Bacterial resistance to antibiotics in vivo. II. Population patterns among staphylococci.

Bliss, Eleanor A. (Bryn Mawr College, Bryn Mawr, Pa.) and Burr M. Alter. Bacterial resistance to antibiotics in vivo. II. Population patterns among staphylococci. J. Bacteriol. 84:125-129. 1962-The general level of resistance to streptomycin of a sensitive strain of Staphylococcus aureus was increased by exposure to the antibiotic in vivo. Although a rise in the minimal inhibitory concentration of streptomycin in broth was seen infrequently, over half the cultures from treated mice showed a shift in the population pattern toward greater tolerance for the antibiotic. A similar change did not occur in staphylococci after exposure in vivo to penicillin or chlortetracycline. Except in the case of highly resistant mutants, the level of population tolerance for streptomycin appears to be related to the concentration of the antibiotic in the tissues of the host, since strains already possessed of a measure of resistance failed to gain in resistance when exposed to streptomycin in vivo. The mechanism of survival and outgrowth of the occasional highly resistant mutant is considered.