Occurrence of Antibiotic Resistant Bacteria in the Legon Sewage Treatment Plant and the Receiving Onyasia Stream; Implications for Wastewater Reuse.

Abstract

Although wastewater treatment plants efficiently reduce the loads of pathogens in wastewater, the conventional treatment processes do not show significant removal of antibiotics, antibiotic resistant bacteria and antibiotic resistant genes, resulting in the introduction of these contaminants into the environment. This has human health implications for wastewater reuse and the use of effluent receiving water bodies as irrigation sources. Humans may be exposed to resistant bacteria and render treatment options for infections caused by resistant pathogens ineffective. In order to assess the occurrence of antibiotic resistance bacteria from the Legon Sewage Treatment Plant effluent and the receiving Onyasia stream, antibiotic resistance profiles of Aeromonas hydrophila, Pseudomonas aeruginosa and Escherichia coli isolated from wastewater and the Onyasia stream were evaluated for resistance to selected antibiotics. Wastewater and surface water samples were collected once per month in triplicate over a six-month period from two sampling sites in the Legon Sewage Treatment Plant (influent and effluent) as well as three sites from the Onyasia stream with reference to the treatment plant discharge point (upstream, outfall and downstream). Aeromonas hydrophila, Pseudomonas aeruginosa and Escherichia coli isolates were tested for resistance to Gentamicin, Amoxicillin clavulanate, Tetracycline, Ciprofloxacin, Cefuroxime, Aztreonam, Imipenem and Ceftazidime using the Kirby-Bauer disc diffusion method. E. coli, Aeromonas hydrophila and Pseudomonas aeruginosa isolates showed high resistance patterns to most tested antibiotics. Escherichia coli and Aeromonas hydrophila isolates were most resistant to Amoxicillin clavulanate (57% and 68% respectively), Cefuroxime (52% and 43% respectively), and Tetracycline (49% and 31% respectively). In contrast, they were susceptible to Imipenem (91% and 78% respectively) Gentamicin (83% and 91%) Aztreonam (74% and 73% respectively), and Ciprofloxacin (71% and 78%). Pseudomonas aeruginosa isolates showed high resistance to Aztreonam (37%) and Ciprofloxacin (33%). Pseudomonas aeruginosa isolates sensitivity to Imipenem (96%), Gentamicin (22%) and Ceftazidime (89%) was high. Resistant rates were high in effluent, outfall and downstream isolates, Significant differences (p < 0.05) were observed between upstream and downstream sampling sites relative to the wastewater treatment plant discharge point (outfall) and the rate of Escherichia coli and Aeromonas hydrophila isolate resistance to Amoxicillin, Cefuroxime and Tetracycline and Pseudomonas aeruginosa isolate resistance to Aztreonam and Ciprofloxacin. There were also levels of multi-drug resistant isolates in downstream sampling site compared to upstream sampling site. Results show that the discharge of treated wastewater effluent into water bodies are potentially significant contributors to the dissemination and persistence of antibiotic resistance in the receiving watershed. These findings also have human health implications for effluent wastewater reuse and the use of the stream as a source of irrigation water.