Auxotypes and antibacterial resistance to gonococci with differing susceptibilities to vancomycin.

Abstract

The responses to vancomycin and 11 other antibacterial drugs and the nutritional requirements of gonococci recovered from two selective media were determined. Single urogenital specimens from 508 patients attending a social hygiene clinic in 1975 yielded 97 strains of Neisseria gonorrhoeae; 95 were recovered on VCNT (a modification of Thayer-Martin medium), always inoculated first, and 69 on LC medium containing lincomycin (4 micrograms/ml) and colistin (5 micrograms/ml). The two drugs at these concentrations in LC medium were not inhibitory for isolates from either medium. Unexpectedly, three isolates on VCNT were susceptible to vancomycin at the concentrations (3 micrograms/ml) in VCNT medium; these three were typically sensitive to penicillins but were hypersusceptible to erythromycin (inhibited by less than or greater than 0.05 micrograms/ml) and rifampin (less than or equal to 0.02 micrograms/ml). Resistance to streptomycin (greater than or equal to 500 micrograms/ml) (22% of the strains) was correlated with increased resistance to penicillins, erythromycin, and rifampin in most instances. All streptomycin-resistant gonococci required proline, or arginine, or none of the test compounds. Strains requiring arginine, hypoxanthine, and uracil were uniformly sensitive to antibiotics but not hypersusceptible. In contrast, six strains of N gonorrhoeae isolated in Denmark required arginine (not satisfied by ornithine), hypoxanthine, and uracil and were hypersusceptible to vancomycin (inhibited by 0.5 micrograms/ml), erythromycin, and rifampin. DNA-mediated transformation showed that all three hypersusceptibilities of one Danish strain were introduced together into a wild-type gonococcus, suggesting that a mutation of an env (envelope) locus might be responsible for the atypical permeability.