Occurrence of resistance to neomycin and kanamycin in Bacillus popilliae and certain serotypes of Bacillus thuringiensis: Mutation potential in sensitive strains

Serotypes of Bacillus thuringiensis and the commercial strain of Bacillus popilliae were examined for their inherent resistance to antibiotics and their mutation potential in respect to neomycin and kanamycin, the presence of which would preclude the use of plasmids marked by genes for resistance to the antibiotics. Clones on initial plates were detected by the recurrence of resistance colonies at superimposable sites on serial replicaplates containing the antibiotic. Susceptible strains were selected for the determination of their antibiotic-resistance mutation potential. Three varieties of B. thuringiensis were found to be doubly resistant, seven varieties were singly resistant (Neo^r), and three other varieties, including B. popilliae, were susceptible to both antibiotics. Estimates of mutation ratios revealed that three serotypes developed no resistant mutants to either antibiotics in populations as high as 3.0 × 10¹⁰; seven other serotypes developed no resistance to kanamycin in populations as high as 4.6 × 10⁹ cells. Three other serotypes exhibited mutation ratios as high as 1.6 × 10^?2. We were unable to determine the mutation ratio for B. popilliae.