Investigation of bacterial hazards in low quality water used for food production in urban and peri-urban areas of Morogoro, Tanzania

PhD Thesis

In Sub Saharan African countries, there is no or limited information on use of low quality water (LQW), hazards in foodstuffs produced using LQW and their associated health risks to humans, animals and the environment. The objective of this study was to investigate faecal bacterial hazards on low quality water; and foodstuffs produced using LQW in Morogoro, Tanzania. This study assessed the extent of E. coli; antimicrobial resistance (AMR) and virulence genes in Extended Spectrum beta lactamase (ESBL) producing strains; and Salmonella spp. contamination in LQW, tilapia and Chinese cabbage (Brassica rapa L. chinensis) irrigated using LQW. The 3M Petrifilm Select E. coli plates were used for enumeration and isolation of E. coli and ESBL producing E. coli at 44.4oC. Isolation of Salmonella spp. was done as per ISO 6579:2002 (E) and its amendment of 2007, followed by; Pulsed Field Gel Electrophoresis (PFGE), genotyping, serotyping and antimicrobial susceptibility testing (AST). Levels of E. coli, ESBL producing E. coli and Salmonella spp. in wastewater were reduced from 5 - <1 log cfu/mL 4 - 0 log cfu/mL and 40 - <400 to <0.04 cfu/mL, respectively, following treatment in wastewater ponds. The ESBL producing E. coli isolates showed broad range of AMR genes in beta- and non-beta lactams antimicrobials including blaCTX-M1, blaCTX-M15, blaOXA-1; aac6, aadA4, aac6Ib, strA, strB; dfrA19, dfrA17, dfrA7; catA1, catB3; qnrA; sul1, sul2; tetA, tetB; and mphA, mrx; virulence genes (hemL, iss, tir, iha, sat, senB); 13 Salmonella serovars including S. Kentucky, S. Chandans, S. Durban and S. Kiambu from LQW and tilapia. Occurrence of E. coli in fish flesh from wastewater was 0.05% and in Mindu dam was 0%; while, in Chinese cabbage irrigated with river water was 86% and in treated wastewater was 10%. The concentration of E. coli in Morogoro river water was higher than the treated wastewater. Tilapia grown in wastewater treatment ponds and vegetables irrigated by treated wastewater were of good quality for human consumption. The quality of treated wastewater from the study sites complied with the WHO/FAO guidelines (1000 cfu/100 mL faecal coliforms) and can be recommended for use on food production.

Danish International Development Assistance (DANIDA) Safe Water for Food (SaWaFo) project (Project Code: 11-058DHI)