STAPHYLOCOCCUS-AUREUS STRAINS DIFFER IN THEIR IN-VITRO RESPONSIVENESSTO HUMAN UROKINASE - EVIDENCE THAT METHICILLIN-RESISTANT STRAINS ARE PREDOMINATELY NONRESPONSIVE TO THE GROWTH-ENHANCING EFFECTS OF UROKINASE

Clinical isolates of Staphylococcus aureus were found to exhibit strai n-specific heterogeneity to the growth-enhancing effects of human urok inase (UK), a proteinase with plasminogen activator activity. Nine out of fourteen (64%) methicillin-sensitive strains of S. aureus were res ponsive to UK in ''in vitro'' cultures. In contrast, 3/29 (10%) methic illin-resistant strains were responsive to the proteinase. When only s trains isolated fr om western Canada were considered, 6/11 methicillin -sensitive strains and 1/26 methicillin-resistant strains were respons ive to UK. The single western Canadian methicillin-resistant strain (s train 456) responsive to UK was one of two isolated from the same pati ent. indicating that the two strains were phenotypically different. St rain 456, resistant to 32 mu g methicillin/mL, was responsive to as li ttle as 50 U UK/mL and enhancement of growth was evident by 9 h of inc ubation at 37 degrees C. This growth enhancement was specific to UK an d not duplicated by equivalent concentrations of other proteins (bovin e serum albumin, trypsin, plasminogen). The results presented indicate differences in the frequency of the UK-responsive phenotype between m ethicillin-sensitive and -resistant S. aureus. These findings indicate that the UK phenotype of S. aureus may have utility in both phenotypi ng clinical isolates, as well as providing insights into the regulatio n of growth in this clinically important organism.