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Please use this identifier to cite or link to this item: http://hdl.handle.net/2328/9311

Title: Low-level resistance of staphylococcus aureus to thrombin-induced platelet microbicidal protein 1 in vitro associated with qacA gene carriage is independent of multidrug efflux pump activity
Authors: Bayer, Arnold S
Kupferwasser, L I
Brown, Melissa Hackett
Skurray, Ronald Anthony
Grkovic, Steve
Jones, T
Mukhopadhay, K
Yeaman, M R
Issue Date: 2006
Citation: Bayer, A.S., Kupferwasser, L.I., Brown, M.H., Skurray, R.A., Grkovic, S., Jones, T., Mukhopadhay, K., & Yeaman, M.R., 2006. Low-level resistance of staphylococcus aureus to thrombin-induced platelet microbicidal protein 1 in vitro associated with qacA gene carriage is independent of multidrug efflux pump activity. Antimicrobial Agents and Chemotherapy, 50(7), 2448-2454.
Abstract: Thrombin-induced platelet microbial protein 1 (tPMP-1), a cationic antimicrobial polypeptide released from thrombin-stimulated rabbit platelets, targets the Staphylococcus aureus cytoplasmic membrane to initiate its microbicidal effects. In vitro resistance to tPMP-1 correlates with survival advantages in vivo. In S. aureus, the plasmid-carried qacA gene encodes a multi-drug transporter, conferring resistance to organic cations (e.g., ethidium [Et]) via proton motive force (PMF)-energized export. We previously showed that qacA also confers a tPMP-1-resistant (tPMP-1r) phenotype in vitro. The current study evaluated whether (i) transporters encoded by the qacB and qacC multidrug resistance genes also confer tPMP-1r and (ii) tPMP-1r mediated by qacA is dependent on efflux pump activity. In contrast to tPMP-1r qacA-bearing strains, the parental strain and its isogenic qacB- and qacC-containing strains were tPMP-1 susceptible (tPMP-1s). Efflux pump inhibition by cyanide m-chlorophenylhydrazone abrogated Etr, but not tPMP-1r, in the qacA-bearing strain. In synergy assays, exposure of the qacA-bearing strain to tPMP-1 did not affect the susceptibility of Et (ruling out Et–tPMP-1 cotransport). The following cytoplasmic membrane parameters did not differ significantly between the qacA-bearing and parental strains: contents of the major phospholipids; asymmetric distributions of the positively charged species, lysyl-phosphotidylglycerol; fatty acid composition; and relative surface charge. Of note, the qacA-bearing strain exhibited greater membrane fluidity than that of the parental, qacB-, or qacC-bearing strain. In conclusion, among these families of efflux pumps, only the multi-drug transporter encoded by qacA conferred a tPMP-1r phenotype. These data suggest that qacA-encoded tPMP-1r results from the impact of a specific transporter upon membrane structure or function unrelated to PMF-dependent peptide efflux.
URI: http://hdl.handle.net/2328/9311
ISSN: 0066-4804
Appears in Collections:0605 - Microbiology

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