Most of the foodborne illness pathogens associated with fresh produce can be spread through faecal contamination. Such contamination events can be direct (e.g. directly applied to the crop, from for example livestock in the form of manure) or indirect (e.g. applied to the crop via contaminated equipment). The technical term for the carriers of indirect contamination is fomite. Fomites are inanimate objects that can carry and spread disease and infectious agents when contaminated with micro-organisms. Fomite is a very broad term which can comprise a huge array of everyday objects that can become fomites. In an agricultural environment; it covers objects as diverse as ropes, dust, tractors, crop leaves, worker's boots, knives, transport crates and field gates (Matthews, 2013; Jung et al., 2014; Balali et al., 2020; Yi et al., 2020). Fomites further spread contamination to people and objects which come into contact with them.
The risks associated with manure contamination of tractors and other equipment used for harvest are difficult to quantify, as not all manure contains foodborne illness causing pathogens. There is very little information in the published literature on the role of manure-contaminated fomites and the probability of pathogen transfer to food crops (Alegbeleye et al 2018). However, it is well recognised that it is not a safe practice to drive a tractor through a field containing livestock (and hence fresh manure) immediately before harvesting a ready-to-eat food crop. Furthermore, most growers would acknowledge a requirement to clean a tractor immediately before its necessary use in a harvest. The best approach is to prevent contamination of equipment in the first place, care should be taken in the storage of harvest equipment away from manures or livestock and wildlife (Alegbeleye et al., 2018).
Validated disinfection protocols are now widely available for small tools such as knives (Tapp et al., 2014) and some tools have been redesigned to be more hygienic (Zhou et al 2012).
Some fomites of relevance to fresh produce growers have been reported by Kaneko et al. (1999). Post-harvest, fresh-cut produce were shown to be contaminated by knives and factory-based processing equipment acting as fomites (Kaneko et al. 1999). It is known that pathogens can persist on equipment surfaces for considerable times. For example Salmonella Typhimurium could be recovered from clean stainless steel for a number of hours after contamination (Moore et al., 2007). The importance of equipment surfaces as points of contamination is underscored by 41 cases of Salmonella Bovismorbificans infection that were traced to a cutting wheel on a lettuce shredder (Stafford et al. 2002). These observations demonstrate that contaminated equipment may continue to contaminate fresh produce for a few hours. It is important that equipment that comes into contact with the edible portion of the crop (e. g. harvesting equipment and cutting tools) is cleaned adequately and sanitised regularly. Cleaning and sanitising of tools and equipment surfaces is particularly important where crops are to be eaten uncooked, such as leafy salads or herbs. In summary, equipment in contact with the edible portion of the crop should be cleaned regularly, against a formal cleaning procedure, and stored and managed in such a way to avoid cross contamination. You can get advice on equipment cleaning and sanitising schedules, as well as suitable food-grade cleaning agents from many cleaning material suppliers. It is best practice to validate your cleaning and sanitising of equipment to ensure that acceptable levels of cleanliness and microbial kill are being achieved. Additional information on the validation of sanitation is available.
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Balali, G.I., Yar, D.D., Afua Dela, V.G. and Adjei-Kusi, P. (2020) Microbial contamination, an increasing threat to the consumption of fresh fruits and vegetables in today’s world. International Journal of Microbiology 2020, 3029295.
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Kaneko, K.-I., Hayashidani, H., Takahashi, K., Shiraki, Y., Limawongpranee, S. and Ogawa, M. (1999) Bacterial contamination in the environment of food factories processing ready-to-eat vegetables. J Food Prot 62, 800–804.
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Yi, J., Huang, K., Young, G.M. and Nitin, N. (2020) Quantitative analysis and influences of contact dynamics on bacterial cross-contamination from contaminated fresh produce. J Food Eng 270, 9.
Zhou, B.I.N., Luo, Y., Millner, P. and Feng, H.A.O. (2012) Sanitation and design of lettuce coring knives for minimizing Escherichia coli O157:H7 contamination. Journal of Food Protection 75, 563-566.