Disc agar diffusion antimicrobial susceptibility tests with .BETA.-lactamase producing Neisseria gonorrhoeae.

Abstract

The emergence of .beta.-lactamase-producing strains of N. gonorrhoeae led to a reexamination of the role of the disc agar diffusion method in susceptibility testing of gonococci. The disc agar diffusion test can be used to screen for .beta.-lactamase production by these organisms. The disc tests were done on GC Agar Base supplemented with 1% Iso VitaleX. An inoculum of 108 colony forming units/ml and a 10-unit-penicillin or a 10-.mu.g-ampicillin disc were used. A zone diameter of .ltoreq. 19 mm was indicative of .beta.-lactamase production. These results were compared with results of chemical tests for .beta.-lactamase and with minimal inhibitory concentrations. Recommendations were also made for a disc test with tetracycline and spectinomycin, but these methods must remain tentative because of the lack of resistant strains.