Studies on Microbial Contamination of Cut and Exposed Onions

Onions (Allium cepa), a vegetable plant is consumed globally for its culinary and medicinal importance. Despite the various health benefits ascribed to onions, several rumours have been spread, especially on the online media as regards its ability to act as a sponge absorbing microorganisms from the atmosphere, once cut open and left exposed in the atmosphere.

This research work involved the exposure of the half portion of an onion at different sites, while culturing the other half immediately without exposure, to serve as a control. Thirty healthy and fresh onion samples were exposed, and the sites of exposure include: living rooms, public conveniences, kitchens, fridge, freezer, and bole joints (roasted plantain eatery).

After inoculation and identification of the cultured microorganisms, Pseudomonas sp., Bacillus cereus, Escherichia coli, Staphylococcus sp., Klebsiella sp., Enterobacter sp., yeast and Aspergillus sp., were isolated with Klebsiella sp., Pseudomonas sp. and Staphylococcus sp. having the highest number of occurrence of 40% having been isolated from twelve test samples each. B. cereus had a percentage occurrence of 30%, having been isolated from nine test samples. E. coli had a 10% occurrence having been isolated from three test samples, while Enterobacter sp. had the lowest rate of occurrence having been isolated in just one test sample. For the fungi isolates, Aspergillus sp. had a percentage occurrence of 76.6% having been isolated in twenty three test samples, while yeast had a percentage occurrence of 66.6%, having been isolated in twenty test samples.

The isolated organisms were all pathogenic organisms, and some such as Staphylococcus sp. and Bacillus sp. have been implicated in causing food poisoning. Some other organisms isolated have also been implicated in the spoilage of onions. It is therefore recommended that users of onions should reduce to the barest minimum the tendency to consume raw cut onion sample.