Investigation Of The CTX-M -ESBLs In Escherichia Coli

The production of Extended-spectrum beta-lactamases (ESBLs) is the most common mechanism of resistance to the third generation cephalosporions and monobactaoms for enterobacterium. The ESBLs is a large species of beta-lactamases that can hydrolyze the cephalosporions, monobactaoms and penicillins, and is mediated by plasmid. ESBLs are mainly produced by Klebsiella pneumoniae and Escherichia coli. A high prevalence of ESBLs among Enterobacteriaceae have been reported worldwide. The genotype of ESBLs differs from country to country, from area to area, even from hospital to hospital in the same area because the different antibacterial agents are used. The ESBLs is divided into five clusters on sequence homology. They are TEM, SHV, CTX-M, OXA and the others groups. China is the area having high prevalence of CTX-M enzymes. In order to clarify the CTX-M genotype in Kunming, we investigate the phenotype of antibiotics-resistance, horizontal transmission of ESBLs and the genotypes of CTX-M in the 197 Escherichia coli (E coli) clinical isolates from the first people's Hospital of Kunming.The isolates producing ESBLs were confirmed by CLSI (Clinical and Laboratory Standard Institute) confirmation test, the susceptibility of antibiotics was detected by Kirby-Bauer disk diffusion method. Conjugation test was used to determine the horizontal transmission of ESBLs, and the ESBLs genes were detected by Polymerase Chain Reaction (PCR). The primers of CTX-M-1, CTX-M-2, CTX-M-8, CTX-M-9 and CTX-M-25 groups were used. The genotypes of beta-lactamases were confirmed by sequencing of the PCR products.There were 104 (52.79%) E.coli isolates producing ESBLs among the 197strains. The difference of the resistance against the 15 antibiotics except the imipenem and amikacin is significant (P<0.01) between isolates producing ESBLs and the non-producing strains. 91 isolates of 104 E.coli producing ESBLs were tested by conjugation. 64 transconjugants were acquired, and the percent of conjugantion was 70.33%. All transconjugants were confirmed to produce ESBLs. 98 strains(94.23%) carried the genes of CTX-M. 38 strains(36.54%) of them were the CTX-M-1 group, and 69 strains(66.35%) were the CTX-M-9 group. 51 transconjugants (79.69%) carried the genes of CTX-M. 18 strains(28.13%) of them were the CTX-M-1 group, and 35 strains(54.69%) were the CTX-M-9 group. Five CTX-M genotypes were confirmed by sequencing of the PCR products. They were the CTX-M-22, CTX-M-28, CTX-M-15, CTX-M-14, CTX-M-27, and the CTX-M-14. There was no isolate carried the genes of CTX-M-2, CTX-M-8 or CTX-M-25 groups.Conclusion: The prevalence of ESBLs in this hospital was high and the horizontal transmission of ESBLs was serious among the clinical E.coli isolates. The CTX-M-14 and CTX-M-22 were the dominant epidemic types in the hospital of Kunming.