EFFECT OF FREEZING OF WATER SAMPLES ON VIABLE COUNTS OF ENVIRONMENTALMYCOBACTERIA

The effect of prolonged storage on mycobacteria and other heterotrophi c bacteria in brook water samples was examined by determination of via ble counts from fresh samples and again after water concentrates had b een stored in nutrient broth at -75 degrees C for 15 months. The count s of mycobacteria were on average three times higher after storage (ra nge of ratio 0.9-10.4). In contrast, the viable counts of other hetero trophic bacteria were reduced by 69%. The increase in mycobacterial co unts was probably due to break-up of microcolonies or release of attac hed bacteria from particles. The possibility of cultivating mycobacter ia from frozen samples is of practical help in large-scale field surve ys.