Bacterial Quorum Sensing and Food Industry

Abstract: Food spoilage and biofilm formation by food‐related bacteria are significant problems in the food industry. Even with the application of modern‐day food preservative techniques, excessive amounts of food are lost due to microbial spoilage. A number of studies have indicated that quorum sensing plays a major role in food spoilage, biofilm formation, and food‐related pathogenesis. Understanding bacterial quorum‐sensing signaling systems can help in controlling the growth of undesirable food‐related bacteria. This review focusses on the various signaling molecules produced by Gram‐negative and Gram‐positive bacteria and the mechanism of their quorum‐sensing systems, types of signaling molecules that have been detected in different food systems using biosensors, the role of signaling molecules in biofilm formation, and significance of biofilms in the food industry. As quorum‐sensing signaling molecules are implicated in food spoilage, based on these molecules potential, quorum‐sensing inhibitors/antagonists can be developed to be used as novel food preservatives for maintaining food integrity and enhancing food safety. Practical Application: Bacteria use signaling molecules for inter‐ and intracellular communication. This phenomenon of bacterial cell‐to‐cell communication is known as quorum sensing. Quorum‐sensing signals are implicated in bacterial pathogenicity and food spoilage. Therefore, blocking the quorum‐sensing signaling molecules in food‐related bacteria may possibly prevent quorum‐sensing‐regulated phenotypes responsible for food spoilage. Quorum‐sensing inhibitors/antagonists could be used as food preservatives to enhance the shelf life and also increase food safety.     

New trends in the development of photodynamic inactivation against planktonic microorganisms and their biofilms in food system

The photodynamic inactivation (PDI) is a novel and effective nonthermal inactivation technology. This review provides a comprehensive overview on the bactericidal ability of endogenous photosensitizers (PSs)-mediated and exogenous PSs-mediated PDI against planktonic bacteria and their biofilms, as well as fungi. In general, the PDI exhibited a broad-spectrum ability in inactivating planktonic bacteria and fungi, but its potency was usually weakened in vivo and for eradicating biofilms. On this basis, new strategies have been proposed to strengthen the PDI potency in food system, mainly including the physical and chemical modification of PSs, the combination of PDI with multiple adjuvants, adjusting the working conditions of PDI, improving the targeting ability of PSs, and the emerging aggregation-induced emission luminogens (AIEgens). Meanwhile, the mechanisms of PDI on eradicating mono-/mixed-species biofilms and preserving foods were also summarized. Notably, the PDI-mediated antimicrobial packaging film was proposed and introduced. This review gives a new insight to develop the potent PDI system to combat microbial contamination and hazard in food industry.     

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。     

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.     

Plasma-activated liquids for mitigating biofilms on food and food contact surfaces

Plasma-activated liquids (PALs) are emerging and promising alternatives to traditional decontamination technologies and have evolved as a new technology for applications in food, agriculture, and medicine. Contamination caused by foodborne pathogens and their biofilms has posed challenges and concerns to the food industry in terms of safety and quality. The nature of the food and the food processing environment are major factors that contribute to the growth of various microorganisms, followed by the biofilm characteristics that ensure their survival in severe environmental conditions and against traditional chemical disinfectants. PALs show an efficient impact against microorganisms and their biofilms, with various reactive species (short- and long-lived ones), physiochemical properties, and plasma processing factors playing a crucial role in mitigating biofilms. Moreover, there is potential to improve and optimize disinfection strategies using a combination of PALs with other technologies for the inactivation of biofilms. The overarching aim of this study is to build a better understanding of the parameters that govern the liquid chemistry generated in a liquid exposed to plasma and how these translate into biological effects on biofilms. This review provides a current understanding of PALs-mediated mechanisms of action on biofilms; however, the precise inactivation mechanism is still not clear and is an important part of the research. Implementation of PALs in the food industry could help overcome the disinfection hurdles and can enhance biofilm inactivation efficacy. Future perspectives in this field to expand existing state of the art to seek breakthroughs for scale-up and implementation of PALs technology in the food industry are also discussed.     

乳酸菌生物膜形成调控及在食品中的应用研究进展

乳酸菌生物膜是乳酸菌为了应对不良环境而聚集形成的一种状态,在许多情况下乳酸菌都是以生物膜的形式存在,因此有必要加深对乳酸菌生物膜的了解和研究。本文综述了乳酸菌生物膜的形成,碳源、金属离子、pH值、抗生素、有害菌和非生物表面对乳酸菌生物膜的影响,以及多种基因对乳酸菌生物膜的调控作用,并介绍了乳酸菌生物膜在食品抑菌和发酵中的应用情况,以期为乳酸菌生物膜今后的形成调控研究和在食品工业中的应用提供参考。     

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.     

Bacterial biofilms associated with food particles in the human large bowel

Bacteria within the gastro-intestinal tract affect host function via production of short-chain fatty acids and synthesis of vitamins. Additionally, the commensal enteric bacteria modulate the immune system and provide protection from potentially pathogenic bacteria. Only recently heterogeneous bacterial biofilms were found to be associated with food particles within the intestinal tract. There are a number of studies investigating the formation and function of pathogenic and single-species biofilms, though few studies have investigated the dynamics of multispecies biofilms, especially with regard to food/microbial/host interactions. The scope of this review is to discuss the current knowledge of bacterial biofilms associated with food particles in the human large bowel, examine the established mathematical models depicting bacterial attachment, and elucidate key areas for further research.     

Antimicrobial peptides generated from milk proteins: a survey and prospects for application in the food industry. A review

Milk proteins constitute a natural reservoir of bioactive peptides with physiological and/or antimicrobial properties, the release of which requires hydrolysis of the precursor molecules by digestive proteases or by fermentation with proteolytic micro‐organisms. Depending on the digestive or microbial proteases used, an array of bioactive peptides would be released either from caseins or whey proteins, but only a small part of these peptides has so far been identified and characterised with respect to their antimicrobial activity. The antimicrobial peptides known thus far have proven to be potent inhibitors to the growth of a wide range of undesirable micro‐organisms of health or spoilage significance. Nevertheless, previous research work has largely been oriented towards their possible application in medicine, which has hindered their high potential as food‐grade biopreservatives and/or as supplements in functional foods. This review attempts to study the literature pertaining to antimicrobial peptides derived from major milk proteins (caseins, α‐lactalbumin and β‐lactoglobulin) upon hydrolysis either by digestive proteases or by fermentation with proteolytic lactic acid bacteria. Their possible application in the food industry and their mechanism of action will also be discussed. Reference antimicrobial peptides produced by living micro‐organisms as innate immune defence components against microbial infections will occasionally be invoked for comparison purposes.     

Residential Bacteria on Surfaces in the Food Industry and Their Implications for Food Safety and Quality

Surface hygiene is commonly measured as a part of the quality system of food processing plants, but as the bacteria present are commonly not identified, their roles for food quality and safety are not known. Here, we review the identity of residential bacteria and characteristics relevant for survival and growth in the food industry along with potential implications for food safety and quality. Sampling after cleaning and disinfection increases the likelihood of targeting residential bacteria. The increasing use of sequencing technologies to identify bacteria has improved knowledge about the bacteria present in food premises. Overall, nonpathogenic Gram‐negative bacteria, especially Pseudomonas spp., followed by Enterobacteriaceae and Acinetobacter spp. dominate on food processing surfaces. Pseudomonas spp. persistence is likely due to growth at low temperatures, biofilm formation, tolerance to biocides, and low growth requirements. Gram‐positive bacteria are most frequently found in dairies and in dry production environments. The residential bacteria may end up in the final products through cross‐contamination and may affect food quality. Such effects can be negative and lead to spoilage, but the bacteria may also contribute positively, as through spontaneous fermentation. Pathogenic bacteria present in food processing environments may interact with residential bacteria, resulting in both inhibitory and stimulatory effects on pathogens in multispecies biofilms. The residential bacterial population, or bacteriota, does not seem to be an important source for the transfer of antibiotic resistance genes to humans, but more knowledge is needed to verify this. If residential bacteria occur in high numbers, they may influence processes such as membrane filtration and corrosion.     

食源性混合菌种生物被膜的形成与种间相互作用

食源性微生物形成的生物被膜是食品生产加工中不容忽视的安全隐患,针对食品生产加工环境中广泛存在的混合菌种生物被膜的研究仍处于起步阶段。该文在现有的理论和研究结果基础上,总结了食源性混合菌种生物被膜的形成规律,归纳介绍了混合被膜中微生物间以竞争和共生为主的种间相互作用及其调控机制,旨在为食品领域混合菌种生物被膜的研究提供借鉴。     

乳酸菌合成共轭亚油酸及其应用研究进展

共轭亚油酸(conjugated linoleic acid,CLA)是一种具有多种生理活性的功能性脂肪酸,在食品、保健品中具有广阔的应用前景。然而,天然来源的CLA含量很低,不能满足人类需求。乳酸菌可以合成CLA,且广泛用于食品加工领域,利用乳酸菌开发富含CLA的功能食品是当今的研究热点。为推动CLA功能食品的研究开发,该文对合成共轭亚油酸乳酸菌的研究进展、合成共轭亚油酸乳酸菌的益生性研究以及将产CLA乳酸菌应用到食品和饲料中的研究现状进行综述,并对利用乳酸菌合成CLA进而应用于功能食品进行展望。     

Salmonella enterica Enteritidis biofilm formation and viability on regular and triclosan-impregnated bench cover materials

Contamination of food contact surfaces by microbes such as Salmonella is directly associated with substantial industry costs and severe foodborne disease outbreaks. Several approaches have been developed to control microbial attachment; one approach is the development of food contact materials incorporating antimicrobial compounds. In the present study, Salmonella enterica Enteritidis adhesion and biofilm formation on regular and triclosan-impregnated kitchen bench stones (silestones) were assessed, as was cellular viability within biofilms. Enumeration of adhered cells on granite, marble, stainless steel, and silestones revealed that all materials were prone to bacterial colonization (4 to 5 log CFU/cm(2)), and no significant effect of triclosan was found. Conversely, results concerning biofilm formation highlighted a possible bacteriostatic activity of triclosan; smaller amounts of Salmonella Enteritidis biofilms were formed on impregnated silestones, and significantly lower numbers of viable cells (1 × 10(5) to 1 × 10(6) CFU/cm(2)) were found in these biofilms than in those on the other materials (1 × 10(7) CFU/cm(2)). All surfaces tested failed to promote food safety, and careful utilization with appropriate sanitation of these surfaces is critical in food processing environments. Nevertheless, because of its bacteriostatic activity, triclosan incorporated into silestones confers some advantage for controlling microbial contamination.     

Evaluation of biohazards in dehydrated biofilms on foodstuff packaging

Plastic materials used for food packaging are clean but not sterile when the food is just packaged. Accidental wet contamination may occur at every moment between packaging and opening by the consumer: on polyethylene (PET), bacteria may adhere strongly and constitute a biofilm in less than 24 h. By rolling on themselves, PET sheets may contaminate food. We tried to show that contact with salted foodstuffs favoured microbial recovery. Four strains were chosen to perform biofilms on PET: Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Escherichia coli. Biofilms were dried up 24 h. Biofilm bacteria were stressed by adhesion, by starvation and by dehydration. However, they were capable of recovery in salted solutions or media, probably because one (or more) stress protected them against another stress. Stress was demonstrated by stress protein production, by mean of electrophoresis, and membrane lesions by mean of flow cytometry. Stress recovery was performed in aqueous salted solutions or salted brain-heart infusion with NaCl 9, 15, 20 and 30 g/l. Staphylococci were more sensitive to these stresses and recovery was a function of salt concentration. Gram-negative bacteria were little affected by stresses; salt effects were less important. If all these biofilms were capable of recovery from stresses in salted media, flexible PET could possibly lead to a health hazard when it is used for wet salt meats, e.g.     

Antimicrobial packaging based on ɛ‐polylysine bioactive film for the control of mycotoxigenic fungi in vitro and in bread

?‐Poly‐l‐ lysine (?‐PL) is a cationic peptide with a broad‐spectrum antimicrobial activity. This study investigates the use of ?‐PL as natural antimicrobial to inhibit fungal growth and to reduce aflatoxins (AFs) production. Antifungal activity of starch biofilms with different concentrations of ?‐Poly‐l‐ lysine (?‐PL) was determined in solid medium against Aspergillus parasiticus (AFs producer) and Penicillium expansum. Then, biofilms were tested as antimicrobial devices for the preservation of bread loaf inoculated with A. parasiticus CECT 2681 and P. expansum CECT 2278. Shelf life and AFs content were examined. Biofilms with concentrations of ?‐PL less than 1.6 mg/cm² showed no fungal growth inhibition in solid medium, while the antifungal activity of the films with greater than 1.6 mg/cm² of ?‐PL was dose dependent. The shelf life of bread inoculated with A. parasiticus was increased by 1 day with the use of films containing 1.6–6.5 mg ?‐PL/cm², while shelf life of bread tainted with P. expansum was increased by 3 day with 6.5 mg ?‐PL/cm². AFs production was greatly inhibited by ?‐PL biofilms (93–100%). Thus, ?‐PL biofilms could be potentially used as antimicrobial device during bread storage as a natural alternative to the synthetic preservatives.

Practical applications

?‐Polylysin is a natural substance from microbial metabolism. Polylysine has a function to prevent a microbe from proliferating by ionic adsorption in the microbe. ?‐polylysine has a wide antibacterial spectrum and has an obvious lethal effect on Gram‐positive and Gram‐negative bacteria, yeast, mold, viruses, etc. It has a good antibacterial effect on the Gram‐negative bacteria E. coli and Salmonellae, which are difficult to control with other natural preservatives. ?‐Polylysine has already been used generally as a food additive in Japan, Korea and other part of world. In the United States, FDA has recognized the polylysine as a GRAS material. Considered the positive results obtained in the study, this compound could be used for the production of antimicrobial biofilms, applied as separator slices in the loaf bread production, to prevent the growth of the mycotoxigenic fungi A. parasiticus and P. expansum, contributing to reduce the use of the synthetically preservatives in bakery industry and also of the negative impact that these compounds could generate on the health of the end users.     

Cold atmospheric pressure plasma for the sanitation of conveyor belt materials: Decontamination efficacy against adherent bacteria and biofilms of Escherichia coli and effect on surface properties

The inactivation efficacy of a cold atmospheric pressure plasma jet against Escherichia coli DH5α adherent cells and biofilms on two conveyor belt materials was evaluated. A 120 s treatment time with a 3 cm treatment distance from the surface reduced both adherent cells (initial 5.6 ± 0.2 log CFU/coupon) and 24 h biofilms (initial 5.8 ± 0.4 log CFU/coupon) on stainless steel (SS) by >4.6 log CFU. While the same treatment reduced adherent cells (initial 5.7 ± 0.5 log CFU/coupon) and 24 h biofilms (initial 6.9 ± 0.5 log CFU/coupon) on polyvinyl chloride (PVC) by 3.8 ± 0.9 and 3.5 ± 0.5 log CFU, respectively. Mature biofilms (72 h grown) were more resistant than 24 h grown biofilms. Lower microbial reductions were observed on scratched surfaces compared to intact ones. No changes were observed in SS and PVC surfaces in terms of chemical properties and visual topography. CAPP is a promising waterless technique for the sanitation of metallic and polymeric conveyor belt surfaces.Industry relevanceCold atmospheric pressure plasma (CAPP) has the potential as waterless technology to inactivate bacteria and their biofilms on food contact surfaces without affecting the material properties and the visual topography. CAPP can be integrated for industrial operation by mounting a CAPP jet on a robotic arm or moving a conveyor belt under a stationary CAPP jet for surface sanitation. This environmental-friendly and residue-free nature technology can be useful in the food industry.     

A review of bread qualities and current strategies for bread bioprotection: Flavor,sensory, rheological,and textural attributes

The unequivocal economical and social values of bread as a staple food commodity lead to constant interests in optimizing its postproduction quality and extending its shelf life, which is related to the maintenance and enhancement of flavors and textural properties, and finally, to the delay of microbial spoilage. The latter has been the subject of a multitude of studies and reviews, in which the different approaches and views were discussed. However, variations in bread freshness, flavor, and textural quality are still of concerns for the bread making industry, in conjunction with the expectation from consumers for bread products with high-quality attributes and free of synthetic ingredients that satisfy their pleasure and their sustainable lifestyle. This review mainly focuses on the quality profiles of bread, including flavor, rheological, textural, and sensorial aspects; on the modalities to assess them; as well as on the conventional and emerging approaches developed so far over the past decades. The applications of lactic acid bacteria (LAB) and enzymes as bioprotective technologies are examined and discussed, along with active packaging and novel processing technologies for either the maintenance or improvement of bread qualities during storage.     

物理场加工中细菌活的非可培养状态相关研究进展

物理场加工技术是一类使用加热、加压和辐射等物理学方法的技术, 其中热加工、超声波、超高压和紫外辐照等技术已被广泛应用于食品加工。近年来多个报道显示, 在物理场加工中细菌可进入活的非可培养状态(viable but non-culturable, VBNC)。VBNC状态指微生物为了适应逆境而进入的一种特殊休眠状态, 在合适条件下能复苏, 甚至可能依然保持致病能力, 这提示我们应该对物理场加工食品的微生物安全予以高度重视。本文主要综述了物理场加工中食源性致病菌和腐败菌VBNC状态的研究进展, 并从共性机制的角度出发分析其形成原因。本文旨在为更好的应用物理场加工技术并保障食品安全提供新思路和新方向。     

生物膜状态对食源性致病菌耐药与毒力的影响研究进展

生物膜是细菌抵御不利环境维持群体稳定性的一种常见的群落形态。生物膜状态增强了食源性致病菌的抗逆性和持久存活力,促进了细菌间的信息传导和物质交换。特别是生物膜状态显著增强了菌株对抗生素的耐受能力,提升了可移动元件在细菌间的转移效率,并且生物膜状态下的细菌具备更强的入侵和感染能力,成为食品安全和人类健康的重要危害。基于此,本文将从生物膜的结构特征与异质性、生物膜对基因突变和基因水平转移的影响、以及群体感应调控等多个角度,简述生物膜状态影响食源性致病菌耐药和毒力的研究进展,以期为深入研究生物膜的生物功能与危害防控提供新的思路。     

Confocal microscopy and microbial viability detection for food research.

Confocal microscopy offers several advantages over other conventional microscopic techniques as a tool for studying the interaction of bacteria with food and the role of food microstructure in product quality and safety. When using confocal microscopy, samples can be observed without extensive preparation processes, which allows for the evaluation of food without introducing artifacts. In addition, observations can be made in three dimensions without physically sectioning the specimen. The confocal microscope can be used to follow changes over a period of time, such as the development of the food structure or changes in microbial population during a process. Microbial attachment to and detachment from food and food contact surfaces with complex three-dimensional (3-D) structures can be observed in situ. The fate of microbial populations in food system depends on processing, distribution, and storage conditions as well as decontamination procedures that are applied to inactivate and remove them. The ability to determine the physiological status of microorganisms without disrupting their physical relationship with a food system can be useful for determining the means by which microorganisms survive decontamination treatments. Conventional culturing techniques can detect viable cells; however, these techniques lack the ability to locate viable cells in respect to the microscopic structures of food. Various microscopic methods take advantage of physiological changes in bacterial cells that are associated with the viability to assess the physiologic status of individual cells while retaining the ability to locate the cell within a food tissue system. This paper reviews the application of confocal microscopy in food research and direct observation of viable bacteria with emphasis on their use in food microbiology.