Shigella species are distinguished from other enteric gram-negative bacilli by their remarkably low infectious dose. Approximately how many organisms are required to cause shigellosis in a healthy adult volunteer?

• A 10^8 to 10^9 organisms
• B 10^5 to 10^6 organisms
• C 10^3 to 10^4 organisms
• D 10 to 100 organisms ✓

Explanation

Shigella has the lowest infectious dose among bacterial enteric pathogens, with as few as 10 to 100 organisms causing disease. This extreme infectivity is due to resistance to gastric acid (compared to Vibrio and Salmonella) and efficient cell invasion. Salmonella and Vibrio cholerae typically require 10^5 to 10^8 organisms. This low dose explains efficient person-to-person transmission.

Reference: Jawetz, Melnick, & Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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