Objective: To characterize the nutritional requirements and potential origin of a fastidious urinary tract Enterococcus faecalis isolate that apparently requires the antimicrobial agent vancomycin to grow.
Design: Case report and detailed microbiologic and molecular epidemiologic analysis.
Setting: University teaching hospital.
Measurements: Growth of the vancomycin-dependent strain was monitored using various standard laboratory media with and without supplementation with vancomycin and other substrates. This strain was compared with other vancomycin-resistant but nondependent E. faecalis strains by examining plasmid profiles 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 isolated repeatedly from the urine of a patient receiving long-term vancomycin therapy. This strain grew in primary culture but not on subculture, suggesting an unusual growth requirement, and ultimately was found to require the glycopeptide antibiotic vancomycin to grow. Strain TJ310 appeared to be closely related to other vancomycin-resistant but nondependent E. faecalis isolates with the vanB genotype previously isolated from the same patient, suggesting that vancomycin dependence may have evolved in vivo in a vancomycin-resistant enterococcal strain during continuous exposure to high concentrations of vancomycin in the urine.
Conclusions: This is the first reported example of a clinical bacterial isolate that requires an antimicrobial agent to grow.