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

Sixty-two antimicrobial agents, including several combinations, were examined for stability at 56 degrees C for 30 min and 121 degrees C for 15 min, respectively. A microtiter broth dilution MIC test and an agar disk diffusion test served to test each chemo-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 > or = 16-fold following autoclaving); the remainder proved heat-stable (MICs raised < or = two-fold after autoclaving). Surprisingly, the beta-lactams, azlocillin, aztreonam, mezlocillin, and oxacillin, were remarkably heat-stable.