Abstract：
Colistin is a polymyxin antimicrobic mainly used to treat infection caused by multi-drug resistant Gram-negative bacteria. Mechanisms of colistin resistance are linked to the mobile colistin resistance (mcr) genes, which are transferable within mobile plasmids. Currently, there is limited research on the environmental dissemination of these genes. The behavioural and morphological characteristics of Apis mellifera L. make honey bees effective environmental bioindicators for assessing the prevalence of antimicrobial-resistant bacteria. This study aims to evaluate the colistin phenotypic and genotypic resistance in environmental Gram-negative bacteria isolated from foraging honey bees, across a network of 33 colonies distributed across the Emilia-Romagna region in Italy. Phenotypic resistances were determined through a microdilution assay using the minimum inhibitory concentration (MIC) with dilutions ranging from 0.5 μg/ml to 256 μg/ml. Strains with MIC values gather than 2 μg/ml were classified as resistant. Also, the identification of the nine mcr genes was carried out using two separate multiplex PCR assays. The study found that 68.5% of isolates were resistant and the genus with the higher resistance rates observed in Enterobacter spp. (84.5%). At least one mcr gene was found in 137 strains (53.3%). The most detected gene was mcr5 (35.3%), which was the most frequently detected gene in the seven provinces, while the least observed was mcr4 (4.8%), detected only in two provinces. These results suggested the feasibility of detecting specific colistin resistance genes in environmentally spread bacteria and understanding their distribution at the environmental level, despite their restricted clinical use. In a One-Health approach, this capability enables valuable environmental monitoring, considering the significant role of colistin in the context of public health.
摘要：
粘菌素是一种多粘菌素抗菌剂，主要用于治疗由多重耐药革兰氏阴性菌引起的感染。粘菌素抗性的机制与移动粘菌素抗性（mcr）基因有关，可在移动质粒内转移。目前,对这些基因的环境传播的研究有限。蜜蜂的行为和形态特征使蜜蜂成为评估抗微生物细菌流行的有效环境生物指标。本研究旨在评估从觅食蜜蜂中分离出的环境革兰氏阴性菌的粘菌素表型和基因型抗性，遍布意大利艾米利亚-罗马涅地区的33个殖民地网络。通过使用最小抑制浓度(MIC)的微量稀释测定确定表型抗性,稀释范围为0.5μg/ml至256μg/ml。MIC值大于2μg/ml的菌株被归类为抗性。此外，9个mcr基因的鉴定是使用两个单独的多重PCR方法进行的。研究发现，在肠杆菌属中，有68.5％的分离株具有耐药性，并且具有较高的耐药率。(84.5%)。在137株菌株中发现至少一个mcr基因(53.3%)。检出最多的基因是mcr5(35.3%),这是七个省最常见的基因，而观察到的最少的是MCR4(4.8%)，仅在两个省发现。这些结果表明，在环境传播细菌中检测特定的粘菌素抗性基因并了解其在环境水平上的分布是可行的，尽管它们的临床使用受到限制。在单一健康方法中，这种能力可以实现有价值的环境监测，考虑到粘菌素在公共卫生方面的重要作用。
