肺炎克雷伯菌中质粒介导的AMPC酶及相关表型研究

Study on plasmid-mediated AmpC β-lactamases and their resistance phenotypes in K.pneumonia

目的证实临床分离的部分肺炎克雷伯菌(KP)除产超广谱Β内酰胺酶(ESBLS)外,还同时产AMPC酶,并探讨了AMPC酶编码基因存在方式。方法对临床分离的可疑同时产ESBLS和其他高活性广谱Β内酰胺酶的8株KP进行接合试验,并对供体菌和接合子同时采用三维试验、ESBLS试验、AMPC酶诱导试验和Β内酰胺类抗生素最低抑菌浓度(MIC)试验测定,并进行AMPC基因携带状态、表达方式和酶活性分析。结果8株KP菌通过接合试验共得到10株接合子,其中有6株供体菌均只得到同时表达AMPC和ESBLS的1种接合子;另2株供体菌,各得2株接合子,1株同时表达AMPC和ESBLS,1株仅表达ESBLS;8株供体菌均未得到单独表达AMPC的接合子。表达AMPC接合子的耐药表型与受体菌非常接近,酶的活性也必须用克拉维酸(CA)和邻氯西林(CLO)两种酶抑制剂才能完全抑制,其中有5株可被头孢西丁(FOX)诱导使某些指示药出现截平现象。结论在KP中,已出现质粒携带的AMPC基因,有可能与编码ESBLS的基因存在于同一质粒上,并具有诱导型和非诱导型两种表达形式。

Objective To confirm that some clinical isolates of K. pneumoniae produce ESBLs and AmpC enzymes as well and to investigate the existing form of the gene encoding AmpC enzymes. Methods The eight isolates which produce ESBLs and other highly active β-lactamases were tested for the transfer of resistant gene. The donors and transconjugants were detected for AmpC gene and activity of the enzymes with three-dimensional test, ESBL test, AmpC inducible test and agar dilution test for MICs to β-lactams. Results Ten transconjugants were obtained from the 8 Kp. Out of the 8 donors, 6 yielded 1 type of transconjugant expressing both ESBLs and AmpC. Each of the other two produced 2 types of transconjugant, one expressing both ESBLs and AmpC and the other expressing ESBLs alone. No transconjugant expressing AmpC only was obtained. The similar resistance phenotypes were observed between the donors and the transconjugants harboufing AmpC genes. The activity of the β-lactamases could only be inhibited with both CA and CLO. When cefoxitin was used as the inducing agent, blunt of the inhibition zones of the indicator antibiotics was observed in 5 of the 8 transconjugants. Conclusion The plasmid-carried AmpC gene is present in K. pneumoniae and it might coexist on the ESBLs-encoding plasmid and that there are two expressions, inducible and non-inducible.