Recurrent linezolid-resistant Enterococcus faecalis infection in a patient with pneumonia

Summary Objective It has been reported that LZD-resistant Enterococcus in the gastrointestinal tract of mice colonizes persistently and shows variable minimum inhibitor concentration (MIC) values. However, the colonization characteristics of Enterococcus with LZD resistance in patients remain elusive. Here, we report the case of a patient with recurrent pneumonia due to infection with LZD-resistant Enterococcus faecalis strains. The colonization characteristics of the strains isolated from this patient were analyzed. Methods Ten E. faecalis strains were isolated from tracheal secretions obtained from the patient during five recurrences of pneumonia over the course of 10 months. Clonal relationships were determined by pulsed-field gel electrophoresis (PFGE) with Sma I-macrorestricted genomic DNA. The susceptibility of the isolates to LZD was determined by Etest in Mueller–Hinton agar. Results The homology of these strains was demonstrated by PFGE, suggesting that occult bacterial colonization by LZD-resistant E. faecalis is possible as late as a year after exposure to LZD. These strains showed variable MICs as determined by the Etest. LZD-resistant isolates contained single or double nucleotide mutations in domain V of 23S rRNA as confirmed by PCR and sequencing. The sensitivity of the strains to vancomycin was demonstrated by broth macrodilution, and vancomycin was an effective clinical treatment on each occasion. Conclusions Our results indicate that LZD-resistant E. faecalis strains may colonize persistently in vivo, leading to recurrent infection.