Which organism is described as obligate anaerobic gram-positive cocci?

• A. Capnocytophaga
• B. Peptostreptococcus
• C. Propionibacterium
• D. Veillonella

Answer: (B)

Obligate anaerobic Gram-positive cocci are round bacteria that stain purple with a Gram stain and require an oxygen-free environment to grow. Peptostreptococcus fits this description: these are Gram-positive cocci that are strict (obligate) anaerobes and are commonly found as part of the normal oral, gastrointestinal, and genitourinary flora, often implicated in polymicrobial abscesses and soft-tissue infections. In the laboratory, they would grow only under anaerobic conditions and appear as Gram-positive cocci on microscopy.

Capnocytophaga is a Gram-negative organism with slender, fusiform cells and often capnophilic growth, not a Gram-positive cocci. Propionibacterium (Cutibacterium) is a Gram-positive rod, not cocci, and Veillonella is a Gram-negative anaerobic coccus, not Gram-positive.