What is the role of landfills on the development and dissemination of antimicrobial resistant Salmonella on the environment?

Descripción

The raise of antimicrobial resistance (AMR) during last years has become the one of the most important threats for public health worldwide. In fact, the presence of multi-resistant Salmonella strains in animals, humans, and environment complicates bacteria control in both veterinary and human medicine. One of the factors that enhances AMR development is the incorrect waste management, disseminating AMR bacteria through environment and wildlife from other regions, and even from other countries or continents. In this context, urban wildlife could be considered as sentinels of AMR Salmonella, as they play an important role as a bridge between cities and rural areas. Therefore, the aim of this study was to evaluate the presence of Salmonella in two species related to landfills in Madrid region (Spain): white stork (WS, Ciconia ciconia) and lesser black-backed gull (LBBG, Larus fuscus). For this purpose, a cloacal swab was collected from each animal (100 from WS, and 25 from LBBG), and samples were analysed withing 24 hours after recollection. Salmonella detection was performed following ISO 6579-1:2017 (Annex D) guidelines, and isolates were serotyped using the White-Kauffman-Le-Minor scheme. Finally, antimicrobial susceptibility testing was performed by Mueller-Hinton broth micro dilution test regarding ISO 20776-1:2006 recommendations. From all the animals included in the study, 21.6% (27/125) were positive to Salmonella. The occurrence was significantly higher in WS (59.5%, n=22) than in LBBG (13.3%, n=5) (p<0.01). Moreover, from all Salmonella infected WS, 77.3% inhabited landfills and 18.2% the city, while only 4.5% were from rural areas (p<0.01). The most detected serovar was S. enterica ser. Enteritidis, followed by S. enterica ser. Typhimurium, S. enterica ser. Typhimurium monophasic variant, S. enterica ser. Kentucky and S. enterica ser. Abony. Finally, AMR testing revealed a higher proportion of resistance to quinolones and colistin. At this point, it is important to highlight that 62.5% of S. enterica ser. Enteritidis isolates from WS with access to landfills were considered multidrug-resistant bacteria and all of them had the same AMR pattern (CIP-NA-COL), three key antimicrobials for salmonellosis treatment. According to the results, the acquisition of AMR Salmonella seems to be amplified in WS with access to urban residues. This condition is of the utmost importance as WS is a large-distance migrating bird species strongly related to landfills in Spain.