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Cross-contamination of Food by Contaminated Surfaces

Graziella MIDELET1, Thomas BRAUGE1 and Christine FAILLE2

1 Laboratory for Food Safety, ANSES, Boulogne-sur-Mer, France

2 Unité Matériaux et Transformations, CNRS – INRAE – ENSCL, Université de Lille, Villeneuve d’Ascq, France

Globally, the World Health Organization (WHO) estimates that 600 million people become ill each year after eating contaminated food. It was estimated by the World Bank in 2018 that annual production losses due to foodborne illnesses were $95.2 billion with an annual cost of treating the sickness of $15 billion and $5 billion in lost trade in low- and middle-income countries. In the United States, the annual cost of illness due to the major pathogens (Salmonella, Toxoplasma gondii, Listeria monocytogenes, Norovirus, Campylobacter) is estimated to be $15.5 billion in medical expenses and lost productivity (Scharff 2012). The symptoms associated with these diseases vary depending on the pathogen. They are mainly digestive (diarrhea, vomiting), but can go to more serious and even fatal forms such as meningoencephalitis with L. monocytogenes or hemolytic uremic syndrome (HUS) following an infection with a Shiga toxin-producing Escherichia coli (STEC).

Contaminations can occur at different levels of the field to “fork” scenario. In animals, for example, they can occur while the animal is still alive, in its wild or farmed environment, and also post-mortem, during the preservation of the product, due to the dissemination of pathogens from the digestive contents to the consumed parts. Contamination can also occur during the processing of the product, either directly through human handling and the industrial environment, or indirectly, for example, with contaminated water. Indeed, cross-contamination is defined as the direct or indirect transfer of bacteria or other microorganisms from a contaminated product to a non-contaminated product (Pérez-Rodríguez et al. 2008). It can occur at any stage of food production, and also during distribution and even in restaurants and at the consumer’s premises. There are three main types of cross-contamination: food-to-food, equipment-to-food and person-to-food. The most common errors that cause cross-contamination (Bennett et al. 2013) are the inadequate cleaning of processing equipment or utensils (67%) and storage in a contaminated environment (39%). Handlers’ hands have also been shown to be involved in 42% of foodborne outbreaks between 1975 and 1998 in the United States (Kadariya et al. 2014).

It has long been recognized that the surfaces of workshops and equipment in the food industry are involved in the contamination of food and ultimately the cause of a significant amount of food poisoning. For example, a study conducted in 1995 by the World Health Organization in Europe revealed that 25% of food poisoning was associated with cross-contamination (equipment surfaces, operators) (Tirado and Schmidt 2001). Beyond the deaths recorded, the social and economic costs can be extremely significant with a destroyed brand image for the company and also for an entire sector.

The Cleaning and Disinfection (C&D) operation is a fundamental operation in the food industry because it must control the post-contamination of food related to materials and the environment. The implementation of a C&D plan is a regulatory obligation described in the EU feed and food law (“Hygiene Package” 2006). Thus, the EC 178/2002 regulation (General Food Law) indicates that no foodstuff should be put on the market if it is dangerous, i.e. harmful or unfit for consumption. Moreover, in the regulation on the hygiene of foodstuffs (EC 852/2004), it is required that any hazard be identified that should be prevented, eliminated or reduced to an acceptable level. Furthermore, in the regulation EC 2073/2005 on microbiological criteria for foodstuffs, Article 5.2 stipulates that manufacturers must control bacterial contamination in their environments (premises, facilities, equipment). In addition, in France, since 2018, the EGAlim law indicates that corrective action plans must be implemented following the detection of a pathogen in the production environment, and they must be communicated to the authorities. But a number of factors including a non-effective C&D plan can lead to the persistence of bacteria in the company. This notion of persistence has been described for many years in the environment of different food industries and during food epidemics and is mainly due to the presence of bacterial biofilms on surfaces which can be difficult to eliminate if not treated quickly.

1.1. Surface contamination

Biofilms are microbial communities (bacteria, fungi, algae or protozoa) colonizing a biotic or abiotic surface, and frequently included in a matrix of extracellular exopolymers, which protects them from environmental aggressions encountered in companies. Bacterial biofilms, the most frequent in agro-industrial environments, are composed of various species, pathogenic and non-pathogenic. In addition, the presence of inaccessible areas or those difficult to access thorough cleaning in the workshops (ceiling, walls) is conducive to the development of these bacterial biofilms that can detach from their medium and spread in the industrial environment. These complex microbial communities sometimes have the ability to persist on surfaces despite C&D operations. Furthermore, the massive use of detergents and disinfectants can lead to the adaptation of bacteria to this chemical stress and to an increased resistance to subsequent stresses.

1.1.1. Viable but non-culturable cells (VBNCs)

Different environmental and physicochemical factors (temperature, pH, salts, natural light) can induce in bacteria the appearance of VBNC forms (Besnard et al. 2002), which cannot grow on routine agar media but still have a metabolic activity. Generally speaking, this VBNC state is considered as a strategy of the cells to ensure their survival in unfavorable conditions. When conditions become favorable again, bacteria in the VBNC state can return to a culturable state, as has been shown for Vibrio strains following an increase in temperature or a restored availability of nutrients (Su et al. 2013). These VBNC forms are also often found within biofilms, as in pathogenic bacteria such as Staphylococcus aureus (Pasquaroli et al. 2014) and L. monocytogenes (Gião and Keevil 2014; Brauge et al. 2020), and some bacteria retain pathogenicity in this form (Oliver 2005). Hygiene procedures can also be the cause of the appearance of VBNC forms (Brauge et al. 2020). Once in the food, the VBNC forms can revive, multiply and even regain virulence after resuscitation into culturable cells in the case of pathogens (Li et al. 2014). In addition, the nature of surfaces is an environmental factor that can impact the culturability and viability of adhered bacteria (Silva et al. 2008).

1.1.2. Persistence of strains in agroindustrial environments

The notion of persistence of strains in industrial environments has often been reported in the literature as it could be the cause of recontamination of food (Nakari et al. 2014). Indeed, bacteria, such as L. monocytogenes, Pseudomonas sp. and Staphylococcus sp., are able to resist and survive the selection pressures found in production facilities (biocide, temperatures, pH.). Other authors (Demaître et al. 2021) have examined the presence and genetic diversity of L. monocytogenes in three pork cutting plants in Belgium (868 samples). They suggested occasional introduction and repeated contamination and also the establishment of some persistent clones adapted to meat in all cutting plants. It was also shown that Vibrio strains are able to form biofilms on different equipment in the fish industry during the process and that these biofilms were still detected after C&D procedures (Bonnin-Jusserand et al. 2019). Another study (Palma et al. 2020) correlated the persistence in the industrial environment with the intrinsic properties of certain types of L. monocytogenes, such as their ability to form biofilms, their high tolerance to environmental stresses (osmotic shock, desiccation, low temperature) linked to adaptive proteomic responses as well as their resistance to disinfectants and heavy metals. Furthermore, food processing environments are known to be a hypothetical reservoir of genetic elements that can be mobilized and transferred between microbial communities offering ecological advantages to the recipient bacteria. For example, quaternary ammonium compounds are often used as biocide in the food industry, and it has recently been shown that isolates of L. monocytogenes could show increased resistance to this biocide through the expression of genes encoding efflux pumps located on transposable genetic elements (transposon, plasmid) (emrE, qacH, brcABC) or on the chromosome (lde, mdrL), and that they were associated with genes for resistance to heavy metals (arsenic and cadmium). Recent work has shown that interactions and symbiosis of microorganisms, in addition to inherent genetic and external environmental factors, contribute to the persistence of L. monocytogenes in food production environments...