Growth Characteristics of Microorganisms Occurring in Penicillin-Treated Brucella abortus Cultures

Abstract

Summary and Conclusions

Microorganisms capable of producing L-colonies were detected in penicillin-treated broth cultures of B. abortus, 3183, throughout a 7-day incubation period by subcultures made to agar plates containing penicillin. Isolation of comparable numbers of bacterial colonies from the same cultures when subcultures were made to antibiotic-free agar plates, and absence of L-colonies on the latter plates, indicates that most cell wall-defective forms capable of producing L-colonies were also capable of reverting to bacteria. Bacteria with increased resistance to penicillin were isolated from some treated broth cultures and after reversion of B. abortus L-phase variants. Failure to show an increase in the number of colony-forming organisms during 7 days of incubation in penicillin-treated broth cultures suggests that a steady state existed in these cultures. Persistence of B. abortus on the surface of agar plates containing penicillin points up the fact that survival of bacteria under inhibitory conditions may not necessarily require induction of cell wall-defective forms, or development of resistance, in the intervening period of time. Finally, results presented in this paper substantiate earlier evidence suggesting that microorganisms occurring in penicillin-treated cultures of B. abortus, 3183, cannot reproduce themselves in a cell wall-defective state for a prolonged period of time, and that most are unstable L-phase variants.