Development of Resistance to Penicillin by Pneumococci

Abstract

SummaryThe present study has shown the following: (1) Two strains of pneumococcus developed resistance to penicillin as a result of serial passage through mice treated with this drug. (2) The rate at which resistance developed and the degree of resistance acquired varied significantly with the different strains. (3) The resistance of the one strain tested was not impaired by 30 serial passages through normal mice, indicating that, once established, resistance to penicillin is retained for a considerable period. (4) The development of resistance to penicillin in vivo was accompanied by an increase in resistance to this drug in vitro. (5) The response of the pneumococci to sulfonamides was not altered by the development of resistance to penicillin.