Salmonella typhi, S. paratyphi A, B, C

Question 1

General Features and habitat of Salmonella Typhi and Paratyphi

Answer 1

Gram – (Rod shape)
Habitat- animal intestine and gallbladder; human pathogen (Enterobacteriaceae)
Motile with peritrichous (many) flagella

Question 2

Biochemical Properties of Salmonella Typhi and Paratyphi

Answer 2

Facultative anaerobe (to distinguish between S. enteritidis)

Facultative intracellular- in macrophages

Capsule- Vi antigen (to distinguish between S. enteritidis)

Acid labile- require higher number of organism to produce damage

H2S + (slower than S. enteritidis),

lactose non-fermenter (-)

Question 3

Pathogenesis of Salmonella Typhi and Paratyphi

Answer 3

Transmitted by fecal-oral route

1 Primary bacteremia (first 2 weeks)- asymptomatic phase

Bacteria entering M-cells (in Peyer’s patches) and eaten by enteral macrophages

Delivered to mesenteric lymph node via macrophage, then to the blood

Multiplication in different organs- liver’s Kuepfer cells, gallbladder, lung, intestines

2 Secondary bacteremia (after 2 weeks)- systemic inflammation

High number of bacteria after multiplication. some return to Peyer’s patch

Multiplication occurs again, causing also ulceration and perforation

Question 4

Clinical Features Typhoid (Enteric Fever) of Salmonella Typhi and Paratyphi

Answer 4

Flu-like symptoms- fever (gradually increasing) with headache, muscle pain and weakness

Rose-colored macules (only in 25% of patients)- on chest and abdomen

“Pea-soup” diarrhea

Osteomyelitis in sickle cell disease patients (#1 cause in sickle-cell disease patients)

Complications- hepatitis, meningitis, pneumonia, arthritis and perforation of intestines

Question 5

Diagnosis of Salmonella Typhi and Paratyphi

Answer 5

Culture- from stool, blood (hemoculture), or urine (positive only after the 2nd week):

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

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

Brillant-green medium: no color (salmonella is lactose negative, E. Coli will show red)

Bismuth-sulfite medium: black color (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

Question 6

Treatment of Salmonella Typhi and Paratyphi

Answer 6

Fluoroquinolones, Ampicillin, Trimethoprim and Sulfamethoxazole (TMP-SMX), Ceftriaxone

Question 7

Prevention of Salmonella Typhi and Paratyphi

Answer 7

Live attenuated vaccine- not obligatory

Question 8

Paratyphoid

Answer 8

S. paratyphi (serotypes- A, B and C) causing “Typhoid-like” disease which is similar to typhoid (i.e. abdominal typhus)