Reversal of methicillin resistance in Staphylococcus aureus by thioridazine.
OBJECTIVE
Thioridazine has been shown to reverse oxacillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) in vitro. The aim of this study was to investigate whether thioridazine alone or in combination with oxacillin affects the transcription of the methicillin resistance gene mecA and the protein level of the encoded protein PBP2a.


METHODS
Viability of MRSA was determined in liquid media in the presence of oxacillin or thioridazine alone or in combination. Transcription of mecA was analysed by primer extension, and the protein level of PBP2a was analysed by western blotting in the presence of thioridazine and oxacillin.


RESULTS
We observed an increased susceptibility of MRSA towards oxacillin in the presence of thioridazine compared with bacteria grown with oxacillin or thioridazine alone. Transcription of mecA was reduced with increasing concentrations of thioridazine in the presence of a fixed amount of oxacillin. Furthermore, the protein level of PBP2a was reduced when bacteria were treated with the combination of oxacillin and thioridazine. The two drugs also affected the mRNA level of the beta-lactamase gene, blaZ.


CONCLUSIONS
The present study indicates that reversal of methicillin resistance by thioridazine in MRSA may be explained by a reduced transcription of mecA and blaZ, resulting in a reduced protein level of PBP2a.
Klitgaard
Janne K
JK
Department of Clinical Microbiology, Institute of Clinical Research, University of Southern Denmark, Odense University Hospital, Odense, Denmark. jkklitgaard@health.sdu.dk
Skov
Marianne N
MN
Kallipolitis
Birgitte H
BH
Kolmos
Hans Jørn
HJ
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis; D004357:Drug Synergism; D020869:Gene Expression Profiling; D016106:Methicillin Resistance / Q000187:drug effects*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D010068:Oxacillin / Q000494:pharmacology*; D046915:Penicillin-Binding Proteins; D012329:RNA, Bacterial / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D013881:Thioridazine / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D046915:Penicillin-Binding Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; C487789:mecA protein, Staphylococcus aureus; D013881:Thioridazine; D010068:Oxacillin