Community-Acquired MRSA Literature: Commentary by Dr. John G. Bartlett -- April 2007

John G. Bartlett, MD


April 06, 2007

Tenover FC, McDougal LK, Goering RV, et al. Characterization of a strain of community-associated methicillin-resistant Staphylococcus aureus widely disseminated in the United States. J Clin Microbiol. 2006;44:108-118. The goal of the study was to characterize the strain of Staphylococcus aureus designated USA300-0114, which is the major cause of skin and soft-tissue infections among diverse populations with community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections in the United States.

Methods: The test strains were recovered from prisoners in Mississippi, Texas, and Georgia; athletes and sports teams; military recruits; children from Tennessee and Texas; and Grady Hospital in Atlanta, Georgia. Genomic comparisons were made with 3 other lineages of S aureus: USA100, USA400, and USA500. Testing included antibiotic susceptibility, pulsed-field gel electrophoresis (PFGE), gel pattern analyses, SCCmec typing, polymerase chain reaction (PCR) assays for antibiotic resistance factors and Panton-Valentine leukocidin (PVL), plasmid analysis, microarray analysis, and selected sequence analysis. The results showed what the study investigators consider to be extraordinary homology for the USA-0114 strains, considering the diversity of populations infected in widespread geographic areas.

The USA300 strains were most closely related to the USA500 strains, but the latter are more likely to be resistant to multiple antibiotics and to cause nosocomial infections. There were 6 genes present in the USA300-0114 strains that were not present in the USA500 strains, including PVL genes.

Compared with the USA400 strains, the USA300-0114 strains contained 27 virulence or antibiotic resistance genes that were not present in USA400, including several that are involved in fibronectin binding.

The comparison with the USA100 lineages showed that there were 21 resistance or virulence genes in the USA300-0114 strains that were lacking in the USA100 strains. Again, this included several cell adhesion genes and the PVL gene.

Antibiotic sensitivity test results for 187 strains of the USA300 isolates are summarized in the Table .

The study investigators concluded that USA300-0114 is a highly stable strain of S aureus, and is widely disseminated in the United States and other parts of the world. The antibiotic resistance of the strain continues to evolve through plasmid acquisition. Comparative genomics with other S aureus lineages, including USA100, 400, and 500, shows genes that are specific to USA300-0114 and may yield useful information in terms of understanding its pathogenesis.

Three isolates were D-test-positive and ermC-positive.


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