Antibiotic resistance, antimicrobial residues and bacterial community composition in urban wastewater

Antibiotic resistance in urban aquatic environments: can it be controlled?

“…sustaining the hypothesis that, during wastewater treatment, the presence of active antibiotic molecules may impose selective pressure on ARB. Positive correlations between the concentration of antibiotics and rearrangements of the microbial communities, or resistance determinants have been reported (Novo et al 2013Rodriguez-Mozaz et al 2015). These evidences are supported also by the demonstration of the selective potential of subinhibitory concentrations of antibiotics (Andersson and Hughes 2014).…”

“…Since domestic wastewater contains antibiotic residues, it is arguable that such residues can impose selective effects on ARB, although, as discussed above, the low concentrations found in wastewater can make this issue controversial. Some recent reports have assessed possible correlations be-tween antibiotics and metals concentration and the microbiota in wastewater or in freshwater samples (Graham et al 2011;Huerta et al 2013;Novo et al 2013;Narciso-da-Rocha et al 2014;Varela et al 2014;Rodriguez-Mozaz et al 2015). As hypothesized by the authors, these studies showed significant positive correlations between the concentration of antibiotic residues or metals and ARB&ARG or specific bacterial com-munity members in aquatic environments.…”

“…In a study comparing different conventional treatment systems-activated sludge, trickling filter, and submerged aerated filter-it was concluded that the most important factor on antibiotic resistance removal was the capacity of the treatment to remove bacteria, while longer retention times, as those used in la-goons, could be considered a factor favoring antibiotic resistance proliferation Novo and Manaia 2010). In other studies, it was shown that some resistance types, such as quinolone resistance in coliforms or enterococci, tend to become more prevalent in the final effluent, after activated sludge treatment, than in the raw wastewater and this effect could be noticed mainly in the winter (Ferreira da Silva et al 2006;Łuczkiewicz et al 2010;Novo et al 2013). Although it is nowadays very difficult to identify the best technology to avoid antibiotic resistance selection, an important conclusion can be drawn: Irrespective of any significant variation on the antibiotic resistance prevalence, a well-functioning wastewater treatment plant with secondary treatment will discharge continuously to the environment high doses of ARB&ARG (Vaz-Moreira et al 2014;Fig.…”

“…While human medicine, mainly in what concerns antibiotics administration in health care units, tends to use last-generation antibiotics of classes of fluoroquinolones, cephalosporins, or carbapenems, in animal production, "older" antibiotics such as tetracyclines, sulfonamides, or penicillins are preferred (WHO 2014; EFSA/ECDC 2015; Done et al 2015). The use of different antibiotics for animal production and for human medicine may explain the observation of distinct correlations between the bacterial community composition and antibiotic-resistant populations and the concentration in wastewater of tetracyclines, sulfonamides, and penicillins or fluoroquinolones (Novo et al 2013;Varela et al 2014). Nevertheless, it is suggested that both sources of contamination with antibiotic residues are probably associated with antibiotic resistance dissemination and bacterial community disturbance.…”

“…In particular, the complexity of waste-or fresh-water composition in terms of nutrients, particles and microbiota, may make difficult a reliable prediction of the bioavailability of antibiotic residues or of their effects on target bacteria. In spite of these shortcomings, in wastewater, it was possible to demonstrate that the concentration of ciprofloxacin, tetracycline, sulfamethoxazole, or arsenic could be correlated with the prevalence of ARB, the abundance of the genes blaTEM, vanA, or intI1 (related with beta-lactam and vancomycin resistance and class 1 integrons, respectively) or the increase of populations of Bacteroidetes, Clostridia, or Proteobacteria of the classes Gamma or Epsilon (Novo et al 2013;Narciso-da-Rocha et al 2014;Varela et al 2014). Also in surface water and sediments, similar correlations were observed, suggesting that in the environment downstream the wastewater treatment plant, selective pressures may still be exerting some effects.…”