Ecotoxicity and antibiotic resistance genes in hydrobionts of the Azov Sea

Antimicrobial resistance is a major global health problem. Natural ecosystems, especially aquatic environments and aquatic animals, are important reservoirs of ARGs and antibiotic-resistant bacteria (ARB). The presence of ARGs in the microbiome of seafood may lead to their transfer to human bacteria. While most ARG research focus on water and sediments, the role of aquatic organisms (fish, shellfish, jellyfish) as reservoirs and vectors of ARGs is poorly understood. The aim of this work is to assess ARGs distribution in bacteria associated with aquatic organisms in different ecological niches of the Azov Sea (mollusks, jellyfish and fish) using PCR analysis and to study toxicity of aquatic organisms' tissues using a battery of whole-cell bacterial lux-biosensors, as well as to search for a correlation between samples toxicity and ARGs content in them. We also evaluate the potential relationship between toxicity levels in aquatic organisms, the frequency of ARGs and mobile genetic elements (MGEs) detected. In the course of the work, it was found that the most common are the genes that determine resistance to monobactams blaCTX-M and carbapenems blaVIM-1. Microbial communities of mollusks and fish are characterized by gill bacteria being more contaminated with ARGs than the gut microbiome, which is due to the constant and direct contact of the gill epithelium with polluted aquatic environment. Statistical analysis revealed a positive link between the toxicity of the organs in which the bacteria are localized and the presence of a number of ARGs was found; these findings highlight that tissue toxicity caused by endogenous toxins or external xenobiotic pollutants creates an unfavorable internal environment. A correlation was also discovered between the content of individual genes, which probably indicates their colocalization on the same mobile elements of the genome. This information may be useful for better understanding the spread of antimicrobial resistance genes in aquatic animals.