Listeria monocytogenes and Salmonella enterica affect the expression of nisin gene and its production by Lactococcus lactis

The mechanism of Enterococcus faecium on the virulence of Listeria monocytogenes during the storage of fermented sausages by whole genome analysis

This study investigated the safety characteristics and potential probiotic properties of Enterococcus faecium by using whole genome analysis, and then explored the effect of this strain on the virulence of Listeria monocytogenes in vitro and during the storage of fermented sausages. Results showed that E. faecium B1 presented enterocin A, B, and P, enterolysin A, and UviB, and the exotoxin related genes and exoenzyme related genes were not detected in the genome of E. faecium B1. However, the adherence genes including acm and scm were present in this strain, which also positively correlated with characteristics related to probiotic potential. In addition, E. faecium could adapt to the condition of fermented sausages, and decrease the survival of L. monocytogenes in vitro and in vivo. The expression of the virulence genes (prfA, hly, inlA, and inlB) and sigB-related genes (prli42, rsbT, rsbU, rsbV, rsbW, and sigB) were all inhibited by E. faecium B1 to different extents during the storage of fermented sausages at 4 °C. Moreover, compared with the E. faecium B1 group, the expression level of entA, entB, and entP genes of E. faecium B1 in the co-culture of fermented sausages was increased during the storage, which may be the inhibition mechanism of E. faecium B1 on L. monocytogenes. These results demonstrated that E. faecium B1 could potentially be used as bio-protection to control L. monocytogenes in meat products.

A review of potential antibacterial activities of nisin against Listeria monocytogenes: the combined use of nisin shows more advantages than single use

Listeria monocytogenes is a foodborne pathogen causing serious public health problems. Nisin is a natural antimicrobial agent produced by Lactococcus lactis and widely used in the food industry. However, the anti-L. monocytogenes efficiency of nisin might be decreased due to natural or acquired resistance of L. monocytogenes to nisin, or complexity of the food environment. The limitation of nisin as a bacteriostatic agent in food could be improved using a combination of methods. In this review, the physiochemical characteristics, species, bioengineered mutants, and antimicrobial mechanism of nisin are reviewed. Strategies of nisin combined with other antibacterial methods, including physical, chemical, and natural substances, and nanotechnology to enhance antibacterial effect are highlighted and discussed. Additionally, the antibacterial efficiency of nisin applied in real meat, dairy, and aquatic products is evaluated and analyzed. Among the various binding treatments, the combination with natural substances is more effective than the combination with physical and chemical methods. However, the combination of nisin and nanotechnology has more potential in terms of the impact on food quality.

Postbiotics as the new frontier in food and pharmaceutical research

Food is the essential need of human life and has nutrients that support growth and health. Gastrointestinal tract microbiota involves valuable microorganisms that develop therapeutic effects and are characterized as probiotics. The investigations on appropriate probiotic strains have led to the characterization of specific metabolic byproducts of probiotics named postbiotics. The probiotics must maintain their survival against inappropriate lethal conditions of the processing, storage, distribution, preparation, and digestion system so that they can exhibit their most health effects. Conversely, probiotic metabolites (postbiotics) have successfully overcome these unfavorable conditions and may be an appropriate alternative to probiotics. Due to their specific chemical structure, safe profile, long shelf-life, and the fact that they contain various signaling molecules, postbiotics may have anti-inflammatory, immunomodulatory, antihypertensive properties, inhibiting abnormal cell proliferation and antioxidative activities. Consequently, present scientific literature approves that postbiotics can mimic the fundamental and clinical role of probiotics, and due to their unique characteristics, they can be applied in an oral delivery system (pharmaceutical/functional foods), as a preharvest food safety hurdle, to promote the shelf-life of food products and develop novel functional foods or/and for developing health benefits, and therapeutic aims. This review addresses the latest postbiotic applications with regard to pharmaceutical formulations and commercial food-based products. Potential postbiotic applications in the promotion of host health status, prevention of disease, and complementary treatment are also reviewed.

In Vitro-In Vivo Correlation for the Antibacterial Effect of Lactiplantibacillus plantarum as a Topical Healer for Infected Burn Wound

Difficulties in delivering antimicrobial agents to wound areas and emersion of multiple drug resistant organisms (MDROs) have converted managing burn infections into a complicated task in medicine. Probiotics emerged not only as a probable solution for burn infections but also as an accelerator in the healing process. The probability of in vitro-in vivo correlation (IVIVC) in probiotic activity leads to lower costs in finding new therapeutic options. Simulated wound fluid (SWF) was used to evaluate the antibacterial function of Lactiplantibacillus plantarum in wounds. The growth parameters in SWF were evaluated using a logistic model to predict growth behavior in the wound area. In addition, probiotic antimicrobial activity and secretion of antibacterial substances in SWF were also studied. Data were used to select the initial dose and apply frequency for in vivo study. The wound models were infected by two main pathogens (Pseudomonas aeruginosa or Staphylococcus aureus). In vitro results showed less lag time associated with considerable acid production in SWF. In the following, secretion of antimicrobial substances and co-aggregation with pathogens became more important. The susceptibility of pathogens to these factors was different, and culture medium affected the yield of each factor involved in eliminating pathogens. Histological analysis and macroscopic examination of wounds revealed probiotics as effective as positive control or more. There were some differences in the antibacterial functions of probiotics in simulated and real wound environments. The in vitro effect of probiotics on removal of pathogens was not the same as the trend seen in vivo.

The effect of ultrasound treatment in combination with nisin on the inactivation of Listeria innocua and Escherichia coli

Ultrasound, alone or in combination with natural antimicrobials, is a novel food processing technology of interest to replace traditional food decontamination methods, as it is milder than classical sterilisation (heat treatment) and maintains desirable sensory characteristics. However, ultrasound efficacy can be affected by food structure/composition, as well as the order in which combined treatments are applied. More specifically, treatments which target different cell components could result in enhanced inactivation if applied in the appropriate order. The microbial properties i.e. Gram positive/Gram negative can also impact the treatment efficacy. This work presents a systematic study of the combined effect of ultrasound and nisin on the inactivation of the bacteria Listeria innocua (Gram positive) and Escherichia coli (Gram negative), at a range of cavitation conditions (44, 500, 1000 kHz). The order of treatment application was varied, and the impact of system structure was also investigated by varying the concentration of Xanthan gum used to create the food model systems (0 - 0.5% w/v). Microbial inactivation kinetics were monitored, and advanced microscopy and flow cytometry techniques were utilised to quantify the impact of treatment on a cellular level. Ultrasound was shown to be effective against E. coli at 500 kHz only, with L. innocua demonstrating resistance to all frequencies studied. Enhanced inactivation of E. coli was observed for the combination of nisin and ultrasound at 500 kHz, but only when nisin was applied before ultrasound treatment. The system structure negatively impacted the inactivation efficacy. The combined effect of ultrasound and nisin on E. coli was attributed to short-lived destabilisation of the outer membrane as a result of sonication, allowing nisin to penetrate the cytoplasmic membrane and facilitate cell inactivation.

A review on preparation and chemical analysis of postbiotics from lactic acid bacteria

Postbiotics may be defined as soluble metabolites released by food-grade microorganisms during the growth and fermentation in complex microbiological culture, food or gut. It is rich in high and low molecular weight biologically active metabolites. There are still gaps concerning these substances, mainly how to use them for food applications. Although the most recent work on preparation and application of postbiotics from several probiotics are very encouraging, the suitability of postbiotics to combat microorganisms that deal with food safety should be tested mainly by analyzing the chemical composition and conducting antagonistic tests. Consequently, foods can effectively benefit from an identified postbiotic with a defined effect. This review approached the recent advances in relation to the preparation of postbiotics from lactic acid bacteria. The function of different instrumental analysis techniques and factors affecting the chemical composition of postbiotics were also comprehensively reviewed.