Cytoplasmic membrane proteins of spectinomycin-susceptible and -resistant strains of Neisseria gonorrhoeae

Abstract

Cytoplasmic membranes were isolated and examined from two spectinomycinsusceptible and three spectinomycin-resistant clinical strains of Neisseria gonorrhoeae. A laboratory-derived spectinomycin-resistant mutant, obtained by serial passage on gradually increasing concentrations of the antibiotic, and a susceptible revertant, spontaneously arising from one of the resistant clinical strains, were also studied. Sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis revealed that a major protein, comprising about 7% of total cytoplasmic membrane protein (molecular weight 24,000), was absent in the three clinically isolated spectinomycin-resistant strains. In a revertant, this protein reappeared. During treatment of one of the susceptible strains with spectinomycin, the protein disappeared. However, this correlation was not maintained in the laboratory-derived spectinomycin-resistant mutant. This mutant was of comparable resistance to the clinical isolates, but the 24,000-molecular-weight protein was present in normal quantities. In addition, spectinomycin resistance in clinical isolates was variable compared with stable resistance exhibited by the laboratoryderived mutant. These findings suggested that differences in laboratory-derived versus clinical spectinomycin resistance may be due to different types ofresistance mutations.