Disk diffusion and disk elution tests with A-56268 and erythromycin

Zones of inhibition around 15g A-56268 disks were essentially the same size as those around 15g erythromycin disks. If the same MIC breakpoints are to be used for defining susceptible categories for both macrolides, interpretive zone size standards for erythromycin disk tests may also be used for A-56268 disk tests. Against anaerobic bacteria, the two macrolides were only marginally effective when broth dilution tests were incubated in anaerobic jars. The aerobically incubated thioglycolate broth disk elution test indicated that both macrolides were much more effective against anaerobes. Three 15g disks eluted in 5 ml thioglycolate provided satisfactory results.