Penicillin (cloxacillin)-tolerant Staphylococcus aureus from bovine mastitis: identification and lack of correlation between tolerance in vitro and response to therapy in vivo.
Twenty-four isolates of Staphylococcus aureus from naturally occurring cases of bovine mastitis were examined in vitro for resistance to cloxacillin. All strains produced penicillinase and none showed intrinsic resistance (methicillin resistance) to cloxacillin. The minimum inhibitory concentration of cloxacillin for all these strains was normal (low) but differences were found between them in their sensitivities to the bactericidal action. Three were considered to be tolerant to cloxacillin and a further five possibly so. In a mouse model of mastitis there was no difference in the response to intramammary therapy with cloxacillin between cloxacillin-sensitive or tolerant strains of S aureus and a known methicillin-resistant strain was similarly sensitive to cloxacillin therapy in vivo. It is concluded that cloxacillin tolerance may have little clinical significance in mastitis therapy.
D000208:Acute Disease; D000818:Animals; D002417:Cattle; D003023:Cloxacillin / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008414:Mastitis, Bovine / Q000188:drug therapy* / Q000382:microbiology; D008712:Methicillin / Q000494:pharmacology; D051379:Mice; D010403:Penicillin Resistance; D011247:Pregnancy; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000472:pathogenicity; D014774:Virulence
D003023:Cloxacillin; D008712:Methicillin