Bacterial diversity and antibiotic resistance in water habitats: searching the links with the human microbiome

Abstract

Water is one of the most important bacterial habitats on Earth. As such, water represents also a major way of dissemination of bacteria between different environmental compartments. Human activities led to the creation of the so-called urban water cycle, comprising different sectors (waste, surface, drinking water), among which bacteria can hypothetically be exchanged. Therefore, bacteria can be mobilized between unclean water habitats (e.g. wastewater) and clean or pristine water environments (e.g. disinfected and spring drinking water) and eventually reach humans. In addition, bacteria can also transfer mobile genetic elements between different water types, other environments (e.g. soil) and humans. These processes may involve antibiotic resistant bacteria and antibiotic resistance genes. In this review, the hypothesis that some bacteria may share different water compartments and be also hosted by humans is discussed based on the comparison of the bacterial diversity in different types of water and with the human-associated microbiome. The role of such bacteria as potential disseminators of antibiotic resistance and the inference that currently only a small fraction of the clinically relevant antibiotic resistome may be known is discussed.

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

“…In-deed, the fate of antibiotic resistance during wastewater treatment and in the environment may depend on the resistance genes and genetic environment, the host of the gene, and the permissiveness of the receiving environment. Several studies have demonstrated that wastewater treatment using different technologies and complying with the established recommendations regarding treatment efficiency removes, in general, ARB at the same rate as the total bacteria Rizzo et al 2013b;Vaz-Moreira et al 2014). 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. 2a).…”

“…The environment is doubly associated with antibiotic resistance: firstly, because the environment is the natural source of antibiotic resistance genes (ARG), including those harbored by commensal and pathogenic bacteria that threat humans and other animals (D 'Costa et al 2011;Vaz-Moreira et al 2014); and secondly, because the environment is nowadays a major receptor of contaminant antibiotic-resistant bacteria (ARB) and ARG, released from humans and other animals that do not only accumulate in the environment but also spread across different niches (Rizzo et al 2013b;Vredenburg et al 2014;Vaz-Moreira et al 2014). A major driver for the dissemination of antibiotic resistance is supposed to be the use of antibiotics, which, between the years of 2000 and 2010, increased in 36 %, with major contributions from Brazil, Russia, India, China, and South Africa (Van Boeckel et al 2014).…”

“…An impor-tant fraction of these antibiotics is discharged in sewage, together with bacteria of human and animal origin (Michael et al 2013;Rizzo et al 2013b). For its part, water is one of the most important habitats and routes of propagation of bacteria, playing a major role in the dissemination of antibiotic resistance between the environment and humans and other animals (Vaz-Moreira et al 2014). The urban water cycle comprises two major stages, the abstraction of surface or ground water for drinking water purposes, and the collection, transport, and treatment of sewage with its final discharge in the environment.…”

“…1). In addition, the urban water cycle creates multiple situations, in which microbial communities can suffer important rearrangements, including the elimination or enhancement of antibiotic resistance Rizzo et al 2013b;Vaz-Moreira et al 2014; Fig. 1).…”