Varying linezolid susceptibility of vancomycin-resistant Enterococcus faecium isolates during therapy: a case report.
OBJECTIVE
Linezolid is an oxazolidinone antibiotic used in the treatment of infections caused by vancomycin-resistant enterococci. Resistance to linezolid has been associated with a G2576U mutation in domain V of the 23S rRNA.


METHODS
We present clinical details and susceptibility data from multiple Enterococcus faecium strains isolated from a liver transplant patient over 13 months. MICs of linezolid, vancomycin and quinupristin/dalfopristin were determined using Etest. Molecular typing was performed by pulsed-field gel electrophoresis. Domain V of the 23S rRNA gene in the vancomycin-resistant Enterococcus faecium was amplified. Linezolid concentrations were analysed by HPLC.


RESULTS
We report the emergence of resistance to linezolid in a vancomycin-resistant Enterococcus faecium during linezolid treatment. After discontinuation of the linezolid therapy, the isolate reverted to susceptibility. However, after re-administration of linezolid the vancomycin-resistant Enterococcus faecium became resistant to linezolid again. The isolates that were resistant to linezolid had a G2576T mutation in their 23S rDNA.


CONCLUSIONS
We describe a clinical case that shows the shift of a vancomycin-resistant Enterococcus faecium from linezolid resistance to susceptibility and then back to resistance again related to linezolid therapy.
Swoboda
Stefanie
S
Pharmacy Department, University of Heidelberg, Im Neuenheimer Feld 670, D-69120 Heidelberg, Germany. stefanie.swoboda@med.uni-heidelberg.de
Fritz
Stefan
S
Martignoni
Marcus E
ME
Feldhues
Rita A
RA
Hoppe-Tichy
Torsten
T
Buchler
Markus W
MW
Geiss
Heinrich K
HK
D000081:Acetamides / Q000494:pharmacology* / Q000627:therapeutic use; D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D016984:Enterococcus faecium / Q000187:drug effects* / Q000235:genetics; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy* / Q000382:microbiology*; D006801:Humans; D000069349:Linezolid; D016031:Liver Transplantation; D008297:Male; D008826:Microbial Sensitivity Tests; D009154:Mutation; D023303:Oxazolidinones / Q000494:pharmacology* / Q000627:therapeutic use; D013997:Time Factors; D020713:Vancomycin Resistance; D014769:Virginiamycin / Q000494:pharmacology
D000081:Acetamides; D000900:Anti-Bacterial Agents; D023303:Oxazolidinones; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; D000069349:Linezolid