Chair of Microbiology, Virology, and Immunology

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Chair of Microbiology, Virology, and Immunology
Proteus. Morganella. Providencia.
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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.
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Classification of the Enterobacteriaceae Genera
Escherichia Shigella
Edwardsiella Salmonella
Citrobacter Klebsiella
Enterobacter Hafnia
Serratia Proteus
Providencia Morganella
Yersinia Erwinia
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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.
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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.
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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.
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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 GC 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.
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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.
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Toxin production. - a gluco-lipo-protein complex
with which their toxic, antigenic, and
immunogenic properties are associated
- haemolytic properties (O124 and others)
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endotoxins and thermolabile neurotropic
exotoxins - haemotoxins and
pyrogenic substances, proteinases,
deoxyribonucleases, urease, phosphatase,
hyaluronidase, amino acid decarboxylases
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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
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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.
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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.
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Enteric Fever, Paratyphoid Salmonellae
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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.
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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.
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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 Vi-agglutinins
produce fine-granular agglutination.
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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
H-antigens, are known as diphasic, while those
which possess only the specific H-antigen are
monophasic.
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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).
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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.
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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 fifth-sixth
week of the disease and eventually lead to
recovery from the disease.
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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.
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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 O- and Vi-antigens.
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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.
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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.
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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.
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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.
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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.
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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).