Clonal heterogeneity of clinical isolates of vancomycin-resistant Enterococcus faecium with unique vanS

Objective To examine the clonal diversity of vancomycin‐resistant enterococci (VRE). Methods A total of 900 clinical isolates of enterococci were obtained, and VRE isolates were subjected to antimicrobial susceptibility tests, biochemical fingerprinting with the PhPlate system (PhP), ribotyping and pulsed‐field gel electrophoresis (PFGE) typing. Results Forty‐nine of all enterococcal isolates were resistant to high levels of vancomycin (MIC ≥ 128) and identified as Enterococcus faecium. Biochemical fingerprinting with PhP showed that the VRE isolates were highly diverse (diversity index, D_i = 0.93) and belonged to 24 PhP‐types. The VRE could be separated into 34 and 27 types with PFGE and ribotyping, giving diversity indices of 0.98 and 0.97, respectively. The PFGE method was more discriminatory than ribotyping and PhP system for E. faecium isolates. A combination of either of the two typing methods resulted in at least 44 types. Furthermore, sequencing analysis of vanS of Tn1546 showed one nucleotide mutation (C→A) at position 5727 in comparison with the prototype BM4147, which was found to be unique in all Iranian VRE isolates. Conclusion The isolated clinical VRE strains were highly diverse in Tehran.