Rapid identification of pathogenic neisserias using the Identicult-Neisseria test

A rapid enzymatic method using chromogenic substrates for the rapid identification of pathogenic neisseria (Identicult-Neisseria, Scott Laboratories Inc., CA, USA) was tested in parallel with the rapid carbohydrate utilization test (RCUT) and the Phadebact Monoclonal GC Test against 198 consecutive clinical isolates of oxidase-positive Gram-negative diplococci (118 Neisseria gonorrhoeae, 76 N. meningitidis and four N. lactamica). On initial testing the Identicult-Neisseria gave a 95% overall concordance (97.5% N. gonorrhoeae, 90.8% N. meningitidis) with the RCUT and Phadebact tests; the corresponding figures after repeat testing were 98% overall concordance (98.3% N. gonorrhoeae, 97.4% N. meningitidis). Two of the three strains of N. gonorrhoeae mis-identified as N. meningitidis on primary testing were also mis-identified on repeat testing. Seven strains of N. meningitidis were mis-identified on initial testing (six as Moraxella catarrhalis and one as N. lactamica) and two on repeat testing (both as Mor. catarrhalis). We conclude that the Identicult-Neisseria is not sufficiently reliable for the culture confirmation of gonococci and meningococci.