A virulence-associated gene microarray: a tool for investigation of the evolution and pathogenic potential of Staphylococcus aureus

1 Genomics Proteomics and Bioinformatics Unit, Health Protection Agency (Colindale), 61 Colindale Avenue, London NW9 5HT, UK 2 Laboratory of Healthcare Associated Infection, Health Protection Agency (Colindale), 61 Colindale Avenue, London NW9 5HT, UK Correspondence Nicholas A. Saunders nick.saunders{at}hpa.org.uk An oligonucleotide probe microarray for investigation of the evolution of epidemic Staphylococcus aureus strains has been constructed. The array comprises 383 probes based on virulence-associated genes present in four key strains. Twelve strains including seven for which the complete chromosomal nucleotide sequence was available were tested on the array. Twenty-six per cent of the probes were able to differentiate between strains to give a minimum of two gene differences between pairs. A gene difference distance tree based on the array data had approximately the same topology as one prepared using concatenated MLST sequences. Differences in the topologies of these trees were found to indicate that large-scale recombination events had occurred during the evolution of the species. One such occurrence appears to have been a key event in the genesis of the EMRSA-15 clone (ST22) that currently represents the most prevalent methicillin-resistant S. aureus (MRSA) in the UK. Abbreviations: EMRSA, epidemic methicillin-resistant S. aureus ; MRSA, methicillin-resistant S. aureus ; MSSA, methicillin-sensitive S. aureus A supplementary table listing the genes included on the microarray is available in Microbiology Online.