Shigella

Question 1

Species of medical importance

Answer 1

Shigella sonnei
Shigella flexneri
Shigella dysenteriae
Shigella boydii

Question 2

Distinguishing features

Answer 2

Gram negative rods, nonmotile, non lactose fermenters

Question 3

Reservoir

Answer 3

Human colon only (no animal carriers)

Question 4

Transmission

Answer 4

Fecal-oral spread, person to person

Question 5

Pathogenesis

Answer 5

-Endotoxin triggers inflammation
-No H antigens
-Shigellae invade M cells
-Shiga toxin :
Produced by S. Dysenteriae,type I
Three activities: neurotoxicity, cytotoxic, enterotoxic
AB component toxin is internalized in human cells; inhibits protein synthesis by clipping 60S ribosomal subunit

Question 6

Disease

Answer 6

Enterocolitis / shigellosis
Organisms invade producing bloody diarrhea
Fever
Lower abdominal cramps tenesmus; diarrhea first watery then bloody

Question 7

Diagnosis

Answer 7

Isolation from stool during illness and culture on selective media