Plastisphere and Planktonic Communities in Italian Lakes: Distribution of Antibiotic Resistance Genes and Potential Pathogenic Taxa

Microplastic-associated biofilms (plastisphere) have been proposed as potential reservoirs of antibiotic resistance genes (ARGs), potential pathogens, and opportunistic microorganisms. However, information on freshwater ecosystems remains limited. In this study, the occurrence and distribution of selected ARGs, predicted resistance-associated functional profiles, and potentially pathogenic bacterial taxa were investigated in the plastisphere and planktonic communities of four Italian lakes. Quantitative PCR was used to quantify four ARGs (blaCTX-M, tetA, sul2 and ermB), while 16S rRNA gene datasets were analyzed to identify potentially pathogenic bacterial genera and reconstruct predicted resistance-associated functional profiles. ARGs were detected more frequently and at higher relative abundance in the plastisphere than in surrounding waters, although their distribution was highly heterogeneous among lakes and sampling sites. In particular, blaCTX-M was frequently detected on microplastics (MPs) but only rarely in planktonic communities. Predicted resistance-associated functional profiles showed a clear separation between plastisphere and planktonic communities, with MP-associated biofilms characterized by a higher contribution of resistance- and stress-associated functions. No consistent enrichment of potentially pathogenic bacterial genera was observed on MPs. Overall, freshwater plastisphere communities may represent distinct microbial microhabitats in which ARGs and resistance-associated functions accumulate more frequently than in surrounding waters, although local ecological conditions appear to strongly influence their distribution.