J Bacteriol Virol.  2010 Dec;40(4):179-189. 10.4167/jbv.2010.40.4.179.

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

Affiliations
  • 1Department of Clinical Laboratory Science, Catholic University of Pusan, Busan, Korea. kschang@cup.ac.kr

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.

Keyword

Vancomycin resistant enterococci (VRE); E. faecium; E. gallinarum; E. faecalis; van gene; IS gene

MeSH Terms

Acetamides
Anti-Bacterial Agents
Coat Protein Complex I
Cross Infection
DNA
Enterococcus
Enterococcus faecium
Genotype
Oxazolidinones
Phenotype
Plasmids
Vancomycin
Vancomycin Resistance
Linezolid
Acetamides
Anti-Bacterial Agents
Coat Protein Complex I
DNA
Oxazolidinones
Vancomycin

Figure

  • Figure 1. Detection of vanA gene in genomic and plasmid DNA of VRE isolates from patients by PCR using vanA primer set. Amplified PCR products were analyzed by 1% agarose gel electrophoresis. A, B: Genomic DNA, C, D: plasmid DNA. vanA was detected in both genomic and plasmid DNA from all of VRE isolates except for reference Enterococcus faecium (R; ATCC 19434). M: 100 bp plus ladder DNA molecular size marker, R: reference Enterococcus faecium (ATCC 19434).

  • Figure 2. Detection of IS1216V and IS1542 gene in plasmid DNA of VRE isolates from patients by PCR using specific primer set. The amplified PCR products were analyzed by 1% agarose gel electrophoresis. Plasmid DNA was extracted by using LaboPass Plasmid Mini Purification kit. IS1216V was detected strongly in plasmids from VRE1-5 and 7-8 except for reference Enterococcus faeciem (ATCC 19434), 6, 10-11. The gene was weakly amplified in those from VRE9. IS1542 was detected in VRE2, 3, 5, 7 and 9-11. M: 100 bp plus ladder DNA molecular size marker, R: reference Enterococcus faecium (ATCC 19434), VRE, vancomycin-resistant enterococci.

  • Figure 3. Change of vanA gene in plasmid of VRE isolates through serial passage using BHI broth without vancomycin. vanA was detected weakly in plasmids from VRE 7 and 9, which are E. gallinarum isolates, but not changed in those from VRE 4 and 11, Enterococcus faecium isolates. VRE 2 & 4: VR-E. faecium, VRE10 & 11: VR-E. gallinarum, VRE2: vanA phenotype with IS1216V and IS1542, VRE4: vanA phenotype with only IS1216V, VRE10: vanA phenotype with only IS1542, VRE11: vanB phenotype with only IS1542. M: 100 bp plus ladder DNA molecular size marker, VRE, vancomycin-resistant enterococci. p10: 10th passaged VRE in normal growth media. p11: changed media to broth with 10 μg/ml of vancomycin


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