Bacterial biofilms in food processing environments: a review of recent developments in chemical and biological control

Biofilms are immobile communities of micro‐organisms attached to any surface, such as stainless steel or a food matrix surface or on packaging material. They may be composed of a single species, but more generally, in the natural environment, they consist of mixed species together with an extracellular matrix. Biofilms provide a common mechanism of persistence for a number of bacterial species especially in food processing environments, and therefore, prevention of biofilm formation and the removal of preformed biofilms are an important issue for the food industry. This article reviews the current understanding on the formation of biofilms and recent developments in biological and chemical methods for prevention and removal.     

The current knowledge on the application of anti-biofilm enzymes in the food industry

Biofilms are encountered on nearly all wet surfaces, with their development being often unwanted due to the serious problems they can cause in different fields, including in the food sector. They are recognized as the preferential microbial lifestyle due to the numerous advantages for the embedded cells. Biofilm cells are highly resistant to stress conditions, particularly to antimicrobials, as their complex and compact structure hampers the penetration of antimicrobials and the access to the deep positioned cells. The increased resistance to the currently employed control strategies emphasizes the urgent need of new alternative and/or complementary eradication approaches. To this direction, the use of enzymes is an interesting alternative anti-biofilm approach due to their capability to degrade crucial components of the biofilm matrix, cause cell lysis, promote biofilm disruption and interrupt the cell-to-cell signaling events governing biofilm formation and maintenance. This review provides an overview of the enzymes used for biofilm control, their targets and examples of effective applications.     

Promising strategies to control persistent enemies: Some new technologies to combat biofilm in the food industry—A review

Biofilm is an advanced form of protection that allows bacterial cells to withstand adverse environmental conditions. The complex structure of biofilm results from genetic-related mechanisms besides other factors such as bacterial morphology or substratum properties. Inhibition of biofilm formation of harmful bacteria (spoilage and pathogenic bacteria) is a critical task in the food industry because of the enhanced resistance of biofilm bacteria to stress, such as cleaning and disinfection methods traditionally used in food processing plants, and the increased food safety risks threatening consumer health caused by recurrent contamination and rapid deterioration of food by biofilm cells. Therefore, it is urgent to find methods and strategies for effectively combating bacterial biofilm formation and eradicating mature biofilms. Innovative and promising approaches to control bacteria and their biofilms are emerging. These new approaches range from methods based on natural ingredients to the use of nanoparticles. This literature review aims to describe the efficacy of these strategies and provide an overview of recent promising biofilm control technologies in the food processing sector.     

Biofilm formation in the industry: A review

Abstract

Biofilm and biofouling refer to biological deposits on any surface. Biofilms consist of both microbes and their extracellular products, usually polysaccharides. The purpose of biofilm is to protect the microbes from hostile environments or to act as a trap for nutrient acquisition. Biofilm formation causes problems in many branches of industry, such as in industrial water systems and the medical and process industries. Besides causing problems in cleaning and hygiene, biofilm may cause energy losses and blockages in condenser tubes, cooling fill materials, water and wastewater circuits, and heat exchange tubes, and on ship hulls. Biofilm can also present microbial risks due to the release of pathogens from cooling towers or by reducing water quality in drinking water distribution systems. In the medical industry biofilm is referred to as glycocalyx when diseases of the lungs or the gastrointestinal or urinary tract are involved.     

Biofilms in the Spotlight: Detection,Quantification, and Removal Methods

Microorganisms can colonize and subsequently form biofilms on surfaces, which protect them from adverse conditions and make them more resistant than their planktonic free‐living counterparts. This is a major concern in the food industry because the presence of biofilms has significant implications for microbial food contamination and, therefore, for the transmission of foodborne diseases. Adequate hygienic conditions and various preventive and control strategies have consequently been developed to ensure the provision of safe, good‐quality food with an acceptable shelf‐life. This review focuses on the significance of biofilms in the food industry by describing the factors that favor their formation. The interconnected process among bacteria known as “quorum sensing,” which plays a significant role in biofilm development, is also described. Furthermore, we discuss recent strategic methods to detect, quantify, and remove biofilms formed by pathogenic bacteria associated with food processing environments, focusing on the complexity of these microbial communities.     

Beneficial biofilm formation by industrial bacteria Bacillus subtilis and related species

Biofilms are densely packed multicellular communities of microorganisms attached to a surface or interface. Bacteria seem to initiate biofilm formation in response to specific environmental cues, such as nutrient and oxygen availability. Biofilms undergo dynamic changes during their transition from free-living organisms to sessile biofilm cells, including the specific production of secondary metabolites and a significant increase in the resistivity to biological, chemical, and physical assaults. Bacillus subtilis is an industrially important bacterium exhibiting developmental stages. It forms rough biofilms at the air-liquid interface rather than on the surface of a solid phase in a liquid, due to the aerotaxis of the cells. Biofilm formation by B. subtilis and related species permits the control of infection caused by plant pathogens, the reduction of mild steel corrosion, and the exploration of novel compounds. Although it is obviously important to control harmful biofilm formation, the exploitation of beneficial biofilms formed by such industrial bacteria may lead to a new biotechnology.     

食品工业中混合菌生物被膜的形成、相互作用与新型控制策略

细菌黏附在食品或食品接触表面并形成生物被膜可能导致设备损坏、食品变质甚至人类疾病。混合菌生物被膜作为细菌在食品工业中的主要存在形式,与单菌生物被膜相比,对消毒剂和抗菌素往往具有更强的抗性。然而,混合菌生物被膜的形成与种间相互作用十分复杂,其在食品工业中的潜在作用仍有待探索。本文总结了混合菌生物被膜的形成和种间相互作用以及近年来的新型控制策略,并对未来食品工业中混合菌生物被膜的污染防控进行了展望,旨在为混合菌生物被膜在食品工业中的深入研究以及制定高效的新型控制策略提供理论依据和参考,以期更好地保障食品安全与公众健康。     

Role of Bacillus species in biofilm persistence and emerging antibiofilm strategies in the dairy industry

Biofilm-forming Bacillus species are often involved in persistent contamination and spoilage of dairy products. They therefore present a major microbiological challenge in the field of dairy food quality and safety. Due to their substantial physiological versatility, Bacillus species can survive in various parts of dairy manufacturing plants, leading to a high risk of product spoilage and potential dissemination of foodborne diseases. Furthermore, biofilm and heat-resistant spore formation make these bacteria challenging to eliminate. Thus, some strategies have been employed to remove, prevent, or delay the formation of Bacillus biofilms in the dairy industry, but with limited success. Lack of understanding of the Bacillus biofilm structure and behavior in conditions relevant to dairy-associated environments could partially account for this situation. The current paper reviews dairy-associated biofilm formation by Bacillus species, with particular attention to the role of biofilm in Bacillus species adaptation and survival in a dairy processing environment. Relevant model systems are discussed for the development of novel antimicrobial approaches to improve the quality of dairy food. © 2020 Society of Chemical Industry     

Current and Recent Advanced Strategies for Combating Biofilms

Biofilms are matrix‐enclosed microbial aggregates that adhere to a biological or nonbiological surface. Biofilm formation is a significant problem in the medical, food, and marine industries and can lead to substantial economic and health problems. The complex microbial community of a biofilm is highly resistant to antibiotics and sanitizers and confers persistent survival that is a challenge to overcome. There are several conventional approaches to combating biofilms, physical and/or mechanical removal, chemical removal, and the use of antimicrobials, sanitizers, or disinfectants to kill biofilm organisms. However, biofilms are highly resistant to these approaches as opposed to planktonic cells. Thus, novel approaches other than the conventional methods are urgently needed. In this review, we discuss current and new advanced antibiofilm strategies that are superior to the conventional method in terms of addressing the biofilm problem for the improvement of healthcare, food safety, and in industrial processes.     

食品加工过程中细菌生物被膜的危害及控制

生物被膜中的微生物生活在一个由胞外聚合物（EPS）形成的环境中,它的形成是微生物生长过程中的一个保护模式,允许细胞在恶劣的环境中生存并分散到新的环境中。食品加工过程中有害菌形成的生物被膜对食品工业的危害极大,可使微生物残存增加,加工设备无法严格清洗、消毒,导致产品受到污染。该文在收集、研究现有文献的基础上归纳介绍了生物被膜的特点及其形成过程和形成机制,概述了生物被膜的危害、控制及检测方法,旨在提高人们对生物被膜的认识,推动该领域的研究发展。     

Recent Applications of Advanced Control Techniques in Food Industry

Process control has become increasingly important for the food industry since the last decades due to its capability of increasing yield, minimizing production cost, and improving food quality. New developments for control strategies such as artificial neural networks and model-based controls as well as their applications have brought several new prospects to the food industry. Food processes are mostly nonlinear and show different process dynamics with various raw materials and different processing conditions. Therefore, advanced process control techniques are highly invaluable compared to classical control approaches. In this review, advanced control strategies, particularly model-based controllers, fuzzy logic controllers, and neural network-based controllers, are firstly described with their main characteristics. A number of applications of the advanced control strategies are then discussed according to different food processing industries such as baking, drying, fermentation/brewing, dairy, and thermal/pressure food processing.     

Efficacy of two cleaning and sanitizing combinations on Listeria monocytogenes biofilms formed at low temperature on a variety of materials in the presence of ready-to-eat meat residue

Biofilms in the food-processing industry are a serious concern due to the potential for contamination of food products, which may lead to decreased food quality and safety. The effect of two detergent and sanitizer combinations on the inactivation of Listeria monocytogenes biofilms was studied. Combination A uses a chlorinated-alkaline, low-phosphate detergent, and dual peracid sanitizer. Combination B uses a solvated-alkaline environmental sanitation product and hypochlorite sanitizer. The survival of bacterial biofilms placed at 4 and 10 degrees C and held for up to 5 days was also addressed. To simulate conditions found in a ready-to-eat meat-processing environment, biofilms were developed in low-nutrient conditions at 10 degrees C (with and without meat and fat residue) on a variety of materials found in a plant setting. Included were two types of stainless steel, three materials for conveyor use, two rubber products, a wall, and floor material. Biofilms developed on all surfaces tested; numbers at day 2 ranged from 3.2 log on silicone rubber to 4.47 log CFU/cm2 on Delrin, an acetal copolymer. Biofilm survival during storage was higher at 4 degrees C (36.3 to 1,621%) than 10 degrees C (4.5 to 83.2%). Small amounts of meat extract, frankfurters, or pork fat reduced biofilm formation initially; with time, the biofilm cell number and survival percentage increased. Cleaning efficacy was surface dependent and decreased with residue-soiled surfaces; biofilms developed on the brick and conveyor material were most resistant. Both detergents significantly (P < 0.05) removed or inactivated biofilm bacteria. The sanitizers further reduced biofilm numbers; however, the reduction was not significant in most cases for the dual peracid. Using a benchmark efficacy of >3-log reduction, combination A was only effective on 50.0% of the samples, Combination B, at 86.1%, was more effective.     

群体感应抑制剂调控食源性微生物生物膜形成的研究进展

食源性微生物的生物膜是附着在固体表面上形成的具有空间组织的群落,因其能够附着在食品工业环境中的生物或非生物表面,且对消毒剂和抗菌剂能产生抗药性,通常难以控制,被认为是造成设备损坏、能源成本增加、食物变质和引起食源性疾病的原因之一,给食品工业带来了巨大的挑战。研究发现群体感应在生物膜的形成中起至关重要的作用,可以通过阻断群体感应系统来控制生物膜的形成。因此,群体感应抑制剂可以作为控制生物膜形成的新策略,在食品工业中对控制生物膜的形成具有巨大潜力。本文综述了生物膜的形成、群体感应系统及其对生物膜的调控作用,介绍了群体感应抑制剂的调控机制及其分类,为通过群体感应抑制剂调控生物被膜的形成提供研究思路。     

食品加工环境胁迫因素对单核细胞增生李斯特菌生物膜形成的影响研究进展

单核细胞增生李斯特菌（以下简称单增李斯特菌）生物膜的生长可导致反复的食物污染。食品加工储藏常用的冷藏、干燥、酸处理以及消毒剂处理等使微生物长期处于胁迫环境下，对生物膜的形成产生影响。本文总结了常见的食品加工胁迫因素对单增李斯特菌生物膜形成的影响，其中重点介绍消毒剂处理对单增李斯特菌生物膜形成的影响，同时从膜流动性相关的适应策略、生物膜形成相关蛋白和基因调控表达的角度阐述胁迫条件下单增李斯特菌生物膜的形成机制。胁迫环境下单增李斯特菌生物膜形成的研究有助于揭示真实环境下其生物膜的形成及变化规律；充分考虑环境因素设定清洁、消毒标准有利于降低食源性致病菌传播的潜在风险。     

Removal of Salmonella enterica serovar Typhimurium and Cronobacter sakazakii biofilms from food contact surfaces through enzymatic catalysis

Bacterial biofilms are highly difficult to control, hence significant economic resources have been allocated to develop strategies to eradicate them. This study evaluated the effect of an enzymatic treatment to be used as a cleaning product to control the presence of biofilms. Two different materials used in the food industry, polystyrene and stainless steel, were tested using Salmonella Typhimuirum and Cronobacter sakazakii. Biofilm formation was carried out by inoculating the surfaces with a standardized concentration of 4 log (CFU cm⁻²) and incubated for 48 hr with renewal of nutrients. The biofilm formation and subsequent enzymatic treatment were quantified using fluorescence microscopy and the conventional culture method. The enzymatic treatment showed significant reductions of 2–3 log (CFU cm⁻²) in biofilm cells, which was attributed to the degradation of the extracellular matrix and the further detachment of both microorganisms. The maximum biofilm detachment obtained with the preventive formula was 46.67%; however, this percentage could be increased by applying an aggressive treatment or by adding a subsequent disinfection step that would eliminate adhered microbial cells. Further, the enzymatic cleaning treatment could be exploited as a potent technology to control bacterial adherence and biofilm formation in the food industry.     

Current and future interventions for improving poultry health and poultry food safety and security: A comprehensive review

Poultry is thriving across the globe. Chicken meat is the most preferred poultry worldwide, and its popularity is increasing. However, poultry also threatens human hygiene, especially as a fomite of infectious diseases caused by the major foodborne pathogens (Campylobacter, Salmonella, and Listeria). Preventing pathogenic bacterial biofilm is crucial in the chicken industry due to increasing food safety hazards caused by recurring contamination and the rapid degradation of meat, as well as the increased resistance of bacteria to cleaning and disinfection procedures commonly used in chicken processing plants. To address this, various innovative and promising strategies to combat bacterial resistance and biofilm are emerging to improve food safety and quality and extend shelf-life. In particular, natural compounds are attractive because of their potential antimicrobial activities. Natural compounds can also boost the immune system and improve poultry health and performance. In addition to phytochemicals, bacteriophages, nanoparticles, coatings, enzymes, and probiotics represent unique and environmentally friendly strategies in the poultry processing industry to prevent foodborne pathogens from reaching the consumer. Lactoferrin, bacteriocin, antimicrobial peptides, cell-free supernatants, and biosurfactants are also of considerable interest for their prospective application as natural antimicrobials for improving the safety of raw poultry meat. This review aims to describe the feasibility of these proposed strategies and provide an overview of recent published evidences to control microorganisms in the poultry industry, considering the human health, food safety, and economic aspects of poultry production.     

Multipopulation model of membrane-aerated biofilms

Biofilms cultivated on oxygen-filled gas-permeable membranes grow differently than conventional biofilms, as the chemical species required for growth diffuse from different sides of the biofilm. Oxygen is delivered directly to the base of the biofilm by the membrane, while organic substrates and other soluble nutrients are provided to the upper surface of the biofilm via the water in which the membranes are immersed. This counterdiffusion of nutrients results in a growth environment very different from that of conventional biofilms that receive both oxygen and other nutrients from the water. In recent years, membrane-supported biofilms have been shown to simultaneously remove chemical oxygen demand (COD) and inorganic nitrogen from wastewater in laboratory studies. Several investigators have developed computer models of these biofilms, but they have all focused on a single population of aerobic bacteria. While these models are useful in characterizing the behavior of these biofilms in pure cultures, they are not useful in modeling the behavior of the biofilms in mixed cultures such as those found in wastewater treatment. In this study, a multipopulation biofilm model was developed that includes aerobic heterotrophs, nitrifiers, denitrifiers, and acetoclastic methanogens. The model was constructed with Aquasim software and can predict the COD and inorganic nitrogen removal behavior observed previously in experimental studies. In this paper we present examples of predicted biofilm behavior and compare the results of this multiple-population model with the single-population models published previously. In addition, the behavior of the biofilm is discussed in terms of application to wastewater treatment.     

食品接触表面生物被膜形成机制及防控方法研究进展

食源性致病菌的生物被膜是固着在食品接触表面上形成的具有一定空间组织的多细胞群体结构。因生物被膜具有极强的黏附性和抗逆性,常规消杀手段难以对其进行有效防控,造成食品安全隐患并严重威胁消费者身体健康。本文归纳了近年来国内外食源性致病菌生物被膜在形成机制及防控方法方面的相关研究。以生物被膜黏附性提高、菌体状态改变和抗逆性增强的3个主要特点为核心,总结讨论了细菌的长链附属结构、群体感应系统及胞外聚合物在生物被膜的形成过程中的作用,并将生物被膜的防控策略分为物理、化学和生物法3类,分别分析了各类方法的作用原理及优缺点,旨在为食品领域生物被膜的高效防控方法的开发提供理论指导,以期更好地实现食品微生物的安全有效防控。     

单核细胞增生李斯特菌生物被膜交叉污染评估进展

单核细胞增生李斯特菌（Listeria monocytogenes）（以下简称单增李斯特菌）是一种引发李斯特菌病罹患者高住院率和高死亡率的食源性致病菌,其可在冷、热、干燥和消毒剂处理等不利条件下黏附于食品接触表面并进一步形成难以清除的生物被膜。交叉污染是单增李斯特菌传播的主要途径,生物被膜的形成提高了单增李斯特菌在工厂和厨房环境持续传播和污染的可能性,可引发相关食源性疾病暴发和食品召回等,从而造成健康和经济损失。本文首先介绍了单增李斯特菌生物被膜的胞外聚合物组分,并从外部生存环境和内部微生物自身因素两方面总结了影响单增李斯特菌生物被膜交叉污染转移的因素;进一步重点从研究类型和细菌收集两方面阐述了生物被膜交叉污染的相关研究进展;最后,归纳总结了针对单增李斯特菌生物被膜形成早期的防控策略,展望该领域的研究前景,以期为科学评估和早期精准防控单增李斯特菌生物被膜交叉污染的潜在风险提供理论依据。     

Formation of biofilm at different nutrient levels by various genotypes of Listeria monocytogenes

Strains of Listeria monocytogenes differ in their ability to form biofilms. The objectives of this study were to determine whether genetically related strains have similar biofilm-forming capacities and what effect nutrient concentration has on the ability of different strains to produce biofilms. Biofilms of 30 strains of L. monocytogenes, obtained from a variety of sources were grown on stainless steel in tryptic soy broth (TSB) or in a 1:10 dilution of TSB (DTSB) for 24 h at 32 degrees C. The amount of biofilm formed was determined with image analysis after cells were stained with bisBenzimide H 33258 (Hoechst 33258). The strains were genetically subtyped by repetitive element sequence-based PCR (rep-PCR) with the primer set rep-PRODt and rep-PROG5. Data were analyzed with an analysis of variance and Duncan's multiple range test. Eleven strains produced the same amount of biofilm in both media. Fourteen strains produced more biofilm in TSB than in DTSB. Five strains produced more biofilm in DTSB than in TSB. Serotype 4b strains produced more biofilm in TSB than did serotype 1/2a strains, whereas serotype 1/2a strains produced more biofilm in DTSB than did serotype 4b strains. Growth in DTSB resulted in decreased biofilm accumulation for serotype 4b strains. There was no correlation between genetic subtype and the amount of biofilm accumulation. These results indicate that strains of serotype 1/2a and serotype 4b differ in the regulation of their biofilm phenotype. The poor biofilm accumulation of serotype 4b isolates when grown in DTSB could be a factor in the predominance of serogroup 1/2 strains in food processing plants, where nutrients may be limited.