Variants of Escherichia coli , Pseudomonas aeruginosa , and Bacillus subtilis Requiring Streptomycin

Abstract

Strains of E. coli, P. aeruginosa, and B. subtilis that had developed resistance to streptomycin when grown on synthetic media yielded better and more rapid growth in the presence of the antibiotic. A variant of B. subtilis was isolated which produced a spreading growth on nutrient agar containing 150 and 300 [gamma]/ml. of streptomycin. These rod-shaped organisms grew only when streptomycin was present and only under anaerobic conditions. A few streptomycin-resistant organisms, similar to the type A meningococcus were also observed; these were aerobic, nongranular rods. The basal medium was similar to that of Grossowicz (1945) except for the exclusion of glucose, Na thiosulfate, sodium d-gluta-mate, and thiamine. The medium contained only NH4Cl as a X source and excluded all C-containing compds. The organisms could not grow until certain C-compds. were added. Streptomycin stimulated the growth of all the organisms when glucose was present. Only P. aeruginosa was stimulated when formate was present. B. subtilis growth in the presence of streptomycin and glucose reached its maximum within 24 hrs.; when Na d-glutamate was added, growth was maintained for the whole period of observation at the max. level it had reached with glucose alone. This level decreased on removing NH4Cl.