Infective dose of shigella is:

Ans: a (100) Ref: Ananthanarayan,7th ed, p. 287Infective dosesShigella- 100Salmonella- 103 to 106Vibriae- >1010 (water source)- 102-104 (food source)Campylobacter- 104YersiniaEnterocolitica- 10 -109EHEC- 10-100Shigella:It is an aerobe and facultative anaerobe.All members of enterobacteriacea, including shigella are MR +ve except Klebsiella which is a MR -ve.All shigellae are lactose fermenters except Shigella sonneii which is late lactose fermenting shigella.Shigella are classified on the basis of mannitol fermentation.Special features of Shigella dysentriae Type 11. Catalase is produced by all except Shigella dysentriae Type 1 (catalase -ve).2. It produces a powerful exotoxin and is an example of an exotoxin produced by gram -ve bacillus.3. It produces the most severe form of bacillary dysentery.4. It is the most common cause for HUS in India.5. It has invasive properties and can be demonstrated by sereny test.6. GI symptoms are caused by invasion and not by toxin.7. Mannitol is fermented by all except Shigella dysenteriae Type 1 (mannitol non fermenter).