Inhibition of Listeria monocytogenes biofilms by bacteriocin-producing bacteria isolated from mushroom substrate

Synergizing postharvest physiology and nanopackaging for edible mushroom preservation

The cultivation of edible mushrooms is increasing because of their widely recognized nutritional benefits. Advancements in cultivation techniques have facilitated large-scale mushroom production, meeting the growing consumer demand. This rise in cultivation has led to an increasingly urgent demand for advanced postharvest preservation methods to extend the shelf life of these mushrooms. The postharvest preservation of fresh edible mushrooms involves complex physiological changes and metabolic activities closely associated with gas composition, microbial presence, moisture content, ambient temperature, and enzymatic activity. Preserving edible mushrooms through various preservation strategies (physical, chemical, biological, and nanopackaging approaches) relies on regulating postharvest factors. Nanopackaging can preserve mushrooms' sensory and nutritional qualities due to the specific characteristics of nanomaterials, such as antimicrobial properties and gas/moisture barriers. Furthermore, the review explores current trends, fundamental mechanisms, and upcoming challenges in utilizing nanomaterials, particularly their capacity to enhance the "cell wall" integrity of edible mushrooms by regulating postharvest factors.

Impairment of Listeria monocytogenes biofilm developed on industrial surfaces by Latilactobacillus curvatus CRL1579 bacteriocin

The effect of lactocin AL705, bacteriocin produced by Latilactobacillus (Lat.) curvatus CRL1579 against Listeria biofilms on stainless steel (SS) and polytetrafluoroethylene (PTFE) coupons at 10 °C was investigated. L. monocytogenes FBUNT showed the greatest adhesion on both surfaces associated to the hydrophobicity of cell surface. Partially purified bacteriocin (800 UA/mL) effectively inhibited L. monocytogenes preformed biofilm through displacement strategy, reducing the pathogen by 5.54 ± 0.26 and 4.74 ± 0.05 log cycles at 3 and 6 days, respectively. The bacteriocin-producer decreased the pathogen biofilm by ∼2.84 log cycles. Control and Bac- treated samples reached cell counts of 7.05 ± 0.18 and 6.79 ± 0.06 log CFU/cm2 after 6 days of incubation. Confocal scanning laser microscopy (CLSM) allowed visualizing the inhibitory effect of lactocin AL705 on L. monocytogenes preformed biofilms under static and hydrodynamic flow conditions. A greater effect of the bacteriocin was found at 3 days independently of the surface matrix and pathogen growth conditions at 10 °C. As a more realistic approach, biofilm displacement strategy under continuous flow conditions showed a significant loss of biomass, mean thickness and substratum coverage of pathogen biofilm. These findings highlight the anti-biofilm capacity of lactocin AL705 and their potential application in food industries.

Idiosyncratic invasion trajectories of human bacterial pathogens facing temperature disturbances in soil microbial communities

Current knowledge about effects of disturbance on the fate of invaders in complex microbial ecosystems is still in its infancy. In order to investigate this issue, we compared the fate of Klebsiella pneumoniae (Kp) and Listeria monocytogenes (Lm) in soil microcosms. We then used environmental disturbances (freeze-thaw or heat cycles) to compare the fate of both invaders and manipulate soil microbial diversity. Population dynamics of the two pathogens was assessed over 50 days of invasion while microbial diversity was measured at times 0, 20 and 40 days. The outcome of invasion was strain-dependent and the response of the two invaders to disturbance differed. Resistance to Kp invasion was higher under the conditions where resident microbial diversity was the highest while a significant drop of diversity was linked to a higher persistence. In contrast, Lm faced stronger resistance to invasion in heat-treated microcosms where diversity was the lowest. Our results show that diversity is not a universal proxy of resistance to microbial invasion, indicating the need to properly assess other intrinsic properties of the invader, such as its metabolic repertoire, or the array of interactions between the invader and resident communities.

Bacteriocins: potentials and prospects in health and agrifood systems

Bacteriocins are highly diverse, abundant, and heterogeneous antimicrobial peptides that are ribosomally synthesized by bacteria and archaea. Since their discovery about a century ago, there has been a growing interest in bacteriocin research and applications. This is mainly due to their high antimicrobial properties, narrow or broad spectrum of activity, specificity, low cytotoxicity, and stability. Though initially used to improve food quality and safety, bacteriocins are now globally exploited for innovative applications in human, animal, and food systems as sustainable alternatives to antibiotics. Bacteriocins have the potential to beneficially modulate microbiota, providing viable microbiome-based solutions for the treatment, management, and non-invasive bio-diagnosis of infectious and non-infectious diseases. The use of bacteriocins holds great promise in the modulation of food microbiomes, antimicrobial food packaging, bio-sanitizers and antibiofilm, pre/post-harvest biocontrol, functional food, growth promotion, and sustainable aquaculture. This can undoubtedly improve food security, safety, and quality globally. This review highlights the current trends in bacteriocin research, especially the increasing research outputs and funding, which we believe may proportionate the soaring global interest in bacteriocins. The use of cutting-edge technologies, such as bioengineering, can further enhance the exploitation of bacteriocins for innovative applications in human, animal, and food systems.

Diversity of the Microbiota of Traditional Izmir Tulum and Izmir Brined Tulum Cheeses and Selection of Potential Probiotics

High-throughput DNA sequencing (HTS) was used to study the microbial diversity of commercial traditional Izmir Tulum (IT) and Izmir Brined Tulum (IBT) cheeses from Izmir, Türkiye. Simultaneously, cultivation-dependent methods were used to isolate, identify and characterize bacterial strains displaying probiotic potential. At the phylum level, Firmicutes dominated the microbiota of both cheese types comprising >98% of the population. Thirty genera were observed, with Streptococcus being the most abundant genus and with Streptococcus thermophilus and S. infantarius subsp. infantarius being the most abundant species. Genera, including Bifidobacterium and Chryseobacterium, not previously associated with IT and IBT, were detected. IT cheeses displayed higher operational taxonomic units (OTUs; Richness) and diversity index (Simpson) than IBT cheeses; however, the difference between the diversity of the microbiota of IT and IBT cheese samples was not significant. Three Lacticaseibacillus paracasei strains isolated from IBT cheeses exhibited probiotic characteristics, which included capacity to survive under in vitro simulated gastrointestinal conditions, resistance to bile salts and potential to adhere to HT-29 human intestinal cells. These findings demonstrate that Tulum cheeses harbor bacterial genera not previously reported in this cheese and that some strains display probiotic characteristics.

Nisin Z Potential for the Control of Diabetic Foot Infections Promoted by Pseudomonas aeruginosa Persisters

Diabetic foot ulcers (DFU) are a major complication of diabetes mellitus and a public health concern worldwide. The ability of P. aeruginosa to form biofilms is a key factor responsible for the chronicity of diabetic foot infections (DFIs) and frequently associated with the presence of persister cells. These are a subpopulation of phenotypic variants highly tolerant to antibiotics for which new therapeutic alternatives are urgently needed, such as those based on antimicrobial peptides. This study aimed to evaluate the inhibitory effect of nisin Z on P. aeruginosa DFI persisters. To induce the development of a persister state in both planktonic suspensions and biofilms, P. aeruginosa DFI isolates were exposed to carbonyl cyanide m-chlorophenylhydrazone (CCCP) and ciprofloxacin, respectively. After RNA extraction from CCCP-induced persisters, transcriptome analysis was performed to evaluate the differential gene expression between the control, persisters, and persister cells exposed to nisin Z. Nisin Z presented a high inhibitory effect against P. aeruginosa persister cells but was unable to eradicate them when present in established biofilms. Transcriptome analysis revealed that persistence was associated with downregulation of genes related to metabolic processes, cell wall synthesis, and dysregulation of stress response and biofilm formation. After nisin Z treatment, some of the transcriptomic changes induced by persistence were reversed. In conclusion, nisin Z could be considered as a potential complementary therapy for treating P. aeruginosa DFI, but it should be applied as an early treatment or after wound debridement.

Recent advances in quality preservation of postharvest golden needle mushroom (Flammulina velutiper)

The golden needle mushroom (Flammulina velutiper) is one of the most productive mushrooms in the world. However, F. velutiper experiences continuous quality degradation in terms of changes in color and textural characteristics, loss of moisture, nutrition and flavor, and increased microbial populations due to its high respiratory activity during the postharvest phase. Postharvest preservation techniques, including physical, chemical and biological methods, play a vital role in maintaining postharvest quality and extending the shelf life of mushrooms. Therefore, in this study, the decay process of F. velutiper and the factors affecting its quality were comprehensively reviewed. Additionally, the preservation methods (e.g., low-temperature storage, packaging, plasma treatment, antimicrobial cleaning and 1-methylcyclopropene treatment) for F. velutiper used for the last 5 years were compared to provide an outlook on future research directions. Overall, this review aims to provide a reference for developing novel, green and safe preservation techniques for F. velutiper. © 2023 Society of Chemical Industry.

Lactic acid bacteria biofilms and their antimicrobial potential against pathogenic microorganisms

The continuous growth of pathogenic microorganisms and associated biofilms poses severe public health challenges, particularly in food and clinical environments. However, these difficulties have enabled scientists to develop novel and safe methods for combating pathogens. The use of biofilms produced by lactic acid bacteria (LAB) against pathogenic bacteria has recently gained popularity. This review provides an in-depth look at LAB biofilms, their distribution, and mechanisms of action against pathogenic bacteria. More importantly, the bioactive substances produced by LAB-forming biofilm may be active against undesirable microorganisms and their products, which is of great interest in improving human health. Therefore, this review implies that a combination of LAB biofilms and other LAB products like bacteriocins could provide viable alternatives to traditional methods of combating pathogenic microorganisms and their biofilms.

In silico and In vitro Analysis of Nigella sativa Bioactives Against Chorismate Synthase of Listeria monocytogenes: a Target Protein for Biofilm Inhibition

Listeria monocytogenes have the ability to form biofilms, which aid in the contamination of food and the evasion of antimicrobials. Consumption of L. monocytogenes laden food can promote mild to severe infection in humans and cause serious health issues. Therefore, biofilm development by L. monocytogenes is considered to be a major concern for both healthcare and food safety. This study attempted to target chorismate synthase, an essential protein predicted to be involved in the biofilm pathway. Nigella sativa is renowned for its applications in folk medicine; hence, bioactive ingredients reported were used for molecular docking studies. In the absence of a three-dimensional structure of chorismate synthase from L. monocytogenes, a homology model was generated using the Modeller program. A model with the highest DOPE score was chosen and validated. The reliable model was subjected to docking studies with 30 ligands from N. sativa. From this approach, α-longipinene was unveiled as the best hit. Further in vitro studies demonstrated the antibiofilm potential of α-longipinene against L. monocytogenes. Overall, the study reveals lead molecules from N. sativa as promising antibiofilm agents against L. monocytogenes. Hence, extended investigation with lead molecules will provide sustainable strategies to prevent biofilm-mediated problems due to L. monocytogenes.

Inhibitory Effect of Bacillus licheniformis Strains Isolated from Canine Oral Cavity

Bacillus licheniformis is used in a broad spectrum of areas, including some probiotic preparations for human and veterinary health. Moreover, B. licheniformis strains are known producers of various bioactive substances with antimicrobial and antibiofilm effects. In searching for new potentially beneficial bacteria for oral health, the inhibitory effect of B. licheniformis strains isolated from canine dental biofilm against pathogenic oral bacteria was evaluated. The antimicrobial effect of neutralized cell-free supernatants (nCFS) was assessed in vitro on polystyrene microtiter plates. Furthermore, molecular and morphological analyses were executed to evaluate the production of bioactive substances. To determine the nature of antimicrobial substance present in nCFS of B. licheniformis A-1-5B-AP, nCFS was exposed to the activity of various enzymes. The nCFS of B. licheniformis A-1-5B-AP significantly (p < 0.0001) reduced the growth of Porphyromonas gulae 3/H, Prevotella intermedia 1/P and Streptococcus mutans ATCC 35668. On the other hand, B. licheniformis A-2-11B-AP only significantly (p < 0.0001) inhibited the growth of P. intermedia 1/P and S. mutans ATCC 35668. However, enzyme-treated nCFS of B. licheniformis A-1-5B-AP did not lose its antimicrobial effect and significantly (p < 0.0001) inhibited the growth of Micrococcus luteus DSM 1790. Further studies are needed for the identification of antimicrobial substances.

Ability of Two Strains of Lactic Acid Bacteria To Inhibit Listeria monocytogenes by Spot Inoculation and in an Environmental Microbiome Context

We evaluated the ability of two strains of lactic acid bacteria (LAB) to inhibit L. monocytogenes using spot inoculation and environmental microbiome attached-biomass assays. LAB strains (PS01155 and PS01156) were tested for antilisterial activity toward 22 phylogenetically distinct L. monocytogenes strains isolated from three fruit packing environments (F1, F2, and F3). LAB strains were tested by spot inoculation onto L. monocytogenes lawns (10⁸ and 10⁷ CFU/mL) and incubated at 15, 20, 25, or 30°C for 3 days. The same LAB strains were also cocultured at 15°C for 3, 5, and 15 days in polypropylene conical tubes with L. monocytogenes and environmental microbiome suspensions collected from F1, F2, and F3. In the spot inoculation assay, PS01156 was significantly more inhibitory toward less concentrated L. monocytogenes lawns than more concentrated lawns at all the tested temperatures, while PS01155 was significantly more inhibitory toward less concentrated lawns only at 15 and 25°C. Furthermore, inhibition of L. monocytogenes by PS01156 was significantly greater at 15°C than higher temperatures, whereas the temperature did not have an effect on the inhibitory activity of PS01155. In the assay using attached environmental microbiome biomass, L. monocytogenes concentration was significantly reduced by PS01156, but not PS01155, when cocultured with microbiomes from F1 and F3 and incubated for 3 days at 15°C. Attached biomass microbiota composition was significantly affected by incubation time but not by LAB strain. This study demonstrates that LAB strains that may exhibit inhibitory properties toward L. monocytogenes in a spot inoculation assay may not maintain antilisterial activity within a complex microbiome.

IMPORTANCEListeria monocytogenes has previously been associated with outbreaks of foodborne illness linked to consumption of fresh produce. In addition to conventional cleaning and sanitizing, lactic acid bacteria (LAB) have been studied for biocontrol of L. monocytogenes in food processing environments that are challenging to clean and sanitize. We evaluated whether two specific LAB strains, PS01155 and PS01156, can inhibit the growth of L. monocytogenes strains in a spot inoculation and in an attached-biomass assay, in which they were cocultured with environmental microbiomes collected from tree fruit packing facilities. LAB strains PS01155 and PS01156 inhibited L. monocytogenes in a spot inoculation assay, but the antilisterial activity was lower or not detected when they were grown with environmental microbiota. These results highlight the importance of conducting biocontrol challenge tests in the context of the complex environmental microbiomes present in food processing facilities to assess their potential for application in the food industry.

An Exploration of Listeria monocytogenes, Its Influence on the UK Food Industry and Future Public Health Strategies

Listeria monocytogenes is a Gram-positive intracellular pathogen that can cause listeriosis, an invasive disease affecting pregnant women, neonates, the elderly, and immunocompromised individuals. Principally foodborne, the pathogen is transmitted typically through contaminated foods. As a result, food manufacturers exert considerable efforts to eliminate L. monocytogenes from foodstuffs and the environment through food processing and disinfection. However, L. monocytogenes demonstrates a range of environmental stress tolerances, resulting in persistent colonies that act as reservoirs for the reintroduction of L. monocytogenes to food contact surfaces and food. Novel technologies for the rapid detection of L. monocytogenes and disinfection of food manufacturing industries have been developed to overcome these obstacles to minimise the risk of outbreaks and sporadic cases of listeriosis. This review is aimed at exploring L. monocytogenes in the UK, providing a summary of outbreaks, current routine microbiological testing and the increasing awareness of biocide tolerances. Recommendations for future research in the UK are made, pertaining to expanding the understanding of L. monocytogenes dissemination in the UK food industry and the continuation of novel technological developments for disinfection of food and the food manufacturing environment.

Preclinical Safety Assessment of Bacillus subtilis BS50 for Probiotic and Food Applications

Despite the commercial rise of probiotics containing Bacillaceae spp., it remains important to assess the safety of each strain before clinical testing. Herein, we performed preclinical analyses to address the safety of Bacillus subtilis BS50. Using in silico analyses, we screened the 4.15 Mbp BS50 genome for genes encoding known Bacillus toxins, secondary metabolites, virulence factors, and antibiotic resistance. We also assessed the effects of BS50 lysates on the viability and permeability of cultured human intestinal epithelial cells (Caco-2). We found that the BS50 genome does not encode any known Bacillus toxins. The BS50 genome contains several gene clusters involved in the biosynthesis of secondary metabolites, but many of these antimicrobial metabolites (e.g., fengycin) are common to Bacillus spp. and may even confer health benefits related to gut microbiota health. BS50 was susceptible to seven of eight commonly prescribed antibiotics, and no antibiotic resistance genes were flanked by the complete mobile genetic elements that could enable a horizontal transfer. In cell culture, BS50 cell lysates did not diminish either Caco-2 viability or monolayer permeability. Altogether, BS50 exhibits a robust preclinical safety profile commensurate with commercial probiotic strains and likely poses no significant health risk to humans.

Combating biofilms of foodborne pathogens with bacteriocins by lactic acid bacteria in the food industry

Most foodborne pathogens have biofilm-forming capacity and prefer to grow in the form of biofilms. Presence of biofilms on food contact surfaces can lead to persistence of pathogens and the recurrent cross-contamination of food products, resulting in serious problems associated with food safety and economic losses. Resistance of biofilm cells to conventional sanitizers urges the development of natural alternatives to effectively inhibit biofilm formation and eradicate preformed biofilms. Lactic acid bacteria (LAB) produce bacteriocins which are ribosomally synthesized antimicrobial peptides, providing a great source of nature antimicrobials with the advantages of green and safe properties. Studies on biofilm control by newly identified bacteriocins are increasing, targeting primarily onListeria monocytogenes, Staphylococcus aureus, Salmonella, and Escherichia coli. This review systematically complies and assesses the antibiofilm property of LAB bacteriocins in controlling foodborne bacterial-biofilms on food contact surfaces. The bacteriocin-producing LAB genera/species, test method (inhibition and eradication), activity spectrum and surfaces are discussed, and the antibiofilm mechanisms are also argued. The findings indicate that bacteriocins can effectively inhibit biofilm formation in a dose-dependent manner, but are difficult to disrupt preformed biofilms. Synergistic combination with other antimicrobials, incorporation in nanoconjugates and implementation of bioengineering can help to strengthen their antibiofilm activity. This review provides an overview of the potential and application of LAB bacteriocins in combating bacterial biofilms in food processing environments, assisting in the development and widespread use of bacteriocin as a promising antibiofilm-agent in food industries.

Novel Chronic Wound Healing by Anti-biofilm Peptides and Protease

Chronic wounds have made a challenge in medical healthcare due to their biofilm infections, which reduce the penetrance of the antibacterial agents in the injury site. In infected wounds, the most common bacterial strains are Staphylococcus aureus and Pseudomonas aeruginosa. Biofilm disruption in chronic wounds is crucial in wound healing. Due to their broad-spectrum antibacterial properties and fewer side effects, anti-biofilm peptides, especially bacteriocins, are promising in the healing of chronic wounds by biofilm destruction. This study reviews the effects of antimicrobial and anti-biofilm agents, including bacteriocins and protease enzymes as a novel approach, on wound healing, along with analyzing the molecular docking between a bacterial protease and biofilm components. Among a large number of anti-biofilm bacteriocins identified up to now, seven types have been registered in the antimicrobial peptides (AMPs) database. Although it is believed that bacterial proteases are harmful in wound healing, it has recently been demonstrated that these proteases like the human serine protease, in combination with AMPs, can improve wound healing by biofilm destruction. In this work, docking results between metalloprotease from Paenibacillus polymyxa and proteins of S. aureus and P. aeruginosa involved in biofilm production, showed that this bacterial protease could efficiently interact with biofilm components. Infected wound healing is an important challenge in clinical trials due to biofilm production by bacterial pathogens. Therefore, simultaneous use of proteases or anti-biofilm peptides with antimicrobial agents could be a promising method for chronic wound healing.

Properties of the Extracellular Polymeric Substance Layer from Minimally Grown Planktonic Cells of Listeria monocytogenes

The bacterium Listeria monocytogenes is a serious concern to food processing facilities because of its persistence. When liquid cultures of L. monocytogenes were prepared in defined media, it was noted that planktonic cells rapidly dropped out of suspension. Zeta potential and hydrophobicity assays found that the cells were more negatively charged (−22, −18, −10 mV in defined media D10, MCDB 202 and brain heart infusion [BHI] media, respectively) and were also more hydrophobic. A SEM analysis detected a capsular-like structure on the surface of cells grown in D10 media. A crude extract of the extracellular polymeric substance (EPS) was found to contain cell-associated proteins. The proteins were removed with pronase treatment. The remaining non-proteinaceous component was not stained by Coomassie blue dye and a further chemical analysis of the EPS did not detect significant amounts of sugars, DNA, polyglutamic acid or any other specific amino acid. When the purified EPS was subjected to attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, the spectra obtained did not match the profile of any of the 12 reference compounds used. An x-ray diffraction (XRD) analysis showed that the EPS was amorphous and a nuclear magnetic resonance (NMR) analysis detected the presence of glycerol. An elemental energy dispersive x-ray (EDX) analysis showed traces of phosphorous as a major component. In conclusion, it is proposed that the non-proteinaceous component may be phospholipid in nature, possibly derived from the cell wall lipoteichoic acid.

Bacteriocin-a potential antimicrobial peptide towards disrupting and preventing biofilm formation in the clinical and environmental locales

Biofilm, a consortium of microbial cells, protected by extracellular polymeric matrix, is considered a global challenge due to the inherent antibiotic resistance conferred by its lifestyle. Besides, it poses environmental threats causing huge damage in food industries, fisheries, refineries, water systems, pharmaceutical industries, medical industries, etc. Living in a community of microbial populations is most critical in the clinical field, making it responsible for about 80% of severe and chronic microbial diseases. The necessity to find an alternative approach is the need of the hour to solve these crises. So far, many approaches have been attempted to disrupt the initial stage of biofilm formation, including adherence and maturation. Bacteriocins are a group of antimicrobial peptides, produced by bacteria having the potential to disrupt biofilm either by itself or in combination with other drugs than antibiotic counterparts. A clear understanding on mechanisms of bacterial biofilm formation, progression, and resistance will surely lead to the development of innovative, effective biofilm control strategies in pharmaceutical, health care industries and environmental locales.

Effectiveness of current hygiene practices on minimization of Listeria monocytogenes in different mushroom production-related environments

BACKGROUND

The commercial production of Agaricus bisporus is a three stage process: 1) production of compost, also called "substrate"; 2) production of casing soil; and 3) production of the mushrooms. Hygiene practices are undertaken at each stage: pasteurization of the substrate, hygiene practices applied during the production of casing soil, postharvest steam cookout, and disinfection at the mushroom production facilities. However, despite these measures, foodborne pathogens, including Listeria monocytogenes, are reported in the mushroom production environment. In this work, the presence of L. monocytogenes was evaluated before and after the application of hygiene practices at each stage of mushroom production with swabs, samples of substrate, casing, and spent mushroom growing substrates.

RESULTS

L. monocytogenes was not detected in any casing or substrate sample by enumeration according to BS EN ISO 11290-2:1998. Analysis of the substrate showed that L. monocytogenes was absent in 10 Phase II samples following pasteurization, but was then present in 40% of 10 Phase III samples. At the casing production facility, 31% of 59 samples were positive. Hygiene improvements were applied, and after four sampling occasions, 22% of 37 samples were positive, but no statistically significant difference was observed (p > .05). At mushroom production facilities, the steam cookout process inactivated L. monocytogenes in the spent growth substrate, but 13% of 15 floor swabs at Company 1 and 19% of 16 floor swabs at Company 2, taken after disinfection, were positive.

CONCLUSION

These results showed the possibility of L. monocytogenes recontamination of Phase III substrate, cross-contamination at the casing production stage and possible survival after postharvest hygiene practices at the mushroom growing facilities. This information will support the development of targeted measures to minimize L. monocytogenes in the mushroom industry.

Ability of Three Lactic Acid Bacteria to Grow in Sessile Mode and to Inhibit Biofilm Formation of Pathogenic Bacteria

In this study, we explored the effect of three lactic acid bacteria (LAB), i.e. Enterococcus sp CM9, Enterococcus sp CM18 and Enterococcus faecium H3, and their supernatants, on seven biofilm-forming pathogenic strains isolated from human urinary tract or nose infections. By quantitative biofilm production assay, a strong adherence ability of Enterococcus sp CM9 and Enterococcus sp CM18 was revealed while E. faecium H3 resulted to be moderately adherent. Inhibition tests demonstrated an antimicrobial activity of LAB against pathogens.The presence of cell free supernatant (CFS) of CM9 and CM18 strains significantly decreased the adhesion of S. aureus 10,850, S. epidermidis 4,296 and E. coli FSL24. The CFS of H3 strain was effective against S. epidermidis 4,296 and P. aeruginosa PA1FSL biofilms only. Biofilm formation of K. pneumoniae Kp20FSL, A. baumannii AB8FSL and ESBL+ E. coli FS101570 have not been affected by any CSF while P. aeruginosa PA1FSL biofilm increase in presence of CM9 and CM18 CFS.Confocal Laser Scanning Microscopy revealed that K. pneumoniae Kp20FSL biofilm was inhibited by Enterococcus sp CM9, when grown together.Our results suggest that the LAB strains and/or their bacteriocins can be considered as potential tools to control biofilm formation of some bacterial pathogens.

Persistent and sporadic Listeria monocytogenes strains do not differ when growing at 37 °C, in planktonic state, under different food associated stresses or energy sources

Background

The foodborne pathogen Listeria monocytogenes causes the potentially lethal disease listeriosis. Within food-associated environments, L. monocytogenes can persist for long periods and increase the risk of contamination by continued presence in processing facilities or other food-associated environments. Most research on phenotyping of persistent L. monocytogenes’ has explored biofilm formation and sanitizer resistance, with less data examining persistent L. monocytogenes’ phenotypic responses to extrinsic factors, such as variations in osmotic pressure, pH, and energy source availability. It was hypothesized that isolates of persistent strains are able to grow, and grow faster, under a broader range of intrinsic and extrinsic factors compared to closely related isolates of sporadic strains.

Results

To test this hypothesis, 95 isolates (representing 74 isolates of 20 persistent strains and 21 isolates of sporadic strains) from a series of previous studies in retail delis, were grown at 37 °C, in (i) stress conditions: salt (0, 5, and 10% NaCl), pH (5.2, 7.2, and 9.2), and sanitizer (benzalkonium chloride, 0, 2, and 5 μg/mL) and (ii) energy sources: 25 mM glucose, cellobiose, glycogen, fructose, lactose, and sucrose; the original goal was to follow up with low temperature experiments for treatments where significant differences were observed. Growth rate and the ability to grow of 95 isolates were determined using high-throughput, OD₆₀₀, growth curves. All stress conditions reduced growth rates in isolates compared to control (p < 0.05). In addition, growth varied by the tested energy sources. In chemically defined, minimal media there was a trend toward more isolates showing growth in all replicates using cellobiose (p = 0.052) compared to the control (glucose) and fewer isolates able to grow in glycogen (p = 0.02), lactose (p = 2.2 × 10^− 16), and sucrose (p = 2.2 × 10^− 16). Still, at least one isolate was able to consistently grow in every replicate for each energy source.

Conclusions

The central hypothesis was rejected, as there was not a significant difference in growth rate or ability to grow for retail deli isolates of persistent strains compared to sporadic strains for any treatments at 37 °C. Therefore, these data suggest that persistence is likely not determined by a phenotype unique to persistent strains grown at 37 °C and exposed to extrinsic stresses or variation in energy sources.

Post-process treatments are effective strategies to reduce Listeria monocytogenes on the surface of leafy greens: A pilot study

Growth of L. monocytogenes is among the most important factors affecting the risk of human listeriosis. In ready to eat leafy greens, the use of anti-Listeria treatments represents a good alternative to inhibit growth during storage. Several commercially available antimicrobial agents have been suggested as effective intervention strategies. Among them, phage preparations and bacteriocin-producing strains have shown promising results against L. monocytogenes. In this study, we investigate the efficacy of two commercially available surface treatments, the bacteriophage formulation PhageGuard Listex (Micreos Food Safety B.V., NL) and the bacteriocin-producing culture SafePro® (CHR Hansen, DK) to inactivate L. monocytogenes in fresh-cut curly endive after processing and during storage. Fresh-cut endive was inoculated with a cold-adapted L. monocytogenes cocktail of 6 strains (4.4 ± 0.0 log cfu/g) and treated with the anti-Listeria treatments. The treatments were applied using a spray system at two different places within the processing line, on the conveyor belt and in the centrifuge. A total of 5 different treatments were applied: i) Untreated (CT); ii) PhageGuard Listex on the conveyor belt (Listex_Conveyor); iii) PhageGuard Listex during centrifugation (Listex_Centrifuge); iv) SafePro on the conveyor belt (SafePro_Conveyor); and v) SafePro during centrifugation (SafePro_Centrifuge). Samples were stored 3 days at 5 °C plus 5 days at 8 °C. PhageGuard Listex treatment reduced L. monocytogenes in fresh-cut endive by 2.5 logs, regardless of the place of treatment application (conveyor belt or centrifuge). On the other hand, SafePro only reduced L. monocytogenes by 0.2 and 0.4 logs, at the conveyor belt and centrifuge, respectively. Maximum L. monocytogenes reductions of about 3.5 log units were observed in fresh-cut endive treated with PhageGuard Listex after 3 days of storage. At the end of the shelf life (8 days), the initial trends were maintained and the fresh-cut curly endive treated with PhageGuard Listex showed the lowest L. monocytogenes concentration. However, by the end of the shelf-life, L. monocytogenes showed higher levels (1.3-fold) than immediately after the application of the treatment. One hypothesis could be that L. monocytogenes cells, which were able to survive the anti-Listeria treatments, were also able to proliferate under the specific storage conditions. Based on the obtained results, PhageGuard Listex seems to be a promising decontamination agent for leafy greens aiming to reduce growth of the bacteria but further work is needed.

Inhibition of L. monocytogenes Biofilm Formation by the Amidase Domain of the Phage vB_LmoS_293 Endolysin

Listeria monocytogenes is a ubiquitous Gram-positive bacterium that is a major concern for food business operators because of its pathogenicity and ability to form biofilms in food production environments. Bacteriophages (phages) have been evaluated as biocontrol agents for L. monocytogenes in a number of studies and, indeed, certain phages have been approved for use as anti-listerial agents in food processing environments (ListShield and PhageGuard Listex). Endolysins are proteins produced by phages in the host cell. They cleave the peptidoglycan cell wall, thus allowing release of progeny phage into the environment. In this study, the amidase domain of the phage vB_LmoS_293 endolysin (293-amidase) was cloned and expressed in Escherichia. coli (E. coli). Muralytic activity at different concentrations, pH and temperature values, lytic spectrum and activity against biofilms was determined for the purified 293-amidase protein. The results showed activity on autoclaved cells at three different temperatures (20 °C, 37 °C and 50 °C), with a wider specificity (L. monocytogenes 473 and 3099, a serotype 4b and serogroup 1/2b-3b-7, respectively) compared to the phage itself, which targets only L. monocytogenes serotypes 4b and 4e. The protein also inhibits biofilm formation on abiotic surfaces. These results show the potential of using recombinant antimicrobial proteins against pathogens in the food production environment.

Biofilms in Food Processing Environments: Challenges and Opportunities

This review examines the impact of microbial communities colonizing food processing environments in the form of biofilms on food safety and food quality. The focus is both on biofilms formed by pathogenic and spoilage microorganisms and on those formed by harmless or beneficial microbes, which are of particular relevance in the processing of fermented foods. Information is presented on intraspecies variability in biofilm formation, interspecies relationships of cooperativism or competition within biofilms, the factors influencing biofilm ecology and architecture, and how these factors may influence removal. The effect on the biofilm formation ability of particular food components and different environmental conditions that commonly prevail during food processing is discussed. Available tools for the in situ monitoring and characterization of wild microbial biofilms in food processing facilities are explored. Finally, research on novel agents or strategies for the control of biofilm formation or removal is summarized.

Bacterial Inactivation by Using Plastic Materials Activated with Combinations of Natural Antimicrobials

Natural antimicrobials have gained interest as possible inhibitors of biofilm formation. The aim of the present study was to determine the efficacy of antimicrobials derived from essential oils (carvacrol, thymol) plus bacteriocin AS-48 immobilized on two plastic supports (low density polyethylene and polyethylene–polyamide films) on bacterial inactivation. The polyethylene–polyamide vacuum-packaging plastic film activated with a combination of thymol plus enterocin AS-48 was the most effective in reducing the concentrations of viable planktonic and sessile cells for Listeria innocua, Lactobacillus fructivorans, Bacillus coagulans, and Bacillus licheniformis. Results from the study highlight the potential of polyethylene–polyamide film activated with thymol plus enterocin AS-48 for reducing the viable cell concentrations of spoilage Gram-positive bacteria and Listeria in both planktonic and sessile states.

Lactic Acid Bacteria (LAB) and Their Bacteriocins as Alternative Biotechnological Tools to Control Listeria monocytogenes Biofilms in Food Processing Facilities

Bacteriocins are antimicrobial peptides produced by bacteria Gram-negative and Gram-positive, including lactic acid bacteria (LAB), organisms that are traditionally used in food preservation practices. Bacteriocins have been shown to have an aptitude as biofilm controlling agents in Listeria monocytogenes biofilms, a major risk for consumers and the food industry. Biofilms protect pathogens from sanitization procedures, allowing them to survive and persist in processing facilities, resulting in the cross-contamination of the end products. Studies have been undertaken on bacteriocinogenic LAB, their bacteriocins, and bioengineered bacteriocin derivatives for controlling L. monocytogenes biofilms on different surfaces through inhibition, competition, exclusion, and displacement. These alternative strategies can be considered promising in preventing the development of resistance to conventional sanitizers and disinfectants. Bacteriocins are "friendly" antimicrobial agents, and with high prevalence in nature, they do not have any known associated public health risk. Most trials have been carried out in vitro, on food contact materials such as polystyrene and stainless steel, while there have been few studies performed in situ to consolidate the results observed in vitro. There are strategies that can be employed for prevention and eradication of L. monocytogenes biofilms (such as the establishment of standard cleaning procedures using the available agents at proper concentrations). However, commercial cocktails using alternatives compounds recognized as safe and environmental friendly can be an alternative approach to be applied by the industries in the future.

Current Knowledge on Listeria monocytogenes Biofilms in Food-Related Environments: Incidence, Resistance to Biocides, Ecology and Biocontrol

Although many efforts have been made to control Listeria monocytogenes in the food industry, growing pervasiveness amongst the population over the last decades has made this bacterium considered to be one of the most hazardous foodborne pathogens. Its outstanding biocide tolerance capacity and ability to promiscuously associate with other bacterial species forming multispecies communities have permitted this microorganism to survive and persist within the industrial environment. This review is designed to give the reader an overall picture of the current state-of-the-art in L. monocytogenes sessile communities in terms of food safety and legislation, ecological aspects and biocontrol strategies.

Diversity of Listeria monocytogenes strains isolated from Agaricus bisporus mushroom production

AIMS

The aims of this study were to characterize the genetic diversity of Listeria monocytogenes isolates obtained from commercial mushroom production, to establish the persistence, recontamination and the risk of cross-contamination from the working environment to the final products, creating awareness about the presence of L. monocytogenes thus helping to prevent the possibility of cross-contamination.

METHODS AND RESULTS

From an extensive analysis of commercial mushroom production, analysed with BS EN ISO 11290-1:1996/Amd 1:2004 and BS EN ISO 11290-2:1998/Amd 1:2004, 279 L. monocytogenes isolates were obtained. All of the isolates were characterized by pulsed-field gel electrophoresis, species PCR and serogroup PCR. All the isolates were confirmed as L. monocytogenes; 30·1% were serogroup 1/2b-3b-7, 40·8% were serogroup 1/2a-3a and 29·1% were serogroup 4b-4d-4e. There were 77 pulsotypes from the 279 isolates, 40 of the pulsotypes had only one strain and 37 had two or more strains, indicating great diversity in the isolates.

CONCLUSIONS

The high genetic diversity is indicative of the fact that current hygiene practices are successful at removing L. monocytogenes but that recontamination of the production environment is frequent.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained are very valuable in creating awareness of L. monocytogenes in mushroom production and for the improvement of hygiene practices.

Fighting biofilms with lantibiotics and other groups of bacteriocins

Biofilms are sessile communities of bacteria typically embedded in an extracellular polymeric matrix. Bacterial cells embedded in biofilms are inherently recalcitrant to antimicrobials, compared to cells existing in a planktonic state, and are notoriously difficult to eradicate once formed. Avenues to tackle biofilms thus far have largely focussed on attempting to disrupt the initial stages of biofilm formation, including adhesion and maturation of the biofilm. Such an approach is advantageous as the concentrations required to inhibit formation of biofilms are generally much lower than removing a fully established biofilm. The crisis of antibiotic resistance in clinical settings worldwide has been further exacerbated by the ability of certain pathogenic bacteria to form biofilms. Perhaps the most notorious biofilm formers described from a clinical viewpoint have been methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa, Gardnerella vaginalis and Streptococcus mutans, the latter of which is found in oral biofilms. Due to the dearth of novel antibiotics in recent decades, compounded by the increasing rate of emergence of resistance amongst pathogens with a propensity for biofilm formation, solutions are urgently required to mitigate these crises. Bacteriocins are a class of antimicrobial peptides, which are ribosomally synthesised and often are more potent than their antibiotic counterparts. Here, we review a selection of studies conducted with bacteriocins with the ultimate objective of inhibiting biofilms. Overall, a deeper understanding of the precise means by which a biofilm forms on a substrate as well as insights into the mechanisms by which bacteriocins inhibit biofilms is warranted.

Novel Biocontrol Methods for Listeria monocytogenes Biofilms in Food Production Facilities

High mortality and hospitalization rates have seen Listeria monocytogenes as a foodborne pathogen of public health importance for many years and of particular concern for high-risk population groups. Food manufactures face an ongoing challenge in preventing the entry of L. monocytogenes into food production environments (FPEs) due to its ubiquitous nature. In addition to this, the capacity of L. monocytogenes strains to colonize FPEs can lead to repeated identification of L. monocytogenes in FPE surveillance. The contamination of food products requiring product recall presents large economic burden to industry and is further exacerbated by damage to the brand. Poor equipment design, facility layout, and worn or damaged equipment can result in Listeria hotspots and biofilms where traditional cleaning and disinfecting procedures may be inadequate. Novel biocontrol methods may offer FPEs effective means to help improve control of L. monocytogenes and decrease cross contamination of food. Bacteriophages have been used as a medical treatment for many years for their ability to infect and lyse specific bacteria. Endolysins, the hydrolytic enzymes of bacteriophages responsible for breaking the cell wall of Gram-positive bacteria, are being explored as a biocontrol method for food preservation and in nanotechnology and medical applications. Antibacterial proteins known as bacteriocins have been used as alternatives to antibiotics for biopreservation and food product shelf life extension. Essential oils are natural antimicrobials formed by plants and have been used as food additives and preservatives for many years and more recently as a method to prevent food spoilage by microorganisms. Competitive exclusion occurs naturally among bacteria in the environment. However, intentionally selecting and applying bacteria to effect competitive exclusion of food borne pathogens has potential as a biocontrol application. This review discusses these novel biocontrol methods and their use in food safety and prevention of spoilage, and examines their potential to control L. monocytogenes within biofilms in food production facilities.

Inhibition strategies of Listeria monocytogenes biofilms-current knowledge and future outlooks

There is an increasing trend in the food industry on the Listeria monocytogenes biofilm formation and inhibition. This is attributed to its easy survival on contact surfaces, resistance to disinfectants or antibiotics and growth under the stringent condition used for food processing and preservation thereby leading to food contamination products by direct or indirect exposure. Though, there is a lack of conclusive evidences about the mechanism of biofilm formation, in this review, the concept of biofilm formation and various chemical, physical, and green technology approaches to prevent or control the biofilm formed is discussed. State-of-the-art approaches ranging from the application of natural to synthetic molecules with high effectiveness and non-toxicity targeted at the different steps of biofilm formation could positively influence the biofilm inhibition in the future.

A review on Lactococcus lactis: from food to factory

Lactococcus lactis has progressed a long way since its discovery and initial use in dairy product fermentation, to its present biotechnological applications in genetic engineering for the production of various recombinant proteins and metabolites that transcends the heterologous species barrier. Key desirable features of this gram-positive lactic acid non-colonizing gut bacteria include its generally recognized as safe (GRAS) status, probiotic properties, the absence of inclusion bodies and endotoxins, surface display and extracellular secretion technology, and a diverse selection of cloning and inducible expression vectors. This have made L. lactis a desirable and promising host on par with other well established model bacterial or yeast systems such as Escherichia coli, Saccharomyces [corrected] cerevisiae and Bacillus subtilis. In this article, we review recent technological advancements, challenges, future prospects and current diversified examples on the use of L. lactis as a microbial cell factory. Additionally, we will also highlight latest medical-based applications involving whole-cell L. lactis as a live delivery vector for the administration of therapeutics against both communicable and non-communicable diseases.