Role of Horizontal Transfer of the Transposon Tn1546in the Nosocomial Spread ofvanAVancomycin-Resistant Enterococci at a Tertiary Care Hospital in Korea

Abstract

Objective:To investigate the epidemiologic characteristics of vancomycin-resistant enterococci (VRE) infection.Design.An epidemiologic description by means of chromosomal DNA fingerprinting and transposon typing.Setting.A 2,200-bed tertiary care hospital in Korea.Patients.First VRE isolates were obtained from patients hospitalized from April 1997 to December 2001.Interventions.Thevangenotypes of isolates were identified by means of multiplex polymerase chain reaction (PCR). The macro-restriction patterns of chromosomal DNA were determined by pulsed-field gel electrophoresis (PFGE). The transposon Tn1546was typed by means of 2 sets of long PCR restriction fragment-length polymorphism analysis, which wereClaI restriction of a 10.4-kb region fromorf1tovanZandDdeI restriction of a 4.4-kb region fromvanRtovanX.Results.VRE isolates were recovered from 215 patients. All werevanAgenotype. PFGE analysis of the 215 isolates showed 172 types, including 21 clusters composed of 64 isolates and 151 types of as many isolates. Each type was composed of 2-10 isolates; the isolates within each PFGE cluster were detected within a 10-month period and mostly shared a transposon type. Transposon typing classified 169 strains into 15 types and 158 strains belonged to 4 major transposon clusters. Each of these 4 transposon clusters was isolated from patients treated in 5-22 different wards during a 31-52 month period and consisted of 9-80 PFGE types. Each of the other 11 types were found in only one strain.Conclusions.Our findings suggest that the horizontal transfer of Tn1546has a major role in the nosocomial spread ofvanAVRE. Clonal spread of VRE seemed to contribute to short-term dissemination in limited areas.