Several European animal nutrition companies have incorporated essential oils (EOs) into animal feed as a result of the prohibition of antibiotics to promote animal growth. Previous studies of EOs have highlighted the absence of bacterial resistance for these substances, although most of the published works focus on studying their tolerance to subinhibitory doses. For this study, oregano essential oil (OEO) was chosen for its proven inhibitory and bactericidal activity. This study is an in vitro assay of the possible induction of Salmonella enterica serovar Typhimurium strains with reduced susceptibility to OEO by mutation, seeking to calculate the mutant prevention concentration (MPC) since this is an important measurement for the control Salmonella's resistance to fluoroquinolones such as enrofloxacin (ENR), the treatment of choice for this infection. To establish the MPC, we used a bacterial inoculum ≥109 colony-forming unit (CFU)/mL and examined the bases for points of resistance to ENR and mutations of target genes of the quinolone resistance determining region (QRDR). The three strains of Salmonella Typhimurium used in this study showed an MPC of four times the minimum inhibitory concentration (MIC) for ENR. In all cases, strains with reduced susceptibility to ENR were obtained, although none reached the point of resistance. The QRDR characterization region was in all cases of wild type (wt). Two of the strains tested with OEO grew at a concentration of 1 × MIC, which could be strains with reduced susceptibility, associated with mutation or not. In this case, the MPC was 2 × MIC. Once isolated and identified as Salmonella Typhimurium, the MIC against OEO of all strains obtained in the induction test indicated a possible reduction in susceptibility. However, the result obtained for both strains coincided with MIC of the original strains, rejecting a priori such a reduced susceptibility of Salmonella Typhimurium to OEO.

中文翻译：

---

鼠伤寒沙门氏菌菌株对牛至精油和恩诺沙星的敏感性降低：一种体外测定。

由于禁止使用抗生素来促进动物生长，一些欧洲动物营养公司已将精油（EOs）掺入动物饲料中。尽管大多数已发表的著作都集中于研究其对亚抑制剂量的耐受性，但对EO的先前研究强调了对这些物质不存在细菌耐药性。在本研究中，选择牛至精油（OEO）来证明其具有抑制和杀菌活性。这项研究是一项体外测定，旨在通过突变诱使对OEO敏感性降低的沙门氏菌血清型鼠伤寒沙门氏菌菌株，试图计算突变预防浓度（MPC），因为这是控制沙门氏菌对氟喹诺酮类药物耐药性的重要指标。恩诺沙星（ENR），选择这种感染的治疗方法。为了建立MPC，我们使用≥109菌落形成单位（CFU）/ mL的细菌接种物，并检查了对ENR的抗性点和喹诺酮抗性决定区域（QRDR）的靶基因突变的碱基。本研究中使用的三种鼠伤寒沙门氏菌菌株的MPC值是ENR最低抑制浓度（MIC）的四倍。在所有情况下，都获得了对ENR敏感性降低的菌株，尽管没有一个菌株达到耐药点。在所有情况下，QRDR表征区域均为野生型（wt）。用OEO测试的菌株中，有两个以1×MIC的浓度生长，这可能是敏感性降低的菌株，无论是否与突变相关。在这种情况下，MPC为2×MIC。一旦分离并鉴定为鼠伤寒沙门氏菌，在诱导试验中获得的所有菌株的针对OEO的MIC均表明敏感性可能降低。但是，两种菌株获得的结果均与原始菌株的MIC相吻合，这先验地拒绝了鼠伤寒沙门氏菌对OEO的敏感性降低。