Modelling Staphylococcus aureus-induced septicemia using NMR

R. Plummer,¹ J. Bodkin,² T.W. Yau,^1,4 D. Power,³ N. Pantarat,³ T.J. Larkin,¹ D. Szekely,¹ W.A. Bubb,¹ T.C. Sorrell,³ C.J. Garvey⁴ and P.W. Kuchel,¹ ¹School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia, ²School of Chemistry, University of New South Wales, NSW 2052, Australia, ³Centre for Infectious Diseases and Microbiology, University of sydney and Westmead Millennium Institute, Westmead, NSW 2145, Australia and ⁴Australian Nuclear Science and Technology Organisation, Menai, NSW 2234, Australia.

We present a novel NMR-based study of the molecular aspects of the “attack” on human red blood cells (RBCs) by growing bacteria. Staphylococcus aureus expresses virulence factors, including α-haemolysin, which contribute to the clinical condition known as septic shock (Bhakdi & Tranum-Jensen, 1991). α-Haemolysin is a pore-forming toxin and its secretion increases the permeability of a range of mammalian cell types infected with S. aureus (McEwen & Arion, 1985). ³¹P NMR spectra of the probe molecules dimethyl methylphosphonate (DMMP) and hypophosphite (HPA) in RBC suspensions show separate intra- and extracellular resonances (Kirk & Kuchel, 1986). These resonances coalesced over time in RBC suspensions inoculated with S. aureus or pure α-haemolysin, due to increasing permeability of the RBC membrane. Increased RBC permeability resulted in leakage of intracellular proteins, plus an increase in the exchange rates of the solutes between the intra- and extracellular compartments, both effects contributing to the coalescence of the split peaks (Plummer et al., 2007). The addition of antibiotics prevented peak coalescence and enabled the minimal inhibitory concentration (MIC) for eight strains of S. aureus to be determined for oxacillin and erythromycin. The MIC values obtained by using ³¹P NMR spectroscopy were within one dilution of the MICs obtained using the standard National Committee for Clinical Laboratory Standards (NCCLS) method (Jones, 1986). The results are encouraging for the use of NMR spectroscopy in clinical microbiology.

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Plummer R, Bodkin J, Yau TW, Power D, Pantarat N, Larkin TJ, Szekely D, Bubb WA, Sorrell TC & Kuchel PW. (2007) Magnetic Resonance in Medicine, 58: 656-65.

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