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Vancomycin-resistant S. aureus genes less prevalent since 2009
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Genes responsible for transferring vancomycin resistance among Staphylococcus aureus have declined since 2009, according to recent data.
CDC researchers examined 826 isolates of vancomycin-resistant enterococcus (VRE) and 752 isolates of MRSA from two health care institutions in Michigan, where the majority of US vancomycin-resistant S. aureus (VRSA) cases have occurred. These isolates were examined for Inc18 and pSK41, genes that allow the transfer of vancomycin resistance between organisms. VRE samples were most commonly collected from urine (54%) or blood (20.7%), while MRSA often were recovered from blood (38.2%), wound or swab samples (26.2%) or abscesses (9.8%). Collection periods ranged from 2006 to 2013 for VRE and 2009 to 2011 for MRSA.
“Vancomycin is one of the few antimicrobial agents that can treat infections caused by drug-resistant strains of S. aureus, such as MRSA,” researcher Alice Y. Guh, MD, MPH, medical officer at the CDC, said in a press release. “Because alternative treatments are limited, widespread emergence of VRSA would pose a significant clinical and public health threat.”
Inc18 was present in 1.5% of tested VRE isolates, while 2.5% of MRSA isolates were positive for pSK41. Inc18 was more prevalent in VRE from 2006 to 2009 than from 2010 to 2013 (P=.04). Although no data were available for MRSA isolates from 2006 to 2009, the researchers wrote that the low prevalence observed from 2010 to 2013 supported the gene’s decline.
“Reasons for such a decrease are unknown but could reflect changes in the ecology of VRE due to natural fluctuations or interventions designed to reduce health care-associated VRE,” Guh said. “Further evaluation is needed to confirm our findings and to better describe the evolving epidemiology of VRSA.”
Disclosure: One researcher reports having received grant support from AstraZeneca, Cempra, Cerexa, Cubist, Durata Therapeutics, Forest Research Institute, Merck, Pfizer and Tetraphase Pharmaceuticals.
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