Shigella

Question 1

Characteristics of shigella

Answer 1

Non-lactose
Human-specific
Non-motile
Enterobacteriaceae
Gram -
Facultative anaerobe

Question 2

4 species of shigella

Answer 2

S. dysenteriae (1)
S. flexneri (2a)
S. boydii
S. sonnei

Question 3

Characteristics of shigellosis

Answer 3

Severity varies from diarrhoea to dysentery
Occurs in developing countries
60% mortality in kids
Water, human-human

Question 4

Characteristics of dysentery

Answer 4

Infective dose 10-10^4 live cells
12-50h after infection
Fever, cramps, liquid stools often become bloody
Lasts 3-4d or 10-14d in severe cases
Asymptomatic carriage for several months

Question 5

How does shigella cause infection?

Answer 5

Invasion of epithelial cells of the colon
Plasmid-determined character
Genes from INV plasmid like those from chromosomal SPI-1
Intra-cellular multiplication in cytoplasm

Question 6

How does Shiga toxin cause intoxication?

Answer 6

StxAB genes on chromosome but not phage
AB5 structure binds glycolipid Gb3 (cell surface)
Internalised A1 subunit acts on 28S rRNA of the 60S ribosomal subunit

Question 7

Where is Shiga toxin most commonly found?

Answer 7

S. dysenteriae