ANTIMICROBIAL RESISTANCES OF SALMONELLA STRAINS ISOLATED FROM HUMAN, WILD BOAR, AND ENVIRONMENTAL SAMPLES FROM 2018 TO 2020 IN THE NORTHWEST OF ITALY

Salmonellosis is the second most common zoonosis reported in Europe in 2020 [1], and antimicrobial resistance (AMR) in foodborne pathogens such as Salmonella is a major concern for public health safety [2]. The interface between the environment, wild animals and humans contributes to the emergence of antimicrobial resistant bacteria [3]. Integrated surveillance of AMR is one of the top priorities of the European Union [4]. From a one-health perspective, this study aimed to investigate the serotypes and antimicrobial resistance profiles of Salmonella spp. strains circulating in humans, environment and wild boars in Liguria region from 2018 to 2020. A total of 517 Salmonella spp. strains were analysed. In details: Sixty strains were isolated from liver of wild boars hunted in Liguria, according to ISO 6579:2002/COR. 1, 2004, 193 environmental strains have been previously isolated and 264 human strains were conferred by different hospitals in Liguria, isolated from patients showing clinical signs referred to salmonellosis. Serotype identification was carried out in accordance to ISO/TR 6579-3, 2014. Antimicrobial resistance was evaluated in 415 typed isolates using the Kirby-Bauer method according to Clinical and Laboratory Standard Institute guidelines. Human and environmental isolates were tested against to 18 molecules and isolates from wild boar against 12 molecules. S. Typhimurium monophasic variant 1.4.[5].12:i:-, S. Veneziana and S. Newport were the most prevalent serotypes identified in humans, environmental samples and wild boar, respectively. The degree of antimicrobial resistance varied according to different sources, with 80.4% of Salmonella isolates from humans, 50.0% of those obtained from environment and 7.7% from wild boars displaying resistance for at least one molecule. We uncovered highest levels of resistance against to the combinations of sulfadiazine + sulfamerazine + sulfamethazine, in human (93.3%; 95% CI=87.0– 97.0) and environmental strains (74.2%; 95% CI=62.0–84.2) and trimethoprim + sulfamethoxazole (human strains: 66.7%; 95% CI=43.0–85.4), (environmental strains: 58.3%; 95% CI= 36.6–77.9), while only one resistance pattern was observed against to trimethoprim + sulfamethoxazole in wild boar isolates. Multiple resistant patterns (≥ 2 molecules) were observed in both environmental and human isolates, which concurrently displayed resistant behaviour to up to 5 and 8 antibiotics, respectively. Notwithstanding, multiple resistant patterns often occurred among human serotypes (58.9%; 95% CI=51.5–66.1) compared with environmental isolates (16.4%; 95% CI=8.8–27.0). Fortunately, apart a high resistance observed against azithromycin in environmental strains, the resistances against high critically important molecules observed were generally low. Considering the public health safety, this is an important observation, being these molecules essential for specific treatments in humans.