New selective media for isolation of clostridia from faecal specimens

Two selective media, novobiocin-colistin agar (NCA) and colistin-crystal violet agar (CCA), were developed for isolating clostridia from human and animal faeces. The basal medium was modified Eggerth-Gagnon agar. The NCA medium contains novobiocin (8 micrograms ml-1) and colistin (8 micrograms ml-1) and the CCA medium contains colistin (10 micrograms ml-1) and crystal violet (10 micrograms ml-1). Nine faecal specimens were cultured. Clostridia isolated on these media were similar to those on non-selective media, and higher than those isolated after heat treatment. However, more clostridial species were isolated on the new selective media compared with the non-selective medium. These selective agars were particularly useful for enumerating and isolating clostridia from human faeces.