Single-Strand Conformational Polymorphism (SSCP) Analysis Of Quinolone-resistance-determining Region (QRDR) In GyrA Gene Of Pathogenic Porcine Escherichia Coli

142 strains porcine pathogenic Escherichia coli were investigated by MIC tests of four fluoroquinolones(FQNs). The results showed that the resistance rates of four FQNs were 78.8%(Ciprofloxacin, CIP), 56. 3%(Enrofloxacin, ENR), 65. 5%(Norfloxacin, NOR) and 76.8% (Oxfloxacin, OFL) respectively. Above 70.5% strains presented multi-drug resistance. The results showed porcine pathogenic E. coli presented serious FQ-resistance.Stable higher level FQN-resistant strains of porcine E.coli were obtained by serial passages on agar containing subinhibitory concentration of CIP from four sensitive strains WJPE3-2, MYPE1-4, MSPE6, WJPE2-1. The results showed that different times of MIC values of CIP were promoted by induce test were between 4-512. Furthermore, the MIC values of Enrofloxacin, Norfloxacin and Oxfloxacin of each induced strain were also enhanced to different times. The results showed FQ-resistant strains could be induced under lower concentration of FQNs.About 300bp products were obtained by Polymerase Chain Reaction (PCR) from Qiu^olone-resistance-detennining region (QRDR) in gyrA gene. Method of SSCP was founded to detect mutations of PCR products by using the polyacrylamide gel(12%, Arc:Bis=29:l),5% glycerin, IxTBE, under conditions of 4'c, 10 - 12 hours and silver-staining. Results of SSCP analysis of induced strains were all coincided with sequencing results that showed two bases changed at code 83(tcg-ttg) and code 87(gac-tac).The sequences of PCR products were registered in GenBank. 85.7% sensitive strainspresented the same SSCP-pattems with that of ATCC25922 and 90.0% resistant strains showed SSCP-patterns different from that of sensitive reference.SSCP analysis could been adopted to detect the nucleotide sequence mutations in gyrA gene. It characterized economy, simplicity and relative specificity.