The effect of penicillin on genetic changes and temporary modifications in populations of brucellae.

During the isolation of penicillin resistant mutants of Brucella abortus, B. suis, or B. melitensis two effects of the antibiotic were observed: (1) rapid population changes involving the establishment of nonsmooth mutants during growth in increasing concentrations of penicillin; and (2) the occurrence of smooth, penicillin resistant cells whose phenotype differed depending on whether they grew in the presence or absence of penicillin. An analysis of these effects will be described in this report.