International Journal of Environmental Research and Public Health Review Microbial Biofilms in the Food Industry—A Comprehensive Review Conrado Carrascosa 1,*, Dele Raheem 2 , Fernando Ramos 3,4 , Ariana Saraiva 1 and António Raposo 5,* 1 Department of Animal Pathology and Production, Bromatology and Food Technology, Faculty of Veterinary, Universidad de Las Palmas de Gran Canaria, Trasmontaña s/n, 35413 Arucas, Spain; [email protected] 2 Northern Institute for Environmental and Minority Law (NIEM), Arctic Centre, University of Lapland, 96101 Rovaniemi, Finland; braheem@ulapland.fi 3 Pharmacy Faculty, University of Coimbra, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal; [email protected] 4 REQUIMTE/LAQV, R. D. Manuel II, Apartado 55142 Oporto, Portugal 5 CBIOS (Research Center for Biosciences and Health Technologies), Universidade Lusófona de Humanidades e Tecnologias, Campo Grande 376, 1749-024 Lisboa, Portugal * Correspondence: [email protected] (C.C.); [email protected] (A.R.) Abstract: Biofilms, present as microorganisms and surviving on surfaces, can increase food cross- contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an ex- tracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspec- tives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, Citation: Carrascosa, C.; Raheem, D.; and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, Ramos, F.; Saraiva, A.; Raposo, A. they are also considered responsible for damage to food processing equipment. Hence the need to Microbial Biofilms in the Food gain good knowledge about all of the factors favouring their development or growth, such as the Industry—A Comprehensive Review. attachment surface, food matrix components, environmental conditions, the bacterial cells involved, Int. J. Environ. Res. Public Health 2021, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms 18, 2014. https://doi.org/10.3390/ in the food industry due to the resistance of disinfectants and the mechanisms developed for their ijerph18042014 survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and Academic Editor: Paul B. Tchounwou biofilm-associated proteins. Received: 26 December 2020 Keywords: biofilms; food industry; food microbiology; food safety Accepted: 7 February 2021 Published: 19 February 2021 Publisher’s Note: MDPI stays neutral 1. Introduction with regard to jurisdictional claims in Typically, bacteria bind to surfaces and form spatially structured communities inside published maps and institutional affil- a self-produced matrix, which consist of extracellular polymeric substances (EPS) known iations. as biofilms [1,2]. Biofilms imply major challenges for the food industry because they allow bacteria to bind to a range of surfaces, including rubber, polypropylene, plastic, glass, stainless steel, and even food products, within just a few minutes, which is followed by mature biofilms developing within a few days (or even hours) [3]. Copyright: © 2021 by the authors. Since ancient times, this sessile life form has been followed as an excellent survival Licensee MDPI, Basel, Switzerland. technique for microorganisms, given the protective barrier generated and physiological This article is an open access article changes made by the biofilm matrix, while it fights against the adverse environmental distributed under the terms and circumstances faced typically by bacteria in man-made and natural settings, even in food- conditions of the Creative Commons processing facilities [4,5]. Hence, biofilms are believed responsible for damaged equipment, Attribution (CC BY) license (https:// more expensive energy costs, outbreaks, and food spoilage [5–8]. Biofilms have become creativecommons.org/licenses/by/ more robust to disinfections in many wide-ranging food industries, such as processing 4.0/). Int. J. Environ. Res. Public Health 2021, 18, 2014. https://doi.org/10.3390/ijerph18042014 https://www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2021, 18, x FOR PEER REVIEW 2 of 32 ment, more expensive energy costs, outbreaks, and food spoilage [5–8]. Biofilms have be- come more robust to disinfections in many wide-ranging food industries, such as pro- cessing seafood, brewing, dairy processing, and meat and poultry processing [9] There is compelling evidence for biofilm lifestyle making them more resilient to antimicrobial agents, particularly compared to planktonic cells (Figures 1 and 2). This entails having to Int. J. Environ. Res. Public Health 2021, 18, 2014 2 of 31 remove them from surfaces of food processing plants, which poses a massive task [10–12]. Microbiological surface management is relevant for assessing and making decisions as to whether residual microbial species are found at a suitable level, and if harmful mi- seafood, brewing, dairy processing, and meat and poultry processing [9] There is com- croorganismspelling evidence are for removed. biofilm lifestyleThe obtained making results them more will resilientallow criteria to antimicrobial to be set, agents,such as how toparticularly clean surfaces compared and food to planktonic product cellsquality (Figures [13,14].1 and 2). This entails having to remove them from surfaces of food processing plants, which poses a massive task [10–12]. Figure 1. Biofilm formation and development stages. Figure 1. Biofilm formation and development stages. Microbiological surface management is relevant for assessing and making decisions as toSensory whether tests residual that involve microbial visually species inspecting are found at surfaces a suitable with level, good and lighting, if harmful smelling unpleasantmicroorganisms odours, are and removed. feeling The encrusted obtained or results greasy will surfaces allow criteria are run to beas set,a process such as regula- tionhow to to instantly clean surfaces overcome and food visible product sanitation quality defects, [13,14]. while microbiological evaluations are often madeSensory to testsguarantee that involve consis visuallytency with inspecting microbial surfaces standards with good and lighting,to make smellingimprovements tounpleasant sanitation odours, procedures and feeling [15]. The encrusted fact that or greasy visual surfaces inspection are run cannot as aprocess coincide regulation with bacterial to instantly overcome visible sanitation defects, while microbiological evaluations are often counts has been well-documented [16]. The hygienic conditions of food-contact surfaces made to guarantee consistency with microbial standards and to make improvements to mustsanitation be properly procedures examined [15]. The for fact all that of the visual above-cited inspection purposes. cannot coincide Lack withof convergence bacterial be- tweencounts the has various been well-documented approaches followed [16]. The to hygienic detect conditionsand quantify of food-contact biofilms does, surfaces however, makemust it be more properly difficult examined for the for food all of industry the above-cited to locate purposes. the most Lack effective of convergence ones [17]. The Hazardbetween Analysis the various and approaches Critical Control followed Points to detect (HACCP) and quantify system biofilms and good does, however,manufacturing practicesmake it morehave difficultbeen developed for the food to regulate industry tofood locate safety the and most quality. effective Bacterial ones [17]. biofilms The are notHazard directly Analysis mentioned and Critical in the Control HACCP Points system (HACCP) employed system andon food good manufacturingprocessing facilities. Hence,practices an have updated been developed HACCP tosystem regulate that food contem safetyplates and quality. evaluating Bacterial biof biofilmsilms in are food not envi- directly mentioned in the HACCP system employed on food processing facilities. Hence, ronments, and establishes an apt sanitation plan, is expected to provide much clearer con- an updated HACCP system that contemplates evaluating biofilms in food environments, taminationand establishes information, an apt sanitation and to plan, facilitate is expected production to provide in the much food clearer industry’s contamination biofilm-free processinginformation, systems and to [18]. facilitate The importance production in and the im foodpact industry’s of biofilms biofilm-free on the food processing industry have becomesystems clear [18]. Thein several importance works and impactwhere ofthe biofilms cross-contamination on the food industry is havecommon become among clear these foodin several products, works with where a wide the cross-contamination range of pathogens, is commonincluding among Listeria these monocytogenes food products,, Yersinia enterocoliticawith a wide, rangeCampylobacter of pathogens, jejuni, including SalmonellaListeria spp., monocytogenes Staphylococcus, Yersinia spp., Bacillus enterocolitica cereus, , and EcherichiaCampylobacter coli O157:H7 jejuni, Salmonella [19]. spp., Staphylococcus spp.,