Heat stability of the antimicrobial activity of sixty-two antibacterial agents

Sixty-two antimicrobial agents, including several combinations, were examined for stability at 56°C for 30min and 121°C for 15min, respectively. A microtiter broth dilution MIC test and an agar disk diffusion test served to test eachchemo-agent for residual antimicrobial activity. Eleven drugs were partially heat-labile (MICs raised four- to eight-fold after autoclaving) and 26 drugs were heat-labile (MICs raised≥ 16-fold following autoclaving); the remainder proved heat-stable (MICs raised ≤ two-fold after autoclaving). Surprisingly, the β-lactams, azlocillin, aztreonam, mezlocillin, and oxacillin, were remarkably heat-stable.