Purulent material from a cerebral abscess shows Gram-positive cocci in chains and gram-negative bacilli with pointed ends on Gram stain. Based on these smear findings, which combination of anaerobic organisms is most likely?

Purulent material from a cerebral abscess shows Gram-positive cocci in chains and gram-negative bacilli with pointed ends on Gram stain. Based on these smear findings, which combination of anaerobic organisms is most likely?

• A. Veillonella sp. and Clostridium sp.
• B. Eubacterium sp. and Veillonella sp.
• C. Peptostreococcus sp. and Nocardia sp.
• D. Fusobacterium sp. and Peptostreptococcus sp.

Answer: (D)

Two different anaerobic organisms are suggested by the smear: a Gram-positive coccus in chains and a Gram-negative bacillus with pointed ends. The Gram-negative bacilli with pointed ends fit Fusobacterium, a common anaerobic oral bacterium with fusiform rods. The Gram-positive cocci in chains in an anaerobic context from an oral source point to Peptostreptococcus (Peptostreptococcus sp.), another frequent contributor to polymicrobial brain abscesses. Together, Fusobacterium and Peptostreptococcus neatly explain both observed morphologies and the infection’s typical origin. The other options mix organisms whose Gram-stain appearances don’t match both features seen on the smear (for example, Veillonella are Gram-negative cocci, Clostridium and Eubacterium are rods, and Nocardia is an aerobic, filamentous actinomycete).

Two different anaerobic organisms are suggested by the smear: a Gram-positive coccus in chains and a Gram-negative bacillus with pointed ends. The Gram-negative bacilli with pointed ends fit Fusobacterium, a common anaerobic oral bacterium with fusiform rods. The Gram-positive cocci in chains in an anaerobic context from an oral source point to Peptostreptococcus (Peptostreptococcus sp.), another frequent contributor to polymicrobial brain abscesses. Together, Fusobacterium and Peptostreptococcus neatly explain both observed morphologies and the infection’s typical origin.

The other options mix organisms whose Gram-stain appearances don’t match both features seen on the smear (for example, Veillonella are Gram-negative cocci, Clostridium and Eubacterium are rods, and Nocardia is an aerobic, filamentous actinomycete).