URINARY-TRACT INFECTION WITH AN ENTEROCOCCUS-FAECALIS ISOLATE THAT REQUIRES VANCOMYCIN FOR GROWTH

Objective: To characterize the nutritional requirements and potential origin of a fastidious urinary tract Enterococcus faecalis isolate tha t apparently requires the antimicrobial agent vancomycin to grow. Desi gn: Case report and detailed microbiologic and molecular epidemiologic analysis. Setting: University teaching hospital. Measurements: Growth of the vancomycin-dependent strain was monitored using various standa rd laboratory media with and without supplementation with vancomycin a nd other substrates. This strain was compared with other vancomycin-re sistant but nondependent E. faecalis strains by examining plasmid prof iles and pulsed-field gel electrophoresis patterns of genomic DNA and by analyzing vancomycin-resistance genes identified by the polymerase chain reaction. Results: An E. faecalis isolate, strain TJ310, was iso lated repeatedly from the urine of a patient receiving long-term vanco mycin therapy. This strain grew in primary culture but not on subcultu re, suggesting an unusual growth requirement, and ultimately was found to require the glycopeptide antibiotic vancomycin to grow. Strain TJ3 10 appeared to be closely related to other vancomycin-resistant but no ndependent E. faecalis isolates with the vanB genotype previously isol ated from the same patient, suggesting that vancomycin dependence may have evolved in vivo in a vancomycin-resistant enterococcal strain dur ing continuous exposure to high concentrations of vancomycin in the ur ine. Conclusions: This is the first reported example of a clinical bac terial isolate that requires an antimicrobial agent to grow.