Production of biofilm by Listeria monocytogenes in different materials and temperatures

Biofilm formation comparison of Vibrio parahaemolyticus on stainless steel and polypropylene while minimizing environmental impacts and transfer to grouper fish fillets

This study investigated the influence of food contact surface materials on the biofilm formation of Vibrio parahaemolyticus while attempting to minimize the impact of environmental factors. The response surface methodology (RSM), incorporating three controlled environmental factors (temperature, pH, and salinity), was employed to determine the optimal conditions for biofilm formation on stainless steel (SS) and polypropylene (PP) coupons. The RSM results demonstrated that pH was highly influential. After minimizing the impacts of environmental factors, initially V. parahaemolyticus adhered more rapidly on PP than SS. To adhere to SS, V. parahaemolyticus formed extra exopolysaccharide (EPS) and exhibited clustered stacking. Both PP and SS exhibited hydrophilic properties, but SS was more hydrophilic than PP. Finally, this study observed a higher transfer rate of biofilms from PP to fish fillets than from SS to fish fillets. The present findings suggest that the food industry should consider the material of food processing surfaces to prevent V. parahaemolyticus biofilm formation and thus to enhance food safety.

Blackthorn fruit peel polyphenol extracts and photodynamic effect under blue light against Listeria monocytogenes

Photodynamic inactivation is an emerging antimicrobial treatment that can be enhanced by employing exogenous photosensitizers to eradicate foodborne pathogens. This study investigated a novel combinatory strategy to eradicate Listeria monocytogenes using blackthorn fruit peel (BFP) and blue light (BL). Extracts of BFP were characterized in terms of polyphenolic content, individual constituents, and antioxidant and antimicrobial activity. The concentration of phenolic compounds and antioxidant activity were both found to be determinants of antimicrobial activity. It was further speculated that flavonols, predominantly quercetin and rutin, were responsible for the activity of BFP against L. monocytogenes. A combination of BFP and BL resulted in a rapid inactivation of the pathogen by up to 4 log CFU/mL at 58.5 J/cm2, corresponding to 15 min BL illumination. Flow cytometry analysis revealed that the bacterial cells lost activity and suffered extensive membrane damage, exceeding 90% of the population. After photosensitizing L. monocytogenes with the BFP constituents quercetin and rutin, a 1.3-log reduction was observed. When applied together, these compounds could inflict the same damaging effect on cells as they did individually when effects were added. Therefore, the results indicate that BFP represents a natural source of (pro-)photosensitizers, which act additively to create inactivation effects. This study may help identify more effective plant-based photosensitizers to control L. monocytogenes in food-related applications.

Visible light-activated dye-sensitized TiO2 antibacterial film: A novel strategy for enhancing food safety and quality

Antibacterial packaging holds promise in addressing food spoilage by inactivating bacteria, but current antimicrobial packaging solutions face challenges like depletion of antibacterials and concerns of antibiotic abuse. In response to these limitations of existing packaging materials, we developed a novel antibacterial packaging film by incorporating titanium dioxide (TiO2)- tetra(4-carboxyphenyl) porphyrin (TcPP) conjugates into cellulose nanofibrils (CNF) films. Unlike conventional antimicrobial packaging, this film harnesses visible light energy to excite electrons from TcPP to TiO2, generating reactive oxygen species (ROS) that inactivate bacteria without relying on antibiotics. Results demonstrated that the film reduced 4.5, 4.6, 4.1, and 4.7-log Escherichia coli, Pseudomonas fluorescens, Leuconostoc lactis, and Listeria innocua, respectively, in phosphate-buffered saline within 72 h under 6000 lux light (3.13 mW/cm2). The antimicrobial efficacy decreased as the light intensity decreased. Notably, it retains significant antimicrobial properties even under an extremely low light intensity of 600 lux (0.60 mW/cm2). The analysis also revealed that singlet oxygen and hydrogen peroxide are the major generated ROS from the film under light exposure. When applied to cucumbers, the film reduced E. coli by 3.5 logs after 48-hour light exposure. The designed photocatalytic antibacterial film represents a major advancement in sustainable food preservation, reducing food waste by extending the shelf life of fresh produce.

Strategic manipulation of biofilm dispersion for controlling Listeria monocytogenes infections

Listeria monocytogenes (L. monocytogenes), a gram-positive foodborne pathogen that can easily cause listeriosis. It secretes extracellular polymers and forms biofilms that are highly resistant to disinfection methods, such as UV light and germicides, posing risks to food processing equipment and food quality. Dispersion of biofilm is the cycle of its formation in which the bacteria return to planktonic state and become susceptible to antimicrobials, the strategic manipulation of biofilm dispersion is thus heralded as a novel and promising approach for the effective control of biofilm-related infections. Compared to the traditional methods, it is more effective to start with the composition of biofilms, cut off the production of their constituent substances, and genetically reduce the probability of biofilm formation. Meanwhile, the dispersion of bacteria can be supplemented with exogenous substances, making long-term control possible. This paper provides a brief but comprehensive overview of the mechanisms of L. monocytogenes biofilms or cross-contamination and their resistance properties, and facilitates our understanding and control of the prevention and containment of L. monocytogenes biofilm contamination based on the biofilm's active and passive diffusion strategies. This work provides practical guidelines for the food industry to guard against the enduring threat to food safety due to L. monocytogenes biofilms.

Biofilm formation by Listeria monocytogenes from the meat processing industry environment and the use of different combinations of detergents, sanitizers, and UV-A radiation to control this microorganism in planktonic and sessile forms

This study aimed to evaluate the ability of biofilm formation by L. monocytogenes from the meat processing industry environment, as well as the use of different combinations of detergents, sanitizers, and UV-A radiation in the control of this microorganism in the planktonic and sessile forms. Four L. monocytogenes isolates were evaluated and showed moderate ability to form biofilm, as well as carried genes related to biofilm production (agrB, agrD, prfA, actA, cheA, cheY, flaA, sigB), and genes related to tolerance to sanitizers (lde and qacH). The biofilm-forming isolates of L. monocytogenes were susceptible to quaternary ammonium compound (QAC) and peracetic acid (PA) in planktonic form, with minimum inhibitory concentrations of 125 and 75 ppm, respectively, for contact times of 10 and 5 min. These concentrations are lower than those recommended by the manufacturers, which are at least 200 and 300 ppm for QAC and PA, respectively. Biofilms of L. monocytogenes formed from a pool of isolates on stainless steel and polyurethane coupons were subjected to 14 treatments involving acid and enzymatic detergents, QAC and PA sanitizers, and UV-A radiation at varying concentrations and contact times. All treatments reduced L. monocytogenes counts in the biofilm, indicating that the tested detergents, sanitizers, and UV-A radiation exhibited antimicrobial activity against biofilms on both surface types. Notably, the biofilm formed on polyurethane showed greater tolerance to the evaluated compounds than the biofilm on stainless steel, likely due to the material's surface facilitating faster microbial colonization and the development of a more complex structure, as observed by scanning electron microscopy. Listeria monocytogenes isolates from the meat processing industry carry genes associated with biofilm production and can form biofilms on both stainless steel and polyurethane surfaces, which may contribute to their persistence within meat processing lines. Despite carrying sanitizer tolerance genes, QAC and PA effectively controlled these microorganisms in their planktonic form. However, combinations of detergent (AC and ENZ) with sanitizers (QAC and PA) at minimum concentrations of 125 ppm and 300 ppm, respectively, were the most effective.

Influence of slope, material, and temperature on Listeria monocytogenes and Pseudomonas aeruginosa mono- and dual-species biofilms

Understanding factors influencing Listeria monocytogenes biofilms aid in developing more effective elimination/prevention strategies. This study examined the effect of temperature (4 °C, 21 °C, 30 °C), materials (stainless steel 316 L with 2B and 2 R finishes, glass, and polypropylene), and slope (0°/horizontal or 90°/vertical) on mono- and dual-species biofilms using two L. monocytogenes strains and one Pseudomonas aeruginosa strain. All biofilms were grown in 10% TSB for 24 h and analyzed using culture-based methods. Additionally, the architecture of monospecies biofilms was studied using fluorescence microscopy. Overall, P. aeruginosa showed higher biofilm formation potential (6.2 log CFU/cm2) than L. monocytogenes (4.0 log CFU/cm2). Temperature greatly influenced P. aeruginosa and varied for L. monocytogenes. The slope predominantly influenced L. monocytogenes monospecies biofilms, with cell counts increasing by up to 2 log CFU/cm2. Surface material had little impact on biofilm formation. The study highlights the varying effects of different parameters on multispecies biofilms and the importance of surface geometry.

Biofilm formation in food industries: Challenges and control strategies for food safety

Various pathogens have the ability to grow on food matrices and instruments. This grow may reach to form biofilms. Bacterial biofilms are community of microorganisms embedded in extracellular polymeric substances (EPSs) containing lipids, DNA, proteins, and polysaccharides. These EPSs provide a tolerance and favorable living condition for microorganisms. Biofilm formations could not only contribute a risk for food safety but also have negative impacts on healthcare sector. Once biofilms form, they reveal resistances to traditional detergents and disinfectants, leading to cross-contamination. Inhibition of biofilms formation and abolition of mature biofilms is the main target for controlling of biofilm hazards in the food industry. Some novel eco-friendly technologies such as ultrasound, ultraviolet, cold plasma, magnetic nanoparticles, different chemicals additives as vitamins, D-amino acids, enzymes, antimicrobial peptides, and many other inhibitors provide a significant value on biofilm inhibition. These anti-biofilm agents represent promising tools for food industries and researchers to interfere with different phases of biofilms including adherence, quorum sensing molecules, and cell-to-cell communication. This perspective review highlights the biofilm formation mechanisms, issues associated with biofilms, environmental factors influencing bacterial biofilm development, and recent strategies employed to control biofilm-forming bacteria in the food industry. Further studies are still needed to explore the effects of biofilm regulation in food industries and exploit more regulation strategies for improving the quality and decreasing economic losses.

Controlling of foodborne pathogen biofilms on stainless steel by bacteriophages: A systematic review and meta-analysis

This study investigates the potential of using bacteriophages to control foodborne pathogen biofilms on stainless steel surfaces in the food industry. Biofilm-forming bacteria can attach to stainless steel surfaces, rendering them difficult to eradicate even after a thorough cleaning and sanitizing procedures. Bacteriophages have been proposed as a possible solution, as they can penetrate biofilms and destroy bacterial cells within, reducing the number of viable bacteria and preventing the growth and spread of biofilms. This systematic review and meta-analysis evaluates the potential of bacteriophages against different biofilm-forming foodborne bacteria, including Cronobacter sakazakii, Escherichia coli, Staphylococcus aureus, Pseudomonas fluorescens, Pseudomonas aeruginosa and Listeria monocytogenes. Bacteriophage treatment generally causes a significant average reduction of 38 % in biofilm formation of foodborne pathogens on stainless steel. Subgroup analyses revealed that phages are more efficient in long-duration treatment. Also, applying a cocktail of phages is 1.26-fold more effective than applying individual phages. Phages at concentrations exceeding 107 PFU/ml are significantly more efficacious in eradicating bacteria within a biofilm. The antibacterial phage activity decreases substantially by 3.54-fold when applied at 4 °C compared to temperatures above 25 °C. This analysis suggests that bacteriophages can be a promising solution for controlling biofilms in the food industry.

Growth, biofilm formation, and motility of Listeria monocytogenes strains isolated from food and clinical samples located in Shanghai (China)

Listeria monocytogenes is a common foodborne pathogen that frequently causes global outbreaks. In this study, the growth characteristics, biofilm formation ability, motility ability and whole genome of 26 L. monocytogenes strains isolated from food and clinical samples in Shanghai (China) from 2020 to 2022 were analyzed. There are significant differences among isolates in terms of growth, biofilm formation, motility, and gene expression. Compared with other sequence type (ST) types, ST1930 type exhibited a significantly higher maximum growth rate, the ST8 type demonstrated a stronger biofilm formation ability, and the ST121 type displayed greater motility ability. Furthermore, ST121 exhibited significantly high mRNA expression levels compared with other ST types in virulence genes mpl, fbpA and fbpB, the quorum sensing gene luxS, starvation response regulation gene relA, and biofilm adhesion related gene bapL. Whole-genome sequencing (WGS) analyses indicated the isolates of lineage I were mostly derived from clinical, and the isolates of lineage II were mostly derived from food. The motility ability, along with the expression of genes associated with motility (motA and motB), exhibited a significantly higher level in lineage II compared with lineage I. The isolates from food exhibited significantly higher motility ability compared with isolates from clinical. By integrating growth, biofilm formation, motility phenotype with molecular and genotyping information, it is possible to enhance comprehension of the association between genes associated with these characteristics in L. monocytogenes.

The ARIMA model approach for the biofilm-forming capacity prediction of Listeria monocytogenes recovered from carcasses

The present study aimed to predict the biofilm-formation ability of L. monocytogenes isolates obtained from cattle carcasses via the ARIMA model at different temperature parameters. The identification of L. monocytogenes obtained from carcass samples collected from slaughterhouses was determined by PCR. The biofilm-forming abilities of isolates were phenotypically determined by calculating the OD value and categorizing the ability via the microplate test. The presence of some virulence genes related to biofilm was revealed by QPCR to support the biofilm profile genotypically. Biofilm-formation of the isolates was evaluated at different temperature parameters (37 °C, 22 °C, 4 °C and - 20 °C). Estimated OD values were obtained with the ARIMA model by dividing them into eight different estimation groups. The prediction performance was determined by performance measurement metrics (ME, MAE, MSE, RMSE, MPE and MAPE). One week of incubation showed all isolates strongly formed biofilm at all controlled temperatures except - 20 °C. In terms of the metrics examined, the 3 days to 7 days forecast group has a reasonable prediction accuracy based on OD values occurring at 37 °C, 22 °C, and 4 °C. It was concluded that measurements at 22 °C had lower prediction accuracy compared to predictions from other temperatures. Overall, the best OD prediction accuracy belonged to the data obtained from biofilm formation at -20 °C. For all temperatures studied, especially after the 3 days to 7 days forecast group, there was a significant decrease in the error metrics and the forecast accuracy increased. When evaluating the best prediction group, the lowest RMSE at 37 °C (0.055), 22 °C (0.027) and 4 °C (0.024) belonged to the 15 days to 21 days group. For the OD predictions obtained at -20 °C, the 15 days to 21 days prediction group had also good performance (0.011) and the lowest RMSE belongs to the 7 days to 15 days group (0.007). In conclusion, this study will guide in using indicator parameters to evaluate biofilm forming ability to predict optimum temperature-time. The ARIMA models integrated with this study can be useful tools for industrial application and risk assessment studies using different parameters such as pH, NaCl concentration, and especially temperature applied during food processing and storage on the biofilm-formation ability of L. monocytogenes.

Investigation of the seasonal prevalence, phenotypic, and genotypic characteristics of Listeria monocytogenes in slaughterhouses in Burdur

AIM

This study examined Listeria monocytogenes isolates from two slaughterhouses in Burdur province, southern Turkey, over four seasons for antibiotic resistance, serogroups, virulence genes, in vitro biofilm forming capacity, and genetic relatedness.

METHODS AND RESULTS

Carcass (540) and environment-equipment surface (180) samples were collected from two slaughterhouses (S1, S2) for 1 year (4 samplings). Of the 89 (12.4%) positive isolates, 48 (53.9%) were from animal carcasses, and 41 (46.1%) from the environment-equipment surfaces. Autumn was the peak season for Listeria monocytogenes compared to summer and spring (P < 0.05). In addition, the most common serotype between seasons was 1/2c. Except for plcA and luxS genes, all isolates (100%) harbored inlA, inlC, inlJ, hlyA, actA, iap, flaA genes. Listeria monocytogenes isolates were identified as belonging to IIc (1/2c-3c; 68.5%), IVb (4b-4d-4e; 29.2%), and IIa (1/2a-3a; 2.2%) in the screening using multiplex polymerase chain reaction-based serogrouping test. A total of 65 pulsotypes and 13 clusters with at least 80% homology were determined by using pulsed field gel electrophoresis on samples that had been digested with ApaI. Thirty-four (38.2%) of the isolates were not resistant to any of the 14 antibiotics tested. The antibiotic to which the isolates showed the most resistance was rifampicin (44.9%). Serotype 1/2c was the most resistant serotype to antibiotics. Despite having biofilm-associated genes (inlA, inlB, actA, flaA, and luxS), a minority (11%) of isolates formed weak biofilm.

CONCLUSION

This study revealed seasonal changes prevalence of Listeria monocytogenes, particularly higher in autumn, posing a greater risk of meat contamination. Notably, Serotype 1/2c showed significant prevalence and antibiotic resistance. Indistinguishable isolates indicated cross-contamination, underscoring the importance of prioritized training for slaughterhouse personnel in sanitation and hygiene protocols.

Environmental persistence of Listeria monocytogenes and its implications in dairy processing plants

Listeriosis, an invasive illness with a fatality rate between 20% and 30%, is caused by the ubiquitous bacterium Listeria monocytogenes. Human listeriosis has long been associated with foods. This is because the ubiquitous nature of the bacteria renders it a common food contaminant, posing a significant risk to the food processing sector. Although several sophisticated stress coping mechanisms have been identified as significant contributing factors toward the pathogen's persistence, a complete understanding of the mechanisms underlying persistence across various strains remains limited. Moreover, aside from genetic aspects that promote the ability to cope with stress, various environmental factors that exist in food manufacturing plants could also contribute to the persistence of the pathogen. The objective of this review is to provide insight into the challenges faced by the dairy industry because of the pathogens' environmental persistence. Additionally, it also aims to emphasize the diverse adaptation and response mechanisms utilized by L. monocytogenes in food manufacturing plants to evade environmental stressors. The persistence of L. monocytogenes in the food processing environment poses a serious threat to food safety and public health. The emergence of areas with high levels of L. monocytogenes contamination could facilitate Listeria transmission through aerosols, potentially leading to the recontamination of food, particularly from floors and drains, when sanitation is implemented alongside product manufacturing. Hence, to produce safe dairy products and reduce the frequency of outbreaks of listeriosis, it is crucial to understand the factors that contribute to the persistence of this pathogen and to implement efficient control strategies.

High-Pressure Processing-Impacts on the Virulence and Antibiotic Resistance of Listeria monocytogenes Isolated from Food and Food Processing Environments

High-pressure processing (HPP) is one of the non-thermal methods of food preservation considered to be safe but may cause an increase/decrease in virulence potential and antibiotic resistance. The aim of the present study was to evaluate the survival of L. monocytogenes isolates after high-pressure processing (200 and 400 MPa for 5 min) and to determine changes in phenotypic and genotypic antibiotic resistance and virulence after this treatment. The 400 MPa treatment was shown to be effective in reducing pathogens to safe levels; however, the potential for cell recovery during storage was observed. In addition, studies on changes in virulence indicated possibilities related to a decrease in actA gene expression, overexpression of the hly and osfX gene, and an increase in biofilm-forming ability. The studies on changes in antibiotic resistance of isolates showed that all isolates showing initial susceptibility to lincomycin, fosfomycin, trimethoprim/sulfamethoxazole, and tetracycline became resistant to these antibiotics, which was associated with an increase in the values of minimum inhibitory concentrations. An increase in the expression of antibiotic resistance genes (mainly tetA_1, tetA_3, tetC) was also observed (mainly after the application of 200 MPa pressure), which was isolate dependent. However, it is noteworthy that the induced changes were permanent, i.e., they persisted even after the restoration of optimal environmental conditions. The results presented in our work indicate that the stress occurring during HPP can affect both phenotypic and genotypic changes in the virulence and antibiotic resistance potential of pathogens isolated from food and food processing environments. The potential associated with cell recovery and persistence of changes may influence the spread of virulent isolates of pathogens with increased antibiotic resistance in the food and food processing environment.

The influence of stress factors on selected phenotypic and genotypic features of Listeria monocytogenes - a pilot study

BACKGROUND

Listeria monocytogenes are Gram-positive rods, widespread in the environment due to their wide tolerance to changing conditions. The apilot study aimed to assess the impact of six various stresses (heat, cold, osmotic, acid, alkali, frozen) on phenotypic features: MIC of antibiotics (penicillin, ampicillin, meropenem, erythromycin, co-trimoxazole; gradient stripes), motility, ability to form a biofilm (crystal violet method) and growth rate (OD and quantitative method), expression level of sigB (stress induced regulator of genes), agrA, agrB (associated with biofilm formation) and lmo2230, lmo0596 (acid and alkali stress) (qPCR) for three strains of L. monocytogenes.

RESULTS

Applied stress conditions contributed to changes in phenotypic features and expression levels of sigB, agrA, agrB, lmo2230 and lmo0596. Stress exposure increased MIC value for penicillin (ATCC 19111 - alkaline stress), ampicillin (472CC - osmotic, acid, alkaline stress), meropenem (strains: 55 C - acid, alkaline, o smotic, frozen stress; 472CC - acid, alkaline stress), erythromycin (strains: 55 C - acid stress; 472CC - acid, alkaline, osmotic stress; ATCC 19111 - osmotic, acid, alkaline, frozen stress), co-trimoxazole (strains: 55 C - acid stress; ATCC 19111 - osmotic, acid, alkaline stress). These changes, however, did not affect antibiotic susceptibility. The strain 472CC (a moderate biofilm former) increased biofilm production after exposure to all stress factors except heat and acid. The ATCC 19111 (a weak producer) formed moderate biofilm under all studied conditions except cold and frozen stress, respectively. The strain 55 C became a strong biofilm producer after exposure to cold and produced a weak biofilm in response to frozen stress. Three tested strains had lower growth rate (compared to the no stress variant) after exposure to heat stress. It has been found that the sigB transcript level increased under alkaline (472CC) stress and the agrB expression increased under cold, osmotic (55 C, 472CC), alkali and frozen (472CC) stress. In contrast, sigB transcript level decreased in response to acid and frozen stress (55 C), lmo2230 transcript level after exposure to acid and alkali stress (ATCC 19111), and lmo0596 transcript level after exposure to acid stress (ATCC 19111).

CONCLUSIONS

Environmental stress changes the ability to form a biofilm and the MIC values of antibiotics and affect the level of expression of selected genes, which may increase the survival and virulence of L. monocytogenes. Further research on a large L. monocytogenes population is needed to assess the molecular mechanism responsible for the correlation of antibiotic resistance, biofilm formation and resistance to stress factors.

Listeria monocytogenes Biofilms in Food-Associated Environments: A Persistent Enigma

Listeria monocytogenes (LM) is a bacterial pathogen responsible for listeriosis, a foodborne illness associated with high rates of mortality (20-30%) and hospitalisation. It is particularly dangerous among vulnerable groups, such as newborns, pregnant women and the elderly. The persistence of this organism in food-associated environments for months to years has been linked to several devastating listeriosis outbreaks. It may also result in significant costs to food businesses and economies. Currently, the mechanisms that facilitate LM persistence are poorly understood. Unravelling the enigma of what drives listerial persistence will be critical for developing more targeted control and prevention strategies. One prevailing hypothesis is that persistent strains exhibit stronger biofilm production on abiotic surfaces in food-associated environments. This review aims to (i) provide a comprehensive overview of the research on the relationship between listerial persistence and biofilm formation from phenotypic and whole-genome sequencing (WGS) studies; (ii) to highlight the ongoing challenges in determining the role biofilm development plays in persistence, if any; and (iii) to propose future research directions for overcoming these challenges.

Prevention of surface colonization and anti-biofilm effect of selected phytochemicals against Listeria innocua strain

This work aimed to determine the ability of Listeria innocua (L.i.) to colonize eight materials found in food-processing and packaging settings and to evaluate the viability of the sessile cells. We also selected four commonly used phytochemicals (trans-cinnamaldehyde, eugenol, citronellol, and terpineol) to examine and compare their efficacies against L.i. on each surface. Biofilms were also deciphered in chamber slides using confocal laser scanning microscopy to learn more about how phytochemicals affect L.i. The materials tested were silicone rubber (Si), polyurethane (PU), polypropylene (PP), polytetrafluoroethylene (PTFE), stainless steel 316 L (SS), copper (Cu), polyethylene terephthalate (PET), and borosilicate glass (GL). L.i. colonized Si and SS abundantly, followed by PU, PP, Cu, PET, GL, and PTFE surfaces. The live/dead status ranged from 65/35% for Si to 20/80% for Cu, and the estimates of cells unable to grow on Cu were the highest, reaching even 43%. Cu was also characterized by the highest degree of hydrophobicity (ΔG^TOT = -81.5 mJ/m²). Eventually, it was less prone to attachment, as we could not recover L.i. after treatments with control or phytochemical solutions. The PTFE surface demonstrated the least total cell densities and fewer live cells (31%) as compared to Si (65%) or SS (nearly 60%). It also scored high in hydrophobicity degree (ΔG^TOT = -68.9 mJ/m²) and efficacy of phytochemical treatments (on average, biofilms were reduced by 2.1 log₁₀ CFU/cm²). Thus, the hydrophobicity of surface materials plays a role in cell viability, biofilm formation, and then biofilm control and could be the prevailing parameter when designing preventive measures and interventions. As for phytochemical comparison, trans-cinnamaldehyde displayed greater efficacies, with the highest reductions seen on PET and Si (4.6 and 4.0 log₁₀ CFU/cm²). The biofilms in chamber slides exposed to trans-cinnamaldehyde revealed the disrupted organization to a greater extent than other molecules. This may help establish better interventions via proper phytochemical selection for incorporation in environment-friendly disinfection approaches.

Evaluation of Listeria monocytogenes biofilms attachment and formation on different surfaces using a CDC biofilm reactor

Listeria monocytogenes can adapt, persist, and form biofilms on food premises surfaces, representing a challenge for food safety, since they led to disease transmission, food contamination and spoilage during production. Physical interventions (scrubbing and wiping) can help controlling formation, nevertheless when biofilms are formed, they are usually very resistant to current control strategies used in the food industry. Biofilm attachment and formation is influenced by environment characteristics, substrate properties and microbial motility. The purpose of this study was to evaluate the ability of L. monocytogenes to attach and form biofilms on different surfaces (wood, nylon, and polycarbonate) representative of the materials used during produce harvesting and storage. Multi-strain L. monocytogenes biofilms were grown in a CDC Biofilm reactor at 20 ± 2 °C up to 96-h and characterized for: a) attachment strength by enumerating cells after rinsing; b) hydrophobicity and interfacial tension by contact angle measurements; c) biofilm architecture by Laser Scanning Confocal Microscopy. All experiments were done in triplicate. Material, incubation, and solvent significantly affected the hydrophobicity and wetting properties of L. monocytogenes biofilms (P < 0.05). The type of material and incubation time significantly influenced hydrophobicity and wetting properties of L. monocytogenes biofilms (P < 0.05). Highest contact angle and lowest interfacial tension were observed on polycarbonate coupons. The data presented contributes to understanding Listeria biofilms grow on different surfaces commonly used in produce harvesting and storage. The data obtained in this study can be used when evaluating intervention strategies to control this pathogen in food premises.

Effects of Selected Essential Oils on Listeria monocytogenes in Biofilms and in a Model Food System

The composition of 18 essential oils was determined using gas chromatography-mass spectrometry, and their antilisterial activity was evaluated by the disk diffusion method, followed by the determination of the minimum inhibitory and minimum bactericidal concentrations. The most active essential oils were oregano, thyme, cinnamon, winter savory, and clove, with MIC values ranging from 0.09 to 1.78 µL/mL. We investigated the biofilm-forming potential of Listeria monocytogenes on polystyrene at 5 °C, 15 °C, and 37 °C in three different media. The formation of biofilm was found to be dependent on the temperature and the availability of nutrients. After treatment with selected essential oils, the reduction in biofilm biomass was in the range of 32.61% and 78.62%. Micromorphological changes in the L. monocytogenes treated by oregano and thyme essential oils were observed in the form of impaired cell integrity and cell lyses by using scanning electron microscope. Oregano and thyme essential oils (MIC and 2MIC) significantly (p < 0.05) reduced the population of L. monocytogenes in minced pork meat during storage at 4 °C. In conclusion, the obtained results indicated the good activity of some selected essential oils on L. monocytogenes, with bacteriostatic, bactericidal, and antibiofilm effects at very low concentrations.

Influence of temperature on regulation of key virulence and stress response genes in Listeria monocytogenes biofilms

Temperature is a major determinant of Listeria (L.) monocytogenes adherence and biofilm formation on abiotic surfaces. However, its role on gene regulation of L. monocytogenes mature biofilms has not been investigated. In the present study, we aimed to evaluate the impact of temperature up- and down-shift on L. monocytogenes biofilms gene transcription. L. monocytogenes strain EGD-e biofilms were first developed on stainless steel surfaces in Brain Heart Infusion broth at 20 °C for 48 h. Then, nutrient broth was renewed, and mature biofilms were exposed to 10 °C, 20 °C or 37 °C for 24 h. Biofilm cells were harvested and RNA levels of plcA, prfA, hly, mpl, plcB, sigB, bapL, fbpA, fbpB, lmo2178, lmo0880, lmo0160, lmo1115, lmo 2089, lmo2576, lmo0159 and lmo0627 were evaluated by quantitative RT-PCR. The results revealed an over-expression of all genes tested in biofilm cells compared to planktonic cells. When biofilms were further allowed to proliferate at 20 °C for 24 h, the transcription levels of key virulence, stress response and putative binding proteins genes plcA, sigB, fbpA, fbpB, lmo1115, lmo0880 and lmo2089 decreased. A temperature-dependent transcription for sigB, plcA, hly, and lmo2089 genes was observed after biofilm proliferation at 10 °C or 37 °C. Our findings suggest that temperature differentially affects gene regulation of L. monocytogenes mature biofilms, thus modulating attributes such as virulence, stress response and pathogenesis.

Biofilm Formation From Listeria monocytogenes Isolated From Pangasius Fish-processing Plants

Biofilm formation of Listeria monocytogenes in food processing environments cause potential source of cross-contamination to foodstuffs; hence, the control of biofilm is currently addressed to find effective solutions for preventing biofilm formation or eliminating the established one. Forty-five strains of Listeria monocytogenes isolated from Pangasius fish-processing plants were studied for their capability to form a biofilm on 96-well microtiter plate by using the conventional crystal violet staining. Additionally, the inhibitory effect of biofilm formation by food additives including monascus pigment and ε-polylysine was examined. The average OD value showing biofilm mass of all 45 strains L. monocytogenes increased with an increasing temperature and time (p < 0.05). Monascus pigment and ε-polylysine significantly decreased biofilm formation by 80 ± 5.5% and 20 ± 5.9%, respectively, at the tested concentration (p < 0.05) Further, the effects of lysozyme (0.1 mg/mL) alone or in combination with slightly acidic hypochlorous water (SAHW) with 40 mg/L available chlorine or sodium hypochlorite (NaOCl) with 100 mg/L available chlorine against 7-d established biofilm of L. monocytogenes were investigated. The results indicated that slightly acidic hypochlorous water alone exhibited significant antibacterial activity (p < 0.05), decreasing the viable count by 5.2 ± 0.5 log CFU/mL. It seems that sequential treatment of lysozyme and SAHW showed an additional efficacy against biofilm of L. monocytogenes on polystyrene plate surface, reducing 70% of biomass of biofilm and 7.6 ± 0.3 log of biofilm viable cells (p < 0.05). Additionally, SAHW exhibited greater bactericidal activity against viable biofilm cells than NaOCl did. This result reveals that SAHW is a promising disinfectant agent against L. monocytogenes and the potential alternative to NaOCl in practice.

Cultivation Conditions of Spinach and Rocket Influence Epiphytic Growth of Listeria monocytogenes

Leafy vegetables are associated with Listeriosis outbreaks due to contamination with Listeria monocytogenes. To date, contradictory findings were reported on spinach, rocket, and kale, where some studies reported growth of L. monocytogenes, while others did not. Thus, the current study investigated the reason for conflicting findings by producing leafy vegetables, where cultivation factors were known for growth potential studies. Of all polytunnel produce, kale Nero di Toscana demonstrated the highest growth potential (2.56 log cfu g−1), followed by spinach F1 Cello (1.84 log cfu g−1), rocket Buzz (1.41 log cfu g−1), spinach F1 Trumpet (1.37 log cfu g−1), and finally rocket Esmee (1.23 log cfu g−1). Thus, plant species and variety influenced L. monocytogenes growth potentials. Moreover, significantly lower growth potentials of 0.3 log cfu g−1 were identified when rocket Buzz was cultivated in open fields (1.11 log cfu g−1) instead of a polytunnel. The opposite effect was observed for spinach F1 Trumpet, where growth potentials increased significantly by 0.84 log cfu g−1 when cultivated in open fields (2.21 log cfu g−1). Furthermore, a significant seasonality effect between batches was found (p < 0.05). This study revealed that spinach and rocket cultivation conditions are at least co-factors in the reporting of differing growth potentials of L. monocytogenes across literature and should be considered when conducting future growth potential studies.

Listeria monocytogenes Outbreaks Related to Commercially Produced Caramel Apples: Developments in Sanitation, Product Formulation, and Packaging: A Review

ABSTRACT

Prior to a deadly 2014 listeriosis outbreak, caramel apples were not thought to be vehicles for the foodborne pathogen Listeria monocytogenes. The purpose of this review article is to summarize what has been learned from research prompted by this outbreak. This overview includes descriptions of the two L. monocytogenes infection outbreaks related to prepackaged caramel apples and a brief discussion of apple sanitation, the production processes used to make caramel apples, and research on ways to prevent future outbreaks associated with caramel apples. A qualitative analysis of the literature and interviews with current caramel apple manufacturers were conducted. Sanitation, packaging, and storage procedures used by manufacturers in the past may not effectively inactivate L. monocytogenes from contaminated product. Novel apple sanitation methods and product formulations to control L. monocytogenes on caramel apples have been developed and, in some cases, implemented in commercial production.

HIGHLIGHTS

Inhibition of Lactobacillus fermentum SHY10 on the white membrane production of soaked pickled radish

The formation of white bio-membrane (shenghua) on the surface of pickle leads to uneatable and spoiled products, which has been the key problem restricting the development of Sichuan pickle industry. In this study, the 17 microorganisms in the white membrane of pickled radish were screened and identified, of which Candida parapsilosis was the main strain causing "shenghua". The membrane-forming ability of Candida parapsilosis was determined by crystal violet staining to explore its adaptability to the fermentation environment concerning temperature and oxygen. It was found that Candida parapsilosis had the strongest membrane-forming capacity under the aerobic condition at 37°C, with the highest OD595 nm value reached to 3.473 ± 0.07 at 72 h post inoculation. This research identified Lactobacillus fermentum SHY10 to be the inhibitor of the membrane production of Candida parapsilosis via the Oxford cup method on a Petri dish, and via co-inoculation with Candida parapsilosis in pickles. Furthermore, this study specified that the cell-free supernatant (CFS) of L. fermentum SHY10 had the most significant inhibitory effects and likely to result from protein substances in the CFS. Proteases treated CFS had significantly reduced inhibitory effects against membrane formation, which confirmed that the active component was protein substances. Overall, this study identified a functional LAB strain with significant inhibitory effects against the white membrane formation in pickles, which provide a safe and consumer-friendly solution for the membrane problem in the fermented vegetable industry.

Electrochemical Control of Biofilm Formation and Approaches to Biofilm Removal

This review deals with microbial adhesion to metal-based surfaces and the subsequent biofilm formation, showing that both processes are a serious problem in the food industry, where pathogenic microorganisms released from the biofilm structure may pollute food and related material during their production. Biofilm exhibits an increased resistance toward sanitizers and disinfectants, which complicates the removal or inactivation of microorganisms in these products. In the existing traditional techniques and modern approaches for clean-in-place, electrochemical biofilm control offers promising technology, where surface properties or the reactions taking place on the surface are controlled to delay or prevent cell attachment or to remove microbial cells from the surface. In this overview, biofilm characterization, the classification of bacteria-forming biofilms, the influence of environmental conditions for bacterial attachment to material surfaces, and the evaluation of the role of biofilm morphology are described in detail. Health aspects, biofilm control methods in the food industry, and conventional approaches to biofilm removal are included as well, in order to consider the possibilities and limitations of various electrochemical approaches to biofilm control with respect to potential applications in the food industry.

Biofilm formation and genomic features of Listeria monocytogenes strains isolated from meat and dairy industries located in Piedmont (Italy)

Listeria monocytogenes is considered a major challenge for the food industry as it can persist for long periods in food processing plants by forming biofilms. The aims of this study were: i) to assess the biofilm producing ability of 57 Listeria monocytogenes isolates previously subjected to whole-genome sequencing (WGS); ii) to compare the levels of biofilm formation with the presence or absence of biofilm associated genes. To determine the presence or absence of a known set of biofilm associated genes, a comparative genomic analysis was performed on each strain. Among Listeria monocytogenes isolates, 58 %, 38.5 % and 3.5 % exhibited weak, moderate or strong biofilm production, respectively. No difference in biofilm production was observed between food and environmental isolates. The percentage of Listeria monocytogenes strains isolated from meat products (57 %) classified as moderate or strong biofilm producers was higher than the percentage obtained for strains isolated from dairy products (28 %). The presence of the Stress Survival Islet 1, the arsD stress gene and the truncated inlA protein was significantly associated with increased levels of biofilm. Combining biofilm phenotype with molecular and genotyping data may provide the opportunity to better understand the relationship between genes linked to biofilm formation in Listeria monocytogenes.

Listeria monocytogenes - How This Pathogen Survives in Food-Production Environments?

The foodborne pathogen Listeria monocytogenes is the causative agent of human listeriosis, a severe disease, especially dangerous for the elderly, pregnant women, and newborns. Although this infection is comparatively rare, it is often associated with a significant mortality rate of 20-30% worldwide. Therefore, this microorganism has an important impact on food safety. L. monocytogenes can adapt, survive and even grow over a wide range of food production environmental stress conditions such as temperatures, low and high pH, high salt concentration, ultraviolet lights, presence of biocides and heavy metals. Furthermore, this bacterium is also able to form biofilm structures on a variety of surfaces in food production environments which makes it difficult to remove and allows it to persist for a long time. This increases the risk of contamination of food production facilities and finally foods. The present review focuses on the key issues related to the molecular mechanisms of the pathogen survival and adaptation to adverse environmental conditions. Knowledge and understanding of the L. monocytogenes adaptation approaches to environmental stress factors will have a significant influence on the development of new, efficient, and cost-effective methods of the pathogen control in the food industry, which is critical to ensure food production safety.

Controlling Listeria monocytogenes Growth and Biofilm Formation Using Flavonoids

ABSTRACT

The aim of this study was to investigate the ability of natural plant-derivate products (flavonoid compounds) to inhibit the growth and biofilm-forming ability of Listeria monocytogenes. A collection of 500 synthetic and natural flavonoids were tested individually on strains of L. monocytogenes for their antimicrobial and antibiofilm activity. The flavonoids were tested against a L. monocytogenes cocktail of five strains at a concentration of 100 μM to determine their effect on planktonic growth. The optical density was measured every hour for 24 h at 37°C, and every hour for 48 h at 22°C. A total of 17 flavonoids were chosen for further study because of their ability to significantly reduce the growth of L. monocytogenes up to 97%. An additional two flavonoids that increased planktonic growth were chosen as well to investigate whether they had the same effect on biofilm growth. A lower concentration of flavonoid compounds (50 μM) was selected to investigate the individual effects on L. monocytogenes biofilm formation using (i) stainless steel coupons to quantify biomass using crystal violet staining and (ii) glass slides using confocal laser scanning microscopic (CLSM) imaging to observe the biofilm architecture. The 19 flavonoids showed various levels of L. monocytogenes biofilm growth inhibition, ranging from 2 to 100% after 48 h of incubation at 22 or 10°C. This includes 18 of the 19 flavonoids significantly (P ≤ 0.05) inhibiting L. monocytogenes biofilm formation on stainless steel coupons under at least one of the testing conditions. However, only one flavonoid compound demonstrated significant biofilm inhibition (P ≤ 0.05) under all conditions tested. Furthermore, 8 of the selected 19 flavonoid compounds showed visible reductions through CLSM in L. monocytogenes biofilm formation. Overall, we identified five flavonoid compounds to be promising antibiofilm and antimicrobial agents against L. monocytogenes.

HIGHLIGHTS

Anti-Biofilms’ Activity of Garlic and Thyme Essential Oils against Salmonella typhimurium

Biofilm control by essential oil (EO) application has recently increased to preclude biofilm production on foods and environmental surfaces. In this work, the anti-biofilm effects of garlic and thyme essential oils using the minimum inhibitory concentration (MIC) method against Salmonella typhimurium recovered from different abattoir samples were investigated along with the virulence genes (InvA, SdiA and Stn genes), and the antimicrobial susceptibility profile of S. typhimurium as well. The obtained results revealed that S. typhimurium contaminated abattoir samples to varying degrees. The InvA gene was investigated in all isolates, whereas the SdiA and Stn genes were observed in four and three isolates, respectively. Utilizing the disc diffusion method, S. typhimurium isolates demonstrated substantial resistance to most of the examined antibiotics with a high multiple antibiotic resistance index. S. typhimurium isolates demonstrated biofilm formation abilities to various degrees at varied temperatures levels (4 °C and 37 °C). In conclusion, the obtained samples from the research area are regarded as a potential S. typhimurium contamination source. Furthermore, garlic essential oil (GEO) has more potential to inhibit S. typhimurium biofilm at different sub-minimum inhibitory concentrations as compared to thyme essential oil (TEO). Therefore, these EOs are considered as potential natural antibacterial options that could be applied in food industry.

Formation of Biofilm by Tetragenococcus halophilus Benefited Stress Tolerance and Anti-biofilm Activity Against S. aureus and S. Typhimurium

Tetragenococcus halophilus, a halophilic lactic acid bacterium (LAB), plays an important role in the production of high-salt fermented foods. Generally, formation of biofilm benefits the fitness of cells when faced with competitive and increasingly hostile fermented environments. In this work, the biofilm-forming capacity of T. halophilus was investigated. The results showed that the optimal conditions for biofilm formation by T. halophilus were at 3–9% salt content, 0–6% ethanol content, pH 7.0, 30°C, and on the surface of stainless steel. Confocal laser scanning microscopy (CLSM) analysis presented a dense and flat biofilm with a thickness of about 24 μm, and higher amounts of live cells were located near the surface of biofilm and more dead cells located at the bottom. Proteins, polysaccharides, extracellular-DNA (eDNA), and humic-like substances were all proved to take part in biofilm formation. Higher basic surface charge, greater hydrophilicity, and lower intracellular lactate dehydrogenase (LDH) activities were detected in T. halophilus grown in biofilms. Atomic force microscopy (AFM) imaging revealed that biofilm cultures of T. halophilus had stronger surface adhesion forces than planktonic cells. Cells in biofilm exhibited higher cell viability under acid stress, ethanol stress, heat stress, and oxidative stress. In addition, T. halophilus biofilms exhibited aggregation activity and anti-biofilm activity against Staphylococcus aureus and Salmonella Typhimurium. Results presented in the study may contribute to enhancing stress tolerance of T. halophilus and utilize their antagonistic activities against foodborne pathogens during the production of fermented foods.

Inactivation of Polymicrobial Biofilms of Foodborne Pathogens Using Epsilon Poly-L-Lysin Conjugated Chitosan Nanoparticles

A mixed culture (polymicrobial) biofilm provides a favorable environment for pathogens to persist in the food processing environment and to contaminate food products. Inactivation and eradication of such biofilms from food processing environments are achieved by using harsh disinfectants, but their toxicity and environmentally hostile characteristics are unsustainable. This study aims to use food-grade natural nanoparticulated antimicrobials to control mixed-culture biofilms. Chitosan, a natural broad-spectrum antimicrobial biopolymer (polysaccharide) from crustaceans, was derivatized to produce chitosan nanoparticles (ChNP) as a carrier for another broad-spectrum antimicrobial agent, ε-poly-L-lysine (PL), to synthesize ChNP-PL conjugate. The antimicrobial activity of ChNP and ChNP-PL was tested against mixed-culture biofilms. ChNP-PL (~100 nm) exhibited a synergistic antimicrobial and anti-biofilm effect against mono or mixed-culture biofilms of five foodborne pathogens, including Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica serovar Enteritidis, Escherichia coli O157:H7, and Pseudomonas aeruginosa. ChNP-PL treatment prevented biofilm formation by mono or mixed cultures of L. monocytogenes, P. aeruginosa, and E. coli O157:H7, and bacterial counts were either below the detection limit or caused 3.5–5 log reduction. ChNP-PL also inactivated preformed biofilms. In monoculture biofilm, ChNP-PL treatment reduced L. monocytogenes counts by 4.5 logs, S. Enteritidis by 2 logs, E. coli by 2 logs, and S. aureus by 0.5 logs, while ChNP-PL had no inhibitory effect on P. aeruginosa. In vitro mammalian cell-based cytotoxicity analysis confirmed ChNP-PL to have no deleterious effect on intestinal HCT-8 cell line. In conclusion, our results show ChNP-PL has strong potential to prevent the formation or inactivation of preformed polymicrobial biofilms of foodborne pathogens.

Effect of Low Amperage Electric Current on Staphylococcus Aureus-Strategy for Combating Bacterial Biofilms Formation on Dental Implants in Cystic Fibrosis Patients, In Vitro Study

Cystic fibrosis is an inherited disease that affects multiple organs and systems. The oral cavity can serve as a substantial source of bacteria, causing respiratory infections and diseases which continue to dictate the clinical course of the disease and prognosis in patients with CF. Low voltage and electric current could effectively kill bacteria and biofilms, and the activity of milliampere currents could be used as an effective method of fighting bacteria. This study evaluated the effect of low amperage electric current on the formation of Staphylococcus aureus biofilms on dental implants such as titanium and zirconium in patients with cystic fibrosis. Our studies suggest that a constant electric current at a low intensity of 1 mA and 10 mA is inhibiting bacterial adhesion, detaching biofilm-forming bacteria on biomaterials used in dental implants such as titanium and zirconium, and destroying bacterial cells of Staphylococcus aureus strains. In addition, we observed the selection of an appropriate biomaterial for implants in people affected by chronic diseases, such as CF, should be carefully planned.

Effect of the homogenization technique on the enumeration of psychrotrophic bacteria in food absorbent pads

Four methods were tested for enumerating bacteria present in the absorbent pads (AP) used in packaging chicken and other meats. Viable counts were ascertained at day 0 and day 7 (d0 and d7, respectively). Sampling bacterial cells from AP were carried out using a countertop blender, Stomacher, sonication, and blender in combination to sonication. The release of bacterial cells by breaking down the AP with the blender resulted in the highest CFU counts. At d0, a bacterial recovery rate of 94% was obtained with the blender, while the recovery rates using Stomacher or sonication alone were 58% and 73%, respectively. At d7, the Stomacher treatment also gave the lowest colony forming unit (CFU) values in the AP incubated at 7 °C. Sonication of the AP prior to homogenization with the blender did not increase CFU counts. Results suggested that breaking down the AP with a blender gives higher CFU levels than the Stomacher, which is the most commonly used technique for this purpose.

Biofilm growth by Listeria monocytogenes on stainless steel and expression of biofilm-related genes under stressing conditions

This research was carried out to investigate the differences in adhesion and growth during biofilm formation of L. monocytogenes from different sources and clonal complexes. Biofilm by L. monocytogenes (isolates CLIST 441 and 7: both lineage I, serotype 1/2b, CC3; isolates 19 and 508: both lineage II, serotype 1/2c, CC9) was grown on stainless steel coupons under different stressing conditions (NaCl, curing salts and quaternary ammonium compounds-QAC), to determine the expression of different genes involved in biofilm formation and stress response. CLIST 441, which carries a premature stop codon (PMSC) in agrC, formed high-density biofilms in the presence of QAC (7.5% w/v) or curing salts (10% w/v). Reverse Transcriptase-qPCR results revealed that L. monocytogenes isolates presented differences in transcriptional profile of genes related to biofilm formation and adaptation to environmental conditions. Our results demonstrated how L. monocytogenes can survive, multiply and form biofilm under adverse conditions related to food processing environments. Differences in transcriptional expression were observed, highlighting the role of regulatory gene networks for particular serotypes under different stress responses.

Colonisation dynamics of Listeria monocytogenes strains isolated from food production environments

Listeria monocytogenes is a ubiquitous bacterium capable of colonising and persisting within food production environments (FPEs) for many years, even decades. This ability to colonise, survive and persist within the FPEs can result in food product cross-contamination, including vulnerable products such as ready to eat food items. Various environmental and genetic elements are purported to be involved, with the ability to form biofilms being an important factor. In this study we examined various mechanisms which can influence colonisation in FPEs. The ability of isolates (n = 52) to attach and grow in biofilm was assessed, distinguishing slower biofilm formers from isolates forming biofilm more rapidly. These isolates were further assessed to determine if growth rate, exopolymeric substance production and/or the agr signalling propeptide influenced these dynamics and could promote persistence in conditions reflective of FPE. Despite no strong association with the above factors to a rapid colonisation phenotype, the global transcriptome suggested transport, energy production and metabolism genes were widely upregulated during the initial colonisation stages under nutrient limited conditions. However, the upregulation of the metabolism systems varied between isolates supporting the idea that L. monocytogenes ability to colonise the FPEs is strain-specific.

Contribution to determination of extracellular DNA origin in the biofilm matrix

This study is focused on the analysis of extracellular DNA (eDNA) from a biofilm matrix formed by Staphylococcus aureus, Listeria monocytogenes, and Salmonella enterica. The presence of eDNA in the biofilm of all the studied strains was confirmed by confocal laser scanning microscopy using fluorescent dyes with high affinity to nucleic acid. The protocol for eDNA isolation from the biofilm matrix was established, and subsequent characterization of the eDNA was performed. The purified eDNA obtained from the biofilm matrix of all three microorganisms was compared to the genomic DNA (gDNA) isolated from relevant planktonic grown cells. The process of eDNA isolation consisted of biofilm cultivation, its collection, sonication, membrane filtration, dialysis, lyophilisation, and extraction of DNA separated from the biofilm matrix with cetyltrimethylammonium bromide. An amplified fragment length polymorphism (AFLP) was used for comparing eDNA and gDNA. AFLP profiles showed a significant similarity between eDNA and gDNA at the strain level. The highest similarity, with a profile concordance rate of 94.7% per strain, was observed for S. aureus, L. monocytogenes, and S. enterica exhibited lower profiles similarity (78% and 60%, respectively). The obtained results support the hypothesis that the eDNA of studied bacterial species has its origin in the gDNA.

Prevalence, Characterization, and Antimicrobial Susceptibility of Listeria monocytogenes from Raw Beef and Slaughterhouse Environments in Korea

The prevalence of Listeria monocytogenes in raw beef and in slaughterhouse environments was investigated from April 2019 to February 2020. Three hundred raw beef samples were purchased from 50 retailers and 10 restaurants (5 samples per source). One hundred and thirty-four samples from slaughterhouse environments were collected by swabbing (10 × 10 cm) the surfaces, gloves, splitting saw, and drains. L. monocytogenes was detected and identified according to the method described in ISO 11290-1, and confirmed by 16S rRNA sequencing. L. monocytogenes was detected in raw beef (2/300, 0.7%), gloves used in carcass splitting (6/21, 28.6%), the splitting saw (1/18, 5.6%), and the drain zone (1/15, 6.7%). All isolates were serotype 1/2a or 1/2c, based on screening using multiplex PCR-based serogrouping assay and serotyping kit for O-H antigens. Pulsed-field gel electrophoresis (PFGE) following ApaI digestion of eight PFGE pulsotypes and four PFGE groups were identified. Biofilm formation analysis using Crystal Violet staining revealed the highest biofilm formation in strain LM-16, followed by D190613. Although L. monocytogenes isolates were susceptible to most antimicrobials, some resistance to penicillin (8/15, 53.3%) and tetracycline (2/15, 13.3%) was observed. Through PFGE, G190426, G190829, and G200210 isolated from the same location in this study were genetically homologous similar to the LM-16 strain, previously isolated from beef carcass in 2006. These results suggest that LM-16 has been continuously present in biofilms in the slaughterhouse environments since 2006. Our study indicates that L. monocytogenes contamination in raw beef could consistently occur during beef processing in slaughterhouse environments through contact with gloves, splitting saws, and drains.

Biofilm Formation on Dental Implant Biomaterials by Staphylococcus aureus Strains Isolated from Patients with Cystic Fibrosis

Implants made of ceramic and metallic elements, which are used in dentistry, may either promote or hinder the colonization and adhesion of bacteria to the surface of the biomaterial to varying degrees. The increased interest in the use of dental implants, especially in patients with chronic systemic diseases such as cystic fibrosis (CF), is caused by an increase in disease complications. In this study, we evaluated the differences in the in vitro biofilm formation on the surface of biomaterials commonly used in dentistry (Ti-6Al-4V, cobalt-chromium alloy (CoCr), and zirconia) by Staphylococcus aureus isolated from patients with CF. We demonstrated that S. aureus adherence and growth depends on the type of material used and its surface topography. Weaker bacterial biofilm formation was observed on zirconia surfaces compared to titanium and cobalt-chromium alloy surfaces. Moreover, scanning electron microscopy showed clear differences in bacterial aggregation, depending on the type of biomaterial used. Over the past several decades, S. aureus strains have developed several mechanisms of resistance, especially in patients on chronic antibiotic treatment such as CF. Therefore, the selection of an appropriate implant biomaterial with limited microorganism adhesion characteristics can affect the occurrence and progression of oral cavity infections, particularly in patients with chronic systemic diseases.

Diversity of Vibrio parahaemolyticus in marine fishes of Bangladesh

AIMS

To determine the occurrence, diversity, antibiotic resistance and biofilm formation of Vibrio parahaemolyticus isolated from marine fishes in Bangladesh.

METHODS AND RESULTS

A total of 80 marine fishes were obtained from the local markets and examined for the presence of V. parahaemolyticus. All the isolated V. parahaemolyticus were characterized for the presence of virulence markers, thermostable direct hemolysin (TDH) or thermostable direct hemolysin related hemolysin (TRH). Isolates were serotyped and further characterized by enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) typing to analyse the genetic diversity. Moreover, biofilm formation and antibiotic resistance patterns were also determined. About 63·75% (51/80) of the tested marine fishes were contaminated with V. parahaemolyticus. From the contaminated fishes, 71 representatives V. parahaemolyticus were isolated and none of them harboured tdh and trh virulence genes. Nine different O-groups and seven different K-types were found by serological analysis and the dominant serotype was O5:KUT. In ERIC-PCR analysis, eight clusters (A-H) were found and the most common pattern was A (46·5%). All of the isolates were resistant to ampicillin and 78·9% of isolates were resistant to streptomycin. The highest biofilm formation was found at 37°C compared to 25°C and 4°C.

CONCLUSION

Diverse V. parahaemolyticus are present in marine fishes in the local market of Bangladesh with antibiotic-resistant properties and biofilm formation capacity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The widespread prevalence of diverse V. parahaemolyticus in marine fishes is an issue of serious concern, and it entails careful monitoring to ascertain the safety of seafood consumers.

Inhibition of Biofilm Formation and Related Gene Expression of Listeria monocytogenes in Response to Four Natural Antimicrobial Compounds and Sodium Hypochlorite

The aim of this study was to assess the efficacy of four natural antimicrobial compounds (cinnamaldehyde, eugenol, resveratrol and thymoquinone) plus a control chemical disinfectant (sodium hypochlorite) in inhibiting biofilm formation by Listeria monocytogenes CMCC54004 (Lm 54004) at a minimum inhibitory concentration (MIC) and sub-MICs. Crystal violet staining assay and microscopic examination were employed to investigate anti-biofilm effects of the evaluated compounds, and a real-time PCR assay was used to investigate the expression of critical genes by Lm 54004 biofilm. The results showed that five antimicrobial compounds inhibited Lm 54004 biofilm formation in a dose dependent way. Specifically, cinnamaldehyde and resveratrol showed better anti-biofilm effects at 1/4 × MIC, while sodium hypochlorite exhibited the lowest inhibitory rates. A swimming assay confirmed that natural compounds at sub-MICs suppressed Lm 54004 motility to a low degree. Supporting these findings, expression analysis showed that all four natural compounds at 1/4 × MIC significantly down-regulated quorum sensing genes (agrA, agrC, and agrD) rather than suppressing the motility- and flagella-associated genes (degU, motB, and flaA). This study revealed that sub-MICs of natural antimicrobial compounds reduced biofilm formation by suppressing the quorum sensing system rather than by inhibiting flagella formation.

Interference of sanitizers, NaCl and curing salts on Listeria monocytogenes adhesion and subsequent biofilm formation

Listeria monocytogenes, a well-known foodborne pathogen and the causative agent of listeriosis, has the ability to persist in food processing environments due to its high adhesion ability in different surfaces, playing an important role in the food industry. The aim of this study was to assess how the main stressing conditions, usually observed in meat processing facilities (sanitizers, NaCl, curing salts), interfere in L. monocytogenes adhesion and biofilm formation. The isolates, representatives of different L. monocytogenes lineages (n = 6) were subjected to four different sanitizers (S1: quaternary ammonium; S2: peracetic acid, hydrogen peroxide and glacial acetic acid, S3: biguanide polyhexamethylene hydrochloride, S4: hydrogen peroxide) to verify adhesion ability and susceptibility based on minimum inhibitory concentration (MIC). In addition, the isolates adhesion and biofilm were assessed up to 72 h under different conditions: sanitizers (MIC values), curing salts and NaCl (both at 5, 7·5, 10%), at different temperatures (4, 12 and 37°C). Despite the effectiveness of sanitizers, isolates presented higher biofilm development when compared to controls in the presence of quaternary ammonium (S1, 1: 1,024) at 4°C, over the tested time (P < 0·05). Furthermore, different responses were observed for the different L. monocytogenes strains tested, providing a better understanding of the persistence of this pathogen in the food processing facilities.

Genetic Subtyping, Biofilm-Forming Ability and Biocide Susceptibility of Listeria monocytogenes Strains Isolated from a Ready-to-Eat Food Industry

Listeria monocytogenes is a foodborne pathogen of special concern for ready-to-eat food producers. The control of its presence is a critical step in which food-grade sanitizers play an essential role. L. monocytogenes is believed to persist in food processing environments in biofilms, exhibiting less susceptibility to sanitizers than planktonic cells. This study aimed to test the susceptibility of L. monocytogenes in planktonic culture and biofilm to three commercial food-grade sanitizers and to benzalkonium chloride; together with the genetic subtyping of the isolates. L. monocytogenes isolates were collected from raw materials, final products and food-contact surfaces during a 6-year period from a ready-to-eat meat-producing food industry and genetically characterized. Serogrouping and pulsed-field gel electrophoresis (PFGE) revealed genetic variability and differentiated L. monocytogenes isolates in three clusters. The biofilm-forming ability assay revealed that the isolates were weak biofilm producers. L. monocytogenes strains were susceptible both in the planktonic and biofilm form to oxidizing and ethanol-based compounds and to benzalkonium chloride, but not to quaternary ammonium compound. A positive association of biofilm-forming ability and LD₉₀ values for quaternary ammonium compound and benzalkonium chloride was found. This study highlights the need for preventive measures improvement and for a conscious selection and use of sanitizers in food-related environments to control Listeria monocytogenes.