Abstract
Four methicillin-resistant coagulase-negative staphylococci (MRCoNS), one Staphylococcus haemolyticus and three Staphylococcus cohnii, from infections of humans collected via the Ministry of Health National Antimicrobial Resistance Surveillance Net (Mohnarin) program in China were identified as linezolid-resistant. These four isolates were negative for the 23S rRNA mutations, but positive for the gene cfr. Mutations in the gene for the ribosomal protein L3, which resulted in the amino acid exchanges Gly152Asp and Tyr158Phe, were identified in S. haemolyticus 09D279 and S. cohnii NDM113, respectively. In each isolate, the cfr gene was located on a plasmid of ca. 35.4 kb, as shown by S1 nuclease pulsed-field gel electrophoresis and Southern blotting experiments. This plasmid was indistinguishable from the previously described plasmid pSS-02 by its size, restriction pattern, and a sequenced 14-kb cfr-carrying segment. Plasmid pSS-02 was originally identified in staphylococci isolated from pigs. This is the first time that a cfr-carrying plasmid has been detected in MRCoNS obtained from intensive care patients in China. Based on the similarities to the cfr-carrying plasmid pSS-02 from porcine coagulase-negative staphylococci, a transmission of this cfr-carrying plasmid between staphylococci from pigs and humans appears to be likely.
Highlights
Linezolid is an important antimicrobial agent for the therapy of infections caused by gram-positive pathogens, especially methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci
Resistance to oxazolininones can be based on mutations in the central loop of the 23SrRNA gene with the substitution G2576T occurring most frequently; substitutions for T2500A, T2504A and G2215A have been found in staphylococcal isolates from clinical infections, while G2444T, G2447T, A2503G and T2504C have so far only been found among laboratory-derived Staphylococcus strains [3,4]
The S. haemolyticus 09D279 collected in January 2010 and the S. cohnii isolates 09D253 collected in December 2009 and 09D363 collected in March 2010 were obtained from individual patients in hospital A in Shenyang, Liaoning province, whilst S. cohnii NDM113 collected in October 2010 was isolated from a patient in hospital B in Beijing
Summary
Linezolid is an important antimicrobial agent for the therapy of infections caused by gram-positive pathogens, especially methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. Resistance to linezolid was first reported in a methicillin-resistant Staphylococcus aureus (MRSA) clinical isolate in 2001 [2].
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