1243. Molecular evaluation of mupirocin resistances among Staphylococcus aureus collect in United States (USA) hospitals during 2008-2010
Session: Poster Abstract Session: Staphylococcal Resistance and Epidemiology
Saturday, October 22, 2011
Room: Poster Hall B1

Background: Recent reports indicate an escalation in high level resistance (HLR, MIC, ≥512 g/ml) to mupirocin among S. aureus (SA) following by the increased use of this agent to control the carriage of MRSA on skin and in nasal passages as well as for treatment of cutaneous infections. Low-level resistance (LLR; MIC, 4-256 g/ml) arises by mutation of the mupirocin target, isoleucyl-tRNA synthetase, whereas HLR is due to presence of the plasmid encoded mupA, an exogenous isoleucyl-tRNA synthetase. We analyzed mupirocin R rates among SA collected from USA hospitals in a 3 year period and evaluated the R mechanisms against this agent in isolates showing HLR.

Methods: 16,765 SA isolates collected from bloodstream, respiratory and skin and skin structure infections in 77 hospitals located in 41 USA states during 2008-2010 were susceptibility (S) tested by reference broth microdilution methods against mupirocin and comparator agents. All 2009 and 2010 strains displaying HLR to mupirocin were tested for mupA by PCR and results were analyzed by melting curve analysis. nucA was tested as an internal control.

Results: Overall, 4.8% of the SA strains were R to mupirocin (2.5% HLR). S rates were stable over the years (94.9, 96.4 and 95.3% in 2008, 2009 and 2010, respectively). R was more common among MRSA when compared to methicillin-susceptible (MS) SA and rates among these groups showed very small variations over the years. The LLR rate was higher in 2008, whereas HLR seemed to be more elevated in 2010, but no definitive trends were observed. Among 261 HLR SA tested for mupA, only two (0.8%; one MSSA and one MRSA) were negative for the presence of this gene.

Conclusion: Our results demonstrated a stable rate of mupirocin R in a large recent multi-year USA collection of SA strains. mupA was detected in the vast majority (99.2%) of the isolates displaying HLR. Elevated mupirocin R rates noted in prior studies could be due to limited sample sizes or evaluation of isolates from a unique institutional clone.

Subject Category: A. Antimicrobial agents and Resistance

Mariana Castanheira, PhD, Leah Woosley, BS, Gary J. Moet, Rodrigo E. Mendes, Ph.D. and Ronald Jones, MD, Microbiology, JMI Laboratories, North Liberty, IA


M. Castanheira, None

L. Woosley, None

G. J. Moet, None

R. E. Mendes, None

R. Jones, None

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