Study of antibiotic resistance in freshwater ecosystems with low anthropogenic impact

• Published in: The Science of the total environment 2023-01, Vol.857, p.159378-159378, Article 159378
• Main Authors: Navarro, Anna, Sanseverino, Isabella, Cappelli, Francesca, Lahm, Armin, Niegowska, Magdalena, Fabbri, Marco, Paracchini, Valentina, Petrillo, Mauro, Skejo, Helle, Valsecchi, Sara, Pedraccini, Rosalba, Guglielmetti, Stefano, Frattini, Stefano, Villani, Gabriella, Lettieri, Teresa
• Format: Article
• Language: English
• Subjects: Antibiotic resistance; Antibiotic resistance genes (ARG); Antibiotics; Freshwater; Natural bacterial
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.159378

This study aimed to investigate the bacterial diversity and the background level of antibiotic resistance in two freshwater ecosystems with low anthropogenic impact in order to evaluate the presence of natural antimicrobial resistance in these areas and its potential to spread downstream. Water samples from a pre-Alpine and an Apennine river (Variola and Tiber, respectively) were collected in three different sampling campaigns and bacterial diversity was assessed by 16S sequencing, while the presence of bacteria resistant to five antibiotics was screened using a culturable approach. Overall bacterial load was higher in the Tiber River compared with the Variola River. Furthermore, the study revealed the presence of resistant bacteria, especially the Tiber River showed, for each sampling, the presence of resistance to all antibiotics tested, while for the Variola River, the detected resistance was variable, comprising two or more antibiotics. Screening of two resistance genes on a total of one hundred eighteen bacterial isolates from the two rivers showed that blaTEM, conferring resistance to β-lactam antibiotics, was dominant and present in ~58 % of isolates compared to only ~9 % for mefA/E conferring resistance to macrolides. Moreover, β-lactam resistance was detected in various isolates showing also resistance to additional antibiotics such as macrolides, aminoglycosides and tetracyclines. These observations would suggest the presence of co-resistant bacteria even in non-anthropogenic environments and this resistance may spread from the environment to humans and/or animals. [Display omitted] •Bacterial isolates from two low-impacted rivers show resistance to two or more antibiotics.•ARGs were detected in river water samples not experimentally exposed to antibiotics.•blaTEM was found in ~58 % of total isolates upon exposure to antibiotics.•Most isolates belonged to Enterobacterales, Micrococcales and Pseudomonadales orders.