BACTEREMIA DUE TO VANCOMYCIN-DEPENDENT ENTEROCOCCUS-FAECIUM

A recipient of small-bowel and liver transplants developed recurrent f ever and polymicrobial bacteremia due to multiply resistant Enterobact er cloacae and an inducible VanB strain of Enterococcus while receivin g therapy with amikacin, imipenem, and vancomycin. These organisms cou ld not be subcultured onto blood agar but did grow around the vancomyc in disk on a direct-susceptibility test plate. Additional testing conf irmed the strain as E. faecium, which would not grow in the absence of vancomycin. Growth around a disk containing D-alanyl-D-alanine was de monstrated. Spontaneous vancomycin-independent revertants were obtaine d at a frequency of similar to 1 x 10(-6). Two classes of vancomycin-i ndependent revertants were obtained: one that was constitutively vanco mycin resistant and one that was nonconstitutively vancomycin resistan t. We hypothesize that the normal D-ala ligase is not expressed in the vancomycin-dependent strain; thus survival of these strains is depend ent on expression of the VanB ligase, which produces a depsipeptide pr ecursor that is resistant to vancomycin binding. This is the second re ported case involving a clinically important vancomycin-dependent ente rococcal strain. Awareness of the existence of these strains is import ant, especially when clinical and microbiological data are consistent with infection due to a fastidious or nutritionally-deficient organism .