Ecological Overlap and Horizontal Gene Transfer in Staphylococcus aureus and Staphylococcus epidermidis

Abstract

The opportunistic pathogens Staphylococcus aureus and Staphylococcus epidermidis represent major causes of severe nosocomial infection, and are associated with high levels of mortality and morbidity worldwide. These species are both common commensals on the human skin and in the nasal pharynx, but are genetically distinct, differing at 24% average nucleotide divergence in 1,478 core genes. To better understand the genome dynamics of these ecologically similar staphylococcal species, we carried out a comparative analysis of 324 S. aureus and S. epidermidis genomes, including 83 novel S. epidermidis sequences. A reference pan-genome approach and whole genome multilocus-sequence typing revealed that around half of the genome was shared between the species. Based on a BratNextGen analysis, homologous recombination was found to have impacted on 40% of the core genes in S. epidermidis, but on only 24% of the core genes in S. aureus. Homologous recombination between the species is rare, with a maximum of nine gene alleles shared between any two S. epidermidis and S. aureus isolates. In contrast, there was considerable interspecies admixture of mobile elements, in particular genes associated with the SaPIn1 pathogenicity island, metal detoxification, and the methicillin-resistance island SCCmec. Our data and analysis provide a context for considering the nature of recombinational boundaries between S. aureus and S. epidermidis and, the selective forces that influence realized recombination between these species.

Do Staphylococcus epidermidis Genetic Clusters Predict Isolation Sources?

“…Results from a recent genomic analysis of diverse S. epidermidis isolates were consistent with this MLST classification; specifically, genomic group A included MLST groups GC5, GC1, and GC6 and was separated from genomic group B, which included MLST groups GC2 and GC4 (27). Recombination was most extensive in genomic group C, which included MLST group GC3 (27). In this study, using a larger, updated MLST database, we verified that six GCs define the population genetic structure of S. epidermidis.…”

“…GC3 was also rarely isolated from clinical specimens, and it was identified as a cluster with a significant admixture of DNA from all other clusters (26). Results from a recent genomic analysis of diverse S. epidermidis isolates were consistent with this MLST classification; specifically, genomic group A included MLST groups GC5, GC1, and GC6 and was separated from genomic group B, which included MLST groups GC2 and GC4 (27). Recombination was most extensive in genomic group C, which included MLST group GC3 (27).…”

“…Each of the three populations was significantly underrepresented for admixed STs (40); however, subsequent analysis of genome sequences from representatives of these populations identified an important role for recombination in generating their diversity (45). By comparison, the MLST data for S. epidermidis suggest relatively more recombination in hospital-associated GC5 and less recombination in hospital-associated GC6, whereas a subsequent genomic analysis that placed GC5 and GC6 together in a group with GC1 showed recombination in all three of these backgrounds (27). These results indicate that hospital-associated populations of S. epidermidis may not be isolated from recombination with nonhospital populations as has been proposed for E. faecium.…”

Determinación de factores de adhesión asociados a la formación de biopelícula en aislamientos clínicos de Staphylococcus aureus y Staphylococcus epidermidis

“…Este hallazgo es importante ya que este último microorganismo, considerado comensal de piel, o autobionte, es en la actualidad un importante reservorio genético, y a su vez, debido a la transferencia horizontal de genes entre estas especies, ha pasado a ser considerado potencial patobionte, dentro de la clasificación del Microbioma humano. Adicionalmente, proporciona información acerca de cómo S. epidermidis podría interactúar con proteínas de la matriz extracelular humana y su relación con la formación de biopelícula, siendo este un importante factor de persistencia bacteriana en infecciones frecuentes en pacientes neonatales e inmunocomprometidos (20). No obstante a pesar de que existe mucha información sobre MSCRAMMs en Staphylocuccus, se sabe poco sobre los mecanismos moleculares por los cuales estas proteínas conducen a la adhesión bacteriana (21).…”

“…No obstante es importante mencionar que muchos organismos que no pueden transportar plás-midos producen solo microcolonias pero no biopelícula, pero cuando estos organismos reciben plásmidos de bacterias donantes, estos empiezan a producir biopelículas (35)(36)(37).…”