Surveillance of antibiotic resistance determinants in Gaborone and Palapye wastewater treatment facilities

Antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) have been globally considered emerging environmental contaminants that pose a serious concern to human health and the ecosystem. The ubiquitous nature of ARB and ARGs among pathogens from wastewater effluents, indicate that wastewater treatment facilities are major reservoirs for antibiotic resistance determinants, thus contributing to the widespread dissemination of antibiotic resistance. The primary objective of the study was to characterize the antibiotic resistance phenotypic and genotypic characteristics of bacterial isolates from Palapye wastewater treatment facility (PWWTF), Gaborone wastewater treatment plant (GWWTP) and the downstream environments receiving effluent wastewater. A detailed analysis was conducted with respect to the characterization and quantification of bacterial populations (including ARB) in wastewater influent, effluent and downstream environment. Culture dependent and independent approaches were used to determine occurrence, abundance and diversity of the ARB and ARGs in samples of wastewater influent, effluent and downstream environment. The bacterial concentration ranged between 2.1x102CFU/mL-4.2x1011CFU/mL in PWWTF and downstream samples, and between 1.00x101CFU/mL-1.4x108CFU/mL in GWWTP and downstream samples. The study also detected higher frequencies of potentially pathogenic ARB; Staphylococcus species, Escherichia coli, Enterobacter aerogenes, Pseudomonas species, Brucella species, Salmonella species, Listeria species and Campylobacter species, and ARGs to clinically relevant antibiotics; tetA (tetracycline), mphA (macrolides), strB (streptomycin), sul1 (sulphonamide), dfr (trimethoprim) and int1 (mobile ARG cassette) in the samples. Metagenomic analysis of downstream environment of PWWTF also revealed diversity and abundance of bacterial populations belonging to major phyla Cyanobacteria (37%), Proteobacteria (35%), Firmicutes (14%) and the Bacteroidetes (11%). Conclusively, GWWTP had more occurrence and diversity of ARB and ARGs than PWWTF. Taken together the results suggest accumulation of antibiotic resistance determinants in wastewater treatment facilities and subsequent release into the downstream environment, particularly water sources. This research is critical in the development of new water quality monitoring schemes and implementation of policies on the use of effluent and contaminated water particularly for irrigation purposes in Botswana.