Staphylococcus singaporensis sp. nov., a new member of the Staphylococcus aureus complex, isolated from human clinical specimens

Abstract

<i>Staphylococcus argenteus</i> and <i>Staphylococcus schweitzeri</i> are the newest members of the <i>Staphylococcus aureus</i> complex. The number of clinical reports attributed to these new <i>S. aureus</i> complex members is limited. In a retrospective clinical laboratory study conducted over a 4-month period investigating the prevalence of <i>S. argenteus</i> and <i>S. schweitzeri</i>, a total of 43 isolates were selected. Phylogeny based on core-gene multilocus sequence typing (MLST) analysis confirmed that 37 were <i>S. argenteus</i> but a genetically distinct clade of six isolates was identified. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) analyses further supported the classification of these six isolates as a separate species. When compared to <i>S. aureus</i> complex reference genomes, the ANI values were ≤94 % and the dDDH values were <53 %. Based on the seven-gene <i>S. aureus</i> MLST scheme, the six isolates belong to five novel allelic profiles (ST6105, ST6106, ST6107, ST6108 and ST109). Their clinical infection features were similar to <i>S. aureus</i>. Skin and soft tissue infections presented in four out of the six cases. Routine clinical diagnostic identification using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and biochemical profiling does not differentiate these new members from the rest of the complex. Genotypic analysis suggests that the six isolates belong to a novel species, <i>Staphylococcus singaporensis</i> sp. nov. with isolate SS21^T (=DSM 111408^T=NCTC14419^T) designated as the type strain.