Automated count and size evaluation of colonies of bacteria grown in a zonal concentration gradient of antimicrobial agent.

The quantitative study (counting and size and surface evaluation of bacterial colonies) of the activity of an antimicrobial agent against a microbial population growing in solid medium can be performed by an electronic image analyzer. The Zeiss Micro-Videomat allowed the detection of even slight antimicrobial effects, which would be difficult to detect by colony counting alone and would escape the manual procedures of observation. The potential of the new method of investigation was illustrated by the examination of Staphylococcus aureus inhibition zones produced by disks of penicillin G and sulfadiazine.