A Study On Resistance And Genotype Of Multi-drug Escherichia Coli Isolates Producing Plasmid-mediated AmpC β-lactamases

Abstract: Objective: To investigate the genotype distribution andantibiotic resistance of multi-drug Escherichia coli isolates producingplasmid-mediated AmpC β-lactamases. Methods:1. The screening test:AmpC-producing strains were determined by disk diffusion screening testin71strains of E. coil. If the diameter of inhibition zone of cefoxitin wassmaller than18mm, these strains produced AmpC probably. The isolatesharboring AmpC were detected by cefoxitin three-dimensional extract testwith the standard of NCCLS.2. Kerby-Bauer disk diffusion method:71strains of Escherichia coli antibiotic susceptibility test to10antibioticswere performed by Kerby-Bauer disk diffusion method with the standardof NCCLS. ATCC25922was used for quality control.3.PCR: Polymerasechain reatction(PCR) was performed to identify the genotypes ofplasmid-mediated AmpC β-lactamases. The genotypes of MOX, CIT,DHA, ACC, MIR, FOX were detected by PCR.4. Gene sequencing: PCRproducts were visualized on horizontal agarose gels with ethidiumbromide after electrophoresis, and sent to Shanghai Sangonbiotechnology companies were sequenced. Results:1.11strainsharboring AmpC were screened, and8(11.27%) strains were found bycefoxitin three-dimensional extract test.2. Antimicrobial susceptibility test results of71E. coli strains:(1) All the strains were sensitive toimipenem. More than59.15%of them were sensitive to amikacin,cefoxitin, aztreonam and cefepime. They had a lower susceptibility to theother antibiotics.(2) There were24（33.80%）multidrug resistant strains，25（35.21%）double-Resistant strains in71E. coli strains.(3)Theresistante and multi-resistante rates of AmpC-producing strains to allkinds of antibitics were significantly higher than non-AmpC-producingstrains (χ~2test, P <0.05).3. In all these Escherichia coli isolates,2strainswere detected carrying AmpC geng by PCR. They were DHA-1by DNAsequencing. Conclusions:1. It is rare of producing plasmid-mediatedAmpC β-lactamases in this area, and presenting the phenomenon ofmulti-drug resistance.2. The rates of AmpC-producing Escherichia coilare significantly higher than those of non-producing-AmpC to variousantibiotics.3. DHA-1is the major genotype of plasmid-mediated AmpCβ-lactamases in multi-drug Escherichia coli isolates from this area.