Sensitivity of Genus Lactobacillus to Several Kinds of Antimicrobial Agents and Cellular Elongation

Antibacterial activity and morphological effects of many kinds of antimicrobial agents on genus Lactobacillus were investigated. Five strains of 4 species were examined in Rogosa medium. Twenty drugs were tested and the results were as follows : 1) Most of the strains used showed high sensitivity to many kinds of antibiotics except sulfaisoxazol, nalidixic acid, colistin and polymyxin B. 2) Conception and definition of the elongation were discussed by numerical expression and the cells were classified into two major groups, the ordinary cell group and the authentic group with elongation. 3) Elongation of cell body could be seen by incubation with some antibiotics. Particularly, many elongated cell bodis were observed in combination of Lactobacillus acidophilus or L. bulgaricus with piperacillin (PIPC), and L. bulgarics or L. fermentum 1214 with cephalothin (CET). 4) Phenomenon called elongation was recognized in the lower concentrations than the minimum inhibitory concentration (MIC) in each of PIPC and CET. Particularly, it was remarkable in the range of concentration between one-fourth and a half of MIC. 5) Shapes of the elongated cell bodis were classified into 4 major groups. They were a long rod, a filamentous, a spiral and a helical forms. The former two were usually observed under each of PIPC and CET. The spiral elongation was observed in combination of L. bulgaricus with PIPC. The helical type was also seen in combination of PIPC with two species, acidophilus and bulgaricus. 6) Mechanism of elongation was discussed from the viewpoint of activities of PIPC and CET, impediment in the synthesis of cross wall. 7) Elongated cells with multi-nucleoid were usually observed. This phenomenon was considered that DNA synthesis during cellular elongation was not inhibited by these antibiotics. 8) Decrease of the metachromatic bodies in the elongated cell body was observed in many strains. This phenomenon was particularly remarkable in combination of L. bulgaricus with CET.