Molecular characterization of linezolid-resistant CoNS isolates in Japan.

Linezolid has been reported to remain active against 98% of staphylococci with resistance identified in 0.05% of Staphylococcus aureus and 1.4% of CoNS. The objective of this study was to characterize the linezolid-resistance mechanisms in the linezolid-resistant CoNS strains isolated in Japan. Staphylococcus capitis strains exhibiting linezolid MICs >8 mg/L isolated from inpatients between 2012 and 2014 were screened for cfr and mutations in 23S rRNA, L3 and L4 by PCR/sequencing. Isolates were also examined for mutations in the rlmN gene. S. capitis had six 23S rRNA alleles. Five S. capitis isolates displayed linezolid MICs of 8, 16 and 32 mg/L. G2576U mutations were detected in three, four or five copies of 23S rRNA in all isolates. In two isolates exhibiting the highest linezolid MIC (32 mg/L) there was a large deletion in a single copy of 23S rRNA. Repeated 10 bp sequences were found in both 16S and 23S rRNAs, suggesting deletion by recombination between the repeats. One isolate had the mutation Ala-142→Thr in the ribosomal protein L3. All linezolid-resistant isolates also demonstrated mutations in the gene encoding RlmN methyltransferase, leading to Thr-62→Met and Gly-148→Ser. Multiple mechanisms appeared to be responsible for the elevated linezolid resistance in S. capitis isolates: a G2576U mutation in different numbers of copies of 23S rRNA, loss of a single copy of 23S rRNA and a mutation in the ribosomal protein L3, suggesting the accumulation of independent mutational events.

Takaya A ，Kimura A ，Sato Y ，Ishiwada N ，Watanabe M ，Matsui M ，Shibayama K ，Yamamoto T ... -  《-》

Linezolid-resistant clinical isolates of enterococci and Staphylococcus cohnii from a multicentre study in China: molecular epidemiology and resistance mechanisms.

Genetic characterisation of linezolid-resistant Gram-positive cocci in a multicentre study in China has not been reported previously. To study the mechanism underlying the resistance of linezolid-resistant isolates, nine Enterococcus faecalis, one Enterococcus faecium and three Staphylococcus cohnii isolates with various levels of resistance were collected from five hospitals across China in 2009-2012. The nine E. faecalis isolates were classified into seven sequence types, indicating that these linezolid-resistant E. faecalis isolates were polyclonal. Enterococci isolates had reduced susceptibility to linezolid (MICs of 4-8 mg/L) and had mutation of ribosomal protein L3, with three also having mutation of L4, but without the multidrug resistance gene cfr or the 23S rRNA mutation G2576T. The three S. cohnii isolates were highly resistant to linezolid (MICs of 64 mg/L to >256 mg/L), harboured the cfr gene and had the 23S rRNA mutation G2576T. Southern blotting indicated that the cfr gene of these three isolates resided on different plasmids (pHK01, pRM01 and pRA01). In plasmid pHK01, IS21-558 and the cfr gene were integrated into transposon Tn558. In plasmids pRM01 and pRA01, the cfr gene was flanked by two copies of an IS256-like insertion sequence, indicating that the transferable form of linezolid resistance is conferred by the cfr gene. In conclusion, the emergence of linezolid-resistant Gram-positive cocci in different regions of China is of concern. The cfr gene and the 23S rRNA mutation contribute to high-level linezolid resistance in S. cohnii, and the L3 and L4 mutations are associated with low-level linezolid resistance in enterococci.

Chen H ，Wu W ，Ni M ，Liu Y ，Zhang J ，Xia F ，He W ，Wang Q ，Wang Z ，Cao B ，Wang H ... -  《-》

Mechanisms of linezolid resistance in staphylococci and enterococci isolated from two teaching hospitals in Shanghai, China.

Tian Y ，Li T ，Zhu Y ，Wang B ，Zou X ，Li M ... -  《BMC MICROBIOLOGY》

Resistance to linezolid is mediated by the cfr gene in the first report of an outbreak of linezolid-resistant Staphylococcus aureus.

Morales G ，Picazo JJ ，Baos E ，Candel FJ ，Arribi A ，Peláez B ，Andrade R ，de la Torre MA ，Fereres J ，Sánchez-García M ... -  《-》

Co-infection by two linezolid-resistant coagulase-negative staphylococci with two different resistance determinants.

Mazzariol A ，Kocsis E ，Bragagnolo L ，Pellizzer G ，Rassu M ，Cornaglia G ... -  《-》