Response of sensitive and resistant Listeria monocytogenes strains against bacteriocins produced by different Enterococcus spp. strains

Potential of enterocin from Enterococcus durans MF5 in controlling Listeria species

This research paper presents the characterization of an enterocin-producing Enterococcus durans MF5 isolate and the determination of the in vitro antilisterial activity of enterocin produced by this isolate, named Ent-MF5. PCR-based screening for bacteriocin biosynthetic genes revealed that E. durans MF5 harbors multiple enterocin-encoding genes (ent A, B, P and X), classified as class II bacteriocins and enterocin-P of Enterococcus faecium (sharing up to 99% similarity at the genetic level). E. durans MF5 is sensitive to eight clinically important antibiotics and does not possess cytolysin activator -cylA, gelatinase -gelE and hyaluronidase -hylA virulence genes. The antilisterial activity of Ent-MF5 was abolished by trypsin, α-chymotrypsin, protease and proteinase-K. Ent-MF5 showed thermal and pH stability. In addition, the activity of Ent-MF5 was unaffected in the presence of various surfactants (1% SDS, Triton X-100, Tween 20, and Tween 80). Ent-MF5 exhibited antimicrobial activity against Listeria monocytogenes, Listeria innocua, Listeria ivanovii and Listeria seeligeri at concentrations as low as 0.13 μg/ml. Ent-MF5 had a bactericidal effect against L. monocytogenes with a significant reduction in surviving cells at concentrations equal to or greater than 0.13 μg/ml. A 75-100% reduction in L. monocytogenes growth and bactericidal effect determined by CFU counts was observed following treatment with Ent-MF5 at 4.47 μg/ml at time points starting at 2 and 4 h, respectively. Ent-MF5 action is associated with Listeria cell membrane damage, as observed by flow cytometry and fluorescence microscopy. Thus, the effective antilisterial activity and stability of Ent-MF5 presents promising perspectives for application as biopreservatives in the food industry.

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.

Acetolactate Decarboxylase as an Important Regulator of Intracellular Acidification, Morphological Features, and Antagonism Properties in the Probiotic Lactobacillus reuteri

SCORE

This study identifies the coding gene (aldB) of acetolactate decarboxylase (ALDC) as an important regulatory gene of the intracellular pH in Lactobacillus reuteri (L. reuteri), uncovering the important role of ALDC in regulating intracellular pH, morphological features, and antagonism properties in the probiotic organism L. reuteri.

METHODS AND RESULTS

The aldB mutant (ΔaldB) of L. reuteri is established using the homologous recombination method. Compare to the wild-type (WT) strain, the ΔaldB strain shows a smaller body size, grows more slowly, and contains more acid in the cell cytoplasm. The survival rate of the ΔaldB strain is much lower in low pH and simulated gastric fluid (SGF) than that of the WT strain, but higher in simulated intestinal fluid (SIF). The antagonism test demonstrates the ΔaldB strain can inhibit Listeria monocytogenes (L. monocytogenes) and Salmonella more effectively than the WT strain. Additionally, there is a dramatic decrease in the adhesion rate of Salmonella to Caco-2 and HT-29 cells in the presence of the ΔaldB strain compared to the WT strain. Simultaneously analyze, the auto-aggregation, co-aggregation, cell surface hydrophobicity (CSH), hemolytic, temperature, NaCl, oxidative stress, and antibiotic susceptibility of the ΔaldB strain are consistent with the features of probiotics.

CONCLUSION

This study highlights that the aldB gene plays a significant role in the growth and antibacterial properties of L. reuteri.

Potential Impact of Combined Inhibition by Bacteriocins and Chemical Substances of Foodborne Pathogenic and Spoilage Bacteria: A Review

In recent years, food safety caused by foodborne pathogens and spoilage bacteria has become a major public health problem worldwide. Bacteriocins are a kind of antibacterial peptide synthesized by microbial ribosomes, and are widely used as food preservatives. However, when used individually bacteriocins may have limitations such as high cost of isolation and purification, narrow inhibitory spectrum, easy degradation by enzymes, and vulnerability to complex food environments. Numerous studies have demonstrated that co-treatment with bacteriocins and a variety of chemical substances can have synergistic antibacterial effects on spoilage microorganisms and foodborne pathogens, effectively prolonging the shelf life of food and ensuring food safety. Therefore, this paper systematically summarizes the synergistic bacteriostatic strategies of bacteriocins in combination with chemical substances such as essential oils, plant extracts, and organic acids. The impacts of bacteriocins when used individually and in combination with other chemical substances on different food substrates are clarified, and bacteriocin-chemical substance compositions that enhance antibacterial effectiveness and reduce the potential negative effects of chemical preservatives are highlighted and discussed. Combined treatments involving bacteriocins and different kinds of chemical substances are expected to be a promising new antibacterial method and to become widely used in both the food industry and biological medicine.