Proteomic and genomic analysis of methicillin-resistant Staphylococcus aureus (MRSA) exposed to manuka honey in vitro demonstrated down-regulation of virulence markers

Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen. Its resistance to multiple antibiotics and its prevalence in healthcare establishments make it a serious threat to human health that requires novel interventions. Manuka honey is a broad-spectrum antimicrobial agent that is gaining acceptance in the topical treatment of wounds. Because its mode of action is only partially understood, proteomic and genomic analysis was used to investigate the effects of manuka honey on MRSA at a molecular level. Methods: Two-dimensional gel electrophoresis with dual-channel imaging was combined with matrix-assisted laser desorption ionization-time of flight mass spectrometry to determine the identities of differentially expressed proteins. The expression of the corresponding genes was investigated by quantitative PCR. Microarray analysis provided an overview of alterations in gene expression across the MRSA genome. Results: Genes with increased expression following exposure to manuka honey were associated with glycolysis, transport and biosynthesis of amino acids, proteins and purines. Those with decreased expression were involved in the tricarboxylic acid cycle, cell division, quorum sensing and virulence. The greatest reductions were seen in genes conferring virulence (sec3, fnb, hlgA, lip and hla) and coincided with a down-regulation of global regulators, such as agr, sae and sarV. A model to illustrate these multiple effects was constructed and implicated glucose, which is one of the major sugars contained in honey. Conclusions: A decreased expression of virulence genes in MRSA will impact on its pathogenicity and needs to be investigated in vivo.