Gonococcal strains from homosexual men have outer membranes with reduced permeability to hydrophobic molecules

Loci designated penA, penB, and mtr contribute additively to penicillin G resistance in Neisseria gonorrhoeae; the mtr locus also confers resistance to hydrophobic dyes, detergents, and antibiotics, env mutations suppress the phenotypic expression of mtr and penB and are responsible for increased sensitivity to various hydrophobic molecules. We postulated that the host environment is important in the selection of gonococcal strains with these particular outer membrane phenotypes. Thus, mtr strains should predominate in environments that are high in hydrophobic molecules. To test this hypothesis we determined the outer membrane phenotype of 152 strains of N. gonorrhoeae. Rectal and urethral isolates from 58 homosexual men, urethral isolates from 55 heterosexual men, and cervical and rectal isolates from 39 heterosexual women were used in this study. Strains from 43 of the homosexual men were matched with those from heterosexual men with respect to auxotype and year and season of isolation. Cell envelope phenotype was determined for each strain on the basis of its resistance to various hydrophobic compounds. The identity of mtr strains was confirmed by genetic transformation. Among the matched pairs, mtr strains were significantly more prevalent among isolates from homosexual men than among those from heterosexual men (P = 0.03). Serogrouping by coagglutination demonstrated that 17 of 19 mtr strains versus 76 of 131 non-mtr strains belonged to coagglutination group WII (P = 0.01). Coagglutination group WII strains were also associated with homosexuality (P = 0.02). Gonococci were also tested for resistance to fecal lipids, mtr strains were more resistant to growth inhibition by fecal lipids than were non-mtr strains.