Download Enterobacteria

Chair of Microbiology, Virology, and Immunology
PATHOGENIC
ENTEROBACTERIACEAE
The Enterobacteriaceae contain gram negative rods,
which, 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.
Classification of the Enterobacteriaceae
Genera
Escherichia
Edwardsiella
Shigella
Salmonella
Citrobacter
Enterobacter
Serratia
Providencia
Yersinia
Klebsiella
Hafnia
Proteus
Morganella
Erwinia
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.
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.
Escherichia coli.
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.
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.
- a gluco-lipo-protein complex with which their toxic,
antigenic, and immunogenic properties are associated;
haemolytic
properties
(O124
and
others)
- endotoxins and thermolabile neurotropic exotoxins;
- haemotoxins and pyrogenic substances, proteinases,
deoxyribonucleases, urease, phosphatase, hyaluronidase,
amino acid decarboxylases
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
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 Ogroups-6, -15, -78, -148, and others, they produce
thermolabile and thermoresistant enterotoxins.
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.
Enteric Fever,
Paratyphoid Salmonellae
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.
Toxin production. S. typhi contains gluco-lipoprotein
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.
Classification. 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.
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.
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.
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.
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.
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.
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).
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).