Beta-lactam antibiotics resistant Rothia dentocariosa from infected postoperative maxillary cyst: studies on R-plasmid and beta-lactamase.

A cephalexin and penicillin G resistant strain of Rothia dentocariosa was clinically isolated from pus of infected postoperative maxillary cyst. The strain contained multiple plasmids. Plasmid curing tests with rifampicin eliminated cephalexin and penicillin G resistant phenotypic functions and 47 megadalton plasmids from the strain. Beta-Lactamase isolated from the strain hydrolyzed cephalosporin more efficiently than penicillin.