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MRSA Isolate Acquired vanA Resistance During Therapy

Patient had a serious skin condition that may have predisposed to bacterial colonization

THURSDAY, April 17, 2014 (HealthDay News) -- Researchers report that a bloodstream infection of methicillin-resistant Staphylococcus aureus (MRSA) in a patient with a serious skin condition acquired vancomycin resistance during antibiotic therapy, according to a report published in the April 17 issue of the New England Journal of Medicine.

Flávia Rossi, M.D., Ph.D., from the Universidade de São Paulo in Brazil, and colleagues report of a patient with a bloodstream infection caused by a strain of MRSA that was susceptible to vancomycin (designated BR-VSSA) but during antibiotic therapy acquired the vanA gene cluster and became resistant to vancomycin (designated BR-VRSA).

The researchers found that both strains belong to the sequence type 8 community-associated genetic lineage, which carries the staphylococcal chromosomal cassette mec type IVa and the S. aureus protein A gene type t292. Both are related to MRSA lineage USA300 phylogenetically. A conjugative plasmid (55,706 bp [pBRZ01]) was identified that carried the vanA cluster and readily transferred to other staphylococci. There are DNA sequences harbored in the pBRZ01 plasmid that are typical of the plasmid-associated replication genes rep24 or rep21 witnessed in community-associated MRSA strains from Australia (pWBG745).

"The presence and dissemination of community-associated MRSA containing vanA could become a serious public health concern," the authors write.

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