Linezolid Resistance in Methicillin-Resistant Staphylococcus aureus in Korea: High Rate of False Resistance to Linezolid by the VITEK 2 System

As various linezolid resistance mechanisms have been identified in methicillin-resistant Staphylococcus aureus (MRSA), we investigated the molecular characteristics of MRSA with elevated linezolid minimum inhibitory concentrations (MICs), using the VITEK 2 system (bioMérieux, Marcy-l'Étoile, France). Twenty-seven MRSA isolates from 14 patients exhibiting linezolid MICs ≥8 µg/mL were examined by broth microdilution (BMD) test as well as by sequencing for mutations in the 23S rRNA gene or ribosomal proteins (L3, L4, and L22) and the presence of the optrA, cfr, and cfr(B) genes. Of the 27 isolates, four (14.8%) from one patient were confirmed as linezolid resistant by BMD and harbored a 23S rRNA T2500A mutation. The remaining 23 were confirmed as linezolid susceptible, indicating that the linezolid-resistant results were major errors generated by VITEK 2. The most commonly detected mutation (19/27, 70.4%), L3 Gly152Asp, was detected in only linezolid-susceptible isolates. No isolates contained optrA, cfr, or cfr(B) or any L4 or L22 protein alterations. Our results show that the 23S rRNA T2500A mutation was mainly associated with linezolid resistance, while the L3 Gly152Asp mutation was not related to linezolid resistance. A confirmatory test is recommended for VITEK 2 linezolid-resistant results owing to the high probability of false resistant results.

Study on the relationship between erythromyc in sensitivity and drug-resistance gene in Mycoplasma pneumoniae / 国际检验医学杂志

Objective To study the relationship between erythromycin sensitivity and drug-resistance gene in Mycoplasma pneu-moniae(Mp).Methods In 46 erythromycin-resistant MP clinical isolates,domain Ⅴ of 23S rRNA was amplified by polymerase chain reaction(PCR),followed by direct automatic sequencing method.The DNA sequences were compared to find molecular mecha-nisms of drug resistance.Results Among the 46 erythromycin-resistant Mp clinical isolates,44(95.65%)harbored an A-to-G tran-sition mutation at position 2063 in the 23S rRNA gene and 2(4.35%)harbored an A-to-G transition mutation at position 2064,but no A-to-C transition mutation at position 2063 and C-to-G/A transition mutation at position 2617 were detected.Conclusion E-rythromycin-resistant of Mp clinical isolates were closely related to A-to-G transition mutation at position 2063/2064 in domain Ⅴof 23S rRNA genes and the most important was the A2063G transition mutation.Rapid and accurate identification of the genetic mutations in domain Ⅴ of 23S rRNA may be help to diagnose the infection of Mycoplasma pneumoniae,provide the drug-resistant information,and instruct the application of antibiotics reasonably and effectively.