604. Evaluation of Occurrence and Resistance Mechanisms of Pleuromutilins in Staphylococcus aureus Clinical Isolates: Report from the SENTRY Antimicrobial Surveillance Program
Session: Poster Abstract Session: Novel Antimicrobial Agents
Friday, October 21, 2011
Room: Poster Hall B1
Background: Topical antimicrobial agents for treating skin infections have been limited to fusidic acid and mupirocin. Recently, new options (pleuromutilins) have been made clinically available or are in development. This study aimed to evaluate the resistance mechanisms of S. aureus displaying elevated (≥4 mg/mL) tiamulin (pleuromutilins marker) MIC results during the 2010 SENTRY Antimicrobial Surveillance Program.

Methods: 10,029 S. aureus recovered from USA and European hospitals during the 2010 SENTRY Program were processed using CLSI methods (M100-S21, 2011). Twenty one strains showed elevated non-wildtype tiamulin MIC results (≥4 mg/mL). These strains were screened for mutations in the 23S rRNA, L3 and L4, and presence of cfr, vga(A), vga(B) and vga(C) genes using PCR and sequencing. Clonality was examined via PVL genes, SCCmec, agr, spa and MLST typing.

Results: Selected S. aureus isolates were mainly (64%) from Europe (5 countries) and 11 (52.4%) were methicillin-resistant. Ten strains possessed a vga(A) variant and these S. aureus isolates were from the USA or France, with the exception of one strain from Hungary. Two S. aureus strains from the USA and one isolate from France harbored the cfr gene. Mutations in the 23 rRNA and ribosomal proteins (L3/L4) were not observed. Eight strains did not exhibit any of the resistance mechanisms investigated. The majority of S. aureus isolates belonged to ST8 or ST5.

Conclusion: Decreased susceptibility to tiamulin among S. aureus was rare (0.2%) and this result can be also inferred for other available pleuromutilins or those in clinical development. Most of the evaluated isolates demonstrated decreased susceptibility mediated by the presence of an efflux pump (vga[A])-encoding gene or cfr. Target site alterations were not observed in the studied strains, which were mostly associated to commonly detected lineages of S. aureus (ST5 or ST8).

Subject Category: A. Antimicrobial agents and Resistance

Rodrigo E. Mendes, Ph.D., Andrew Costello, Lalitagauri M. Deshpande, Ph.D., Mariana Castanheira, PhD and Ronald Jones, MD, Microbiology, JMI Laboratories, North Liberty, IA


R. E. Mendes, None

A. Costello, None

L. M. Deshpande, None

M. Castanheira, None

R. Jones, None

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