Table 1_Antimicrobial resistance of Enterobacteriaceae in rabbit farms: an underestimated reservoir harboring mcr-1.1.xlsx

IntroductionThe transmission of antimicrobial resistance (AMR), particularly the antimicrobial resistance gene in Enterobacteriaceae, presents a critical challenge to global public health. Sichuan province is the largest producer and consumer of rabbit meat in China. However, few studies have focused on AMR surveillance in rabbits.
MethodsEnterobacteriaceae strains were isolated and identified by MALDI-TOF. The minimum inhibitory concentration (MIC) was determined according to the Clinical and Laboratory Standards Institute. Whole-genome sequencing was performed using the Illumina and Oxford Nanopore Technologies (ONT) platforms.
Results and discussionA total of 73 Enterobacteriaceae strains were isolated, including Klebsiella pneumoniae, Salmonella enterica, Enterobacter hormaechei, and Escherichia coli. Resistance rates to tetracycline, ciprofloxacin, nalidixic acid, sulfamethoxazole-trimethoprim, and ampicillin exceeded 60%. For Escherichia coli isolates showed that ST328, ST22, and ST29 were the primary sequence types, with O178:H7 being the predominant serotype. Remarkably, 48% (35/73) of the isolates carried the mcr-1.1 gene, and among these, 82.9% (29/35) mcr-1.1-positive isolates contained the IncI2 plasmid replicon. The mcr-1.1 gene in Klebsiella pneumoniae, Salmonella enterica and Escherichia coli transferred to a recipient strain. Furthermore, the genetic environment of the mcr-1.1 gene showed that it was flanked by PAP2 and a relaxase. Comparative analysis indicated that the mcr-1.1-positive plasmid exhibited high sequence identity to plasmids from human, porcine, and bovine sources. Notably, a phylogenetic analysis based on core single nucleotide polymorphisms demonstrated that certain rabbit-derived mcr-1-positive Escherichia coli strains clustered within the same evolutionary branch as humanderived strains. These findings indicated that smaller-scale breeding operations, such as rabbit farming, could serve as underrecognized reservoirs of AMR determinants, particularly the mcr-1.1 gene, thus requiring systematic assessment.

引言
抗菌耐药性（antimicrobial resistance, AMR）的传播，尤其是肠杆菌科（Enterobacteriaceae）中的抗菌耐药基因，对全球公共卫生构成严峻挑战。四川省是中国最大的兔肉生产与消费省份，但目前针对兔源抗菌耐药性监测的研究相对匮乏。

材料与方法
肠杆菌科菌株经基质辅助激光解吸电离飞行时间质谱（MALDI-TOF）分离并鉴定。参照临床和实验室标准协会（Clinical and Laboratory Standards Institute, CLSI）的标准测定最低抑菌浓度（minimum inhibitory concentration, MIC）。采用Illumina平台与牛津纳米孔技术（Oxford Nanopore Technologies, ONT）平台完成全基因组测序。

结果与讨论
共分离得到73株肠杆菌科菌株，涵盖肺炎克雷伯菌（Klebsiella pneumoniae）、肠炎沙门氏菌（Salmonella enterica）、霍氏肠杆菌（Enterobacter hormaechei）与大肠埃希氏菌（Escherichia coli）。菌株对四环素、环丙沙星、萘啶酸、复方磺胺甲噁唑（sulfamethoxazole-trimethoprim）与氨苄西林（ampicillin）的耐药率均超过60%。
对大肠埃希氏菌分离株的分析显示，ST328、ST22与ST29为主要序列型，O178:H7为优势血清型。值得注意的是，48%（35/73）的分离株携带mcr-1.1基因，其中82.9%（29/35）的mcr-1.1阳性分离株携带有IncI2型质粒复制子。肺炎克雷伯菌、肠炎沙门氏菌与大肠埃希氏菌中的mcr-1.1基因可转移至受体菌株。进一步分析显示，mcr-1.1基因的遗传环境由PAP2基因与松弛酶（relaxase）侧翼环绕。比较基因组分析显示，携带mcr-1.1基因的质粒与人类、猪源及牛源质粒的序列一致性较高。尤为关键的是，基于核心单核苷酸多态性（core single nucleotide polymorphisms, SNPs）的系统发育分析显示，部分兔源mcr-1阳性大肠埃希氏菌菌株与人类源菌株聚集于同一进化分支。本研究结果表明，兔养殖等小规模养殖活动可作为抗菌耐药性决定因子的未被充分认识的储存库，尤其是mcr-1.1基因，因此需要开展系统性评估。