Antimicrobial Resistance of Salmonella Serovars and Campylobacter spp. Isolated from an Opportunistic Gull Species, Yellow-legged Gull (Larus michahellis)

Wildlife is a natural reservoir of Salmonella and Campylobacter, the most important human foodborne pathogens worldwide. Free-living birds have the potential to transport, over large distances, such zoonotic bacteria that may harbor antimicrobial resistance traits. On the northeastern Iberian coast, we assessed the role of Yellow-legged Gulls (Larus michahellis) as reservoirs of antimicrobial resistance in Salmonella and thermophilic Campylobacter isolates recovered from gulls at three colonies, with varying degrees of dependence on refuse dumps as food sources. Of the 39 Salmonella isolates we tested, 17 were multiresistant (resistance to three antimicrobial families), with eight being Salmonella enterica serovar Typhimurium. Other clinically relevant Salmonella serovars showing multiresistance included Hadar, Bredeney, and Virchow. Relevant Campylobacter antimicrobial resistances were detected among three Campylobacter jejuni isolates, of which all three showed resistance to nalidixic acid, two were resistant to ciprofloxacin, one was resistant to enrofloxacin, and one was resistant to tetracycline. Our results highlight the importance of free-living gulls with opportunistic feeding habits in the dissemination of enteric pathogens resistant to multiple antimicrobial agents of public health concern.