisms to human uroepithelial cells. Of note is that the
rate of nosocomial urinary tract infection per person-day was
significantly greater in patients with diarrhea, particularly in
those with an indwelling urinary catheter.
In addition to fimbrial adhesins, a series of afimbrial
adhesins has been reported. Their role in disease is not yet
firmly established, but it has been demonstrated that at least
one afimbrial adhesins mediated specific binding to
uroepithelial cells.
Recurrent urinary tract infections in premenopausal, sexually
active women frequently can be prevented by the postcoital
administration of a single tablet of an antibacterial agent such
as trimethoprim-sulfamethoxazole, cinoxacin, or cephalexin.
E. coli Systemic Infections. About 300,000 patients in United
States hospitals develop gram-negative bacteremia annually,
and about 100,000 of these persons the of septic shock. As
might be guessed, E. coli is the most common organism
involved in such infections. The ultimate cause of death in
these cases is an endotoxin-induced synthesis and release of
tumor necrosis factor-alpha and IL-1, resulting in irreversible
shock.
The newborn is particularly susceptible to meningitis,
especially during the first month of life. A survey of 132 cases
of neonatal meningitis occurring in the Netherlands reported
that 47% resulted from E. coli and 24% from group B
streptococci. Notice that almost 90% of all cases of E. coli
meningitis are caused by the K1 strain, which possesses a
capsule identical to that occurring on group B meningococci.
Escherichia coif Virulence Factors
Diarrhea-producing
E. coli
Virulence Factors
Enteroroxigenic E. coli
Heat-labile toxin (LT)
Heat-stable
toxin
(ST)
Colonization factors (fimbriae)
Enterohernorrhagic E. coli
Shiga like toxin (SLT-I)
Shiga like toxin II (SLF-II)
Colonisation factors (fimbriae)
Enteroinvasive E. coli
Shiga like toxin (SLT-I)
Shiga like toxin II (SLF-II)
Ability to invade epithelial cells
Enteropathogenic E. coli
Adhesin factor for epithelial cells
Urinary trace infections
P- fimbriae
Meningitis
K-1 capsule
Enteric Fever and Paratyphoid Salmonellae. The
causative agent of enteric (typhoid) fever, Salmonella typhi
was discovered in 1880 by K. Eberth and isolated in pure
culture in 1884 by G. Gaffky.
In 1896 the French scientists C. Archard and R. Bensaude
isolated paratyphoid B bacteria from urine and pus collected
from patients with clinical symptoms of typhoid fever. The
bacterium responsible for paratyphoid A (Salmonella
paratyphi) was studied in detail m 1902 by the German
bacteriologists A. Brion and H. Kayser, and the causative
agent of paratyphoid B {Salmonella schottmuelleri) was
studied in 1900 by H. Schottmueller.
Classification of Salmonella
Genus Salmonella
Species:
Salmonella enterica
Salmonella bongory
Subspecies Salmonella enterica
a. S. choleraesuis
b. S. salamae
c. S. arizonae
d. S. diarizonae
e. S. houtenae
f. S. indica
Morphology. The morphology of the typhoid salmonella
corresponds with the general characteristics of the
Enterobacteriaceae family. Most of the strains are motile and
possess flagella, from 8 to 20 in number. It is possible that the
flagella form various numbers of bunches.
The paratyphoid salmonellae do not differ from the typhoid
organisms in shape, size, type of flagella, and staining
properties.
The typhoid salmonellae possess individual and intraspecies
variability. When subjected to disinfectants, irradiation, and to
the effect of other factors of the external environment they
change size and shape. They may become coccal, elongated
(8-10 mcm), or even threadlike. The G+C content in DNA
ranges between 45 and 49 per cent.
Cultivation. The typhoid and paratyphoid organisms are
facultative anaerobes. The optimum temperature for growth
is 37° C, but they also grow at temperatures between 15 and
41°C. They grow on ordinary media at pH 6.8-7.2. On meatpeptone agar S. typhi forms semitransparent fragile colonies
which are half or one-third the size of E. coli colonies. On
gelatin the colonies resemble a grape leaf in shape. Cultures
on agar slants form a moist transparent film of growth
without a pigment and in meat broth they produce a uniform
turbidity.
On Ploskirev's and Endo's media S. typhi and S. paratyphi
form semitransparent, colourless or pale-pink coloured
colonies. On Levin's medium containing eosin and
methylene blue the colonies are transparent and bluish in
colour, on Drigalski's medium with litmus they are
semitransparent and light blue, and on bismuth-sulphite agar
they are glistening and black. The colonies produced by S.
paratyphi A on nutrient media (Ploskirev's, Endo's, etc.) are
similar to those of S. typhi
Colonies of S. schottmuelleri have a rougher appearance and
after they have been incubated for 24 hours and then left at
room temperature for several days, mucous swellings appear
at their edges. This is a characteristic differential cultural
property.
Fermentative properties. S. typhi does not liquefy gelatin, nor
does it produce indole. It produces hydrogen sulphide, and
reduces nitrates to nitrites. The organisms do not coagulate
milk, but they give rise to a slightly pink colouration in litmus
milk and cause no changes in Rotberger's medium. They
ferment glucose,
mannitol, maltose, levulose, galactose,
raffinose, dextrin, glycerin, sorbitol and, sometimes, xylose,
with acid formation.S. paratyphi ferments carbohydrates, with
acid and gas formation, and is also distinguished by other
properties (Table 3). Two types of S. typhi occur in nature:
xylose-positive and xylose-negative. They possess lysin
decarboxylase, ornithine decarboxylase and oxidase activity.
In the process of dissociation S. typhi changes from the S-form
to the R-form. This variation is associated with loss of the
somatic 0-antigen (which is of most immunogenic value) and,
quite frequently, with loss of the Vi-antigen.
Toxin production. S. typhi contains gluco-lipo-protein
complexes. The endotoxin is obtained by extracting the
bacterial emulsion with trichloracetic acid. This endotoxin is
thermostable, surviving a temperature of 120° C for 30
minutes, and is characterized by a highly specific precipitin
reaction and pronounced toxic and antigenic properties.
Investigations have shown the presence of exotoxic
substances in S. typhi which are inactivated by light, air, and
heat (80° C), as well as enterotropic toxin phosphatase, and
pyrogenic substances.
Antigenic structure. S. typhi possesses a flagellar H-antigen
and thermostable somatic 0- and Vi-antigens. All three
antigens give rise to the production of specific antibodies in
the body, i. e. H-, O-, and Vi-agglutinins. H-agglutinins bring
about a large-flocculent agglutination, while 0- and Viagglutinins produce fine-granular agglutination.
The antigens differ in their sensitivity to chemical
substances. The O-antigen is destroyed by formalin but is
unaffected by exposure to weak phenol solutions. The Hantigen, on the contrary, withstands formalin but is destroyed
by phenol.
S. typhi, grown on agar containing phenol in a ratio of
1:1000, loses the H-antigen after several subcultures. This
antigen is also destroyed on exposure to alcohol. These
methods are employed to obtain the 0-antigen in its pure
form. The H-antigen is isolated by treating the bacterial
emulsion with formalin or by using a broth culture which
contains a large number of flagellar components.
Immunization with H-and 0-antigens is employed for
obtaining the corresponding agglutinating sera.
The discovery of the Vi-antigen isolated from virulent S.
typhi is of great theoretical interest and practical importance.
Vi- and O-antigens are located within the microorganism, on
the surface of the bacterial cell. It is assumed that the Viantigen occurs in isolated areas and is nearer to the surface
than the O-antigen. The presence of Vi-antigens hinders
agglutination of salmonellae by 0-sera, and the loss of the Viantigen restores the O-agglutinability. S. typhi, which
contains Vi-antigens, is not agglutinated by O-sera. Viagglutinating serum is obtained by saturation of S. typhi
serum of animals inoculated with freshly isolated
salmonellae, employing H- and O-antigens. The Vi-antigen is
a labile substance. It disappears from the culture when
phenol is added to the medium and also when the
temperature is low (20 °C) or high (40 ° C). It is completely
destroyed by boiling for 10 minutes and by exposure to
phenol. Exposure to formalin and to temperature of 60° C for
30 minutes produces partial changes in the antigen.
Together with H-, O-, and Vi-antigens, other more deeply
located antigens have been revealed. The latter are detected
during the change transformation of the bacterial cell to the
R-form when the superficial O- and Vi-antigens are lost. The
deeply located antigens are non-specific. Later, salmonellae
were found to possess an M-mucous antigen
(polysaccharide).
It has been ascertained that the Vi-antigen content of cultures
varies, some serovars possessing a large quantity of this
antigen, while others only a small quantity. F. Kauffmann
subdivides all salmonellae containing Vi-antigens into three
groups: (1) pure V-forms with a high Vi-antigen content; (2)
pure W-forms which contain no Vi-antigens; (3) transitional
V-W-forms which possess Vi-antigens and are agglutinated by
O-serum. S. paratyphi have been found to have antigens in
common with isoantigens of human erythrocytes.
Classification. The salmonellae of typhoid fever and paratyphoids
together with the causative agents of toxinfections have been
included in the genus Salmonella (named after the bacteriologist
D. Salmon) on the basis of their antigenic structure and other
properties. At present, about 2000 species and types of this genus
are known.
F. Kauffmann and P. White classified the typhoid-paratyphoid
salmonellae into a number of groups according to antigenic
structure and determined 65 somatic O-antigens. For instance, S.
typhi (group D) contains three different O-antigens — 9, 12, and
Vi. S. paratyphi A alone constitutes group A, and S. schottmuelleri
belongs to group B. It has been proved by F. Andrewes that the
flagellar H-antigen is not homogeneous but is composed of two
phases: phase 1 is specific and agglutinable by specific serum,
phase 2 is non-specific and agglutinable not only by specific, but
also by group sera. Salmonellae, which possess two-phase Hantigens, are known as diphasic, while those which possess only
the specific H-antigen are monophasic.
Resistance. Typhoid and paratyphoid A and B salmonellae
survive in ice for several months, in soil contaminated with
faeces and urine of patients and carriers for up to 3 months,
in butter, cheese, meat and bread for 1-3 months, in soil,
faecal masses, and water for several weeks, and in vegetables
and fruits for 5-10 days. They remain unaffected by
desiccation and live for a long time in dry faeces.
Salmonellae survive for only a short time (3-5 days) in
polluted water owing to the presence of a large number of
saprophytic microbes and substances harmful to pathogenic
microorganisms.
S. typhi and S. paratyphi A are susceptible to heat and are
destroyed at 56° C in 45-60 minutes, and when exposed to
the usual disinfectant solutions of phenol, calcium chloride,
and chloramine, perish in several minutes. The presence of
active chlorine in water in a dose of 0.5-1 mg per litre
provides reliable protection from S. typhi and S. paratyphi A.
Pathogenicity for animals. Animals do not naturally acquire
typhoid fever and paratyphoids. Therefore, these diseases are
anthroponoses. A parenteral injection of the Salmonellae
organisms into animals results in septicaemia and
intoxication, while peroral infection produces no disease. E.
Metchnikoff and A. Bezredka produced a disease similar to
human typhoid fever by enteral infection in apes
(chimpanzee).
Pathogenesis and diseases in man. The causative agent is
primarily located in the intestinal tract. Infection takes place
through the mouth (digestive stage).
Cyclic recurrences and development of certain
pathophysiological changes characterize the pathogenesis of
typhoid fever and paratyphoids.
There is a certain time interval after the salmonellae
penetrate into the intestine, during which inflammatory
processes develop in the isolated follicles and Peyer's
patches of the lower region of the small intestine (invasive
stage).
As a result of deterioration of the defence mechanism of the
lymphatic apparatus in the small intestine the organisms
enter the blood (bacteriemia stage). Here they are partially
destroyed by the bactericidal substances contained in the
blood, with endotoxin formation. During bacteraemia
typhoid salmonellae invade the patient's body, penetrating
into the lymph nodes, spleen, bone marrow, liver, and other
organs (parenchymal diffusion stage). This period
coincides with the early symptoms of the disease and lasts
for a week.
During the second week of the disease endotoxins
accumulate in Peyer's patches, are absorbed by the blood,
and cause intoxication. The general clinical picture of the
disease is characterized by status typhosus, disturbances of
thermoregulation, activity of the central and vegetative
nervous systems, cardiovascular activity, etc.
On the third week of the disease a large number of typhoid
bacteria enter the intestine from the bile ducts and
Lieberkuhn's glands. Some of these bacteria are excreted in
the faeces, while others reenter the Peyer's patches and
solitary follicles, which had been previously sensitized by the
salmonellae in the initial stage. This results in the
development of hyperergia and ulcerative processes. Lesions
are most pronounced in Peyer's patches and solitary follicles
and may be followed by perforation of the intestine and
peritonitis (excretory and allergic stage).
The typhoid-paratyphoid salmonellae together with products
of their metabolism induce antibody production and promote
phagocytosis. These processes reach their peak on the fifthsixth week of the disease and eventually lead to recovery
from the disease.
Clinical recovery (recovery stage) does not coincide with the
elimination of the pathogenic bacteria from the body. The
majority of convalescents become carriers during the first
weeks following recovery, and 3-5 per cent of the cases
continue to excrete the organisms for many months and years
after the attack and, sometimes, for life. Inflammatory
processes in the gall bladder (cholecystitis) and liver are the
main causes of a carrier state since these organs serve as
favourable media for the bacteria, where the latter multiply
and live for long periods. Besides this, typhoid-paratyphoid
salmonellae may affect the kidneys and urinary bladder,
giving rise to pyelitis and cystitis. In such lesions the
organisms are excreted in the urine.
In one, two, or three weeks following marked improvement
in the patient's condition, relapses may occur as a result of
reduced immunobiological activity of the human body and
hence a low-grade immunity is produced.
Due to the wide range in the severity of typhoid fever from
gravely fatal cases to mild ambulant forms it cannot be
differentiated from paratyphoids and other infections by
clinical symptoms. Laboratory diagnosis of these diseases is
of decisive importance. In recent years typhoid fever has
changed from an epidemic to a sporadic infection, being
milder in nature and rarely producing complications. In the
USSR typhoid fever mortality has diminished to one
hundredth that in 1913. Diseases caused by S. paratyphi are
similar to typhoid fever. The period of incubation and the
duration of the disease are somewhat shorter in paratyphoid
infections than in typhoid fever.
Immunity. Immunity acquired after typhoid fever and
paratyphoids is relatively stable but relapses and
reinfections sometimes occur. Antibiotics, used as
therapeutic agents, inhibit the immunogenic activity of
the pathogens, which change rapidly and lose their Oand Vi-antigens.
Laboratory diagnosis. The present laboratory diagnosis of
typhoid fever and paratyphoids is based on the pathogenesis
of these diseases.
1. Isolation of haemoculture. Bacteraemia appears during the
first days of the infection. Thus, for culture isolation 10-15 ml
of blood (15-20 ml during the second week of the disease and
30-40 ml during the third week) are inoculated into 100, 150
and 200 ml of 10 per cent bile broth, after which cultures are
incubated at 37° C and on the second day subcultured onto
one of the differential media (Ploskirev's, Endo's, Levin’s) or
common meat-peptone agar.
The isolated culture is identified by inoculation into a series
of differential media and by the agglutination reaction. The
latter is performed by the glass-slide method using
monoreceptor sera or by the test-tube method using purified
specific sera.
2. Serological method. Sufficient number of agglutinins
accumulate in the blood on the second week of the disease,
and they are detected by the Widal reaction. Diagnostic
typhoid and paratyphoid A and B suspensions are employed
in this reaction. The fact that individuals treated with
antibiotics may yield a low titre reaction must be taken into
consideration. The reaction is valued positive in patient's
serum in dilution 1 : 200 and higher.
The Widal reaction may be positive not only in patients but
also in those who had suffered the disease in the past and in
vaccinated individuals. For this reason diagnostic
suspensions of O- and H-antigens are employed in this
reaction. The sera of vaccinated people and convalescents
contain H-agglutinins for a long time, while the sera of
patients contain O-agglutinins at the height of the disease.
In typhoid fever and paratyphoids the agglutination reaction
may sometimes be of a group character since the patient's
serum contains agglutinins not only to specific but also to
group antigens which occur in other bacteria. In such cases
the patient's blood must be sampled again in 5-6 days and
the Widal reaction repeated. Increase of the agglutinin titre
makes laboratory diagnosis easier. In cases when the serum
titre shows an equal rise with several antigens, 0-, H-, and
Vi-agglutinins are detected separately.
3. A pure culture is isolated from faeces and urine during the
first, second, and third weeks of the disease. The test material
is inoculated into bile broth, Muller's medium, Ploskirev's
medium, or bismuth sulphite agar.
Isolation and identification of the pure culture are performed
in the same way as in blood examination.
Selective media are recommended for isolation of the
typhoid-paratyphoid organisms from water, sewage, milk,
and faeces of healthy individuals. These media slightly
inhibit the growth of pathogenic strains of typhoidparatyphoid organisms and greatly suppress the-growth of
saprophytic microflora.
A reaction for the detection of a rise in the phage titre is
employed in typhoid fever and paratyphoid diagnosis. This
reaction is based on the fact that the specific (indicator)
phage multiplies only when it is in contact with homologous
salmonellae. An increase in the number of phage corpuscles
in the test tube as compared to the control tube is indicative
of the presence of organisms homologous to the phage used.
This reaction is highly sensitive and specific and permits to
reveal the presence of the salmonellae in various substrates
in 11-22 hours without the necessity of isolating the
organisms in a pure culture. The reaction is valued positive
if the increase in the number of corpuscles in the tube
containing the test specimen is not less than 5-10 times that
in the control tube.
When unagglutinable cultures of the typhoid and
paratyphoid organisms are isolated, the agglutination
reaction is performed using Vi-sera. If the latter are not
available, the tested culture is heated for 30 minutes at 60°
C or for 5 minutes at 100° C. The agglutination reaction is
carried out with a suspension of this heated culture.
In some cases a bacteriological examination of duodenal
juice (in search for carriers), bone marrow, and material
obtained from roseolas is conducted.
Phage typing of typho-paratyphoid organisms is sometimes
employed. The isolated culture is identified by type-specific
O- and Vi-phages. Sources of typhoid and paratyphoid
infections are revealed by this method.
Water is examined for the presence of typho-paratyphoid
bacteria by filtering large volumes (2-3 litres) through
membrane filters and subsequent inoculation on plates
containing bismuth sulphite agar. If the organisms are
present, they produce black colonies in 24-48 hours. The
reaction of increase in phage titre is carried out
simultaneously.
Treatment. Patients with typhoid fever and paratyphoids are
prescribed chloramphenicol, oxytetracycline, and nitrofuran
preparations. These drugs markedly decrease the severity of
the disease and diminish its duration. Great importance is
assigned to general non-specific treatment (dietetic and
symptomatic). Treatment must be applied until complete
clinical recovery is achieved, and should never be
discontinued as soon as the bacteria disappear from the
blood, urine, and faeces since this may lead to a relapse.
Mortality has now fallen to 0.2-0.5 per cent (in 1913 it was
25 per cent).
The eradication of the organisms from salmonellae carriers is
a very difficult problem.
Prophylaxis. General measures amount to rendering
harmless the sources of infection. This is achieved by timely
diagnosis, hospitalization of patients, disinfection of the
sources, and identification and treatment of carriers. Of great
importance in prevention of typhoid fever and paratyphoids
are such measures as disinfection of water, safeguarding
water supplies from pollution, systematic and thorough
cleaning of inhabited areas, fly control, and protection of
foodstuff's and water from flies. Washing of hands before
meals and after using the toilet is necessary. Regular
examination of personnel in food-processing factories for
identification of carriers is also extremely important.
In the presence of epidemiological indications specific
prophylaxis of typhoid infections is accomplished by
vaccination. Several varieties of vaccines are prepared:
typhoid vaccine (monovaccine), typhoid and paratyphoid B
vaccine (divaccine).
Good effects are obtained also with a chemical associated
adsorbed vaccine which contains 0- and Vi-antigens of
typhoid, paratyphoid B, and a concentrated purified and
sorbed tetanus anatoxin. All antigens included in the
vaccine are adsorbed on aluminium hydroxide.
A new areactogenic vaccine consisting of the Vi-antigen of
typhoid fever Salmonella organisms has been produced. It
is marked by high efficacy and is used in immunization of
adults and children under seven years of age. When there
are epidemiological indications, all the above-mentioned
vaccines are used according to instructions and special
directions of the sanitary and epidemiological service.