耐药性体外传递和耐药菌体内生存选择性研究

 【目的】为了进一步验证GyrA基因突变与氟喹诺酮耐药性的关系，阐明与染色体无关的细菌耐药性或耐药基因垂直传递和水平传递特点，阐明控制抗菌药使用对控制细菌耐药性的作用。【方法】用PCR方法扩增了细菌GyrA和ParC基因；用耐四环素（TE）、氨苄青霉素（AMP）、复方新诺明（SXT）的大肠杆菌做供体菌，对TE、AMP、SXT敏感的大肠杆菌作受体菌，进行了体外结合传递试验；用耐药菌株在营养琼脂上垂直传递20代；在2组不携带耐药菌的SPF鸡消化道内分别接种多重耐药大肠杆菌和沙门氏菌，接种后混合饲养。【结果】发现耐环丙沙星（CIP）和恩诺沙星（ENR）菌株的GyrA基因表达的氨基酸第73和78位发生改变，parC基因表达的氨基酸没有变化；对TE、AMP、SXT的抗性能够在大肠杆菌之间水平传递，TE的结合传递频率为3×10-7；连传20代后菌株耐药性不变；耐药菌接种后3 d，2组鸡均分离到接种的菌株，但随时间推移，耐环丙沙星的菌株逐渐减少，23 d后消失。【结论】表明细菌对氟喹诺酮药的耐药表型与GyrA基因突变密切相关；细菌的非染色体耐药基因既能水平传播又能垂直传递，耐药菌能在鸡群中迅速扩散，但如果没有抗菌药的压力，又会很快从宿主体内消除。

Studies on Antimicrobial Resistance Transfer in vitro and Existent Selectivity of Avian Antimicrobial-Resistant Enterobacteriaccae in vivo

PCR amplification of bacterial gyrA and ParC genes indicated that amino acid codons of Ser-83 and Asp-87 were mutation from gyrA and parC genes were not mutation in fluoroquinolone-resistant strains. Conjugational transfer test was performed using donor resistant to tetracycline (TE), ampicillin (AMP), Sulfamethoxazole-trimethoprim ( SXT) and recipient sensitive to TE、AMP、SXT. Result showed that resistance of TE、AMP、SXT could transfer among Escherichia coli and frequency of TE conjugal transfer is 3×10-7. Mixed two groups chicken which inoculated multi-antimicrobial-resistant Escherichia coli (E.loli) and multi-antimicrobial-resistant salmonella (sal) respectively. The multi-antimicrobial-resistant E.coli and sal could be isolated from all chicken after inoculated 3days. But CIP-resistant strains decreased during the time run out and disappeared after inoculated 23days. The result indicated antimicrobial-resistant bacteria can diffuse quickly and unforced eliminated quickly from vivo of host if only the chicken without pressure of antibiotic.