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Infection and Immunity, June 2000, p. 3548-3553, Vol. 68, No. 6
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

In Vitro Resistance of Staphylococcus aureus to Thrombin-Induced Platelet Microbicidal Protein Is Associated with Alterations in Cytoplasmic Membrane Fluidity

Arnold S. Bayer,1,2,* Rajendra Prasad,3 Jyotsna Chandra,3 Anjni Koul,3 M. Smriti,3 Archana Varma,3 Ronald A. Skurray,4 Neville Firth,4 Melissa H. Brown,4 Su-Pin Koo,1 and Michael R. Yeaman1,2

Research and Education Institute, St. John's Cardiovascular Research Center and the Division of Infectious Diseases, Harbor-UCLA Medical Center, Torrance, California, 905091; UCLA School of Medicine, Los Angeles, California, 900242; School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India3; and School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia4

Received 15 December 1999/Returned for modification 18 February 2000/Accepted 17 March 2000

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-1r) strains and their genetically related, tPMP-1-susceptible (tPMP-1s) counterpart strains. The tPMP-1r 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-1r strains were found to possess elevated levels of longer-chain, unsaturated membrane lipids, in comparison to their tPMP-1s counterparts. This was reflected in corresponding differences in cell membrane fluidity in the strain pairs, with tPMP-1r 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.


* Corresponding author. Mailing address: Division of Infectious Diseases, Harbor-UCLA Medical Center, St. John's Cardiovascular Research Center (RB2 - Room 225), 1000 West Carson St., Torrance, CA 90509. Phone: (310) 222-6422. Fax: (310) 782-2016. E-mail: Bayer{at}humc.edu.


Infection and Immunity, June 2000, p. 3548-3553, Vol. 68, No. 6
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.



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