Occurrence of multidrug-resistant Escherichia coli and antibiotic resistance genes in a wastewater treatment plant and its associated river water in Harare, Zimbabwe

Abstract

Wastewater treatment plants (WWTPs) have been identified as point sources of antibiotic-resistant bacteria (ARB) and antibiotic- resistance genes (ARG). Due to variations in antibiotic use and prescribing patterns in different countries, it is imperative to establish the  presence of ARB and ARGs in water environments on a country-by-country basis. This study investigated the occurrence of 11 antibiotic- resistance genes (QNRB, DFR14, CTX-M, KPC, Sul1, QNRA, Sul2, ERMB, ERMA, SHV, NDM), and antibiotic-resistant Escherichia coli in a  WWTP and its associated river water in Harare, Zimbabwe. 24 water samples were collected across 3 sites: upstream and downstream of  the WWTP; final effluent of the WWTP. The samples were collected weekly for 8 weeks. Pure cultures of the E. coli isolates were obtained  by membrane filtration (0.45 µm) and repeated streaking on Tryptone Bile X-glucuronide followed by biochemical tests (indole test;  citrate test; motility, indole, and ornithine). Antibiotic resistance profiling was done for 12 antibiotics using the disc diffusion method.  Total genomic DNA was extracted from the 21 water samples and the occurrence of 11 antibioticresistant genes investigated using  conventional PCR. 86 E. coli isolates were obtained from the sampled sites: 28 from the upstream site, 26 from the WWTP effluent, and 32  from the downstream site. The results from chisquared analysis showed a significant association (p < 0.05) between the sampling site and  the percentage of antibiotic-resistant E. coli for all 12 antibiotics investigated. The percentage of E. coli isolates resistant to the tested  antibiotics varied from 29% (ertapenem) to 80.2% (ciprofloxacin). 81 (94.2%) E. coli isolates were resistant to antibiotics from ≥3  classes. Eight (8/11, 72.7%) ARGs were detected in the WWTP effluent and river water samples. Results indicate that the investigated  WWTP and associated river water are reservoirs of ARGs and antibiotic-resistant E. coli, which is a public health concern.