Antibiotic Resistance Profile of Bacteria Isolated from Wastewater Systems in Eastern Ethiopia

Background : Antimicrobial resistance is one of the major public health challenges in the 21st century. In response, World Health Organizations launched a global action plan on antimicrobial resistance since 2015, which is, along with other objectives, aimed to strengthen knowledge of the spread of Antimicrobial resistance through surveillance and research. As wastewater systems are important reservoirs of communal human and animal bacteria, antibiotic residue and resistance genes they are considered as surveillance hotspots. Objective : To assess the antibiotic resistance profile of proposed environmental resistance indicator bacteria in selected wastewater systems of Eastern Ethiopia from Feb. 2018 to Oct. 2019. Method : Three wastewater management systems in Eastern Ethiopia, such as the activated sludge system of Dire Dawa University, waste stabilization pond of Haramaya University and a septic tank of Hiwot Fana Specialized University Hospital were monitored by sampled quarterly over 18 months. A total of 66 samples was collected from 11 sampling locations and a total of 722 Escherichia coli (151), Aeromonas spp. (142), P. aeruginosa (143), E. faecalis (144), and E. faecium (142) were isolated using selective culture media and biochemical tests. Their antimicrobial susceptibility was tested using standard Kirby-Bauer disk diffusion method on the surface of the Mueller-Hinton agar and the result was interpreted according to EUCAST guidelines. Multiple Antibiotic Resistance Index (MARI) was calculated for each isolate and its change in the course of treatment was evaluated. Result : The highest percentage of resistance was seen for ampicillin among isolates of hospital wastewater effluent which is 36(94.7%), 33(91.7%) and 32(88.9%) for E. coli, E. faecalis, and E. faecium respectively. Lower rate of resistance was seen isolates from activated sludge system and gentamicin for isolates of activated sludge wastewater treatment system which is 10(16.4%), 8(13.3%), 11(18.9%), and 12(20.3%) for E. coli, E. faecalis, E. faecium , and P. aeruginosa respectively. MERI value was found to be variable across monitored sites and the course of the wastewater treatment process. Conclusion : The study has found a high level of environmental antibiotic resistance indicator bacteria thrive in the wastewater systems most of which were multi-resistant. Hospital wastewater exhibits higher resistance than the other two wastewater systems. The multi-drug resistance index has significantly increased in the course of the wastewater treatment process, indicating the possible proliferation of resistance in the wastewater treatment system.