Neighbour-joining phylogentic tree of concatenated MLST allele sequences. Concatenated MLST allele sequences representing each strain were downloaded from the MLST database  and used to generate a neighbour joining tree using MEGA 3 . The A domain isotypes carried by strains of each MLST genotype, determined by sequencing and hybridization analysis, are indicated. FnBPA A domain types from strains of ST-80 and ST-45 were determined from sequence data from a previous study of polymorphic genes in S. aureus . The dashed line indicates the separation of the MLST genotypes into Groups 1 and 2, which is based on sequence data from MLST alleles and other unlinked loci .