A comparison of selective media for the isolation of anaerobic bacteria from clinical material

Clinical specimens submitted for anaerobic culture to a Melbourne teaching hospital microbiology laboratory were plated onto 3 types of selective media, to determine which would allow the optimal recovery of anaerobic organisms. The 3 media employed were kanamycin agar (KA), neomycin agar (NA) and nalidixic acid-Tween 80 agar (NAT). The highest isolation rate was achieved on NAT, 89% of the total of all anaerobes isolated being recovered on this medium. A recovery rate of 69% was achieved using NA, while use of KA allowed the isolation of only 56% of all strains. The major difference between 3 media was in the recovery of anaerobic Gram-positive cocci, which accounted for 40% of the total isolates on NAT, 25% on NA, and only 11% on KA. The NAT was also more successful in the isolation of Fusobacterium and Veillonella species. The NAT medium failed, however, to recover Clostridium spp. that were isolated on both NA and KA. There was no significant difference between the 3 media in regard to the recovery of Bacteroides spp.