Response of methicillin-resistant Staphylococcus aureus USA300 to a subinhibitory concentration of thioridazine - alone and in combination with dicloxacillin

ABSTRACT: Subinhibitory concentrations of the neuroleptic drug thioridazine (TDZ) are well-known to enhance the killing of methicillin-resistant S. aureus (MRSA) by β-lactam antibiotics, however, the mechanism underlying the synergy between TDZ and β-lactams is not fully understood. In the present study we have examined the effect of a subinhibitory concentration of TDZ on antimicrobial resistance, the global transcriptome, and the cell wall composition of MRSA USA300. We show that TDZ is able to sensitize the bacteria to several classes of antimicrobials targeting the late stages of peptidoglycan synthesis. Furthermore, our microarray analysis demonstrates that TDZ modulates the expression of genes encoding membrane and surface proteins, transporters, and enzymes involved in amino acid biosynthesis. Interestingly, resemblance between the transcriptional profile of TDZ treatment and the transcriptomic response of S. aureus to known inhibitors of cell wall synthesis suggests that TDZ disturbs peptidoglycan biosynthesis at a stage that precedes transpeptidation. In support of this notion, dramatic changes in the muropeptide profile of USA300 were observed following growth in the presence of TDZ, indicating that TDZ can interfere with the formation of the pentaglycine branches. Strikingly, the addition of glycine to the growth medium relieved the effect of TDZ on the muropeptide profile. Furthermore, exogenous glycine offered a modest protective effect against TDZ-induced β-lactam sensitivity. We propose that TDZ exposure leads to a shortage of intracellular amino acids, including glycine, which is required for the production of normal peptidoglycan precursors with pentaglycine branches, the correct substrate of S. aureus penicillin-binding proteins. Collectively, this work demonstrates that TDZ has a major impact on the cell wall biosynthesis pathway in S. aureus and provides new insights into how MRSA may be sensitized towards β-lactam antibiotics. Staphylococcus aureus USA300 was grown to early exponential phase and treated with TDZ (16 µg/ml) alone or in combination with DCX (0.125 µg/ml) for 30 min. Changes in global gene expression were analyzed using the untreated culture as control. Hybridizations were performed in triplicate using RNA isolated from independent cultures.

ORGANISM(S): Staphylococcus aureus subsp. aureus USA300_FPR3757

SUBMITTER: Mette Thorsing 

PROVIDER: E-GEOD-43759 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress