Bacterial contaminants of African indigenous leafy vegetables and their antibiotics sensitivity characteristics: A case study of Morogoro Municipality, Tanzania

A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN APPLIED MICROBIOLOGY OF SOKOINE UNIVERSITY OF AGRICULTURE. MOROGORO, TANZANIA.A study was conducted in Morogoro Municipality, Tanzania to investigate the bacterial load found on African indigenous leafy vegetables, their sources and their sensitivity to commonly used antibiotics. A total of 126 samples of fresh African indigenous leafy vegetables (amaranth, nightshade and sweet potato leaves), water used for irrigation from rivers and shallow wells and manure fertilised soils were collected at farm sites and market outlets for bacteriological analysis. Bacterial counts were calculated as colony forming units (CFU) per millilitre (CFU/ml) of vegetable washing. The isolates sensitivity or resistances to antibiotics were determined on Muller – Hinton agar plates by the disk diffusion technique. Data was subjected to Analysis of Variance (ANOVA) using SAS Statistical software. Results showed that microorganisms were abundant on the surfaces of the African indigenous leafy vegetables, with nightshade having 1.8 × 105 CFU/ml while amaranth and sweet potato leaves having 1.7 × 105 CFU/ml and 1.5 × 105 CFU/ml respectively. The water used for irrigation from the lower section of the river had significantly (P = 0.03) higher bacterial loads 1.8 × 105 CFU/ml than water from the higher sections. Biochemical tests indicated bacterial isolates from the studied vegetables to be Escherichia coli, Enterobacter aerogenes, Proteus spp, Staphylococcus albus and Bacillus spp. The results show that Escherichia coli, Enterobacter aerogenes and Proteus spp (coliforms) were highly sensitive (>75 %) to enrofloxacin, sulphamethoxazole and ofloxacin antibiotics but resistant to rifampicin. The observed bacterial loads, and sensitivity patterns to commonly used antibiotics reveal the potential adverse health impact of the vegetables on consumers. Proper handling and preparation of vegetables before consumption is highly recommended. Further research covering different African indigenous leafy vegetables in wider agro-ecological areas and sensitivity patterns to commonly used antibiotics is also strongly recommended