Chromosomal penicillin resistance in Staphylococcus aureus strains of phage group II.

The markers coding for serotype B penicillinase (PcB) in wild type strains of group II of S. aureus behaved as chromosomal characters in 6 out of 7 cases. The restriction deficient mutants also to some strains of group I. No extrachromosomal DNA could be detected in the transductants. The low frequency of transduction of chromosomal markers as well as the high restriction barrier seem to limit the spread of these markers outside group II.