Antibiotic susceptibility of biofilm forming potential pathogenic microorganisms on microplastic surfaces in freshwater ecosystems

Microplastics, which have become an important global environmental issue on a daily basis, are increasing the dimensions of the global threat caused by these concerning pollutants due to the presence of potential pathogens forming biofilms on them and their role as vectors in transporting them to aquatic ecosystems. Pathogens found within the biofilm structure formed on microplastics can be transported over long distances in aquatic environments, posing a significant risk to both human health and aquatic organisms. In particular, the presence of antibiotic-resistant bacteria within the biofilm and the spread of resistance in this way not only pose a serious concern for public health but also present a significant risk to environmental health. Therefore, the aim of this study is to identify potential pathogen species among the types of microplastics forming biofilms in the Susurluk Alt basin, where human activity is high, and to determine their antibiotic susceptibilities. In this context, microplastic sampling was performed using a manta microplastic scoop in four different areas with similar physicochemical properties (Uluabat Lake, Karadere, Kocaçay, and Delta). The polymer composition of the collected microplastic samples was identified using ATR-FTIR and Raman spectroscopic methods. Eighty-seven microorganisms isolated from the biofilm layer on different polymer types were identified at the genus/species level using conventional microbiological methods, the MALDI-TOF automated identification system, and DNA sequencing. Their susceptibilities to various antibiotics were determined by the disk diffusion method according to bacterial species. When the polymer structure of microplastic samples was examined, it was found that polypropylene (PP) and polyethylene (PE) were the most abundant. It was observed that both Gram-positive and Gram-negative microorganisms colonized the biofilm layer on these plastic particles. The highest antibiotic resistance was observed in bacterial biofilms on polypropylene microplastics, and these types were found to be particularly prevalent in the Nilüfer region, where human activities are very intense. Among the bacterial species found in the bacterial biofilm on all polymer types, the most common Gram-positive bacteria were coagulase-negative Staphylococci, Staphylococcus aureus, and Enterococcus faecalis, while the most common Gram-negative bacteria were Acinetobacter spp., Stenotrophomonas spp., and Yersinia enterocolitica. It was found that the highest resistance among Gram-positive bacteria was against trimethoprim/sulfamethoxazole, while among Gram-negative bacteria, it was against ampicillin and cefoxitin antibiotics. In conclusion, when evaluated from the perspective of "One Health," which encompasses human, animal, and environmental health, the presence of antibiotic-resistant pathogenic bacteria forming biofilms on microplastics, especially in areas with high pollution, indicates a high potential threat to both public and environmental health by entering the food chain through their role as vectors.