Staphylococcus lugdunensis is recognized as one of the major pathogenic species within the genus Staphylococcus , even though it belongs to the coagulase-negative group. A multilocus sequence typing (MLST) scheme was developed to study the genetic relationships and population structure of 87 S. lugdunensis isolates from various clinical and geographic sources by DNA sequence analysis of seven housekeeping genes ( aroE , dat , ddl , gmk , ldh , recA , and yqiL ). The number of alleles ranged from four ( gmk and ldh ) to nine ( yqiL ). Allelic profiles allowed the definition of 20 different sequence types (STs) and five clonal complexes. The 20 STs lacked correlation with geographic source. Isolates recovered from hematogenic infections (blood or osteoarticular isolates) or from skin and soft tissue infections did not cluster in separate lineages. Penicillin-resistant isolates clustered mainly in one clonal complex, unlike glycopeptide-tolerant isolates, which did not constitute a distinct subpopulation within S. lugdunensis . Phylogenies from the sequences of the seven individual housekeeping genes were congruent, indicating a predominantly mutational evolution of these genes. Quantitative analysis of the linkages between alleles from the seven loci revealed a significant linkage disequilibrium, thus confirming a clonal population structure for S. lugdunensis . This first MLST scheme for S. lugdunensis provides a new tool for investigating the macroepidemiology and phylogeny of this unusually virulent coagulase-negative Staphylococcus .

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