Towards antibiotic-resistance in drinking tap water: evidence of a neglected public health issue

Introduction: The environmental dimension of antibiotic-resistance is increasing recognized by global governance. However, some knowledge gaps still remain on the occurrence and spread of antibiotic-resistance bacteria (ARB) from environmental sources to humans, especially regarding drinking water supply chain. Antibiotic-resistance is neglected from a drinking waters’ regulatory perspective, although it is well known the widespread contamination of water supplies by ARB and their determinants as well as the little effectiveness of water treatments in removing antibiotic resistant genes (ARGs). Given the relevance of drinking waters for public health, this paper mapped the available evidence on ARB, ARGs, and antibiotics in such matrix, defined as water treated at a potabilization plant and provided for drinking use through a water distribution system. Methods: The evidence were collected and syntetized by performing a scoping review (ScR), that was prepared in accordance with the PRISMA extension for ScR. The query was composed of two parts: ("antibiotic-resistant bacteria", "antibiotic-resistant gene", ARB, ARG, antibiotic) were searched in conjunction with ("tap water", "potable water", "finished water", "drinking water"). The search was updated till August 28th 2024, without time limitation, in: Pubmed, Scopus, and Web of Science. Results: Of 11,993 records and 152 full-texts read for elegibilty, 45 articles were included, progressively increasing from 2017 and with the majority of them conducted in upper-middle-income economies (42.2%). Most of the papers focused on detecting ARB, either alone (37.8%) or in combination with ARGs (26.7%). Multidrug-resistance profile was often identified in heterotrophic bacteria (e.g., nontuberculous mycobacteria, Pseudomonas spp., and Aeromonas spp.) and Enterobacteriaceae family, which were especially resistant to penicillins, cephalosporins (including 3rd-generation), macrolides (erythromycin), and tetracyclines in the first case, and (fluoro)quinolones and sulfonamide in the second one. ARGs conferring resistance to β-lactam, sulfonamide, and tetracycline were the most frequently detected. Among antibiotics, sulfonamides and macrolides were reported across countries, although their concentrations were generally low (<10 ng/L) in Europe and the United States. Discussion: The marked increase in publishing rate after 2017 can be explained by the global awareness towards environmental dimension of antibiotic-resistance, e.g., empathised by 2016 United Nations political declaration on Antimicrobial Resistance. Some of the ARB detected in drinking tap waters showed a resistance pattern of critical or high concern according to the 2024 WHO bacterial priority pathogens list on ARB. Such ARB were detected mainly in countries with lower-middle income economies: bacteria belonged to Enterobacteriaceae family that were resistant to 3rd-generation cephalosporin and/or carbapenem, fluoroquinolone-resistant Salmonella spp., carbapenem resistant Pseudomonas aeruginosa, vancomycin-resistant Enterococcus faecium, and methicillin-resistant Staphylococcus aureus. Conclusion: Drinking water has currently received very limited attention in tackling antibiotic-resistance phenomenon. For the first time, this work provides structured evidence on the role of drinking tap water as reservoir and vehicle of ARB, also showing the occurrence of ARGs as well as trace levels of antibiotics. Impact: This paper calls for comprehensive evaluation of antibiotic-resistance phenomenon within drinking water regulations, thus suggesting the need to manage the possibile risks of transmission of antibiotic-resistance from the drinking waters to humans.