ENTERIC BACTERIAL PATHOGENS

E. O. Kravtsova

natural habitat is the intestinal tract of humans and animals.
Genera

(20)
1. Escherichia
2. Salmonellae
3. Shigellae
4. Klebsiellae
5. Yersinia …..

ferment a wide range of carbohydrates, possess a complex antigenic

structure, and produce a variety of toxins and other virulence factors.
This family is characterized biochemically by the ability to ferment glucose with the production of acid or acid and gas, and to reduce nitrates to nitrites.
All members of this family are oxidase-negative.

(E.coli) or non-motile (Shigellae)
Facultative anaerobes
T= 30-37ºC

pH= 7,2-7,5
Endo medium, Ploskirev medium, Levin medium, MacConkey agar.
Oxidase «-», Glucose «+», Lactose «-» ex.E.coli,
Mannitol «+», Indol «-» ex.E.coli, H2S «-» or «+».

dyes (indicators) are used to distinguish lactose-fermenting bacteria that form

colored colonies from non-lactose-fermenting microorganisms producing colorless colonies on such differential media.
These culture media can allow rapid identification of enteric bacteria.

of the Enterobacteriaceae members on the basis of their ability

to ferment glucose and lactose and to liberate sulfides.
Gas formed by carbohydrates fermenters is detected as bubbles or by splitting or displacement of the agar.
Hydrogen sulfide production is evidenced by a black color either throughout the butt, or in a ring formation near the top of the butt.

slant and the butt yellow in color (E. coli).
The lactose-negative

and glucose-positive bacteria show the yellow butt and the red slant (Salmonella, Shigella).
If the bacterium is glucose -negative and lactose-negative, both the butt and the slant remain red.
Hydrogen sulfide production is evidenced by a black color either throughout the butt, or in a ring formation near the top of the butt.

by more than 150 different heat-stable somatic O (lipopolysaccharide) antigens,

more than 100 heat-labile K (capsular) antigens, and more than 50 H (flagellar) antigens.
In Salmonella Typhi the capsular antigen is called Vi- antigen.
The antigenic classification of Enterobacteriaceae often indicates the presence of each specific antigen.

by the fecal-oral route.
They may be responsible for hospital infections.
The

main clinical symptoms are diarrhea, vomiting, temperature.

Methods: bacteriological, serological, biological.

S. typhi, S. paratyphi A, S. paratyphi B,

S. enteritidis, S. typhimurium
The main taxonomic groups of salmonella are:
Family → Genus → Species → Subspecies → Serovar

S. typhi was discovered in 1880 by K. Eberth and isolated in pure culture in 1884 by G.Gaffky.

Salmonella Morphology:
Gram «-» rods
Spores «-» Capsula «-» They are

motile
Cultural properties:
Facultative anaerobes  Chemoorganotrophs
Topt= 35-37̊º C pH= 6,8-7,2
Endo medium, Ploskirev medium – pale pink colonies. Levin medium – blue colonies
MacConkey agar- colourless colonies
Bismuth-Sulfite agar – black colonies.
In MPB they produce a uniform turbidity.

ferments carbohydrates with acid and gas formation.
Lactose «-»

Sucrose «-»
Indol «-», H2S «+»
Gelatin – does not liquefy
Oxidase «-»

, is destroyed by phenol.
Vi – antigen is located on

the surface of the bacterial cell , is destroyed by phenol and temperature.

Kauffmann and White classified Salmonellae according their antigenic structure.

Salmonella have been assigned to serogroups. The O group is

designated by capital roman letter (A, B, C, D).
Each Salmonella serogroup can be identified by the slide agglutination test.

letters and are kept in brackets (phase 1) and by

arabic numerals for phase 2.
The use of specific H- antisera helps to identify the Salmonella serovars.

bread for 1-3 months.
Survive in water and soil for several

weeks.
Susceptible to heat, t= 60-100º C.
Susceptible to disinfectant solutions of phenol, chloramine.

by Salmonella pathogenicity island 1 (SPI-1) delivers effector proteins required for

intestinal invasion and the production of enteritis. 
SPI-1 encodes transcription factors that regulate the expression of some virulence factors of Salmonella, while other transcription factors encoded outside SPI-1 participate in the expression of SPI-1-encoded genes. 
SPI-1 genes are responsible for the invasion of host cells, regulation of the host immune response, the host inflammatory response, apoptosis, and biofilm formation.

by the oral tract.
S. typhi, S. paratyphi A, and

S. paratyphi B are the causative agents of enteric fevers.
Other species of salmonellae are the bacteria causing salmonellosis, a food-borne infectious disease (enteritis).
The enteric fevers are transmitted by the fecal-oral route.

enter the lymphatics (Peyer’s patches) and then the bloodstream. After

an incubation period of 10-14 days, fever, malaise and headache occur due to bacteriemia and toxicity of Salmonella by-products.
The skin may become dotted with small hemorrhages called “roseoles”.
Gastrointestinal symptoms appear late in the course of the disease. Blood cultures are positive only in the first week of the disease.
At the beginning of the second week microbes are carried by the blood to many organs, including the liver, kidneys and the intestine. Salmonellae multiply in intestinal lymphoid tissue, kidneys and are excreted in stools and urine.
The stools and urine cultures give positive results on the second and third week.

the invasion
3rd stage – bacteremia
4th stage – bacterial dissemination
5th stage

– hyperergia and excretion
6th stage – final stage
Immunity acquired is relatively stable but relapses and reinfections sometimes occur.

of the disease.
At the beginning of the second week

microbes are carried by the blood to many organs, including the liver, kidneys and the intestine.
Salmonellae multiply in intestinal lymphoid tissue, gallbladder, kidneys and are excreted in stools and urine. The stools and urine cultures yield positive results on the second and third week.
A positive culture of bile establishes the presence of Salmonella genus in the biliary tract of carriers.

essential.
Susceptibility testing is an important method to choosing a

proper antibiotic, because multiple drug resistance is a big problem in enteric bacteria.

1888 by A. Chantemesse and in 1891 by A. Grigoryev

and F. Widal.
In 1898 this organism was studied in detail by K. Shiga in Japan.
In 1900 S. Flexner in the Philippines isolated dysentery organisms.
Later other bacteria causing dysentery were discovered. According to the current International Nomenclature, all dysentery bacilli are grouped together in one genus known as Shigella.

characterized by fever, bloody diarrhea, and fecal leukocytosis. Classical bacterial

dysentery is associated with infections caused by any of the four Shigella species:
Sh. dysenteriae, Sh. flexneri, Sh. boydii,
Sh. sonnei.

S. boydii,
S. sonnei.

are non-motile

They are facultative anaerobes, but grow best aerobically.

of Shigella sonnei, they do not ferment lactose.
Glucose «+»

Lactose «-»
Mannitol «+» (S.dysenteriae «-») H2S «-»

Antigens: O – somatic antigen, K-surface antigen.

tract; bloodstream invasion is quite rare.
All Shigellae produce endotoxin.

Microabscesses in the wall of the large intestine lead to necrosis of the mucous membrane, superficial ulceration and bleeding.
Shigella dysenteriae also produces a heat-labile exotoxin that affects both the gut and the central nervous system.

short incubation period (1-2 days), there is a sudden onset

of abdominal pain, fever, and watery diarrhea.
A day or so later, as the infection involves the ileum and colon, the number of stools increase; they are less liquid but often contain mucus, pus and blood.
In children and the elderly, loss of water and electrolytes may lead to dehydration, acidosis, and even death.
Infection is followed by a type-specific immune response, but reinfection may occur.

swabs are taken for culture.
BACTERIOLOGICAL EXAMINATION:
The specimen is streaked

on Ploskirev, (MacConkey or Levine EMB agar).
Colorless (lactose-negative) colonies are inoculated into the Kligler iron agar.
Organisms that not produce H2S and produce acid but not gas in the butt of the Kligler agar (glucose «+»), and that are nonmotile should be subjected to the slide agglutination test by specific Shigella antisera.

eubiotics may be effective in limiting multiplication. There are no

vaccines available for immunoprophylaxis of bacterial dysentery.
isolation of patients and disinfection of excreta,
detection of subclinical cases,
sanitary control of water, food, and milk.