Function Of Transposons And Integron Of GeneticMarkers In Multi-drug Resistant β-lactamases-producing Strains Of Escherichia Coli

Objective:To investigate the multi-drug resistance of producing extended spectrum (3-lactamases (ESBLs) Escherichia coli(E. Coil), and analyze the relationships between transposons and integron of genetic markers. Methods:1. Screening test:ESBLs-producing strains were determined by disk diffusion screening test in 71 strains of E. coil. If the diameter of inhibition zone of ceftazidime was smaller than 22mm, that of ceftriaxone was smaller than 25mm, and that of cefotaxime or aztreonam was smaller than 27mm, these strains produced ESBLs probably.2. Confirmatory test:The strains of ESBLs-producing E. coli matched preliminary condition were detected by confirmatory test. Suspect ESBLs-producing strains were determined by ceftazidime and ceftazidime/clavulanic acid, cefotaxime and cefotaxime/clavulanic acid simultaneously, and either of medicines whose diameter of inhibition zone of adding clavulanic acid was larger 5 mm than not adding clavulanic acid.3. Disk diffusion test:The susceptibility of 71 strains of E. coil to 6 antibiotics were detected by disk diffusion which was recommended by the National Committee for Clinical Laboratory Standards (NCCLS). The 6 antibiotics were levofloxacin, streptomycin, cefoxitin, amikacin, cefotaxime and ciprofloxacin. Criteria was according to 2006 NCCLS, and E. coil ATCC 25922 was used for control strain.4. PCR:E. coli DNA was extracted by the TIANamp bacteria DNA kit. Four pairs of primers were designed according to sequences of qacEΔ-sull gene, merA, tnpA and tnpU gene. QacEΔ-sull gene, merA, tnpA and tnpU gene were determined by PCR. PCR products were visualized on horizontal agarose gels with ethidium bromide after electrophoresis and sent to detect the genes’sequences. Results:1 Confirmatory test:There were 35 strains(49.30%) producing ESBLs and 36 strains non-ESBLs-producing strains.2. Disk diffusion test:(1) 45 strains were resistant to levofloxacin,9 strains to cefoxitin,6 strains to amikacin, and 44 strains to ceftazidime. (2) There were 45 multi-drug resistant strains,8 double-resistant strains,11 one-resistant strains, and 7 sensitive strains in 71 E. coli strains.3. MerA detection:Genetic markers of transposons MerA detection rate was 21.24%(15), and positive strains of the tnpA and tnpU were not detected. The detection rate of MerA had significant difference in all resistance patterns(P<0.05). The detection rate of MerA had significant difference in ESBLs-producing strains of different resistance patterns(P<0.05). The detection rate of MerA had no significant difference in non-ESBLs-producing strains of different resistance patterns (P>0.05).4. QacEΔ-sull detection:Genetic markers of class I integron QacE-sull detection rate was 78.57%(55). The detection rate of QacE-sull had significant difference in all resistance patterns(P<0.05). The detection rate of QacE-sull had significant difference in ESBLs-producing strains (P<0.05). The detection rate of QacEΔ-sul1 had no significant difference in non-ESBLs-producing strains(P>0.05).5. Detection of integron in transposons-positive strains:10 strains were found,8 strains in multi-drug resistant pattern,2 strains in double-resistant pattern.6. The detection rate of integron together with MerA in ESBLs-producing strains had significant differences in four resistant patterns (P<0.05). Conclusion:1. The situation of resistance in E. Coil is severe. ESBLs-producing strains are common, especially in the multi-drug resistant pattern.2.The strains of transposons-positive and integron-positive are existed mainly in multi-drug resistant pattern.3.The strains carrying both QacEΔ-sul1 and MerA gene are existed mostly resistant strains, especially in the multi-drug resistant pattern.4. The ESBLs-producing E. coil strains carrying both transposons and integron are frequent in the multi-drug resistant pattern.There factors maybe have some relationship of them in the drug-resistant mechanism.