Sulphonamide resistant commensal Neisseria with alterations in the dihydropteroate synthase can be isolated from carriers not exposed to sulphonamides

BACKGROUND: Development of sulphonamide resistance in Neisseria meningitidis has been suggested to involve horizontal DNA-transfer from a commensal Neisseria species. In this study, we isolated commensal Neisseria from throat specimens and examined the isolates with respect to sulphonamide resistance. RESULTS: Three resistant clones were identified and the resistance phenotype could be explained by amino acid variations in their dihydropteroate synthase, the target molecule for sulphonamides. Some of these variations occurred in positions corresponding to previously detected variations in resistant N. meningitidis. CONCLUSIONS: Sulphonamide resistant commensal Neisseria were isolated from an environment not exposed to sulphonamides, suggesting that resistant Neisseria has become a natural part of the commensal throat flora.