Emergence of linezolid resistance associated with 23S rRNA G2576T mutations in vancomycin-resistant Enterococcus faecium during oxazolidinone therapy.
Iori Urakami, Shinnosuke Fukushima, Shuma Tsuji et al.
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Case in brief
A patient developed persistent vanA-positive vancomycin-resistant Enterococcus faecium bacteremia after allogeneic hematopoietic stem cell transplantation. Serial isolates were assessed during approximately two months of oxazolidinone exposure. Among four isolates analyzed genomically, linezolid MICs rose from 1 to 2, 4, and 8 μg/mL. Later isolates carried G2576T mutations in two of the six 23S rRNA gene copies. Other investigated mechanisms—including G2505A, specified rplC/rplD alterations, and cfr, optrA, or poxtA—were not detected. The report documents resistance emerging during therapy; it does not describe bacteremia resolution.
What made this case unusual
The G2576T mutation was present in only two of six 23S rRNA gene copies, and the affected rrl loci differed between the two mutation-positive isolates.
Diagnostic / clinical pearl
When linezolid MICs rise during therapy for VRE, serial susceptibility testing and assessment for 23S rRNA mutations can help detect emerging resistance; absence of other tested determinants does not exclude this mechanism.