Genotype characterization of plasmid-mediated extended-spectrum beta-lactamases in Southern China

Objective: To investigate the prevalance and genotype characteristics of epidemical gram-negative bacteria producing plasmid-mediated extended-spectrum beta-lactamases (ESBLs) in Southern China. Methods: A total of 1184 clinical isolates of nonrepetitive gram-negative bacteria were collected in 2001 from five different cities in Southern China. ESBLs-producing isolates were identified by phenotypic confirmatory test based on NCCLS criteria. Plasmids conjugation and electroporation, plasmids extraction and their Pst I digest finger-printing analysis, isoelectric focusing, universal primer PCR for TEM, SHV, CTX-M, VEB, PER and SFO gene amplification and DNA sequencing were carried out for ESBLs-gene typing, plasmid location, and E-test for MICs determination of the different genotype. Results: The prevalence of ESBLs-producing strains in gram-negative bacteria is 14.6% (173/1 184). 67 transcongants and 11 electro-transformants obtained from ESBLs producing clinical isolates produce the following ESBLs genotype: 26(33.3%) CTX-M-14, 18(23.1%) CTX-M-3, 11(14.1%) CTX-M-9, 5(6.4%) CTX-M-5, 2(2.6%) CTX-M-13, 6(7.7%) SHV-5, 4(5.1%) SHV-12, 2(2.6%) SHV-2a, and 4(5.1%) unidentified. Twenty three(29.5%) wild strains also carry broad-spectrum beta-lactamases TEM-1 or SHV-1. The above ESBLs genes are located on transferable plasmids with various size (from 35 to 190kb, respectively). CTX-M-type ESBLs are characterized by high-level resistance to cefotaxime. Conclusion: CTX-M-type is the most common genotype in plasmid-mediated ESBLs produced by clinical isolates in Southern China.