BackgroundCoagulase negative staphylococci (CoNS) are commensal bacteria on human skin. Staphylococcus lugdunensis is a unique CoNS which produces various virulence factors and may, like S. aureus, cause severe infections, particularly in hospital settings. Unlike other staphylococci, it remains highly susceptible to antimicrobials, and genome-based phylogenetic studies have evidenced a highly conserved genome that distinguishes it from all other staphylococci.ResultsWe demonstrate that S. lugdunensis possesses a closed pan-genome with a very limited number of new genes, in contrast to other staphylococci that have an open pan-genome. Whole-genome nucleotide and amino acid identity levels are also higher than in other staphylococci. We identified numerous genetic barriers to horizontal gene transfer that might explain this result. The S. lugdunensis genome has multiple operons encoding for restriction-modification, CRISPR/Cas and toxin/antitoxin systems. We also identified a new PIN-like domain-associated protein that might belong to a larger operon, comprising a metalloprotease, that could function as a new toxin/antitoxin or detoxification system.ConclusionWe show that S. lugdunensis has a unique genome profile within staphylococci, with a closed pan-genome and several systems to prevent horizontal gene transfer. Its virulence in clinical settings does not rely on its ability to acquire and exchange antibiotic resistance genes or other virulence factors as shown for other staphylococci.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4978-1) contains supplementary material, which is available to authorized users.
Staphylococcus lugdunensis is a commensal bacterium of human skin that has emerged as a virulent Coagulase-Negative Staphylococcus in both community-acquired and healthcare associated infections. Genotyping methods have shown a clonal population structure of this pathogen but failed to identify hypervirulent lineages. Here, complete genomes of three pathogenic and three carriage S. lugdunensis strains were obtained by Single-Molecule sequencing (PacBio) and compared to 15 complete genomes available in GenBank database. The aim was to identify (i) genetic determinants specific to pathogenic or carriage strains or specific to clonal complexes (CCs) defined by MultiLocus Sequence Typing, and (ii) antibiotic resistance genes and new putative virulence factors encoded or not by mobile genetic elements (MGE). Comparative genomic analysis did not show a strict correlation between gene content and the ability of the six strains to cause infections in humans and in a Galleria mellonella infection model. However, this study identified new MGEs (five prophages, two genomic islands and one plasmid) and genetic variations of some putative virulence-associated loci, especially in CC3 strains. For a clonal population, high variability and eight CC-dependent genetic organizations were observed for the ess locus, which encodes a putative type VII secretion system (T7SS) homologous to that of S. aureus. Further phenotypic and functional studies are needed to characterize this particular CC3 and to evaluate the role of T7SS in the virulence of S. lugdunensis.
Staphylococcus lugdunensis is an emergent virulent coagulase-negative Staphylococcus that is increasingly responsible for severe infections. In an attempt to generate informative sequence data for subtyping S. lugdunensis, we selected and sequenced seven polymorphic variable number of tandem repeats (VNTRs) to develop two new methods: a classic length-based multiple-locus VNTR analysis (MLVA) method and a tandem repeat sequence typing (TRST) method. We assessed their performances compared to two existing methods, multilocus sequence typing (MLST) and multivirulence-locus sequence typing (MVLST) for 128 isolates from diverse clinical settings and geographical origins. The clustering achieved by the four methods was highly congruent, with MLVA discriminating within clonal complexes as defined by MLST. Indeed, MLVA was highly discriminant compared to MLST and MVLST in terms of number of genotypes as well as diversity indexes. Sequencing of the seven VNTRs showed that they were stable, and analysis of sequence polymorphisms provided superior discriminatory power. The typeability, reproducibility, and epidemiological concordance of these new methods were excellent. Of note, no link between clustering and clinical settings was identified. This study demonstrates that MLVA and TRST provide valuable information for molecular epidemiological study of S. lugdunensis, and represent promising tools to distinguish between strains of homogenous lineages in this clonal species.
Coagulase negative staphylococci are normal inhabitant of the human skin flora that account for an increasing number of infections, particularly hospital-acquired infections. Staphylococcus lugdunensis has emerged as a most virulent species causing various infections with clinical characteristics close to what clinicians usually observe with Staphylococcus aureus and both bacteria share more than 70% of their genome. Virulence of S. aureus relies on a large repertoire of virulence factors, many of which are encoded on mobile genetic elements. S. lugdunensis also bears various putative virulence genes but only one complete genome with extensive analysis has been published with one prophage sequence (φSL2) and a unique plasmid was previously described. In this study, we performed de novo sequencing, whole genome assembly and annotation of seven strains of S. lugdunensis from VISLISI clinical trial. We searched for the presence of virulence genes and mobile genetics elements using bioinformatics tools. We identified four new prophages, named φSL2 to φSL4, belonging to the Siphoviridae class and five plasmids, named pVISLISI_1 to pVISLISI_5. Three plasmids are homologous to known plasmids that include, amongst others, one S. aureus plasmid. The two other plasmids were not described previously. This study provides a new context for the study of S. lugdunensis virulence suggesting the occurrence of several genetic recombination’ with other staphylococci.
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