Morphological Studies on the Inhibitory Zones of Several Bacteria by Antibiotics : I. Morphological Typing of the Whole Shape and the Edge of Inhibitory Zone

Susceptibility of 24 bacterial strains (11 genera, 17 species) to 20 antibiotics was examined by the disc method. The inhibitory zones and the stimulated growth zone konwn as Arndt-Schuiz law were morphologically studied and classified. The results were as follows : 1. In general, the Gram-positive bacteria were more susceptible to a greater number of antibiotics than the Gram-negative ones, as many reports previously described. 2. The inoculum size affected the formation of the inhibitory zone. Best results were obtained by the inoculation of 10^4-10^5 CFU/cm^2 for both E. coli and S. aureus. 3. The inhibitory zones were morphologically classified into 5 type (1-5) and each type was sub-classified into 3 types (a-c). The zone-edges were also classified into 3 types (i-iii). 4. Arndt-Schulz law was recognized in most of the combinations, however, Streptomyceses did not show it to any antibiotics. No strains also did it to lincomycin and clindamycin.