抗菌药物对产超广谱β内酰胺酶大肠埃希菌和肺炎克雷伯菌接种效应的研究

The inoculum effect of extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae on antimicrobial susceptibility

目的研究美罗培南、头孢米诺、哌拉西林-他唑巴坦、头孢吡肟、头孢他啶、头孢噻肟和头孢曲松7种常见抗生素对产ESBLS大肠埃希菌和肺炎克雷伯菌的接种效应。方法用微量肉汤稀释法测定7种抗生素对22株产ESBLS大肠埃希菌和肺炎克雷伯菌在标准细菌接种量（5×10^5CFU／mL）和高接种菌量（5×10^7CFU／mL）时的MIC。结果随着接种菌量增加，美罗培南和头孢米诺对所有受试菌株的MIC无接种效应；哌拉西林-他唑巴坦对SHV-12型和1株CTXM-14菌的MIC表现出接种效应；头孢吡肟、头孢他啶、头孢噻肟和头孢曲松存在接种效应的菌种分别占所有受试菌株的86．4％（19／22）、40．9％（9／22）、100％（22／22）和100％（22／22）。结论对22株产ESBLS大肠埃希菌和肺炎克雷伯菌，美罗培南和头孢米诺不存在接种效应，哌拉西林-他唑巴坦对部分基因型ESBLS菌株（SHV-12型和1株CTX-M-14菌株）存在接种效应，头孢吡肟、头孢他啶、头孢噻肟和头孢曲松存在接种效应。

Objective To investigate the inoculum effect of ESBLs producing Esckerichia coli and Klebsiella pneurnoniae on the susceptibility of meropenem, cefminox, piperacillin-tazobactam, cefepime, ceftazidime, cefotaxime and ceftriaxone. Methods Antibiotic susceptibilities were determined using broth microdilution MIC method according to the recommendations of Clinical and Laboratory Standards Institute （CLSI） with standard （5 × 10^5CFU/mL） and 100-fold-higher inoeulum size （5 × 10^7CFU/ mL）. Results The inoculum effect defined as an eight fold or greater MIC increase on the testing with the higher inoculum, was not detected with meropenem or cefminox. Piperacillin-tazobactam was associated with inoculum effect in two isolates （SHV-12 and CTX-M-14）. The percentages of isolates showing inoculum effect with two different inoculum sizes were 86.4% （19/22）, 40.9% （9/22）, 100% （22/22） and 100% （22/22） for cefepime, ceftazidime, eefotaxime and ceftriaxone, respectively. Conclusions In susceptibility testing with ESBLs producing E. coil or K. pneurnoniae isolates, meropenem and cefminox are less influenced by inoculum size. Piperacillin-tazobactam was subjected to inoculum effect in the presence of certain ESBI.s （SHV- 12, one CTX-M-14）. The inoculum effect of ESBLs-producing E. coli or K. pneurnoniae is evident in the tests with cefepime, ceftazidime, cefotaxime and ceftriaxone.