Effectiveness of UV sanitization of vegetables using polymerase chain reaction and microbial culture techniques

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Vegetable related food poisoning is a very serious issue in Ghana and has been linked to a number of diverse health effects such as cholera and deaths. This study focused on assessing the effectiveness of ultraviolet (UV) irradiation to sanitize three vegetables (carrot, cabbage and lettuce) for consumption. Microbial cultures were performed on raw non-sanitized carrots, cabbages, and lettuce to enumerate bacterial colonies, and yeasts and moulds. Biochemical tests were carried out using various media to quantify Gram negative bacteria and enteric pathogens present on raw or untreated vegetables. Also selective sub culturing was carried out to determine the presence of Salmonella spp. and Escherichia coli. The three vegetables were subjected to UV irradiation at different times of 1 hr, 3 hrs, 6 hrs and 9 hrs. The microbial loads of vegetables exposed to the different times of UV irradiation were assessed using microbial culturing for bacteria, yeasts and moulds. Vinegar as a control was used to sanitize the raw vegetables and microbial analysis carried out. Polymerase Chain Reaction (PCR) and gel electrophoresis were used to confirm the effectiveness of UV irradiation. USP gene of size 615 bp specific for E. coli O157: H7 was amplified by PCR using primer sequences of usp-F-5’ CGGCTCTTACATCGGTGCGTTG-3’, and R-5’-GACATATCCAGCCAGCGAGTTC-3’. The results obtained revealed that the untreated raw vegetable samples recorded high microbial loads and tested positive for all microbial assays. The vinegar treated vegetables (control) showed significant reduction in microbes as compared to the untreated raw vegetables. UV irradiation was able to eliminate residual microbes on the three vegetables giving a positive sanitizing effect. It reduced a large number of microbes found on these vegetables than the sanitizing effect of vinegar, though statistically, there was no difference between the sanitizing effects both had on the vegetables. Microbial counts reduced with increase in periods of UV exposure, and this was seen in lanes with bands of E. coli representing untreated raw vegetables and vegetables that have been exposed to 1 hr, 3 hrs and 6 hrs of UV irradiation while 9 hrs of UV exposure had no counts of bacterial colonies as well as yeasts and moulds. UV is thus an effective and convenient approach to reducing microbes on vegetables in various markets in Ghana. It also had no suspected bands of E. coli. Microbial culture techniques and PCR proved to be effective measures for monitoring the efficiency of UV as a vegetable sanitizing agent.
A Thesis submitted to the Department of Biochemistry and Biotechnology College of Science in partial fulfillment of the requirements for the award of MSc degree in Biotechnology,