Molecular Relationship of vanA Glycopeptide Resistance Gene in Enterococci from Hospitalized Patients and Poultry in Korea

Choi, Yeon Hwa; Lee, Yeong Seon; Lee, Jeom Kyu; Yoo, Jae Li; Kim, Chi Kyung; Kim, Bong Su

Abstract

BACKGROUND: Vancomycin-resistant enterococci (VRE) with vanA gene have been reported as a significant nosocomial pathogen. The vanA gene cluster (Tn1546) located on mobile DNA elements is known to be transferable from VRE to other enterococci. The purpose of this study was to investigate the genetic relationship between the vanA VRE strains isolated from hospitalizd patients and poultry.
METHODS
Total 145 isolates, including 58 E. faecium, 12 E. faecalis, 3 E. casseliflavus, and 4 E. gallinarum from humans and 68 E. faecium from poultry, were studied. Antimicrobial susceptibility tests were done by disk diffusion or agar dilution methods and molecular epidemiological analysis was performed by pulsed-field gel electrophoresis (PFGE). The internal and structural regions of vanA gene cluster were analyzed by PCR fragment length polymorphism, restriction enzyme, and sequencing of Orf2D region and vanXY intergenic region. The point mutation at Tn1546 nucleotide position 8234 (G->T) within the vanX gene was screened with DdeI restriction enzyme.
RESULTS
The antibiotic resistance patterns of human isolates were different from those of poultry. PFGE patterns revealed high heterogeneity. Three PCR fragment length patterns in the vanA gene cluster were found : (I) PCR amplicon of the same size as prototype (E. faecium BM4147) in 17% of human isolates and 100% of poultry ones; (II) PCR amplicon for vanXY intergenic region due to an insertion between vanX and vanY genes in 2.5% of human isolates; (III) the insertions in vanX-vanY intergenic and Orf2 regions in 81% of human isolates. The T type in vanX gene of human and poultry isolates was not found.
CONCLUSION
Despite the diverse PFGE patterns, 81% of human and all of poultry isolates belonged to vanA gene cluster type III and I, respectively. These results indicate that the horizontal spread of vanA gene is occurring among genetically diverse strains of VRE in Korea.