Drug Resistance of Staphylococci

On the basis of resistance patterns to penicillins, strains of Staphylococcus aureus highly resistant to penicillin‐G which were isolated from clinical sources, could be classified into 2 groups, A‐1 and A‐2. Group A‐2 is a minor group which accounts for about 10% of these strains and exhibits lower degree of resistance to penicillin‐G and phenethicillin than that exhibited by group A‐1 strains. However, there was no marked difference between both groups in inducible production of penicillinase. The genetic determinants for penicillinase synthesis in strains of both groups were transduced into a recipient and the characteristics of the determinants were compared with each other under identical conditions. The results suggested that the genetic determinants for penicillinase synthesis in groups A‐1 and A‐2 strains differed from each other in both the structural gene for penicillinase production and the regulatory gene for the formation of the repressor.