BETA-LACTAMASE PRODUCTION AND GENETIC LOCATION IN STAPHYLOCOCCUS-AUREUS - INTRODUCTION OF A BETA-LACTAMASE PLASMID IN STRAINS OF PHAGE GROUP-II

Staphylococcus aureus strains of phage group II have increased in freq uency in hospital-acquired infections during recent years. A total of 184 penicillin resistant group II strains from bacteraemia cases in th e years 1961-1990 were analysed for the amount of beta-lactamase produ ced and the location of the beta-lactamase gene. Until 1977 all strain s investigated had a chromosomally located beta-lactamase gene, but si nce then a 21 kb beta-lactamase plasmid has increased in occurrence am ong group II strains, especially among those strains typable only at h igh phage concentrations [100 x Routine Test Dilution (RTD) and 1000 x RTD]. In 1990, 84% of the group II strains contained this plasmid. Pl asmid-containing strains produced more beta-lactamase than strains wit hout the plasmid. S. aureus strains of the 94,96 complex, which since 1984 have decreased in frequency from 18 to 9% in 1993, have remained high producers of beta-lactamase.