He growth inhibitory effects of Lactobacillus casei YIT 9018 on _Mycobacterium tuberculosis and. .V. fortuitum were investigated in LM(Lactobacillus-Mycobacterium) broth which was newly formulated in order to culture both mycobacteria and lactobacilli simultaneously.
1. Forty eight hour simultaneous cultivation of L. casei and M. tuberculosis H37Rv resulted in. total growth inhibition of 7.6X107 cocultured tubercle bacilli, while viable cells of L. casei continuously increased and reached 3.4X1011 from 9.2X107 bacilli per ml of original inoculum. The viable: cell number of M fortuitum temporarily increased up to 6.4x108/ml from 4.4x108/ml at 24 hour-incubation but the numbers eventually decreased to 9.2x107/ml within 48 hours when the viable number of L. casei reached to their maximum 2.9x1011 from 4.4 X 107/ml of original inoculums, and total inhibition was observed at 72 hour-incubation. Meanwhile, the pH of LM broth in which L. casei and mycobacterial species were co cultivated also dropped to pH 3.80-3.95 from pH 6.60 within 48-72 hour-incubation with the variation of viable cell numbers of bacteria tested. Decrease of -the viable cell of mycobacterial species was closely related to decreasing pH value of medium due to increasing concentration of lactic acid produced by lactobacilli.
2. Whether growth inhibition of mycobacteria due to pH change of medium or to lactic acid, was investigated. Such facts were indirectly proved in serial tests. In sterilized saline solution, which was adjusted to pH 3.85, 4.15, and 6.60 with HC1 or lactic acid respectively, L. casei and mycobacteria were inoculated and incubated bor 5 days at 37°C. The viable units of tested organisms at different pHs were investigated every 24 hours. In the pH 4.15 saline solution adjusted with lactic acid, the total growth inhibition of M tuberculosis and M. fortuitum was observed within 24 and 72 hours respectively, while at the same pH adjusted with HCI, the growth of. M tuberculosis was inhibited within 48-72 hours, but cultivable cells of M. f ortuitum remained a. many as 5.18 X 3 0 1ml even at pH 3.85. This clearly indicated that lactic acid played an important role in mycobacterial gowth inhibition, when they were co cultured with lactobacilli.
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