S3. Salmonella, shigella, & yersinia Flashcards
Common characteristics between all 3?
- All members of Enterobacteriaceae family
- Aerobe & facultative family , gram -ve
- motile / non-motile
- ferment glucose
- oxidase NEGATIVE , reduce nitrate to nitrite
- produce lactose nonfermenting colonies on mcConkey agar
- cause disease w/in & outside intestinal tract ( in humans & animal)
Purpose of mcConkey agar?
- used in the differentiation of lactose fermenting from non-fermenting gram negative bacteria
Salmonella?
- gram -ve, motile, produce lactose nonfermenting pale colony on mcConkey agar, black- centered pale colony on tellurite containing media (salmonella-shigella agar) due to the production of H2S (hydrogen sulfide)
Classification of Salmonella?
- Typhoid (humans)
- Salmonella typhi
- Salmonella paratyphi A,B,C
- Non-Typhoid ( animals)
Diseases caused by salmonella?
- Enteric fever (typhoid & paratyphoid fever)
- Caused by S.typhi & S. Paratyphi A,B,C HUMANS ONLY by contaminated food and water
— it is an invasive disease w/ constipation or diarrhea
VERY IMPORTANT pathogenesis of S.typhi
- Ingestion of S.typhi (humans)
- Bacteria multiply in SI
- Goes to mesentric lymph nodes
- Transient bacteremia ( at this stage, patient presents no symptoms bc of low number of bacteria / the bacteria can be isolated in blood/ stool/ urine)
- Invade & multiply in macrophages
Virulence factors of enteric fever organisms
- multiply in macrophages - intracellular pathogen
- S.typhi & S. Paratyphi C possess Virulence capsular antigen
- LPS antigen contributes to production of proinflammatory cytokines (TNF, IL-1, IL-6)
Non-typhoid Salmonella?
- Common serotypes are: S. typhimurium & S.enteritidis
- of not treated cause Gastroenteritis of inflammatory nature (food poisining)
Non-typhoid Salmonella Resevoirs?
Poultry ( intestine), eggs (infection of oviduct), cattle, pet animals ( dogs, snakes, turtles ), lizards
Non-typhoid Salmonella virulence factors?
- multiply in macrophages
- invade intestinal mucosa
- produce enterotoxins ( causing diarrhea
Labratory diagnosis of Enteric fever?
- blood agar
- cultured from urine & stool
- identified from biochemical reaction & confirmed by slide aggulination test w/ specific antisera
- serological test ( widal test which measures rising serum antibody to O and H antigens)
Labratory diagnosis of Non-typhoid Salmonella infections?
- Clinical specimen cultured for Salmonella on enteric media ( mcConkey agar, Salmonella-Shigella agar)
- identification or Salmonella by serotyping available for reference laboratories only
Epidemiology of enteric fever?
- prevelant in developing countries
- organisms have a predilection for gall bladder with establishment of chronic carrier state & excretion in stool ( about 5% typhoid fever patients become carriers)
- food handlers who are carriers can transmil the organism via contaminated food due to poor personal hygiene
- live oral vaccine and Vi antigen-based injectable vaccine available available against S.typhi
Shigella characteristics?
Gram -ve, non-motile, non-capsulated, do not ferment lactose ( S.sonnei is late lactose-fermenter after 24 hrs of incubation) genetically closely related to E.coli ( H2S negative)
Classification of shigella?
- Shigella dysenteriae ( with 15 serotypes) most severe form
- Shigella flexneri ( with 15 serotypes)
- Shigella boydii ( with 20 serotypes)
- Shigella sonnei ( with a single serotype) mildest form
Diseases caused by shigella?
- Causative agent of bacillary dysentery
- S.dysentriae ( particularly serotype1 ) causes very severe disease snd S.sonnei causes mild disease
Virulence factors of shigella>?
- invasive of and multipy in colonic mucosa producing ulcers
- invation mediated by invasion plasmid which encodes invasion plasmid antifens (outer membrane proteins) (omp’s)
- produce of enterotoxins (ShER 1& 2) (shigella enterotoxin) which mediate watery diarrhea preceding dysentery
- S.dysenteraie 1 produces Shiga toxin simlar to that of enterohaemorrhagiv E. Coli resulting in haemolytic uraemic syndrome(HUS)
HUS?
- progressive renal failure
- hemolytic anemia & thrombocytopenia
- most common cause of acute kidney injury in children
- 20% of kids develop hypertension
Diagnoses of shigella?
- mcConkey agar, salmonella-shigella agar
- lactose non-fermenting
- confirmed as shigella by slide agglutination w/ specific antisera
Epidemiology of shigella?
- infectious dose 100-290 organisms
- person - person
- humans (main reservoir)
- infections with S.dysenteriae and S.flexneri predominant in developing countries w/ epidemics due to S.dysenteraie 1
- in developed countries, infection is mainly due to S.sonnei
Yersinia?
- transmitted to humans by food, water, insect vectors
- gram -ve coccobacilli
There are 3 species in the genus Yersinia whatre they?
Y.Enterocolitica
Y.pseudotuberculosis
Y.pestis (causes plague)
Yersinia enterocolitica?
Gram -ve, non-sporing, bacilli, grows on mcConkey afae, producing NLF colony; grows on selective medium CIN agar producing pink “bulls eye” colonies, motile at 25 C, non-motile at 37C
Diseases of yersinia ?
- bloody diarrhea w/ fever and abdominal pain
- pseudoappendicitis- mesenteric lymph adentitis & terminal iileitis mimicking this condition
- sequelae- arthralgia (joint pain), reactive arthritis / Reiters syndrome(inflammation of joints as a reaction to infection elsewhere in the body; autoimmune disease, erythema nodosum ( erythematous nodules under the skin in front of the legs below knees)
