Isolation and identification of bacteria from exposed and sliced Allium cepa (onions)

Abstract

Background and objective: Onions (Allium cepa) are the one of the most important commercial condiments grown and consumed globally. They, are perennials that can be used as a medicine and food. Onions are effective against common cold, heart disease, diabetes, osteoporosis, coughs, and sore throat. It is also rich in proteins, carbohydrates, sodium, potassium, and phosphorus. During storage, some losses occur due to sprouting, drying and rotting that can be caused by some microorganisms particularly fungi. The black mould disease caused by Aspergillus niger is an issue of severe concern in onion production worldwide. This study was aimed at isolating and identifying bacteria on sliced onions (Allium cepa) exposed to air for three days. Materials and methods: Three Onion samples were collected from the General Market Tombia, Yenagoa, Bayelsa. The respective onion samples were aseptically peeled, sliced and exposed one hour , after which, 1g of onion was weighed and the extract was serially diluted. Following serial dilution, it was inoculated on nutrient agar and MacConkey agar separately and incubated at 370C for the next 24 hours. The same protocol was followed after peeling, slicing an exposing the onions for 48hrs and 72hrs. Gram staining and biochemical tests ( catalase test, coagulase test, blood agar, mannitol salt agar, and bile solubility test) was carried out for each isolates for proper identification. Results: Sixteen bacterial isolates were obtained out of which streptococci was found to be the dominant species. Gram staining and biochemical tests have further revealed the hidden insights for cohesive identification. The study confirmed the ten(10) isolates of Coagulase Negative Streptococci that accounted to (63%), four (4) isolates Staphylococcus aureus accounting to( 25%), one (1) isolate of Streptococcus pneumoniae and Streptococcus pyogenes accounting to (6%). All were gram positive; 12 were gram positive cocci and 4 was gram positive bacilli. This could be because gram-positive bacteria are more tolerant to dry conditions than gram-negative bacteria, whose growth could be reduced when a surface is drying. The highest total colony count after 24, 48 and 72 hours incubation 1.24×1010cfu/ml, 3.22×1010cfu/ml and 3.31 x 1011cfu/ml respectively. Conclusion: Findings from this study revealed that some pathogenic gram positive bacteria-can be isolated from onions when peeled and left exposed on kitchen cabinets or other containers. Thus the practice of slicing, onions to air and keeping for days before usage is not hygienic and should be avoided.