Isolation of mycobacteria from contaminated material on selective media.

A procedure more efficient than the earlier ones was developed for the isolation of mycobacteria from heavily contaminated materials. The contaminating microbes were killed by acid decontamination preceded by an incubation of 1 g sample in 5 ml nutrient broth at 33 degrees C for 4 h. The efficiency of isolation was examined using culture media containing varying concentrations of dimetridazole and/or clotrimazole (Canesten Bayer). None of 40 mycobacterial strains representing all 4 Runyon groups was inhibited by 80 micrograms/ml of either of the inhibitors. From the sediment of acid-decontaminated samples, Löwenstein-Jensen medium containing 10 micrograms/ml of both dimetridazole and clotrimazole as well as Petragnani medium with and without glycerol and Sula media were inoculated. Model experiments and processing of 44 routine samples have made likely that aerobic sporeformers on the one hand and fungi and anaerobes on the other are killed, or at least depressed in growth, by pre-incubation combined with the addition of clotrimazole and dimetridazole to the culture medium. Thus, the isolation rate of mycobacteria can be improved.