Taxonomic and Functional Distribution of Bacterial Communities in Domestic and Hospital Wastewater System: Implications for Public and Environmental Health

Abstract

The discharge of untreated hospital and domestic wastewater into receiving water bodies is still a prevalent practice in developing countries. Unfortunately, because of an ever-increasing population of people who are perennially under medication, these wastewaters contain residues of antibiotics and other antimicrobials as well as microbial shedding, the direct and indirect effects of which include the dissemination of antibiotic resistance genes and an increase in the evolution of antibiotic-resistant bacteria that pose a threat to public and environmental health. This study assessed the taxonomic and functional profiles of bacterial communities, as well as the antibiotic concentrations in untreated domestic wastewater (DWW) and hospital wastewater (HWW), using high-throughput sequencing analysis and solid-phase extraction coupled to Ultra-high-performance liquid chromatography Mass Spectrometry (UHPLC-MS/MS) analysis, respectively. The physicochemical qualities of both wastewater systems were also determined. The mean concentration of antibiotics and the concentrations of Cl^-, F^- and PO₄³ were higher in HWW samples than in DWW samples. The phylum Firmicutes was dominant in DWW with a sequence coverage of 59.61% while Proteobacteria was dominant in HWW samples with a sequence coverage of 86.32%. At genus level, the genus Exiguobacterium (20.65%) and Roseomonas (67.41%) were predominant in DWW and HWW samples, respectively. Several pathogenic or opportunistic bacterial genera were detected in HWW (Enterococcus, Pseudomonas and Vibrio) and DWW (Clostridium, Klebsiella, Corynebacterium, Bordetella, Staphylocccus and Rhodococcus) samples. Functional prediction analysis indicated the presence of beta-lactam resistance, cationic antimicrobial peptide (CAMP) resistance and vancomycin resistance genes in HWW samples. The presence of these antibiotic resistance genes and cassettes were positively correlated with the presence of pathogens. These findings show the risk posed to public and environmental health by the discharge of untreated domestic and hospital wastewaters into environmental water bodies.

Keywords: antibiotic resistance genes; antimicrobials; environmental health; public health; untreated wastewater.

Figure 1

Mean concentration of targeted antibiotic compounds in hospital and domestic wastewater samples. Error bars indicate the 95% confidence intervals.

Figure 2

Diversity indices of hospital and domestic wastewater samples (a) Box-plots representing the Alpha diversity indices—ACE, Chao1, Shannon and Simpson. Median values (horizontal line) and interquartile ranges have been depicted in the plots. (b) Principal coordinate analysis (PCoA) based on Bray–Curtis dissimilarities grouped by effluent samples.

Figure 3

Taxonomic profiling of bacterial communities at the phylum level, class level and genus level in the collected hospital and domestic effluents.

Figure 4

Box plots representing the relative abundance (%) of pathogenic bacterial members in collected wastewater samples. Median values (horizontal line) and interquartile ranges have been depicted in the plots.

Figure 5

(a) Relative abundance (%) of different bacterial pathways detected in the wastewater samples (differences in the overall abundance of metabolic genes in the collected effluent samples were significant; p = 0.021). Red bar represented HWW samples and green bar represented DWW samples. (b) Various antibiotic resistance pathways identified in domestic and hospital effluent samples.