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Resistance to Linezolid of Methicillin-Resistant Staphylococcus

Resistance to Linezolid of Methicillin-Resistant Staphylococcus

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‚esist—n™e2to2linezolid2of2methi™illinEresist—nt ƒt—phylo™o™™us2—ureus2—nd2intero™o™™us2with highElevel2resist—n™e2to2—minogly™osides2—t2— thirdElevel2pedi—tri™2hospit—l

Norma Velázquez-Guadarrama1, Juan Carlos Vigueras Galindo1, Gerardo Escalona Venegas1, José Arellano Galindo1, Silvia Giono Cerezo3, and Margarita Nava Frías2

Abstract Background: The emergence of resistance to the oxazolidinones by methicillin-resistant (MRSA) and high-level aminoglycoside-resistant (HLAR) without being exposed to them is one of the main reasons for control of the clinical use of these . Methods: We studied 95 strains of MRSA and HLAR, which were isolated from January 2003 to December 2007 at the Hospital Infantil de México “Federico Gómez.” The strains were identified by conventional tests. susceptibility was evaluated for several antimicrobial agents including ac- cording to the Clinical and Laboratory Standards Institute (CLSI). The high resistance to aminoglycosides was tested by amplification of aac(6’’)-le, aph(2’’)-and ant(6’) in enterococci. Staphylococcal cas- sette chromosomal mec (SCCmec) associated with MRSA was identified by molecular techniques de- scribed previously. Results: All MRSA strains showed SCCmec type II, and 100% of enterococci strains with phenotype HLAR showed genes associated with high-level aminoglycoside resistance; 12% of HLAR enterococci strains showed intermediate values to linezolid (MIC 4 mg/mL) and only one strain was resistant (MIC 128 mg/mL). Of the MRSA strains, 2.2% were resistant to linezolid (MIC 8 mg/mL). Conclusion: Linezolid is a clinically valuable option as a form of therapy. However, continuous surveillance is necessary to determine the emergent risk of resistance strains and to establish guidelines for appropri- ate use. Key words: linezolid, methicillin-resistant Staphylococcus aureus, high-level-resistant aminoglycosides.

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