title: Thioridazine reduces resistance of methicillin-resistant staphylococcus aureus by inhibiting a reserpine-sensitive efflux pump.
abstract: Previous studies suggested that the phenothiazine chlorpromazine (CPZ) could reverse or reduce the antibiotic resistance of bacteria. In some areas of the world, the majority of Staphylococcus aureus isolates are now resistant to methicillin, prompting this study to see whether such resistance can be altered by phenothiazine thioridazine (TZ), an agent with equal antibacterial activity, which is free of the severe side-effects associated with chronic administration of CPZ. The results indicated that, whereas methicillin-sensitive strains of Staphylococcus aureus (MSSA) were not rendered more susceptible to oxacillin, resistance to oxacillin by highly-resistant strains (MRSA) could be significantly reduced by sub-inhibitory concentrations of TZ. Reserpine, an inhibitor of efflux pumps, was also shown to reduce the resistance of MRSA strains to oxacillin in a concentration-dependent manner. The phenothiazines have been shown, by others, to inhibit the efflux pumps of bacteria and the mechanism by which MRSA are rendered more susceptible to oxacillin in the presence of TZ is believed to be due to a similar efflux pump.
authors.affiliation: Unit of Mycobacteriology, UPMM, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Rua da Junqueira 96, 1349-008 Lisboa, Portugal.
authors.forename: Malthe M
authors.initials: MM
authors.lastname: Kristiansen
authors.forename: Clara
authors.initials: C
authors.lastname: Leandro
authors.forename: Diane
authors.initials: D
authors.lastname: Ordway
authors.forename: Marta
authors.initials: M
authors.lastname: Martins
authors.forename: Miguel
authors.initials: M
authors.lastname: Viveiros
authors.forename: Teresa
authors.initials: T
authors.lastname: Pacheco
authors.forename: Joseph
authors.initials: J
authors.lastname: Molnar
authors.forename: Jetre E
authors.initials: JE
authors.lastname: Kristiansen
authors.forename: Leonard
authors.initials: L
authors.lastname: Amaral
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002746:Chlorpromazine / Q000494:pharmacology; D015169:Colony Count, Microbial; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D024881:Drug Resistance, Bacterial / Q000235:genetics; D016106:Methicillin Resistance / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology; D012110:Reserpine / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism; D013881:Thioridazine / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004338:Drug Combinations; D012110:Reserpine; D014700:Verapamil; D013881:Thioridazine; D002746:Chlorpromazine; D010068:Oxacillin