A decade of Salmonella resistance in the French Pig and Pork Industry: Antibiotics, heavy metals, and farm-to-fork transmission

Salmonella enterica is a zoonotic, foodborne pathogen of major public health concern worldwide. In addition to poultry, laying hens, and turkeys, pigs are among the primary animal reservoirs contributing to the transmission of Salmonella to humans. In France, Salmonella remains one of the leading causes of gastroenteritis, with pork and pork-derived products frequently implicated in cases of salmonellosis [1l. The emergence and spread of antibiotic-resistant Salmonella strains is alarming, particularly as antimicrobial resistance (AMR) can compromise treatment efficacy and lead to more severe clinical outcomes. Following the EU ban on antibiotics as growth promoters in 2006 [2l, and the decrease of antibiotic use in livstock in France over the past decade [3l, heavy metals like copper (Cu), zinc (Zn), and silver (Ag) have been used for their antimicrobial and growth-promoting properties. Resistance to bath antibiotics and heavy metals is a growing concern, particularly due to the potential for genetic linkages that facilitate their co-selection and spread. Resistance genes may: Co-localize on the same mobile genetic elements (MGEs), such as plasmids, transposons, and integrons, / Be co-selected under antimicrobial or metal pressure, enhancing their dissemination in various environments, ln Gram-negative bacteria co-localization of antibiotic resistance genes (ARGs) and heavy metal resistance genes (HMRGs) on MGEs have been well-documented [4l_ However, in Salmonella, the epidemiological impact of ARG and HM RG co-selection remain poorly studied.