Abstract：
Salmonella enterica subsp. enterica serovar Infantis (S. Infantis) is one of the \"top five Salmonella serovars\" of clinical significance in the European Union (EU). Antimicrobial resistant and extended spectrum β-lactamase (ESBL) AmpC-producing S. Infantis have been described in food production systems and human clinical samples in Italy. Recently, an increase of MDR S. Infantis carrying blaCTX-M genes involved in 3rd generation cephalosporin resistance was noticed in the EU, including Italy, mainly due to the spread of S. Infantis harboring a pESI-like plasmid. The aim of this study was to investigate the occurrence of the S. Infantis pESI-like plasmid among antibiotic resistant S. Infantis strains isolated at different points of the food chain, and to provide a phylogenetic analysis to gain further insight on their transmission pathways from \'farm to fork\'. MDR S. Infantis strains (n. 35) isolated from 2016 to 2021 at different stages of the food chain (animals, food, food-related environments, and humans) were investigated with in depth molecular characterization using real-time PCR, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) and whole genome sequencing (WGS). Our study reported the occurrence of S. Infantis strains harboring pESI-like plasmids, carrying blaCTX-M-1 genes, in Central Italy, at different sampling points along the food chain. Results confirmed the presence of a plasmid with a molecular size around 224-310 kb, thus consistent with the pESI-like, in 97 % of the 35 samples investigated. Two variants of S. Infantis pESI-like IncFIB(K)_1_Kpn3 were detected, one associated with the European clone carrying blaCTX-M-1 (21 isolates) and the other associated with U.S. isolates carrying blaCTX-M-65 (2 isolates, pESI-like U.S. variant). The majority was resistant to 3rd generation cephalosporins but none of the strains tested positive for the carbapenemase encoding genes. A total of 118 virulence genes were identified in isolates harboring the pESI-like plasmid. cgMLST and SNP-based analysis revealed the presence of one main cluster, composed by strains isolated from the environment, animals, food and humans. The results of this investigation underline the importance of phylogenetic studies to monitor and understand pathogen and AMR spread in a One Health approach.
摘要：
肠沙门氏菌亚种。肠内血清婴儿(S.Infantis）是欧盟（EU）中具有临床意义的“前五名沙门氏菌血清变型”之一。在意大利的食品生产系统和人类临床样品中已经描述了产生抗微生物剂和广谱β-内酰胺酶（ESBL）AmpC的S.Infantis。最近,在欧盟发现了携带涉及第三代头孢菌素耐药性的blaCTX-M基因的MDRS。包括意大利,主要是由于携带pESI样质粒的婴儿链球菌的传播。这项研究的目的是调查在食物链的不同点分离的抗生素抗性S.Infantis菌株中婴儿pESI样质粒的发生。并提供系统发育分析，以进一步了解它们从“农场到叉子”的传播途径。MDRS.Infantis菌株（n。35)从2016年到2021年在食物链的不同阶段分离(动物，食物,与食物有关的环境，和人类)使用实时PCR进行了深入的分子表征研究，S1核酸酶脉冲场凝胶电泳(S1-PFGE)和全基因组测序(WGS)。我们的研究报道了携带pESI样质粒的婴儿链球菌菌株的发生，携带blaCTX-M-1基因，在意大利中部,在食物链的不同采样点。结果证实存在分子大小约为224-310kb的质粒，因此与pESI一致，在调查的35个样本中有97%。检测到两种InfantispESI样IncFIB（K）_1_Kpn3的变体，一个与携带blaCTX-M-1的欧洲克隆相关（21个分离株），另一个与携带blaCTX-M-65的美国分离株相关（2个分离株，类似pESI的美国变体)。大多数对第三代头孢菌素具有抗性，但没有一个菌株对碳青霉烯酶编码基因呈阳性。在携带pESI样质粒的分离株中鉴定出总共118个毒力基因。基于cgMLST和SNP的分析显示存在一个主簇，由从环境中分离出来的菌株组成，动物,食物和人类这项调查的结果强调了系统发育研究以“一个健康”方法监测和了解病原体和AMR传播的重要性。
