Diagnosis of gonorrhoea by culture on a selective medium containing vancomycin, colistin, nystatin and trimethoprim (VCNT). A comparison with Gram-staining and immunofluorescence.

Abstract

Culture media containing antibiotics are widely used for the isolation of Neisseria gonorrhoeae. The best known are those introduced by Thayer and Martin, who originally used ristocetin and Polymyxin B (Thayer and Martin, 1964), and more recently, and more successfully, vancomycin and colistin (Thayer and Martin, 1966). The main fault with these media is their failure to inhibit Proteus species which are found in an important proportion of specimens from the female genital tract. However, Proteus species are usually sensitive to trimethoprim, while pathogenic Neisseriae are relatively resistant, with minimal inhibitory concentrations (MICs) of more than 8 Qug./ml. (Darrell, Garrod, and Waterworth, 1968; Bushby, 1969; Waterworth, 1969). On the basis of these sensitivity results in vitro, trimethoprim seemed to deserve trial as a further selective agent for the isolation of gonococci. This paper reports preliminary experiments and an extensive trial, over a period of 2 years in a Venereal Diseases Clinic, of a medium containing vancomycin, colistin, nystatin, and trimethoprim (VCNT). Early results with this medium have been briefly referred to previously (Lancet, 1970;