Abstract
Staphylococcus haemolyticus is one of the most common pathogens associated with medical-device related infections, but its molecular epidemiology is poorly explored. In the current study, we aimed to better understand the genetic mechanisms contributing to S. haemolyticus diversity in the hospital environment and their impact on the population structure and clinical relevant phenotypic traits. The analysis of a representative S. haemolyticus collection by multilocus sequence typing (MLST) has identified a single highly prevalent and diverse genetic lineage of nosocomial S. haemolyticus clonal complex (CC) 29 accounting for 91% of the collection of isolates disseminated worldwide. The examination of the sequence changes at MLST loci during clonal diversification showed that recombination had a higher impact than mutation in shaping the S. haemolyticus population. Also, we ascertained that another mechanism contributing significantly to clonal diversification and adaptation was mediated by insertion sequence (IS) elements. We found that all nosocomial S. haemolyticus, belonging to different STs, were rich in IS1272 copies, as determined by Southern hybridization of macrorestriction patterns. In particular, we observed that the chromosome of a S. haemolyticus strain within CC29 was highly unstable during serial growth in vitro which paralleled with IS1272 transposition events and changes in clinically relevant phenotypic traits namely, mannitol fermentation, susceptibility to beta-lactams, biofilm formation and hemolysis. Our results suggest that recombination and IS transposition might be a strategy of adaptation, evolution and pathogenicity of the major S. haemolyticus prevalent lineage in the hospital environment.
Highlights
Among the coagulase-negative staphylococci (CoNS), Staphylococcus haemolyticus is one of the most important nosocomial human pathogens worldwide being mainly associated with bloodstream and device-associated infections [1,2,3,4]
In the present study we gained a better understanding of the molecular epidemiology and mechanisms of evolution of S. haemolyticus in the hospital environment by analysis of a geographically diverse collection of nosocomial S. haemolyticus by a combination of genotypic and phenotypic methods
The analysis of S. haemolyticus collection by multilocus sequence typing (MLST) has identified a single worldwide disseminated prevalent genetic lineage of nosocomial S. haemolyticus, designated CC29, which accounted for 91% of the nosocomial S. haemolyticus analyzed
Summary
Among the coagulase-negative staphylococci (CoNS), Staphylococcus haemolyticus is one of the most important nosocomial human pathogens worldwide being mainly associated with bloodstream and device-associated infections [1,2,3,4]. In spite of its clinical relevance, its epidemiology, pathogenicity and evolutionary processes are not well understood. In contrast to S. epidermidis, the molecular basis of S. haemolyticus pathogenicity is elusive, but is probably related to putative hemolysins, adhesins, exonucleases, proteases, and genes encoding a capsular polysaccharide found in its genome [4,6]. Another virulence factor that is crucial for S. haemolyticus infectious process is its ability to produce biofilm, but the biofilm composition is largely unknown and the molecular mechanisms involved have not been elucidated. Unlike S. aureus and S. epidermidis, S. haemolyticus biofilms appear to be polysacharide intercellular adhesion (PIA)-independent and not associated with accumulation-associated protein (Aap) and biofilm associated protein (Bhp) [3]
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