Characterization of Vancomycin-Resistant Enterococci Isolated from Stools and Their Acquisition of Vancomycin Resistance

ABSTRACT

We have isolated 6 vancomycin resistant (VR) Enterococcus faecium and 5 VR-E. gallinarum. Vancomycin resistant enterococcus (VRE) isolates were resistant to multi-drugs, but susceptible to linezolid and quinupristin/dalfopristin. VRE isolates showed 10 VanA phenotypes and 1 VanB phenotype (E. gallinarum). However, all of them showed vanA genotype. vanA gene was detected on both genomic and plasmid DNA from all VRE isolates. Almost of VR-E. faecium had IS1216V which is worldwide type and almost of VR-E. gallinarum had IS1542 which is European type. IS1216V and IS1542 genes were not related with antibiotic types of VRE. Copy numbers of vanA were decreased in VRE with IS1216V or IS1542 but not in VRE with both ISs in broth without vancomycin. The copy numbers of vanA were significantly decreased in VanB phenotype of VRE with IS1542 in broth without vancomycin. Copy numbers of vanA were recovered in the presence of vancomycin. Growth time of reference E. faecium is faster than that of reference E. faecalis when cultured in the broth containing vancomycin. Reference strains cultured in the broth containing vancomycin showed intermediate resistance or resistance to antibiotics without acquisition of van genes. Naturally, multidrug-resistant E. faecium might be fast adapted in the presence of vancomycin compared to E. faecalis. Taken together, VanA phenotype E. gallinarum as well as E. feacium have been increasing in nosocomial infection and showed acquired inducible resistance. E. faecium and E. faecalis showed intermediate resistance in long exposure of vancomycin without acquisition of vanA.