IN-VITRO ACTIVITY OF 15 ANTIMICROBIAL AGENTS AGAINST METHICILLIN-RESISTANT AND METHICILLIN-SUSCEPTIBLE STAPHYLOCOCCUS-INTERMEDIUS

In this study the susceptibility of 91 methicillin-resistant and -susc eptible Staphylococcus intermedius strains (MRSI and MSSI, respectivel y) against 15 antimicrobial agents was determined, The activity of the antimicrobial agents was studied at pH 7.2 and pH 8.5. Methicillin wa s more active at pH 7.2 (28 strains methicillin-resistant) than at pH 8.5 (55 strains methicillin-resistant). Gentamicin showed excellent ac tivity, with only 3 strains resistant at pH 8.5. However, gentamicin w ould have to be administered parenterally, Oxytetracycline cannot be r ecommended for treatment of canine staphylococcal dermatitis, due to t he high percentage (over 25%) of strains that were found to be resista nt, Clindamycin showed little activity in inhibiting growth of the str ains studied, the percent resistance at pH 7.2 was 93.4%. Rifampin beh aved differently at the two pH values, However, a close relationship w as noted between methicillin-resistant and rifampin-resistant strains, particularly at the lower pH, Of the fluoroquinolones, ciprofloxacin or enrofloxacin would be a good useful alternative for the treatment o f methicillin-resistant strains of S. intermedius. Lastly, very high r esistance to sulphamethoxypyridazine was found, as was the case with t rimethoprim and a combination of trimethoprim/sulphamethoxypyridazine, against not only MRSI but also MSSI strains.