ABSTRACT
BACKGROUND: The vanA gene is the most frequently encountered gene among isolates, causing vancomycin-resistant Enterococci (VRE) infections in humans, and it is part of the transposable element Tn1546. Knowledge of the diversity of Tn1546 is important to distinguish between the dissemination of a single VRE clone and the transmission of a particular Tn1546 type through a genetically divergent population of enterococci. Recently, we studied molecular diversity of Tn1546-related elements in enterococci isolated in one hospital to facilitate understanding of the molecular epidemiology of vancomycin resistance. METHODS: Nineteen VanA-type VRE clinical isolates, collected in one university hospital during 1997 and 1999, were investigated for characteristics such as antibiotic resistance, structure of vanA gene cluster and genomic DNA type by means of antibiotic susceptibility test, PCR amplified length polymorphism of vanA gene cluster and pulse-field gel electrophoresis (PFGE), respectively. RESULTS: Nine (A, B1 to B5, C, D and E) different vanA gene cluster types were identified. Three isolates were grouped into vanA gene cluster type A, similar to that of Tn1546 prototype, and twelve isolates were grouped into type B that has an insertion of IS1216V at vanX-Y intergenic region. Type B was further subdivided into B1 to B5 according to the size variation of vanX-Y intergenic region, which was resulted from the insertion of IS1216V and deletions associated with the insertion. Both vanY and vanZ were deleted in three isolates, suggesting that these genes are not essential for vancomycin resistance. Notably, three E. faecalis and three E. faecium strains isolated during the same period were shown to carry the same vanA gene cluster, showing intergenic transmission of vancomycin resistance. CONCLUSION: The presence of variable types of vanA gene cluster among VRE strains isolated in one hospital suggests that several evolutionary changes of vanA gene clusters have occurred during the horizontal spread of resistance gene in the hospital environment. This approach may be useful for monitoring the evolution of VanA resistance.
Subject(s)
Humans , Clone Cells , DNA , DNA Transposable Elements , DNA, Intergenic , Drug Resistance, Microbial , Electrophoresis , Molecular Epidemiology , Multigene Family , Polymerase Chain Reaction , Vancomycin ResistanceABSTRACT
BACKGROUND: The vanA gene is the most frequently encountered gene among isolates, causing vancomycin-resistant Enterococci (VRE) infections in humans, and it is part of the transposable element Tn1546. Knowledge of the diversity of Tn1546 is important to distinguish between the dissemination of a single VRE clone and the transmission of a particular Tn1546 type through a genetically divergent population of enterococci. Recently, we studied molecular diversity of Tn1546-related elements in enterococci isolated in one hospital to facilitate understanding of the molecular epidemiology of vancomycin resistance. METHODS: Nineteen VanA-type VRE clinical isolates, collected in one university hospital during 1997 and 1999, were investigated for characteristics such as antibiotic resistance, structure of vanA gene cluster and genomic DNA type by means of antibiotic susceptibility test, PCR amplified length polymorphism of vanA gene cluster and pulse-field gel electrophoresis (PFGE), respectively. RESULTS: Nine (A, B1 to B5, C, D and E) different vanA gene cluster types were identified. Three isolates were grouped into vanA gene cluster type A, similar to that of Tn1546 prototype, and twelve isolates were grouped into type B that has an insertion of IS1216V at vanX-Y intergenic region. Type B was further subdivided into B1 to B5 according to the size variation of vanX-Y intergenic region, which was resulted from the insertion of IS1216V and deletions associated with the insertion. Both vanY and vanZ were deleted in three isolates, suggesting that these genes are not essential for vancomycin resistance. Notably, three E. faecalis and three E. faecium strains isolated during the same period were shown to carry the same vanA gene cluster, showing intergenic transmission of vancomycin resistance. CONCLUSION: The presence of variable types of vanA gene cluster among VRE strains isolated in one hospital suggests that several evolutionary changes of vanA gene clusters have occurred during the horizontal spread of resistance gene in the hospital environment. This approach may be useful for monitoring the evolution of VanA resistance.
Subject(s)
Humans , Clone Cells , DNA , DNA Transposable Elements , DNA, Intergenic , Drug Resistance, Microbial , Electrophoresis , Molecular Epidemiology , Multigene Family , Polymerase Chain Reaction , Vancomycin ResistanceABSTRACT
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.