产质粒介导Ⅰ型头孢菌素酶细菌的耐药性及基因型研究

目的 了解华南地区产β内酰胺酶中质粒介导的Ⅰ型头孢菌素(AmpC)酶细菌的耐药性及其基因型特征。方法 收集革兰阴性菌临床分离无重复菌株共1187株，采用头孢西丁三维试验检测AmpC酶，Kirby-Bauer琼脂扩散法检测耐药性；质粒结合试验，聚合酶链反应(PCR)通用引物扩增各组基因及测序以确定AmpC酶基因型。结果 革兰阴性菌头孢西丁三维试验阳性率为5．9％(70／1187)，其中质粒介导的AmpC β内酰胺酶的检出率为大肠杆菌4．2％(19／451)，克雷伯菌属4．7％(16／339)，肠杆菌属2．1％(4／190)，产碱杆菌属5．3％(1／19)，不动杆菌属2．2％(1／45)，总检出率为3．5％(41／1187)。药敏显示结合子对头霉素和氨苄西林耐药，对头孢吡肟和亚胺培南敏感。PCR扩增和测序结果证实为blaDHA-1基因和blaACT-1。基因，主要分布于克雷伯菌属和大肠杆菌属。结论 华南地区质粒介导AmpC酶的基因型以DHA-1和ACT-1为主。第四代头孢菌素和碳青霉烯类药物可作为治疗产质粒介导的AmpC酶细菌感染的有效药物。

Study of susceptibility and genotype characterization of plasmid-mediated classⅠcephalosporinase in gram-negative bacteria

OBJECTIVE: To investigate the susceptibility and genotype characteristics of gram-negative bacteria producing plasmid-mediated class I cephalosporinase (AmpC beta lactamase) epidemic in Southern China. METHODS: A total of 1,187 clinical isolates of nonrepetive gram-negative bacteria were collected from different cities in Southern China. AmpC beta lactamase producing isolates were identified by cefoxitin three-dimensional test, and antimicrobial susceptibility test was identified by Kirby-Bauer agar diffusion test; plasmid conjugation, plasmid extraction, universal PCR for gene amplication of corresponding group was done, and the PCR products were sequenced subsequently. RESULTS: The positive rate of cefoxitin three-dimensional test in gram-negative bacteria was 5.9% (70/1,187), and the prevalence of plasmid-mediated AmpC beta lactamase was: E. coli: 4.2% (19/451), Klebsiella: 4.7% (16/339), Enterobacter: 2.1% (4/190), Alcaligenes: 5.3% (1/19), Acinetobacter: 2.2% (1/45) and the total positive rate was: 3.5% (41/1,187). The susceptibility test showed that compared with the clinical isolates, the transconjugations remained resistance to cephamycins and ampicillin, and susceptible to cefepime and imipenem. PCR amplication and sequencing confirmed them to be bla(DHA-1) gene and bla(ACT-1) gene, and they were mainly distributed in Klebsiella and Escherichia. CONCLUSIONS: DHA-1 and ACT-1 were the most common genotypes in plasmid-mediated AmpC beta-lactamase produced by clinical isolates in Southern China. Fourth-generation cephalosporins and carbapenems could be better choices for the treatment of infection caused by AmpC betalactamase producers.