Neisseria gonorrhoeae cell envelope: permeability to hydrophobic molecules

Isogenic variants of antibiotic-resistant and -sensitive Neisseria gonorrhoeae were examined for differences in the inhibition of oxygen uptake by steroid hormones. Mutants designated as env, which possessed cell envelope mutations allowing phenotypic suppression of low-level antibiotic resistance, were more sensitive to steroid hormone inhibition of oxygen uptake than the wild-type parental strains. Possession of an mtr locus, which confers nonspecific resistance to multiple antibiotics, dyes, and detergents, was also associated with an increase in resistance to steroid hormone inhibition of oxygen uptake. The penA2 locus, which confers an eightfold increase in resistance to penicillin, was not responsible for the increased resistance to steroid hormones. Phospholipids in the outer membrane of intact env-2 cells were susceptible to digestion by phospholipase C, indicating exposure of phospholipid head groups on the outer surface. Cells of a wild-type and mtr-2 strain were not susceptible to phospholipase C digestion unless they were pretreated with mixed exoglycosidases. This pretreatment also increased the sensitivity of mtr-2 cells to progesterone inhibition of O2 uptake. These data suggest that the permeability of the gonococcus to hydrophobic antibiotic and steroid molecules is mediated by the degree of phospholipid exposure on the outer membrane.