Biofilm Formation of Listeria monocytogenes and Pseudomonas aeruginosa in a Simulated Chicken Processing Environment

Characterization of emetic Bacillus cereus biofilm formation and cereulide production in biofilm

Bacillus cereus is a well-known foodborne pathogen that can cause human diseases, including vomiting caused by emetic toxin, cereulide, requiring 105-108 cells per gram to cause the disease. The bacterial cells may be eliminated during processing, but cereulide can survive in most processing techniques due to its resistance to high temperatures, extreme pH and proteolytic enzymes. Herein, we reported dynamic processes of biofilm formation of four different types and cereulide production within the biofilm. Confocal laser scanning microscopy (CLSM) images revealed that biofilms of the four different types reach each stage at different time points. Among the extracellular polymeric substances (EPS) components of the four biofilms formed by the emetic B. cereus F4810/72 strain, proteins account for the majority. In addition, there are significant differences (p < 0.05) in the EPS components at the same stage among biofilms of different types. The time point at which cereulide was first detected in the four types of biofilms was 24 h. In the biofilm of B. cereus formed in ultra-high-temperature (UHT) milk, the first peak of cereulide appeared at 72 h. The cereulide content of the biofilms formed in BHI was mostly higher than that of the biofilms formed in UHT milk. This study contributes to a better understanding of food safety issues in the industry caused by biofilm and cereulide toxin produced by B. cereus.

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.

An Evaluation of the Sensitivity and Applicability of a Droplet Digital Polymerase Chain Reaction Assay to Simultaneously Detect Pseudomonas aeruginosa and Pseudomonas fragi in Foods

Achieving effective control over microbial contamination necessitates the precise and concurrent identification of numerous pathogens. As a common bacterium in the environment, Pseudomonas is rich in variety. It not only has pathogenic strains, but also spoilage bacteria that cause food spoilage. In this research, we devised a remarkably sensitive duplex droplet digital PCR (dddPCR) reaction system to simultaneously detect pathogenic Pseudomonas aeruginosa (P. aeruginosa) and spoilage Pseudomonas fragi (P. fragi). By employing comparative genomics, we identified four genes of P. fragi. Through a specific analysis, the RS22680 gene was selected as the detection target for P. fragi, and the lasR gene was chosen for P. aeruginosa, which were applied to construct a dddPCR reaction. In terms of specificity, sensitivity and anti-interference ability, the constructed dddPCR detection system was verified and analyzed. The assay showed excellent sensitivity and applicability, as evidenced by a limit of detection of 100 cfu/mL. When the concentration of natural background bacteria in milk or fresh meat was 100 times that of the target detection bacteria, the method was still capable of completing the absolute quantification. In the simulation of actual sample contamination, P. aeruginosa could be detected after 3 h of enrichment culture, and P. fragi could be detected after 6 h. The established dddPCR detection system exhibits exceptional performance, serving as a foundation for the simultaneous detection of various pathogenic bacteria in food products.

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.

Recent advances on the formation, detection, resistance mechanism, and control technology of Listeria monocytogenes biofilm in food industry

Listeria monocytogenes is an important foodborne pathogen that causes listeriosis, a severe and fatal condition. Biofilms are communities of microorganisms nested within a self-secreted extracellular polymeric substance, and they protect L. monocytogenes from environmental stresses. Biofilms, once formed, can lead to the persistence of L. monocytogenes in processing equipment and are therefore considered to be a major concern for the food industry. This paper briefly introduces the recent advancements on biofilm formation characteristics and detection methods, and focuses on analysis of the mechanism of L. monocytogenes biofilm resistance; Moreover, this paper also summarizes and discusses the existing different techniques of L. monocytogenes biofilm control according to the physical, chemical, biological, and combined strategies, to provide a theoretical reference to aid the choice of effective control technology in the food industry.

Propionate and Butyrate Inhibit Biofilm Formation of Salmonella Typhimurium Grown in Laboratory Media and Food Models

Salmonella is among the most frequently isolated foodborne pathogens, and biofilm formed by Salmonella poses a potential threat to food safety. Short-chain fatty acids (SCFAs), especially propionate and butyrate, have been demonstrated to exhibit a beneficial effect on promoting intestinal health and regulating the host immune system, but their anti-biofilm property has not been well studied. This study aims to investigate the effects of propionate or butyrate on the biofilm formation and certain virulence traits of Salmonella. We investigated the effect of propionate or butyrate on the biofilm formation of Salmonella enterica serovar Typhimurium (S. Typhimurium) SL1344 grown in LB broth or food models (milk or chicken juice) by crystal violet staining methods. Biofilm formation was significantly reduced in LB broth and food models and the reduction was visualized using a scanning electron microscope (SEM). Biofilm metabolic activity was attenuated in the presence of propionate or butyrate. Meanwhile, both SCFAs decreased AI-2 quorum sensing based on reporter strain assay. Butyrate, not propionate, could effectively reduce bacterial motility. Bacterial adhesion to and invasion of Caco-2 cells were also significantly inhibited in the presence of both SCFAs. Finally, two SCFAs downregulated virulence genes related to biofilm formation and invasion through real-time polymerase chain reaction (RT-PCR). These findings demonstrate the potential application of SCFAs in the mitigation of Salmonella biofilm in food systems, but future research mimicking food environments encountered during the food chain is necessitated.

Pseudomonas aeruginosa: A typical biofilm forming pathogen and an emerging but underestimated pathogen in food processing

Pseudomonas aeruginosa (P. aeruginosa) is a notorious gram-negative pathogenic microorganism, because of several virulence factors, biofilm forming capability, as well as antimicrobial resistance. In addition, the appearance of antibiotic-resistant strains resulting from the misuse and overuse of antibiotics increases morbidity and mortality in immunocompromised patients. However, it has been underestimated as a foodborne pathogen in various food groups for instance water, milk, meat, fruits, and vegetables. Chemical preservatives that are commonly used to suppress the growth of food source microorganisms can cause problems with food safety. For these reasons, finding effective, healthy safer, and natural alternative antimicrobial agents used in food processing is extremely important. In this review, our ultimate goal is to cover recent advances in food safety related to P. aeruginosa including antimicrobial resistance, major virulence factors, and prevention measures. It is worth noting that food spoilage caused by P. aeruginosa should arouse wide concerns of consumers and food supervision department.