Nutritional requirements and penicillin susceptibilities of gonococci from pharyngeal and anogenital sites

Neisseria gonorrhoeae was isolated from 5.9% of oropharyngeal specimens obtained from patients attending a clinic for sexually transmitted diseases. Oropharyngeal isolates from 69 patients and anogenital isolated from 97 other patients attending the same clinic were compared. Many of the gonococci could be differentiated by the compounds required for growth in chemically defined media or by differences in the minimum inhibitory concentration (MIC) of penicillin G. Strains with requirements for either proline (Pro-) or arginine (Arg-) or for none of the compounds that are used for differentiation (zero phenotype) were more common in the oropharynx (91.3% of patients) than in anogenital sites (73.2% of patients). On the other hand, gonococci with multiple requirements that include arginine, hypoxanthine, and uracil (AHU strains) were present in oropharyngeal specimens from only three patients (4.4%), but were isolated from anogenital specimens from 18 patients (18.6%). A high susceptibility to penicillin characterised the AHU strains from all sites, as others have reported. The penicillin MIC ranged from 0.003-0.72 microgram/ml for strains with Pro-, Arg-, and zero phenotypes. However, a penicillin MIC greater than or equal to 0.42 microgram/ml was found for 17.6% of oropharyngeal isolates of these types, but for only 4.1% of Pro-, Arg-, and zero isolates from anogenital sites. None of these moderately resistant strains produced beta-lactamase. Our findings indicate that gonococci differ in their ability to colonise the oropharynx successfully.