Assessing the sentinel capacity of mollusks, seawater and sediments for monitoring antimicrobial resistance in the marine environment.

Abstract

INTRODUCTION: Although it is widely recognized that aquaculture activity is particularly relevant to the development and spread of AMR in the aquatic environment, national action plans against AMR typically do not include the marine environment among the compartments targeted for AMR monitoring and surveillance. This study aimed to compare the sentinel capacity of mollusks, seawater, and sediments for AMR surveillance in the marine environment of the Los Lagos region, Chile, usingas indicator bacteria and florfenicol, oxytetracycline, oxolinic acid, and flumequine as target antimicrobials. METHODS: 101 mollusk, 76 seawater and 76 sediment samples were collected simultaneously from 76 sites in the coastal area of the Los Lagos region, Chile, between 2023 and 2024. All samples were subjected to conventional laboratory procedures forisolation. Minimum inhibitory concentrations (MICs) for florfenicol, oxytetracycline, oxolinic acid, and flumequine were estimated for eachisolate, which was then classified as either "wild-type" (WT; i.e., susceptible) or "non-wild-type" (NWT; i.e., tolerant) based on local epidemiological cutoff values (COwt) calculated from the MIC results. The frequency of NWTisolates was calculated for each of the three compartments; significant differences in the probabilities of isolatingand detecting NWTwere assessed using logistic regression models. RESULTS: was isolated in 82.2% of the mollusk, 93.4% of the seawater, and 38.7% of the sediment samples. The COwt values were estimated in 32 μg/mL for florfenicol, 64 μg/mL for oxytetracycline, 1 μg/mL for oxolinic acid, and 2 μg/mL for flumequine. The proportion of NWTamong the four antimicrobials was consistently higher in seawater (25.0% on average), followed by sediments (10.8%) and then mollusks (5.4%). Logistic models indicated that the probabilities of isolatingand detecting NWTfor the four antimicrobials studied significantly depend on the environmental compartment, with seawater having the highest probability. These results should be considered by authorities developing plans to monitor AMR in the marine environment.