Which Shigella species is a late lactose fermenter and produces pink colonies on MacConkey agar after prolonged incubation?
- A Shigella dysenteriae
- B Shigella flexneri
- C Shigella sonnei ✓
- D Shigella boydii
Correct answer: C. Shigella sonnei
Explanation
Shigella sonnei is the only Shigella species that ferments lactose, albeit slowly, producing pink colonies on MacConkey agar after 24-48 hours. S. dysenteriae, S. flexneri, and S. boydii are non-lactose fermenters. This characteristic helps differentiate S. sonnei from other Shigella species in the laboratory. In India, S. flexneri is the most common species, but S. sonnei is notable for late lactose fermentation.
Reference: Ananthanarayan and Panicker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.