title: In vitro resistance of Staphylococcus aureus to thrombin-induced platelet microbicidal protein is associated with alterations in cytoplasmic membrane fluidity.
abstract: Platelet microbicidal proteins (PMPs) are small, cationic peptides which possess potent microbicidal activities against common bloodstream pathogens, such as Staphylococcus aureus. We previously showed that S. aureus strains exhibiting resistance to thrombin-induced PMP (tPMP-1) in vitro have an enhanced capacity to cause human and experimental endocarditis (T. Wu, M. R. Yeaman, and A. S. Bayer, Antimicrob. Agents Chemother. 38:729-732, 1994; A. S. Bayer et al., Antimicrob. Agents Chemother. 42:3169-3172, 1998; V. K. Dhawan et al., Infect. Immun. 65:3293-3299, 1997). However, the mechanisms mediating tPMP-1 resistance in S. aureus are not fully delineated. The S. aureus cell membrane appears to be a principal target for the action of tPMP-1. To gain insight into the basis of tPMP-1 resistance, we compared several parameters of membrane structure and function in three tPMP-1-resistant (tPMP-1(r)) strains and their genetically related, tPMP-1-susceptible (tPMP-1(s)) counterpart strains. The tPMP-1(r) strains were derived by three distinct methods: transposon mutagenesis, serial passage in the presence of tPMP-1 in vitro, or carriage of a naturally occurring multiresistance plasmid (pSK1). All tPMP-1(r) strains were found to possess elevated levels of longer-chain, unsaturated membrane lipids, in comparison to their tPMP-1(s) counterparts. This was reflected in corresponding differences in cell membrane fluidity in the strain pairs, with tPMP-1(r) strains exhibiting significantly higher degrees of fluidity as assessed by fluorescence polarization. These data provide further support for the concept that specific alterations in the cytoplasmic membrane of S. aureus strains are associated with tPMP-1 resistance in vitro.
authors.affiliation: Research and Education Institute, St. John's Cardiovascular Research Center and the Division of Infectious Diseases, Harbor-UCLA Medical Center, Torrance, California, 90509, USA. Bayer@humc.edu
authors.forename: A S
authors.initials: AS
authors.lastname: Bayer
authors.forename: R
authors.initials: R
authors.lastname: Prasad
authors.forename: J
authors.initials: J
authors.lastname: Chandra
authors.forename: A
authors.initials: A
authors.lastname: Koul
authors.forename: M
authors.initials: M
authors.lastname: Smriti
authors.forename: A
authors.initials: A
authors.lastname: Varma
authors.forename: R A
authors.initials: RA
authors.lastname: Skurray
authors.forename: N
authors.initials: N
authors.lastname: Firth
authors.forename: M H
authors.initials: MH
authors.lastname: Brown
authors.forename: S P
authors.initials: SP
authors.lastname: Koo
authors.forename: M R
authors.initials: MR
authors.lastname: Yeaman
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001692:Biological Transport; D001798:Blood Proteins / Q000494:pharmacology*; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects*; D018925:Chemokines; D004251:DNA Transposable Elements; D004352:Drug Resistance, Microbial; D005227:Fatty Acids / Q000032:analysis; D008560:Membrane Fluidity / Q000187:drug effects*; D016254:Mutagenesis, Insertional; D010641:Phenotype; D010743:Phospholipids / Q000032:analysis; D013045:Species Specificity; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics; D001620:beta-Thromboglobulin
chemical_list: D000596:Amino Acids; D000900:Anti-Bacterial Agents; D001798:Blood Proteins; D018925:Chemokines; D004251:DNA Transposable Elements; D005227:Fatty Acids; C061615:PPBP protein, human; D010743:Phospholipids; D001620:beta-Thromboglobulin