The antimicrobial resistance (AMR) is defined as the ability of microorganisms to withstand the effects of antibiotics and is considered a universal threat to humans, animals and the environment. The resistance mechanisms developed by bacteria originate from either the overuse of antibiotics in medical care and animal farming or from the spread of resistant genes among microorganisms. Worldwide, 700.000 people die annually from resistant infections and this means that if no action is taken, the estimated annual deaths attributable to AMR will be 10 million by 2050.
The aim of this report is to discuss the mechanisms of antibiotic action and antibiotic resistance focusing on potential effects in water. Waterbodies have been indeed recognised as a significant reservoir of antibiotics and antibiotic resistance genes (ARG). They contribute to the interchange of resistance genes between pathogenic and non-pathogenic bacteria and they may favour the maintenance of the resistance in the environment.
In this report, a review of the global scientific literature was conducted to show the levels of antibiotics in waste water treatment plants (WWTP), surface waters, agricultural runoff and drinking waters The most frequently monitored antibiotics in WWTP were sulfamethoxazole, ciprofloxacin and trimethoprim, while the most important substances in surface waters were erythromycin, sulfamethoxazole, trimethoprim and sulfamethazine.In parallel, a European database has been consulted to identify the antibiotics monitored in inland surface waters and the co-occurrence of heavy metals and antibiotic resistance in bacteria is discussed. It is indeed known that the chemical environmental pollution caused by heavy metals like silver (Ag), copper (Cu) or zinc (Zn) can co-select for antibiotic resistance. Antibiotics have been frequently detected in different aquatic environments within urban water cycles (waste, surface and drinking water) and, even if the levels are low (in the range of ng/L to µg/L), they could promote the acquisition of resistance by gene transfer between bacteria. The spread of AMR may be however constrained if general safety measures are taken to improve the effectiveness of wastewater treatment processes and to control the use of antibiotics in animal husbandry and in human medical practices. Additionally, new research must be conducted to understand the relationship between antibiotics’ concentration and the selection of resistance determinants in order to experimentally define the minimal concentration of antibiotics (as single and mixture) that induces resistance in bacteria. This factor should be then also considered in the evaluation of the risk assessment of antibiotics in water in order to define their environmental impact