New selective medium for the isolation of Neisseria gonorrhoeae

GC-Lect, a new selective medium for the isolation of Neisseria gonorrhoeae which contains five antimicrobial agents, was evaluated with stock cultures and with 500 clinical specimens. With stock cultures, vancomycin-resistant Staphylococcus epidermidis that grew on modified Thayer-Martin medium (MTM) was inhibited on the new medium. Also, vancomycin-susceptible strains of N. gonorrhoeae were much less inhibited on the new medium than on Martin-Lewis agar or MTM. With oropharyngeal cultures of healthy volunteers, Capnocytophaga species were frequently isolated on MTM from two of three manufacturers but were completely inhibited on GC-Lect. In the clinical study, visible growth of N. gonorrhoeae occurred within 24 h in 72% of the positive cultures on GC-Lect, compared with only 52% on the reference medium. A total of 50 positive cultures were obtained with GC-Lect, compared with 49 obtained with MTM. The selectivity of GC-Lect was superior, with only 19 cultures producing growth of normal flora, compared with 78 cultures on MTM after 24 h of incubation. The selectivity was especially improved on GC-Lect with regard to yeasts (2 versus 30 cultures) and gram-positive cocci (5 versus 31 cultures).