Isolation of Neisseria gonorrhoeae on selective and nonselective media in a sexually transmitted disease clinic

Abstract

To assess the practical significance of reported increases in the prevalence of vancomycin-susceptible strains of Neisseria gonorrhoeae on isolation of this organism, antibiotic-free chocolate agar (CA), modified Thayer-Martin medium (MTM), and a vancomycin-free selective medium (VFSM) were compared in a sexually transmitted disease clinic. Among 326 cervical gonococcal infections detected in a comparison of CA with MTM, 92.0% were detected on CA, compared with 98.2% on MTM (P less than 0.001). Similarly, among 306 cervical infections detected in a comparison of MTM and VFSM, 95.8% of infections were detected with VFSM, compared with 98.4% for MTM (P = 0.10). For 1,632 urethral infections in men, all three media were equivalent, with none detecting fewer than 98% of the infections. Compared with a single inoculation, dual inoculation of MTM increased the diagnostic yield by 1.5% for 206 urethral infections and 2.4% for 83 cervical infections. In our clinic population, MTM is superior to CA or VFSM for the diagnosis of genital gonococcal infections, especially in women. The increased yield that accrued from inoculation of both MTM and either of the other media was not sufficiently high to warrant routine use of this practice in our clinic.