Emergence, Spread of Antimicrobial-Resistant Bacteria and Phylogenetic Relationships in Coastal Ecosystems—Gastropod Phorcus lineatus as a Bioindicator

Coastal environments have been recognized as key reservoirs for antibiotic-resistant bacteria. The present study evaluated marine gastropods, Phorcus lineatus, as potential bioindicators to assess the spread of antibiotic-resistant bacteria. P. lineatus was sampled in four sites, with different anthropogenic pressures, along the northwest Portuguese coastal area. From these specimens, bacteria were isolated and tested for their antimicrobial susceptibility, followed by their phylogenetic and pathotypic determination. All the Escherichia coli isolates showed resistance to at least one antimicrobial agent. The highest levels of multidrug resistance (25%) were observed in E. coli isolates obtained from SITE 2, which is impacted by the city of Porto and industrial settlements, while nearly 17% of these isolates showed a multiple antibiotic resistance (MAR) index higher than 0.2. Among the isolates, phylogroups A and B2 were the most prevalent, followed by phylogroup B1. The isolates of phylogroup A showed a higher prevalence of antimicrobial resistance. This study offers valuable insights into the antibiotic resistance risks posed to marine ecosystems and underscores the need for microbiological monitoring and the development of effective management strategies. The findings suggest P. lineatus as a potential bioindicator of antibiotic-resistant bacteria in marine environments.