Analysis of certain variables in the agar dilution susceptibility test

This study examined (i) the activity of gentamicin added to agar in ratios of 1:100 and 1:1,000 to produce a final concentration of 1 mug/ml, (ii) the uniformity of distribution of gentamicin in agar in relation to the amount of mixing, and (iii) the effect of agar depth on the activity of gentamicin against Pseudomonas aeruginosa. Although the ratio of antibiotic solution to agar had no significant effects on activity of the antibiotic, the amount of mixing did. Agar depth had no significant effect on the activity of gentamicin.