COMPARATIVE IN-VITRO ACTIVITY OF 11-BETA-LACTAM ANTIBIOTICS AGAINST 91 STAPHYLOCOCCUS-INTERMEDIUS STRAINS ISOLATED FROM STAPHYLOCOCCAL DERMATITIS IN DOGS

A study was made of the susceptibility of 91 strains of Staphylococcus intermedius, isolated from staphylococcal dermatitis of dogs, to 11 b eta-lactam antimicrobial agents. The activity of these antimicrobial a gents against all strains was tested at pH 7.2 and 8.5. Finally, a com parative study was made of the susceptibility of these micro-organisms , dividing them into six groups: beta-lactamase positive and negative, methicillin resistant and susceptible and oxacillin resistant and sus ceptible. Only three of the 11 antimicrobial agents studied exhibited satisfactory behaviour at the two pH levels studied: mezlocillin, cefa zolin and cefalotine. There was a good correlation at pH 8.5 between m ethicillin-resistant strains and those resistant to penicillin G, ampi cillin, amoxycillin, cefamandole and cefuroxime. This correlation was not observed, however, between oxacillin-resistant strains and strains resistant to the other antimicrobial agents studied.