Among the four Shigella species, the one that characteristically shows delayed (late) lactose fermentation on MacConkey agar is:
- A Shigella dysenteriae
- B Shigella flexneri
- C Shigella sonnei ✓
- D Shigella boydii
Correct answer: C. Shigella sonnei
Explanation
Shigella species are non-motile, non-lactose fermenters producing pale colonies on MacConkey agar, but S. sonnei is the exception that ferments lactose slowly, forming pink colonies after several days of incubation. This property can cause confusion with other coliforms if plates are read late. S. dysenteriae type 1 is notable for Shiga toxin production, while flexneri and boydii remain uniformly non-lactose fermenting.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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