Kanamycin-vancomycin laked-blood (KVLB) agar incubated anaerobically is primarily used for isolation of which organism?

• A. Bacteroides fragilis
• B. Bifidobacterium dentium
• C. Clostridium perfringens
• D. Peptostreptococcus anaerobius

Answer: (A)

KVLB agar uses antibiotics to suppress competing flora and let a specific anaerobe stand out. Vancomycin blocks growth of Gram-positive bacteria, while kanamycin targets many Gram-negative bacteria; however, the Bacteroides fragilis group is relatively resistant to kanamycin, so they can grow on this medium while most other anaerobes and aerobes are inhibited. The laked blood provides nutrients that support anaerobic growth, helping these organisms form characteristic colonies. Because of this selective setup, KVLB is used primarily to isolate Bacteroides fragilis group from mixed anaerobic specimens. The other organisms listed are Gram-positive and would be inhibited by vancomycin, so they aren’t the primary targets on this medium.