Diagnostics of Infections Caused by Enterobacteriaceae (part 2) Genera: Salmonella, Shigella, Proteus

General
characteristics
of Salmonella
spp.



Gram negative rod



Motile



Non - sporeforming



Do not ferment lactose
on MacConkey agar



Produce gas when
fermenting glucose



Produce H2S from
thiosulfate



Possess O, H, and Vi
(capsular) antigens

All bacteria from the genera

Salmonella belong to two main

species

S. bongori (10 serotypes) – rare

S. choleraesuis – it is divided into 6

subspecies:

S. choleraesuis subsp. arizonae

S. choleraesuis subsp. choleraesuis

S. choleraesuis subsp. diarizonae

S. choleraesuis subsp. houtenae

S. choleraesuis subsp. indica

S. choleraesuis subsp. salamae

Within those subspecies there are known

over 2500 serotypes that are named!

To S. choleraesuis subsp.

choleraesuis belong the most

common serotypes



S. enteritidis



S. typhi



S. paratyphi A, B or C



S. galinarum

In a special Kauffmann-White’s table
there are collected the schemes of
antigenic structure(depending on O and H
antigenes) for all bacteria from the genera
Salmonella

Determinants of Salmonella

pathogenicity



Endotoxin = LPS = lipopolysaccharide

(with an antigenic polysaccharide = antigen

O): fever, hypoglycemia,leucopenia,

hypotension,perfussion disturbances,

activation of C3 and complement,

disseminated intravascular clotting,shock



Invasins: proteins taking part in adherence to,

and penetration of, intestinal epithelial cells.



Factors involved in resistance to phagocytosis



Factors involved in resistance to acidic pH



Vi antigen (capsular polysaccharide with

antiphagocytic properties)

Epidemiology



Reservoir: animals



Invasion route: alimentary, fecal – oral



Portal of entry: epithelium of small intestine



Salmonellosis is usually caused by animal

pathogens that come to humans through

contaminated food ( poultry and eggs)



Typhoid fever and typhoid-like illness are

acquired via fecal-oral route, contaminated

water/food (asymptomatic chronic carriers –

they usually suffer from the disease of biliary

tract; bacteria live here and are excrete with

feces)

Pathogenesis of Salmonella

spp.



Mucosal penetration



Mucosal inflammation
(fluid and electrolyte loss)

Clinical diseases caused by

Salmonella spp.



Typhoid fever/typhus abdominalis (S. typhi)

I week: malaise, fever, aches, pains, constipation

II week: bacteremia (high fever), tender abdomen,

rose-colored spots on the skin, diarrhea;

severe complications are very possible!



Paratyphus/typhoid-like illn. (S.paratyphi ABC)



Gastroenteritis called salmonellosis

(other bacteria from the genera Salmonella, e. g.

S. enteritidis and S. typhimurium) – diarrhea, fever,

abdominal pain, self-limited, lasts 2-5 days;

dehydration and electrolyte imbalance!



Other (rarely): infections of urinary/respiratory

tracts, abscesses, bacteremia, sepsis

Materials for investigation

of Salmonella infections



In salmonellosis the best material for

investigation are feces; bacteria must

be isolated!



If typhoid fever or paratyphus are

suspected: blood culture, feces, urine;

in intestinal phase – a swab of the

ulcer;

bacteria must be isolated!



Culturing: McConkey, special media

(SS, SF)

After isolation of Salmonella

spp.



Biotyping (to assign isolated bacteria to

the genus/genera Salmonella) [API 20E]



Serotyping: confirmation, and assigning to

one of the serotypes by using commercially

prepared diagnostic serum with Salmonella

antisera (slide agglutination test) or on the

basis of the specific immune response of

the patient (the Widal test – 6th week of

infection:



Anti O >1:160 (1:200) or increaseing level-

active disease



Anti H > 1:50



Anti H > 1:200 and low level of anti O – after

vaccination or past disease)

Treatment of Salmonella

infection



Salmonellosis – supportive treatment



Typhoid fever:
I. Chloramphenicol(formerly)
II. Ampicillin and trimethoprim-
sulfamethoxasole (biliary circulation)
(this drugs are more safe so: as
alternative)
III. Quinolones (norfloxacin,
ciprofloxacin) [recent trials] (safe,
effective, biliary circ.)

Control and prevention



From SALMONELLOSIS
Sanitation, immunization of the
animals
that we eat, proper cooking of poultry
products and meat



From TYPHOID FEVER
Sanitation measures, personal hygiene

An effective vaccine is being sought

Characteristi

cs of

Shigella spp.



Gram negative rod



NONMOTILE



Do not ferment lactose
readily on MacConkey
agar



Do not produce gas
from fermentable
carbohydrates



Do not produce H

from thiosulfate

Classification of Shigella

species



S. dysenteriae (belongs to group A) (catalase-
negative, unlike other Enterobacteriaceae)



S. flexneri (belongs to group B)



S. boydii (belongs to group C)



S. sonnei (belongs to group D)

Because of the differences in somatic antigens

(antigens O) and in biochemical properties

Virulence factors of Shigella

spp.



LPS (irritable for intestines)



Invasion plasmid antigens (mediate

attachment to, and penetration of, mucosal

epithelial cells)



Intercellular spread proteins (they facilitate the

spread of bacteria from one cell to another)



SHIGA TOXIN (inhibition of protein synthesis

in humans – mucosal cells’ death); it is a

cytotoxic exotoxin produced only by S.

dysenteriae type 1 or 2 – it causes the most

severe infections

Epidemiology of Shigella

species



True human pathogen (no animal
reservoir)



Transmission: fecal-oral route (direct
contact with infected individual) or
contaminated food and water

Pathogenesis

Ingestion of

organism

Colonisation of large intestine

Micro- abscess

formation

Necrosis of mucosa and superficial

ulceration covered with

pseudomembrane

During recovery – granulation tissue

and scars appear

Clinical diseases caused

by Shigella spp.



Bacterial dysentery/dysenteria
bacilliaris/ shigellosis
(severe abdominal cramps and
frequent, painful passage of low-
volume stools with blood and mucus)



Watery diarrhea (relatively mild
infection)



Gastroenteritis

Shigella dysenteriae

type 1 or 2



Produces Shiga toxin



This toxin causes the hemolytic-uremic
syndrome (disseminated endothelial
damage, leading to intravascular
clotting, hemolysis, and renal failure)

Diagnostics of

shigellosis



Bacteria must be isolated from feces or
rectal swabs



Biotyping (to assign isolated bacteria to
the genus Shigella)



Serotyping: confirmation, and assigning to
one of the subgroups (A/B/C/D) = species
by using samples of serum with various
antibodies for subgroup antigens and
antibodies peculiar to serotypes
(commercially prepared) – latex tests or
slide agglutination tests (to show the
table)

Treatment of shigellosis



Supportive therapy



Antibiotics can be given

(ampicillin, amoxicillin, trimethoprim-

sulfamethoxasole, ciprofloxacin,

azithromycin)

(widespread antibiotic resistance)

Prevention: sanitation and personal

hygiene (because of the fecal-oral

chain of transmission – feces, flies,

fingers)

Proteus genus



Members: P. vulgaris, P.

mirabilis, P.

myxofaciens, P. penneri



Extremely motile

(swarming colonies)



Generally produce

urease (ammonia

creation)



Possess O, H, and K

antigens



Used in Weil-Felix test

(to recognize rickettsiae

infection)

Patogenicity



Virulent factor: endotoxin



Clinical diseases:



Urinary tract infections (kidney stones)



Wound infections,



Septicemia



Food poisoning and diarhhea in neonates



Meningitis



Otitis media

Bacteriological
diagnosis



Speciment: urine, stools, pus, csfluid



Slide (Gram staining)



Culture on McConkey agar, blood agar,
agar (on agar growth H)



Identification :API, ATB

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