Citation: Russo, I.; Bencardino, D.; Napoleoni, M.; Andreoni, F.; Schiavano, G.F.; Baldelli, G.; Brandi, G.; Amagliani, G. Prevalence, Antibiotic-Resistance, and Replicon-Typing of Salmonella Strains among Serovars Mainly Isolated from Food Chain in Marche Region, Italy. Antibiotics 2022, 11, 725. https:// doi.org/10.3390/antibiotics11060725 Academic Editor: Kálmán Imre Received: 9 May 2022 Accepted: 25 May 2022 Published: 28 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). antibiotics Article Prevalence, Antibiotic-Resistance, and Replicon-Typing of Salmonella Strains among Serovars Mainly Isolated from Food Chain in Marche Region, Italy Ilaria Russo 1 , Daniela Bencardino 1 , Maira Napoleoni 2 , Francesca Andreoni 1 , Giuditta Fiorella Schiavano 3 , Giulia Baldelli 1 , Giorgio Brandi 1 and Giulia Amagliani 1, * 1 Department of Biomolecular Sciences, University of Urbino Carlo Bo, 61029 Urbino, Italy; i.russo6@campus.uniurb.it (I.R.); daniela.bencardino@uniurb.it (D.B.); francesca.andreoni@uniurb.it (F.A.); giulia.baldelli@uniurb.it (G.B.); giorgio.brandi@uniurb.it (G.B.) 2 Istituto Zooprofilattico Sperimentale dell’Umbria e Delle Marche “Togo Rosati”, 06126 Perugia, Italy; m.napoleoni@izsum.it 3 Department of Humanities, University of Urbino Carlo Bo, 61029 Urbino, Italy; giuditta.schiavano@uniurb.it * Correspondence: giulia.amagliani@uniurb.it; Tel.: +39-0722-303540 Abstract: Nontyphoidal salmonellosis (NTS) is the second most commonly reported gastrointesti- nal infection in humans and an important cause of food-borne outbreaks in Europe. The use of antimicrobial agents for animals, plants, and food production contributes to the development of antibiotic-resistant Salmonella strains that are transmissible to humans through food. The aim of this study was to investigate the presence and the potential dissemination of multidrug-resistant (MDR) Salmonella strains isolated in the Marche Region (Central Italy) via the food chain. Strains were isolated from different sources: food, human, food animal/livestock, and the food-processing environment. Among them, we selected MDR strains to perform their further characterization in terms of resistance to tetracycline agent, carriage of tet genes, and plasmid profiles. Tetracycline resistance genes were detected by PCR and plasmid replicons by PCR-based replicon typing (PBRT). A total of 102 MDR Salmonella strains were selected among the most prevalent serovars: S. Infantis (n = 36/102), S. Derby (n = 20/102), S. Typhimurium (n = 18/102), and a monophasic variant of S. Typhimurium (MVST, n = 28/102). Resistance to sulfisoxazole (86%) and tetracycline (81%) were the most common, followed by ampicillin (76%). FIIS was the most predominant replicon (17%), followed by FII (11%) and FIB (11%) belonging to the IncF incompatibility group. Concerning the characterization of tet genes, tetB was the most frequently detected (27/89), followed by tetA (10/89), tetG (5/89), and tetM (1/89). This study showed the potential risk associated with the MDR Salmonella strains circulating along the food chain. Hence, epidemiological surveillance supported by molecular typing could be a very useful tool to prevent transmission of resistant Salmonella from food to humans, in line with the One Health approach. Keywords: Salmonella serovars; antibiotic resistance; tet genes; multidrug-resistant (MDR); extensively drug-resistant (XDR); antimicrobial resistance genes (ARGs); plasmid profile; PCR-based replicon typing (PBRT); food chain 1. Introduction Nontyphoidal salmonellosis (NTS) is a common infection mainly caused by the in- gestion of food or beverages contaminated by several zoonotic serovars with the potential to interact with human and animal hosts [1,2]. The most prevalent serovars responsible for human illnesses acquired in the European Union during 2019 were, in decreasing order, S. Infantis, S. Enteritidis, the monophasic variant of S. Typhimurium (MVST), S. Typhimurium, and S. Derby [3]. Antibiotics 2022, 11, 725. https://doi.org/10.3390/antibiotics11060725 https://www.mdpi.com/journal/antibiotics