Superoxol and amylase inhibition tests for distinguishing gonococcal and nongonococcal cultures growing on selective media

Abstract

Two inexpensive screening tests were evaluated singly and in tandem for distinguishing Neisseria gonorrhoeae from other oxidase-positive microorganisms growing on selective gonococcal media. In tests of 728 cultures, including 460 N. gonorrhoeae, 4 Neisseria lactamica, 257 Neisseria meningitidis, and 7 Branhamella catarrhalis, both Superoxol (30% H2O2; J. T. Baker Chemical Co., Phillipsburg, N.J.) and amylase inhibition tests were 100% sensitive (positive) for 20-h cultures of N. gonorrhoeae. Singly, the Superoxol test was 92.7% specific for N. gonorrhoeae, compared with a specificity of 82.3% for the amylase inhibition test. By using tandem screening tests to distinguish gonococci, we achieved an overall specificity of 98.6%. Group A meningococci were the primary source of error in the Superoxol test, with 97% (37 of 38) strains producing gonococcal like reactions for catalase. From 5 to 20% of N. meningitidis serogroups X, Y, Z, and Z' and nontypable strains, as well as about 50% of B. catarrhalis and N. lactamica strains, were also strong catalase producers.