Vibrio Community Structure Shapes the Diversity of Carbenicillin-Hydrolysing Class A β-Lactamase Circulating in...

Coastal environments are increasingly recognised as reservoirs of known antibiotic resistance genes (ARGs), but are less frequently identified as sources of novel ARGs. Here, we investigated class A β-lactamases circulating in European coastal environments used for oyster farming. We examined their diversity, function, and the ecological factors associated with their geographic distribution and environmental dynamics. A high diversity of carbenicillinases was detected in the culturable microbiome of European oysters. The Harveyi and Splendidus clades were key Vibrio lineages structuring the geography of carbenicillinase diversity. The Harveyi clade was primarily associated with the circulation of known carbenicillinases in Mediterranean samples, whereas the Splendidus clade contributed previously uncharacterized carbenicillinase sequences across all Europe. A one-year seasonal monitoring revealed that Vibrio alginolyticus drives the circulation of bla_CARB-42 in the Mediterranean Thau lagoon, with dynamics strongly associated with seawater temperature. bla_CARB-42 conferred intrinsic resistance to both carboxypenicillins and aminopenicillins in V. alginolyticus, which was found in most other species of the Harveyi clade with additional resistances to aztreonam, third-generation cephalosporins and aminoglycosides. Since the Harveyi clade includes major human pathogens, these findings have direct implication for environmental and One Health surveillance, as rising seawater temperatures may increase coastal exposure to antibiotic-resistant Harveyi clade Vibrio.