Mallart Elise, Guerin François, Amoura Ariane, Le Scouarnec Matthieu, Hamon Antoine, El Meouche Imane, Chau Françoise, Lefort Agnès, Fantin Bruno, Cattoir Vincent, de Lastours Victoire
IAME Research Group, UMR1137 INSERM and Uiversité Paris Cité, F-75018 Paris, France.
UMR1230, INSERM and Université Rennes 1, F-35043 Rennes, France.
J Antimicrob Chemother. 2024 May 2;79(5):1051-1059. doi: 10.1093/jac/dkae072.
Temocillin is a narrow spectrum β-lactam active against MDR Enterobacterales. Mechanisms of acquired resistance to temocillin are poorly understood. We analysed resistance mechanisms in clinical isolates of Escherichia coli and evaluated their impact on temocillin efficacy in vitro and in a murine peritonitis model.
Two sets of isogenic clinical E. coli strains were studied: a susceptible isolate (MLTEM16S) and its resistant derivative, MLTEM16R (mutation in nmpC porin gene); and temocillin-resistant derivatives of E. coli CFT073: CFT-ΔnmpC (nmpC deletion), CFTbaeS-TP and CFTbaeS-AP (two different mutations in the baeS efflux-pump gene).Fitness cost, time-kill curves and phenotypic expression of resistance were determined. Temocillin efficacy was assessed in a murine peritonitis model.
MICs of temocillin were 16 and 64 mg/L for MLTEM16S and MLTEM16R, respectively, and 8, 128, 256 and 256 mg/L for E. coli-CFT073, CFT-ΔnmpC, CFTbaeS-TP and CFTbaeS-AP, respectively. No fitness cost of resistance was evidenced. All resistant strains showed heteroresistant profiles, except for CFTbaeS-AP, which displayed a homogeneous pattern. In vitro, temocillin was bactericidal against MLTEM16R, CFT-ΔnmpC, CFTbaeS-TP and CFTbaeS-AP at 128, 256, 512 and 512 mg/L, respectively. In vivo, temocillin was as effective as cefotaxime against MLTEM16R, CFT-ΔnmpC and CFTbaeS-TP, but inefficient against CFTbaeS-AP (100% mortality).
Heteroresistant NmpC porin alteration and active efflux modification do not influence temocillin efficacy despite high MIC values, unfavourable pharmacokinetic/pharmacodynamic conditions and the absence of fitness cost, whereas homogeneously expressed BaeS efflux pump alteration yielding similar MICs leads to temocillin inefficacy. MIC as sole predictor of temocillin efficacy should be used with caution.
替莫西林是一种窄谱β-内酰胺类抗生素，对多重耐药肠杆菌科细菌有活性。对替莫西林获得性耐药的机制了解甚少。我们分析了大肠埃希菌临床分离株的耐药机制，并评估了它们对替莫西林体外和小鼠腹膜炎模型中疗效的影响。
研究了两组同基因临床大肠埃希菌菌株：一株敏感菌株（MLTEM16S）及其耐药衍生物MLTEM16R（nmpC孔蛋白基因突变）；以及大肠埃希菌CFT073的替莫西林耐药衍生物：CFT-ΔnmpC（nmpC缺失）、CFTbaeS-TP和CFTbaeS-AP（baeS外排泵基因的两种不同突变）。测定了适应性代价、时间-杀菌曲线和耐药表型表达。在小鼠腹膜炎模型中评估了替莫西林的疗效。
替莫西林对MLTEM16S和MLTEM16R的MIC分别为16和64mg/L，对大肠埃希菌-CFT073、CFT-ΔnmpC、CFTbaeS-TP和CFTbaeS-AP的MIC分别为8、128、256和256mg/L。未发现耐药的适应性代价。除CFTbaeS-AP表现为均一模式外，所有耐药菌株均表现出异质性耐药谱。在体外，替莫西林对MLTEM16R、CFT-ΔnmpC、CFTbaeS-TP和CFTbaeS-AP的杀菌浓度分别为128、256、512和512mg/L。在体内，替莫西林对MLTEM16R、CFT-ΔnmpC和CFTbaeS-TP的疗效与头孢噻肟相当，但对CFTbaeS-AP无效（死亡率100%）。
尽管MIC值高、药代动力学/药效学条件不利且无适应性代价，但异质性耐药的NmpC孔蛋白改变和主动外排修饰并不影响替莫西林疗效，而均一表达的BaeS外排泵改变导致相似的MIC值却会导致替莫西林无效。仅将MIC作为替莫西林疗效的预测指标时应谨慎使用。
