志贺菌属整合子的耐药贡献与稳定性研究

目的分析志贺菌属整合子对耐药性的贡献及其稳定性。方法对志贺菌属1类、2类整合子的耐药基因盒分别克隆、转化DH5α,观察阳性克隆菌对多种抗生素敏感性的变化。将整合子阳性克隆菌与多重耐药志贺菌进行质粒接合实验,并测定耐药性的改变。对10株耐药谱不同、携带整合子不同的志贺菌属细菌进行无抗生素压力下连续多次传代实验,检测其耐药性及整合子的变化。结果志贺菌属1类整合子耐药基因盒dfrA17-aadA5阳性克隆菌对链霉素和甲氧苄啶的最低抑菌浓度(minimal inhibitory concentration,MIC)分别提高了8倍和32倍;2类整合子耐药基因盒dfrA1-sat1-aadA1阳性克隆菌对链霉素和甲氧苄啶的MIC分别提高了64倍和32倍;整合子阳性克隆菌经质粒接合传递后对抗生素的MIC无改变。1株携带2类整合子的志贺菌属菌株经过多次传代培养后丢失整合子及其耐药性。结论志贺菌属整合子-耐药基因盒系统可引起特定抗生素的耐药性,对质粒接合传递耐药性无影响。志贺菌属的2类整合子可发生丢失。

Drug resistance of Shigella integrons and their stability

Objective To analyze the drug resistance of Shigella integrons and their stability.Methods Drug-resistant gene cassettes of classes 1 and 2 Shigella integrons were cloned and transformed to E.coli DH5α,respectively,to observe changes in sensitivity of positive clones to multiple antibiotics.Positive clones were conjugated with multi-drug resistant Shigella integrons to conduct plasmid conjugating experiments,and drug resistance of and conjugants to antibiotics was detected.Ten drug-resistant S.flexneri strains with different resistant phenotypes and integrons were cultured continuously without any antibiotics,and changes in their resistance and integrons were detected.Results The minimal inhibitory concentration(MIC) of streptomycin and trimethoprim was increased 8-fold and 32-fold,respectively,for the positive clones of class 1 integron gene cassettes dfrA17-aadA5,and 64-fold and 32-fold,respectively,for the positive clones of class 2 integron gene cassettes dfrA1-sat1-aadA1.No change occurred in their drug resistance after conjugation.After 30 times of inoculation without antibiotics,one S.flexneri strain of class 2 Shigella integrons completely lost its resistance andintegron.Conclusion The integron gene cassettes in Shigella can lead to resistance to specific antibiotics and may have no impact on the resistance transferred by plasmid conjugate.Loss of class 2 integrons may occur in Shigella.