Abstract：
Minimum inhibitory concentrations (MIC) assays are often questioned for their representativeness. Especially when foodborne pathogens are tested, it is of crucial importance to also consider parameters of the human digestive system. Hence, the current study aimed to assess the inhibitory capacity of two antibiotics, ciprofloxacin and tetracycline, against Salmonella enterica and Listeria monocytogenes, under representative environmental conditions. More specifically, aspects of the harsh environment of the human gastrointestinal tract (GIT) were gradually added to the experimental conditions starting from simple aerobic lab conditions into an in vitro simulation of the GIT. In this way, the effects of parameters including the anoxic environment, physicochemical conditions of the GIT (low gastric pH, digestive enzymes, bile acids) and the gut microbiota were evaluated. The latter was simulated by including a representative consortium of selected gut bacteria species. In this study, the MIC of the two antibiotics against the relevant foodborne pathogens were established, under the previously mentioned environmental conditions. The results of S. enterica highlighted the importance of the anaerobic environment when conducting such studies, since the pathogen thrived under such conditions. Inclusion of physicochemical barriers led to exactly opposite results for S. enterica and L. monocytogenes since the former became more susceptible to ciprofloxacin while the latter showed lower susceptibility towards tetracycline. Finally, the inclusion of gut bacteria had a bactericidal effect against L. monocytogenes even in the absence of antibiotics, while gut bacteria protected S. enterica from the effect of ciprofloxacin.
摘要：
最低抑制浓度（MIC）测定经常因其代表性而受到质疑。特别是当食源性病原体被检测时，重要的是还要考虑人体消化系统的参数。因此，本研究旨在评估两种抗生素的抑制能力，环丙沙星和四环素，对抗肠道沙门氏菌和单核细胞增生李斯特菌，在具有代表性的环境条件下。更具体地说,从简单的有氧实验室条件开始，逐渐将人类胃肠道（GIT）恶劣环境的各个方面添加到GIT的体外模拟中。这样,包括缺氧环境在内的参数的影响，GIT的物理化学条件(低胃液pH，消化酶，胆汁酸）和肠道微生物群进行了评估。通过包括选定的肠道细菌物种的代表性财团来模拟后者。在这项研究中,建立了两种抗生素对相关食源性病原体的MIC，在前面提到的环境条件下。肠球菌的结果强调了进行此类研究时厌氧环境的重要性，因为病原体在这样的条件下生长。包含物理化学屏障导致肠球菌和单核细胞增生李斯特菌的结果完全相反，因为前者对环丙沙星更敏感，而后者对四环素的敏感性较低。最后,即使在没有抗生素的情况下，肠道细菌也对单核细胞增生李斯特菌具有杀菌作用，而肠道细菌保护肠球菌免受环丙沙星的影响。
