Abstract
A modified single-disc diffusion method was devised for determination of the antibiotic susceptibilityof Lactobacillus by using the soft agar overlayer technique, which had been originally designed forphage titration. In this method, all the test strains of Lactobacillus could grow well on soft agar.
The minimum inhibitory concentrations (MIC), as determined by the modified disc method, ofsix antibiotics (tetracycline, lincomycin, erythromycin, oleandomycin, penicillin G, and chloramphenicol) disagreed with those determined by the agar and tube dilution methods, but were very close to themaximum tolerant concentrations (MTC) for visible growth estimated by the latter methods. Thosedata were obtained successfully by using constant inocula (0.1 ml) of overnight cultures with 130-160Klett units.
A total of 34 strains of Lactobacillus were tested for in vitro sensitivity to 17 antibiotics. As aresult, the antibiotics of the streptomycin group were inactive against all the test strains, except L.acidophilus and L. jugurti. The antibiotics of the macrolide group, mikamycin, penicillin G, andtetracycline were the most active against almost all the strains. The sensitivity to cephalothin variedwith the species and was low in L. casei. The sensitivity of the test strains to 4 antibiotics (cephaloridine, novobiocin, dehydroxymethylfractoridine, and lincomycin) ranged widely from high torelatively low.
