Which organism is primarily used for isolation on KVLB agar in anaerobic culture?

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

Answer: (A)

KVLB agar is a selective medium used to isolate Bacteroides species, especially Bacteroides fragilis, from anaerobic specimens. It contains vancomycin to inhibit most Gram-positive bacteria and kanamycin to suppress many other Gram-negative organisms. The Bacteroides fragilis group is resistant to these antibiotics, so they are able to grow on KVLB while other bacteria are inhibited. The laked blood provides nutrients that help fastidious anaerobes flourish. So this medium is particularly suited to recovering Bacteroides fragilis from mixed anaerobic flora. The other organisms listed are typically inhibited by vancomycin or not as effectively supported by KVLB, which is why they aren’t the primary targets of this medium.