In the laboratory diagnosis of enteric fever, blood culture has the highest yield in the first week of illness. Which culture medium and atmosphere provides optimal recovery of Salmonella Typhi from blood?
- A MacConkey agar aerobically — pink lactose-fermenting colonies
- B Thiosulphate citrate bile salt sucrose (TCBS) agar anaerobically
- C Bile broth or tryptic soy broth with a blood:broth ratio of 1:10 aerobically for 7-10 days ✓
- D Selenite F broth as enrichment followed by XLD agar for 24 hours
Correct answer: C. Bile broth or tryptic soy broth with a blood:broth ratio of 1:10 aerobically for 7-10 days
Explanation
Blood culture for enteric fever uses bile broth (or tryptic soy broth with bile salts) as the liquid medium because bile salts overcome the bacteriostatic effect of blood components. The inoculation ratio of blood to broth (1:8-10) is critical to dilute natural antibodies and complement. Cultures are incubated aerobically at 37°C for up to 7-10 days. MacConkey agar is a solid medium for subculture and does not support primary blood cultures. Selenite F and TCBS are used for stool specimens, not blood cultures.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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