Reduction and Growth Inhibition of Listeria monocytogenes by Use of Anti-Listerial Nisin, P100 Phages and Buffered Dry Vinegar Fermentates in Standard and Sodium-Reduced Cold-Smoked Salmon

Impact of Nisin on Proliferation of Background Microbiota, Pressure-Stressed and Wild-Type Listeria monocytogenes, and Listeria innocua During a Real-Time Shelf-Life Study

With the rapid implementation of high-pressure processing in many sectors of the food industry, considerations associated with pressure-stressed microorganisms are emerging. Nisin was utilized in this study for controlling the proliferation of Listeria monocytogenes and L. innocua inoculated on cold-smoked trout during a 4-week refrigerated shelf-life trial. Wild-type and pressure-stressed phenotypes of Listeria were compared in this study. The pressure-stressed phenotypes were prepared by treating the surrogate strain and pathogen mixture at 103.4 MPa (15K PSI) for 20 min. L. monocytogenes multiplied extensively during the 4-week refrigerated trial and counts were increased (p < 0.05) from 3.68 ± 0.1 log CFU/g on the first week to 6.03 ± 0.1 log CFU/g. Both phenotypes and the surrogate microorganisms illustrated similar (p ≥ 0.05) multiplication trends. Unlike samples subjected to water treatment, nisin was effective (p < 0.05) in keeping the microbial counts lower compared with the controls, particularly earlier during the shelf-life trial. Our study illustrates that the selected surrogate microorganism has comparable sensitivity to nisin relative to L. monocytogenes and thus could be used interchangeably in future public health microbiology challenge studies with similar scope. Additionally, we observed that pressure-stressed L. monocytogenes has proliferation and sensitivity to nisin comparable to wild-type pathogen.

A Review on Recent Trends in Bacteriophages for Post-Harvest Food Decontamination

Infectious diseases resulting from unsafe food consumption are a global concern. Despite recent advances and control measures in the food industry aimed at fulfilling the growing consumer demand for high-quality and safe food products, infection outbreaks continue to occur. This review stands out by providing an overview of post-harvest food decontamination methods against some of the most important bacterial foodborne pathogens, with particular focus on the advantages and challenges of using phages, including their most recent post-harvest applications directly to food and integration into active food packaging systems, highlighting their potential in providing safer and healthier food products. The already approved commercial phage products and the numerous available studies demonstrate their antibacterial efficacy against some of the most problematic foodborne pathogens in different food products, reinforcing their possible use in the future as a current practice in the food industry for food decontamination. Moreover, the incorporation of phages into packaging materials holds particular promise, providing protection against harsh conditions and enabling their controlled and continuous release into the food matrix. The effectiveness of phage-added packaging materials in reducing the growth of pathogens in food systems has been well-demonstrated. However, there are still some challenges associated with the development of phage-based packaging systems that need to be addressed with future research.

Integrating Bacteriocins and Biofilm-Degrading Enzymes to Eliminate L. monocytogenes Persistence

Listeria monocytogenes is a Gram-positive bacterium causing listeriosis, a severe infection responsible for significant morbidity and mortality globally. Its persistence on food processing surfaces via biofilm formation presents a major challenge, as conventional sanitizers and antimicrobials exhibit limited efficacy against biofilm-embedded cells. This study investigates a novel approach combining an engineered polysaccharide-degrading enzyme (CAase) with a bacteriocin (thermophilin 110) produced by Streptococcus thermophilus. Laboratory assays evaluated the effectiveness of this combination in disrupting biofilms and inactivating L. monocytogenes on various surfaces. The results demonstrated that CAase effectively disrupts biofilm structures, while thermophilin 110 significantly reduces bacterial growth and viability. The preliminary trials indicate a dual-action approach offers a potential alternative to conventional treatments, enhancing food safety by effectively controlling Listeria biofilms in food processing environments.

Improving the Quality and Safety of Fish Products with Edible Coatings Incorporating Piscicolin CM22 from a Psychrotolerant Carnobacterium maltaromaticum Strain

The consumption of raw or smoked fish entails significant microbiological risks, including contamination by pathogens such as Listeria monocytogenes, which can cause severe foodborne illnesses. This study explores the preservative use of piscicolin CM22, a novel bacteriocin derived from the psychrotolerant strain Carnobacterium maltaromaticum CM22, in two types of edible coatings (EC): chitosan-based and fish gelatin-based. An initial in vitro characterization of the technological and antimicrobial properties of these ECs with and without bacteriocin was conducted. The efficacy of the edible coatings was subsequently evaluated through shelf life and challenge tests against L. monocytogenes in raw and smoked fish products. The results demonstrated significant antimicrobial activity, with the chitosan-based coating containing piscicolin CM22 being the most effective in reducing microbial counts and maintaining pH and color stability. Furthermore, in the challenge test studies, both ECs effectively controlled L. monocytogenes, showing significant reductions in bacterial counts compared to the controls in fresh tuna, salmon, and smoked salmon. The ECs containing piscicolin CM22 reduced Listeria counts by up to 4 log CFU/g in raw and smoked fish samples, with effective control in smoked salmon for up to 15 days at refrigeration temperature. While further research is required to fully assess their preservation potential, these findings strongly indicate that piscicolin CM22-functionalized edible coatings hold significant potential for improving the quality and safety of fish products.

Isolation and encapsulation of bacteriophage with chitosan nanoparticles for biocontrol of multidrug-resistant methicillin-resistant Staphylococcus aureus isolated from broiler poultry farms

This study was divided into two parts. The first part, the determination of methicillin-resistant Staphylococcus aureus (MRSA) prevalence in 25 broiler chicken farms, with the detection of multidrug resistant MRSA strains. The prevalence of MRSA was 31.8% (159 out of 500 samples) at the level of birds and it was 27% (27 out of 100) in the environmental samples. The highest antimicrobial resistance of the recovered MRSA strains was recorded to streptomycin (96%). All isolates (100%) had multidrug resistance (MDR) to four or more antibiotics with 16 distinct antibiotic resistant patterns, and multiple antibiotic resistance index (MARI) of 0.4-1. The second part, implementing novel biocontrol method for the isolated multidrug resistant MRSA strains through the isolation of its specific phage and detection of its survival rate at different pH and temperature degrees and lytic activity with and without encapsulation by chitosan nanoparticles (CS-NPs). Encapsulated and non-encapsulated MRSA phages were characterized using transmission electron microscope (TEM). Encapsulation of MRSA phage with CS-NPs increasing its lytic activity and its resistance to adverse conditions from pH and temperature. The findings of this study suggested that CS-NPs act as a protective barrier for MRSA phage for the control of multidrug resistant MRSA in broiler chicken farms.