Objective: To study the molecular transmission mechanisms of CTX M 3 ESBLs
producing Gram
negative bacteria for the control
of its spreading. Methods: A total of 378 clinical isolates of Gram
negative bacilli from three hospitals were collected, bacterial susceptibility testing and detection of ESBLs were done. ERIC PCR was carried out for DNA typing of clonal strains, plasmid transfer experiments, fingerprinting analysis, isoelectric focusing, and PCR for TEM, CTX M gene amplification and DNA sequencing was also carried out for ESBLs gene typing and plasmid location. Results: The incidence of ESBLs
producing strains in Gram negative bacilli was 16.9%(64 /378), among them CTX M 3 producing strains account for 20.3% (13 /64). CTX M 3 gene was located on two types of transferable plasmids with size of 66 kb and 75 kb, the 66 kb plasmid also carried beta lactamases TEM 1 gene. Same resistant plasmid could be isolated from strains of different sources producing CTX M 3. Chromosomal DNA homologous analysis indicated that these strains being different clonal strains. Conclusions: The tranomission of CTX M 3 producing strains is mainly mediated by transferable plasmids, and local outbreak of resistant plasmids harbouring CTX M 3 gene possibly had occurred in these hospitals.