Genetic Variation in Spatio-Temporal Confined USA300 Community-Associated MRSA Isolates: A Shift from Clonal Dispersion to Genetic Evolution?

Abstract

IntroductionCommunity-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are increasingly isolated, with USA300-0114 being the predominant clone in the USA. Comparative whole genome sequencing of USA300 isolates collected in 2002, 2003 and 2005 showed a limited number of single nucleotide polymorphisms and regions of difference. This suggests that USA300 has undergone rapid clonal expansion without great genomic diversification. However, whole genome comparison of CA-MRSA has been limited to isolates belonging to USA300. The aim of this study was to compare the genetic repertoire of different CA-MRSA clones with that of HA-MRSA from the USA and Europe through comparative genomic hybridization (CGH) to identify genetic clues that may explain the successful and rapid emergence of CA-MRSA.Materials and MethodsHierarchical clustering based on CGH of 48 MRSA isolates from the community and nosocomial infections from Europe and the USA revealed dispersed clustering of the 19 CA-MRSA isolates. This means that these 19 CA-MRSA isolates do not share a unique genetic make-up. Only the PVL genes were commonly present in all CA-MRSA isolates. However, 10 genes were variably present among 14 USA300 isolates. Most of these genes were present on mobile elements.ConclusionThe genetic variation present among the 14 USA300 isolates is remarkable considering the fact that the isolates were recovered within one month and originated from a confined geographic area, suggesting continuous evolution of this clone.

Contamination of Public Buses with MRSA in Lisbon, Portugal: A Possible Transmission Route of Major MRSA Clones within the Community

“…Fourteen ST8 isolates carry a distinct SCC mec type (Table 1). These variations may represent a continuous evolution of this clone as suggested by others [40].…”

Haemophilus ducreyi Seeks Alternative Carbon Sources and Adapts to Nutrient Stress and Anaerobiosis during Experimental Infection of Human Volunteers

“…With the exception of S. aureus and M. tuberculosis studies, the transcriptomes for all of the abovedescribed pathogens were determined using lavage, urine, stool, or swab samples instead of infected tissue; these samples may not recapitulate gene expression at the site of infection. In the S. aureus study, the in vivo transcriptomes were not compared to the in vitro transcriptome of the infecting strain isolated from each patient but were compared to the in vitro transcriptome of a reference strain belonging to the USA300 clone, which displays intraclonal genetic variability (61). In the M. tuberculosis study, the tissue samples were obtained from patients who had received antituberculosis chemotherapy; as discussed by the authors, the antibiotics may have influenced the in vivo gene expression profile.…”

Staphylococcus aureus toxins – Their functions and genetics

“…PVL genes are found in most CA-MRSA strains, which 8 exhibit increased virulence, e.g. in USA300 (Gillet, Issartel et al 2002;Vandenesch, 9 Naimi et al 2003; Diep, Gill et al 2006;Badiou, Dumitrescu et al 2008;Diep and Otto 10 2008; del Giudice, Blanc et al 2009;Carpaij, Willems et al 2011). CA-MRSA cause typical 11 diseases, namely skin and soft tissue infections (SSTIs), as well as necrotizing 12 pneumonia.…”