Agar dilution method for determination of antibiotic susceptibility of Ureaplasma urealyticum

The agar dilution method was adapted for use in determining antibiotic sensitivities of clinical isolates of Ureaplasma urealyticum. The reproducibility of end points (minimal inhibitory concentrations) for tetracycline was excellent within one dilution; however, for spectinomycin and erythromycin end points increased 2-fold between 3 and 4 days of incubation. When incubation times were held constant for these antibiotics the method was reproducible within two dilutions (4-fold). The use of a Steers' replicator permitted many strains to be tested. Although it is recognized that ureaplasmas present unique problems among mycoplasmas because of their small colony size, suitable developmental studies will make agar dilution an important method for determining antibiotic susceptibilities of ureaplasmas.