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Study says stored Onions are contaminated with pathogenic microorganisms

Sunday Omeike PhD, FASLN

Monday, 28 September 2020

The onion bulb is a highly nutritious vegetable with health benefits consumed either in its fleshy original form or boiled into local and international dishes for aroma and taste.

Onion is widely distributed throughout Nigeria, with over two million metric tons cultivated annually from about 88 million global production. While the bulb is stored in homes in dry spaces and maintained by intermittent sun-drying, these do not save the onion from the devastating effects of microbial infestation.

Due to their presence in virtually every environment known to man, microorganisms have been reported to reduce the durability of the stored onion previously. However, a recent investigation has reported that not only does onion harbor spoilage bacteria, some are pathogenic and cause infections in unsuspecting consumers.

Published in the International Journal of Pathogen Research, microbiologists in the Department of Microbiology, Obafemi Awolowo University, Ile-Ife, examined ability of bacteria isolated from onions to cause spoilage of the vegetable following two weeks of storage.

Using samples sourced from Ile-Ife in Osun State, the investigators, led by Nkem Torimiro, found 42 distinct microbial isolates in tissues of two weeks old onions, and 35 of them are bacterial species. 

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The research further observed that while all the isolates caused onion rot disease, Flavobacterium and Staphylococcus species were confirmed to possess high pathogenicity.

Although Staphylococcus are indigenous and opportunistic bacteria to humans, Flavobacterium species are pathogenic and highly harmful. How this group of bacteria causes severe, life-threatening infection is still unknown, and they wreck havoc when present in individuals with low immunity.

The authors, however, advised individuals distributing onions to take appropriate precautions in order to prevent selling contaminated onions. 

They further recommended that deteriorating onion bulbs should be separated from fresh ones to avoid cross-contamination.


Torimiro, N., Makinde, I. O., Omole, R. K. and Daramola, O. B. 2020. Deterioration profile of postharvest onion (Allium cepa L.) bulbs induced by potential pathogenic microorganisms. International Journal of Pathogen Research, 5 (2): 39-45.

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