Salmonella genus and salmonellosis

Question 1

General features and habitat of Salmonella enteritidis

Answer 1

Gram – (Rod shape)

Habitat- normal human and animal intestinal flora
(Enterobacteriaceae)

Motile with peritrichous (many) flagella

Question 2

Biochemical Properties of Salmonella enteritidis

Answer 2

Facultative intracellular- in macrophages

Capsule

Acid labile- require higher number of organism to produce damage

H2S + (all H2S positive are motile),

lactose non-fermenter (-)

Question 3

Pathogenesis of Salmonella enteritidis

Answer 3

Reservoir- zoonosis like chicken, duck eggs, pets’ feces and some other animals (swine…)

Transmitted by ingesting food (i.e. eating chicken or eggs)
Bacteria enter via oral route by contaminated food or drinks.
Reach the small and large intestine, causing inflammatory lesions (localized to intestine)

Incubation time of 14-48 hours

Question 4

Clinical Features
Salmonellosis
(Gastroenteritis) of Salmonella enteritidis

Answer 4

Inflammatory diarrhea
Abdominal pain
Vomiting
Dizziness

In children, elderly or immunocompromised- sepsis, meningitis (invasive infection)
Asymptomatic carriage can be another consequence

Question 5

Diagnosis of Salmonella enteritidis

Answer 5

Culture- from stool, blood (in case of sepsis), food leftover culture for public health

Feces culture in enrichment medium containing selenite (Leifson medium), then plated:

Eosin-Methylene Blue (EMB) medium: pink colonies (lactase negative)

Brillant-green medium: Lactose, dextrose, saccharose with Andrade indicator will appear
with no color (salmonella is lactose negative, E. Coli will show red)

Bismuth-sulfite medium: on bismuth salt + sodium sulfite medium, salmonella H2S production will cause bismuth sulfide to be colored black (selective for salmonella)

Salmonella-Shigella (Hektoen) medium: black colonies (to distinguish from shigella)

Serology:
Slide agglutination- specific antibody to identify bacteria ‘O’ and ‘H’ antigens

Gruber-Widal test (tube agglutination)- serial dilutions of Ag to detect Ab in serum

Phage typing- for public health purpose

Question 6

Treatment of Salmonella enteritidis

Answer 6

Self-limiting (around 1 week)- supportive therapy of fluid and electrolytes replacement

In neonates or invasive infection- Ampicillin, Fluoroquinolones, 3rd gen. Cephalosporin

Question 7

Salmonella Genus additional info :

Answer 7

Wide host specificity: (both human and animal)
Normal flora in the GI of animal
Causing in human gastroenteritis (zoonosis infection)
S. enteritiditis, S. typhimurium

Adapted to human:
Only human pathogen causing enteric fever
S. typhi, S. paratyphi (A, B, and C)

*Salmonella enterica is new collective name containing 7 subspecies, including- S. enteritiditis, S. typhimurium and S. typhi