Transferable β-lactamase. A new mechanism for in vitro penicillin resistance in Streptococcus faecalis

Abstract

Although enterococci are relatively resistant to penicillin, the mechanism of resistance is largely unknown and enzymatic inactivation does not play a role. In this study, an isolate of Streptococcus faecalis was found to have beta lactamase activity resulting in complete inactivation of penicillin. With a high inoculum, this strain was resistant to >1,000 μg/ml of penicillin. Penicillin resistance and beta lactamase activity were transferred by conjugation at a high frequency to an enterococcal laboratory recipient strain together with two plasmids of molecular size 34 x 106 and 56 x 106, thus demonstrating the emergence of plasmid-mediated penicillin resistance in the genus Streptococcus.