Abstract:

Objective  To detect the genotypes and resistance of producing CTX-M type extended-spectrum β-lactamase E.coli isolates. Methods  ESBLs was confirmed with phenotypic confirmatory test; blaCTX-M, blaCTX-M-1, -2, -8, -9, -25 genotypes were detected with polymerase chain reaction (PCR); MIC was determined with broth dilution method. Results  Of the 83 Escherichia coli isolates, 45 were ESBLs-producing strains, and 44 produced CTX-M-type ESBLs. Of these 44 isolates, 12 produced blaCTX-M-1, 29 produced blaCTX-M-9 and 3 produced both blaCTX-M-1 and blaCTX-M-9. The blaCTX-M-2, blaCTX-M-8 and blaCTX-M -25 genotypes were not detected. No imipenem-resistant strains were found. All 44 strains showed resistance to cefazolin, cefotaxime, and ceftriaxone. The drug resistance rates of CTX-M-1 strain to ceftazidime, cefepime, aztreonam, levofloxacin and gentamicin were 91.6%, 91.6%, 100%, 100% and 83.3%. The drug resistance rates of CTX-M-9 strain to ceftazidime, cefepime, aztreonam, levofloxacin and gentamicin were 44.8%, 41.4%, 55.2%, 89.7% and 58.6%. There was significant difference between the two rates concerning ceftazidime, cefepime, and aztreonam (P＜0.05). Conclusion  The blaCTX-M is the major genotype producing ESBLs, in which blaCTX-M-9 is dominant. CTX-M-9 strains are more sensitive to ceftazidime, cefepime and aztreonam than CTX-M-1 strains.

Key words: Escherichia coil; CTX-M type extended-spectrum β-lactamase; Genotype;  Resistance