BACTERIAL RESISTANCE TO ANTIBIOTICS

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Abstract
Penicillin resistance can be developed in vitro during subcultivation on artificial media containing increasing concns. of penicillin. It has also been developed in vivo by repeated passage of a strain of meningococcus through mice treated with subcurative doses of penicillin. Penicillin resistance develops slowly because the resistant mutants have only a little higher resistance than the bacterial population in which they arise. Development of penicillin resistance by penicillin-sensitive bacteria is seldom a serious clinical problem in the treatment of human infections. Development of penicillin resistance during treatment should not be confused with replacement of penicillin-sensitive bacteria by naturally resistant ones, as secondary invaders. Streptomycin resistance can develop very rapidly in vitro or in vivo owing to the appearance of streptomycin-resistant variants which arise in the bacterial population by the process of mutation. These mutants are of 2 types, both of which are resistant, and one of which is dependent on streptomycin for its growth in vitro and in vivo. Both types can arise among the microbial inhabitants of the upper respiratory passage of animals and patients during treatment with streptomycin.