[Antibiotic sensitivity of Bacillus thuringiensis var. galleriae strains]

Bacillus thuringiensis strains forming colonies of the S and R morphology were found to be susceptible to streptomycin, chloramphenicol, rifampicin, neomycin, lincomycin, monomycin, kanamycin, and resistant to ampicillin and polymyxin. The S strains were shown to be susceptible to tetracycline (Tets), whereas the R strains were either susceptible (Tets) or resistant (Tetr). The population of Tetr strains was heterogeneous in its resistance to tetracycline (the frequency of Tetr cells was from 10(-4) to 1). The incubation with a subinhibiting concentration of tetracycline (2 micrograms/ml) caused "induction", which decreased in the presence of chloramphenicol, in the Tetr strains. No "induction" was detected in Tets strains. No significant differences were found in the plasmid composition of the Tets and Tetr strains, and no correlation was established between the presence of plasmids and the resistance to tetracycline. It may be concluded therefore that determinants for the resistance to tetracycline are located in the chromosomes. Possible factors causing the resistance to tetracycline in B. thuringiensis are discussed.