Evaluation of Bactericidal Effects of Phenyllactic Acid on Escherichia coli O157:H7 and Salmonella Typhimurium on Beef Meat

Antifungal mechanism of phenyllactic acid against Mucor investigated through proteomic analysis

The primary inhibitory targets of phenyllactic acid (PLA, including D-PLA and L-PLA) on Mucor were investigated using Mucor racemosus LD3.0026 isolated from naturally spoiled cherry, as an indicator fungi. The results demonstrated that the minimum inhibitory concentration (MIC) of PLA against Mucor was 12.5 mmol·L-1. Results showed that the growing cells at the tip of the Mucor were not visibly deformed, and there was no damage to the cell wall following PLA treatment; however, PLA damaged the cell membrane and internal structure. The results of isobaric tags for relative and absolute quantification (iTRAQ) indicated that the Mucor mitochondrial respiratory chain may be the target of PLA, potentially inhibiting the energy supply of Mucor. These results indicate that the antifungal mechanism of PLA against mold is independent of its molecular configuration. The growth of Mucor is suppressed by PLA, which destroys the organelle structure in the mycelium and inhibits energy metabolism.

Transcriptomic analyses of Vibrio parahaemolyticus under the phenyllactic acid stress

Phenyllactic acid (PLA) generally recognized as a natural organic acid shows against Vibrio parahaemolyticus activity. In this study, V. parahaemolyticus ATCC17802 (Vp17802) was cultured under the stress of 1/2MIC PLA, and then the antibacterial mechanisms were explored via transcriptomics. The minimum inhibitory concentration (MIC) of PLA against Vp17802 was 3.2 mg/mL, and the time-kill analysis resulted that Vp17802 was inhibited. PLA was able to destroy the bacterial membrane, leading to the leakage of intracellular substances and decline of ATP levels. The RNA-sequencing analysis results indicated that 1616 significantly differentially expressed genes were identified, among which 190 were up-regulated and 1426 were down-regulated. Down-regulation of the icd2 gene in the TCA cycle mediates blockage of tyrosine metabolic, arginine biosynthesis, and oxidative phosphorylation, causing insufficient energy supply of Vp17802. Moreover, PLA could cause amino acids, metal ions, and phosphate transporters to be blocked, affecting the acquisition of nutrients. The treatment by PLA altered the expression of genes encoding functions involved in quorum sensing, flagellar assembly, and cell chemotaxis pathway, which may be interfering with the biofilm formation in Vp17802, reducing cell motility. Overall, 1.6 mg/mL PLA inhibited the growth of Vp17802 by disrupting to uptake of nutrients, cell metabolism, and the formation of biofilms. The results suggested a new direction for exploring the activity of PLA against Vp17802 and provided a theoretical basis for bacterial pathogen control in the food industry. KEY POINTS: •RNA sequencing was carried out to indicate the antibacterial mechanism of Vp17802. •The icd2 gene in the TCA cycle mediates blockage of metabolic of Vp17802. •The biofilm formation has interfered with 1.6 mg/mL PLA, which could reduce cell motility and virulence.

Antibacterial efficacy of phenyllactic acid against Pseudomonas lundensis and Brochothrix thermosphacta and its synergistic application on modified atmosphere/air-packaged fresh pork loins

Microbial contamination is a crucial problem that is difficult to solve for the meat industry. Therefore, this study explored the antibacterial efficacy of phenyllactic acid (PLA) against Pseudomonas lundensis (PL) and Brochothrix thermosphacta (BT) solely and in combination (PL + BT). It also provided insights into its synergistic preservation effect during inoculation in chilled (4 °C) fresh pork loins under air (AP) and modified atmosphere packaging (MAP). The minimum inhibitory concentration (MIC) of PLA was 10 mg/mL. Growth kinetics, scanning electron microscopy (SEM), zeta potential, and cell viability investigations showed that PLA treatment exhibited reduced bacterial growth, aided morphological alterations, and leakage in cell membrane integrity in vitro. Nonetheless, PLA and MAP (70 %N2/30 %CO2) showed an excellent synergistic antibacterial ability against spoilage indicators(total glucose, pH, TVB-N, and TBARS), bacterial counts than AP, without impairing organoleptic acceptability. These results demonstrate the broad antibacterial efficacy of PLA as a biopreservative for the meat industry.

Rapid detection of Shiga-toxin-producing Escherichia coli O157:H7 based on a colorimetric loop-mediated isothermal amplification (cLAMP) assay using a molecular beacon paired with HRPzyme

Contamination by Escherichia coli O157:H7 is considered a threat in the livestock and food industries. Therefore, it is necessary to develop methods for the convenient and rapid detection of Shiga-toxin-producing E. coli O157:H7. This study aimed to develop a colorimetric loop-mediated isothermal amplification (cLAMP) assay using a molecular beacon to rapidly detect E. coli O157:H7. Primers and a molecular beacon were designed for targeting the Shiga-toxin-producing virulence genes (stx1 and stx2) as molecular markers. Additionally, Bst polymerase concentration and amplification conditions for bacterial detection were optimized. The sensitivity and specificity of the assay were also investigated and validated on artificially tainted (100-104 CFU/g) Korean beef samples. The cLAMP assay could detect 1 × 101 CFU/g at 65 °C for both genes, and the assay was confirmed to be specific for E. coli O157:H7. The cLAMP takes about an hour and does not require expensive devices (e.g., thermal cycler and detector). Hence, the cLAMP assay proposed herein can be used in the meat industry as a fast and simple way to detect E. coli O157:H7.

Effect of Alcaligenes sp. on corrosion behavior of X65 steel in simulated offshore oilfield-produced water

In this paper, the effect of Alcaligenes sp. on the corrosion process of X65 steel was investigated by using non-targeted metabolomics techniques for comprehensive characterization of metabolites, combined with surface analysis techniques and electrochemical testing. The results showed that the organic acids produced by Alcaligenes sp. accelerated the corrosion process of X65 steel in the early stage, and the presence of Alcaligenes sp. promoted the deposition of stable corrosion products and minerals in the middle and late stages. In addition, proteoglycans and corrosion inhibiting substances were enriched on the metal surface, which enhanced the stability of the film. The combined effect of multiple factors makes the mixed film of biofilm and corrosion products more dense and complete, which effectively inhibits the corrosion of X65 steel.

Recent development of phenyllactic acid: physicochemical properties, biotechnological production strategies and applications

Phenyllactic acid (PLA) is capable of inhibiting the growth of many microorganisms, showing a broad-spectrum antimicrobial property, which allows it to hold vast applications in the: food, feed, pharmaceutical, and cosmetic industries, especially in the field of food safety. Recently, the production of PLA has garnered considerable attention due to the increasing awareness of food safety from the public. Accordingly, this review mainly updates the recent development for the production of PLA through microbial fermentation and whole-cell catalysis (expression single-, double-, and triple-enzyme) strategies. Firstly, the: physicochemical properties, existing sources, and measurement methods of PLA are systematically covered. Then, the inhibition spectrum of PLA is summarized, and synchronously, the antimicrobial and anti-biofilm mechanisms of PLA on commonly pathogenic microorganisms in foods are described in detail, thereby clarifying the reason for extending the shelf life of foods. Additionally, the factors affecting the production of PLA are summarized from the biosynthesis and catabolism pathway of PLA in microorganisms, as well as external environmental parameters insights. Finally, the downstream treatment process and applications of PLA are discussed and outlined. In the future, clinical data should be supplemented with the metabolic kinetics of PLA in humans and to evaluate animal toxicology, to enable regulatory use of PLA as a food additive. A food-grade host, such as Bacillus subtilis and Lactococcus lactis, should also be developed as a cell vector expressing enzymes for PLA production from a food safety perspective.

Coenzyme self-sufficiency system-recent advances in microbial production of high-value chemical phenyllactic acid

Phenyllactic acid (PLA), a natural antimicrobial substance, has many potential applications in the food, animal feed, pharmaceutical and cosmetic industries. However, its production is limited by the complex reaction steps involved in its chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, enzymatic or whole-cell catalysis was developed as an alternative method for PLA production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value PLA. Specially, the advantages and disadvantages of the using of the three kinds of substrates, which includes phenylpyruvate, phenylalanine and glucose as starting materials by natural or engineered microbes is summarized. Notably, the bio-conversion of PLA often requires the consumption of expensive coenzyme NADH. To overcome the issues of NADH regeneration, efficiently internal cofactor regeneration systems constructed by co-expressing different enzyme combinations composed of lactate dehydrogenase with others for enhancing the PLA production, as well as their possible improvements, are discussed. In particular, the construction of fusion proteins with different linkers can achieve higher PLA yield and more efficient cofactor regeneration than that of multi-enzyme co-expression. Overall, this review provides a comprehensive overview of PLA biosynthesis pathways and strategies for increasing PLA yield through biotechnology, providing future directions for the large-scale commercial production of PLA and the expansion of downstream applications.

Redefining methods for augmenting lactic acid bacteria robustness and phenyllactic acid biocatalysis: Integration valorizes simplicity

The production of phenyllactic acid (PLA) has been reported by several researchers, but so far, no mention has been made of augmented PLA production using an orchestrated assembly of simple techniques integrated to improve lactic acid bacteria (LAB) metabolism for the same. This review summarizes sequentially tailoring LAB growth and metabolism for augmented PLA catalysis through several strategies like monitoring LAB sustenance by choosing appropriate starter PLA-producing LAB strains isolated from natural environments, with desirably fastidious growth rates, properties like acidification, proteolysis, bacteriophage-resistance, aromatic/texturing-features, etc.; entrapping chosen LAB strains in novel cryogels and/or co-cultivating two/more LAB strains to improve their biotransformation potential and promote growth dependency/sustainability; adopting adaptive evolution methods designed to improve LAB strains under selection pressure inducing desired phenotypes tolerant to stress factors like heat, salt, acid, and solvent; monitoring physico-chemical LAB fermentation factors like temperature, pH, dissolved oxygen content, enzymes, and cofactors for PLA biosynthesis; and modulating purification/downstream processes to extract substantial PLA yields. This review paper serves as a comprehensive preliminary guide that can evoke a strategic experimental plan to produce industrial-scale PLA yields using simple techniques orchestrated together in the pursuit of conserving time, effort, and resources.

3-Phenyllactic acid generated in medicinal plant extracts fermented with plant-derived lactic acid bacteria inhibits the biofilm synthesis of Aggregatibacter actinomycetemcomitans

In the present study, the effect of PLA on a periodontic pathogen, Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans), the biofilm, and virulence-related genes was investigated. We confirmed that two lactic acid bacteria (LAB) strains isolated from plant sources, Lactiplantibacillus plantarum MSC-C2 and Pediococcus pentosaceus K40, secrete PLA into the de Man, Rogosa & Sharpe (MRS) broth when supplemented with phenyl pyruvic acid (PPA) as a precursor to PLA. Moreover, PLA was generated in the fermentation broths of two medicinal plant extracts, Paeonia lactiflora Pall (PR) and Carthamus tinctorius (CT), when used by each LAB strain and each extract supplemented with PPA. We determined that the minimum inhibitory concentration (MIC) of PLA against A. actinomycetemcomitans was 20 mM. PLA significantly decreased biofilm formation and suppressed the transcription of pgA, ltxA, and cdtB genes, which encode the poly-N-acetylglucosamine (PGA) polysaccharide of biofilm matrix and exotoxins leukotoxin and cytolethal distending toxin (CDT), respectively. The PLA produced by the MSC-C2 and K40 strains was increased several times by the addition of PPA to the MRS broth. The anti-biofilm effect of the extracts from the fermentation broth was proportional to the increasing PLA concentration, while a cumulatively higher effect than that of PLA alone suggested a combinational effect of PLA and the other metabolites, such as lactic acid (LA). Among the two medicinal plants, PLA, produced after the addition of PPA, was higher in PR extract in case of both the LAB strains. PLA production by the MSC-C2 strain in the PR extract reached 4.8 ± 0.23 mM, which was obviously higher than that in the MRS broth (3.88 ± 0.12 mM) supplemented with 1 mg/ml PPA. The activity to inhibit biofilm formation in the fermented PR extract was clearly high. PLA formed in the fermented PR extract downregulated the dispersin B encoding the dspB gene together with pgA, ltxA, and cdtB. In conclusion, this study shows a promising activity of PLA against the A. actinomycetemcomitans biofilm and virulence genes. In addition, the combinational effect of PLA and the medicinal plant extract can be achieved by fermentation with a specific plant-derived LAB strain.

Analysis of scenarios to reduce the probability of acquiring hemolytic uremic syndrome associated with beef consumption

The objective of this study was to develop a quantitative microbial risk assessment (QMRA) model to evaluate potential risk mitigation strategies to reduce the probability of acquiring hemolytic uremic syndrome (HUS) associated with beef consumption in Argentina. Five scenarios were simulated to evaluate the effect of interventions on the probability of acquiring HUS from Shiga toxin-producing Escherichia coli (STEC)-contaminated ground beef and commercial hamburger consumption. These control strategies were chosen based on previous results of the sensitivity analysis of a baseline QMRA model ( Brusa et al., 2020). The application of improvement actions in abattoirs not applying Hazard Analysis and Critical Control Points (HACCP) for STEC would result 7.6 times lower in the probability that consumers acquired HUS from ground beef consumption, while the implementation of improvements in butcher shops would lead to a smaller reduction. In abattoirs applying HACCP for STEC, the risk of acquiring HUS from commercial hamburger consumption was significantly reduced. Treatment with 2% lactic acid, hot water and irradiation reduced 4.5, 3.5 and 93.1 times the risk of HUS, respectively. The most efficient interventions, in terms of case reduction, being those that are applied in the initial stages of the meat chain.

Some Important Metabolites Produced by Lactic Acid Bacteria Originated from Kimchi

Lactic acid bacteria (LAB) have been used for various food fermentations for thousands of years. Recently, LAB are receiving increased attention due to their great potential as probiotics for man and animals, and also as cell factories for producing enzymes, antibodies, vitamins, exopolysaccharides, and various feedstocks. LAB are safe organisms with GRAS (generally recognized as safe) status and possess relatively simple metabolic pathways easily subjected to modifications. However, relatively few studies have been carried out on LAB inhabiting plants compared to dairy LAB. Kimchi is a Korean traditional fermented vegetable, and its fermentation is carried out by LAB inhabiting plant raw materials of kimchi. Kimchi represents a model food with low pH and is fermented at low temperatures and in anaerobic environments. LAB have been adjusting to kimchi environments, and produce various metabolites such as bacteriocins, γ-aminobutyric acid, ornithine, exopolysaccharides, mannitol, etc. as products of metabolic efforts to adjust to the environments. The metabolites also contribute to the known health-promoting effects of kimchi. Due to the recent progress in multi-omics technologies, identification of genes and gene products responsible for the synthesis of functional metabolites becomes easier than before. With the aid of tools of metabolic engineering and synthetic biology, it can be envisioned that LAB strains producing valuable metabolites in large quantities will be constructed and used as starters for foods and probiotics for improving human health. Such LAB strains can also be useful as production hosts for value-added products for food, feed, and pharmaceutical industries. In this review, recent findings on the selected metabolites produced by kimchi LAB are discussed, and the potentials of metabolites will be mentioned.

Phenyl lactic acid alleviates Samonella Typhimurium-induced colitis via regulating microbiota composition, SCFA production and inflammatory responses

Colitis caused by non-typhoidal Salmonella (NST) infection is increasingly serious and widespread, so new effective treatment strategies with little or no side-effects are urgently needed. Our previous research found that phenyl lactic acid (PLA) derived from Lactobacillus plantarum ZJ316 can effectively inhibit Salmonella enterica Typhimurium (S. Typhimurium). In this study, we further investigated the protective effects of this PLA against S. Typhimurium-induced colitis in mice. An infection model was established using female C57BL/6J mice by oral administration of 109 CFU mL-1 of S. Typhimurium, and PLA was supplied for 10 days after infection. In colitic mice, PLA administration reduced the disease activity index, prevented the colon shortening and spleen enlargement, decreased liver enzyme (AST and ALT) activities, and alleviated the colonic tissue damage. RT-qPCR analysis showed that PLA significantly down-regulated the levels of NF-κB, TLR4 and pro-inflammatory cytokines (IFN-γ, IL-1β and TNF-α), but stimulated the mRNA expression of the anti-inflammatory cytokine IL-10. Changes in intestinal microecology were analyzed by 16S rRNA sequencing. PLA modulated colonic microbiota dysbiosis by increasing the abundance of Lactobacillus, Butyricicoccus and Roseburia, and reducing Salmonella and Alloprevotella at the genus level. In addition, PLA significantly increased the concentrations of short-chain fatty acids (SCFAs) in the colon, especially propionic acid and butyric acid. These findings revealed that PLA has potential benefits on alleviating S. Typhimurium-induced colitis mainly through intestinal microbiota regulation and inflammation elimination, providing a new perspective for the NTS infection treatment strategy.