WATER FOR AGRICULTURE IN MBEYA, TANZANIA: A MIXED-METHODS APPROACH TO ASSESS MICROBIAL CONTAMINANTS IN IRRIGATION WATER SOURCES AND PERCEPTIONS OF ASSOCIATED PUBLIC HEALTH RISKS

Abstract

Irrigated agriculture heavily depends on both surface water and groundwater sources. However, these water sources face increasing pressure from climate variability, population growth, and contamination risks. Improving understanding of the microbiological and chemical quality of irrigation water is essential for advancing food safety and public health. Nonetheless, there are no known studies that have evaluated these contamination risks in irrigation water sources in Mbeya, Tanzania. To address these knowledge gaps, my dissertation research involved: 1) a field- and laboratory-based study using culture-based and molecular approaches to quantify the presence of E. coli (susceptible and antibiotic-resistant strains) and characterize total bacterial communities in groundwater and surface water used for agricultural irrigation; and 2) a cross-sectional survey study to evaluate the knowledge and perceptions of agricultural workers regarding irrigation water quality. My specific aims were as follows: 1) To quantify fecal indicator bacteria (e.g., E. coli ) in surface water bodies and groundwater used for agricultural irrigation and test recovered bacterial isolates for resistance to select antibiotics in Mbeya, Tanzania; 2) To investigate taxonomic profiles of bacterial microbiota in groundwater and surface water sources used for agricultural irrigation through shotgun metagenomic sequencing; and 3) To evaluate the knowledge and perceptions of agricultural workers in Mbeya, Tanzania on the chemical and microbial quality of irrigation water through a validated survey instrument. Overall, my results indicate that E. coli is highly prevalent in both groundwater and surface water sources throughout the dry and rainy seasons, including at frequencies that may increase the risk of crop and produce contamination, potentially leading to foodborne illness. Surface water had higher E. coli levels than groundwater during both dry and rainy seasons, indicating its increased vulnerability to fecal contamination. Interestingly, I also observed a high prevalence of resistance to ampicillin and tetracycline, two of the most widely prescribed and accessible antibiotics in Tanzania. These findings reflected patterns that have been documented in clinical settings, indicating that the frequent overuse of these antibiotics in both human and veterinary medicine may be contributing to the persistence and spread of resistant E. coli strains in the environment. Beyond these culture-based findings, my metagenomic analysis of bacterial taxonomic profiles demonstrated that microbial communities had distinct differences between groundwater and surface water sources. Groundwater was dominated by environmentally-linked taxa and surface waters had higher levels of fecal-related and opportunistic bacteria. Finally, my cross-sectional survey study revealed that while workers are generally aware of irrigation water quality, they have a limited understanding of the specific microbial and chemical aspects of irrigation water and its associated health risks, underscoring the need for targeted outreach and education. In summary, my overall dissertation findings are the first of their kind from Southern Tanzania, and indicate that irrigation water resources in this area have elevated levels of microbial contaminants that could pose risks to food safety and public health. Addressing these challenges requires strengthening agricultural workers’ knowledge and perceptions of contamination risks, as improved awareness is critical for enhancing water management practices, and ultimately reducing the burden of foodborne diseases in farming communities.