Assessment of salmonella and generic Escherichia coli contamination and consumer risk factors for onions (Allium cepa l.)

Fresh produce is a crucial component of a healthy and balanced diet; however, it can become contaminated with pathogenic microorganisms during production, distribution, and processing from farm to table. The fact that these products are often consumed in their unprocessed or minimally processed from increases the risk of foodborne illness. Onions, which are widely consumed both worldwide and in our country, hold an important place among these products. In recent years, cases of Salmonella-related foodborne illnesses associated with onion consumption have been reported in different parts of the world. Although no Salmonella outbreak linked to onion consumption has yet been reported in our country, identifying the potential risk is important for public health. In this study; I) to monitor the possible presence of Salmonella spp. and generic Escherichia coli in dry and green onions sold in markets throughout the year, II) to investigate survival of S. enterica and generic E. coli under different storage conditions in damaged dry onions during their shelf life and III) to conduct surveys for determination of the onion-based food safety knowledge levels and hygiene practices of consumers and restaurant/cafeteria employees for the risk assessment of onion-related foodborne illnesses. Onion samples collected over twelve months were evaluated using microbiological analyses. Detection of Salmonella was performed by confirming the presence of the InvA gene region in suspicious isolates using PCR. The presence and population of E. coli were determined based on colony formation on selective chromogenic agar using the spread plate method. The total mesophilic aerobic bacteria (TMAB) population in green onions was measured on a general-purpose medium using the spread plate method. Ampicillin-resistant Salmonella spp. and generic E. coli were inoculated into intact and damaged dry onion samples, which were then stored at 4 °C and 23 °C for 56 days, with microbial changes monitored throughout. The surveys were administered through both online and face-to-face methods, responses were evaluated over a 120-day period, and the relationships between demographic variables and levels of knowledge and practice were analyzed. According to the findings in this study, Salmonella was not detected in either type of onion. However, a high prevalence (55%) of generic E. coli was detected in green onions, and a considerable level (9%) was found in dry onions. E. coli loads increased particularly during the summer months, reaching up to 4.76 log CFU/g. Similarly, TMAB populations in green onions rose during summer, reaching up to 8.78 log CFU/g. These values indicate a high microbiological risk, especially in green onions. Shelf-life studies have shown that in sound dry onions, pathogens declined to undetectable levels within two weeks, whereas in damaged samples, particularly at room temperature, bacterial populations increased in the initial days and persisted at high levels up to day 56. Survey results showed that consumers had lower knowledge and practice levels compared to food service employees, although significant knowledge gaps and incorrect practices were common in both groups. In particular, awareness that consuming raw onions could lead to foodborne illness was low, and incorrect practices were frequently observed regarding the use of damaged onions, hygienic preparation, and the storage of chopped onions. In conclusion, the findings of this study demonstrate that raw onions may pose microbiological risks throughout the production-to-consumption chain. The high E. coli and TMAB levels detected in green onions and the prolonged survival of pathogens in damaged dry onions highlight the importance of strict hygiene practices. Survey results indicate substantial knowledge gaps and improper practices among both consumers and industry workers. Therefore, in order to reduce the risks arising from onions, hygiene rules must be meticulously implemented at all stages of the food chain, and stakeholders must be made aware.