Shigella spp.

Question 1

Shigella spp.

Morphology

Answer 1

Gr- rods, non-spore forming
O, K & pili

Question 2

Shigella spp.

Antigenic structure

Answer 2

LPS - O, capsule - K and pili

Question 3

Shigella spp.

Diagnostic characteristics

Answer 3

non-motile
Glu fermenter, NON-lac fermenter (except S. sonnei)
Catalase + & oxidase -

Question 4

Shigella spp.

Media

Answer 4

MacConkey & levine –> no color change (lac) (except S. sonnei)
Kligler’s Iron –> red top, yellow bottom

Question 5

Shigella spp.

Shigella pathogenesis (+ transmission)

Answer 5

Fecal-oral
attach & invade Peyer’s patches –> T3 secretion system (proteins into macrophages & target cells) –> membrane ruffling & bacterial engulfement –> replication –> actin filament rearrangement into tails (motility) –> cell-to-cell passage = stay inside protected.
Eventuallly induce apoptosis –> inflammation –> spreading via cell debris to deeper tissues –> clinical symptoms

Question 6

Shigella spp.

Pathogenicity

Answer 6

Shiga toxin (exotoxin)
A & B –> bind Gb3 on intestinal villi & renal endothelial cells –> stop protein synthesis (A bind ribosomal RNA) –> symptoms

Question 7

Shigella spp.

Clinical findings (symptoms 1st & 2nd, incubaiton)

Answer 7

Incubaiton: 1-4days
1st: sudden abdominal pain, fever & watery diarrhea (enterotoxin)
2nd: abdominal cramps & tenesmus with pus & blood in feces
Complications: dehydration, acidosis, hemolytic uremic syndrome & death.

Question 8

Shigella spp.

Hemolytic uremic syndrome

Answer 8

5-10% of infecte children<10y/o
destruction of glomerular endothelial cells –> platelet activation –> thrombin activation –> microthrombi formation –> decreased GFR –> acute renal failure
Increases: creatinine & urea
Decreases: GFR, RBCs and Hgb (& thrombocytopenia)

Question 9

Shigella spp.

Prophylaxis & treatment

Answer 9

1. Non-specific (sanitation; food & water, sewage disposal & fly control, isolation of patients, carrier identification and antibiotic treatment of infected)
2. Antibiotics & symptomatic