Abstract: Minimum Bactericidal Concentration (MBC) is an important in vitro parameter of antimicrobial potency but has not yet been measured for Staphylococcus pseudintermedius, the main causative organism of canine pyoderma. This study was carried out to determine the MBC of representative antimicrobials against mecA-negative and -positive S. pseudintermdius. Fifty nine mecA-negative and 33 mecA-positive isolates were tested for Minimum Inhibitory Concentration (MIC) of eight antimicrobials by Broth Microdilution Method. Subsequently, MBC was determined as concentration at which ≥99.9% decrease in bacterial counts was achieved by sub-cultivating suspensions at concentrations greater than MIC. As a result, cephalexin (LEX), Amoxicillin-Clavulanic acid (AMC), Orbifloxacin (ORB) and Fosfomycin (FOF) had MBC:MIC ratio of ≤4 whereas trimethoprim-Sulfamethoxazole (SXT) had MBC:MIC ratio of ≤16. In contrast, Minocycline (MIN), Erythromycin (ERY) and Clindamycin (CLI) had MBC:MIC ratio of ≥4. In mecA-negative isolates, among the tested antimicrobials, FOF had the lowest MBC-resistance rate (8.5%) followed by AMC (13.6%) LEX (16.9%) ORB (33.9%) SXT (33.9%) whereas MIN, ERY and CLI had high MBC-resistance rates (71.2-96.6%). On the other hand, in mecA-positive isolates, all tested antimicrobials had >50% of MBC-resistance rates (69.7-100%). Notably, the resistant-level MIC value of MIN was not detected in either mecA-negative or -positive isolates. The present data indicate that FOF is a superior bactericidal drug against mecA-negative isolates whereas MINO can be effective bacteriostatic drugs for mecA-positive and -negative isolates of S. pseudintermedius.
Kazuki Harada, Aiko Iguchi and Yoshiaki Hikasa, 2014. Determination of Minimum Bactericidal Concentrations of Antimicrobials Used for Canine Pyoderma Against Staphylococcus pseudintermedius. Journal of Animal and Veterinary Advances, 13: 958-962.