Antibiotic activities of the natural antimicrobial substance produced by Lactobacillus paracasei FX-6 against Pseudomonas putida

Polymethoxylated flavones from the leaves of Vitex negundo have fungal-promoting and antibacterial activities during the production of broad bean koji

Broad bean paste is a popular condiment in Asian countries. Leaves of Vitex negundo Linn. were used extensively in China during the koji-making of broad bean paste. Spreading V. negundo leaves on raw broad beans during fermentation was able to facilitate the rapid growth of fungi to form mature koji. We isolated two strains of fungi from mature koji, and four strains of bacteria from the rotten broad beans resulting from a failed attempt. According to microbial activity assays, two polymethoxylated flavones, 5-hydroxy-3,6,7,8,3',4'-hexamethoxy flavone (HJ-1) and 5,4'-dihydroxy-3,6,7,8,3'-pentamethoxy flavone (HJ-2) were isolated from V. negundo leaves, and the fungal growth promotion and inhibition of bacterial growth of these two compounds were found to improve the production of broad bean koji. This study reveals the compounds present in V. negundo leaves with bioactivity against important microbes in koji manufacture, and provides a theoretical basis for the application of V. negundo in broad bean paste production.

Antibacterial activity and mechanism of cell-free supernatants of Lacticaseibacillus paracasei against Propionibacterium acnes

Propionibacterium acnes (P. acnes) is an anaerobic and gram-positive bacterium involved in the pathogenesis and inflammation of acne vulgaris. This study particularly focuses on the antimicrobial effect of Lacticaseibacillus paracasei LPH01 against P. acnes, a bacterium that causes acne vulgaris. Fifty-seven Lactobacillus strains were tested for their ability to inhibit P. acnes growth employing the Oxford Cup and double dilution methods. The cell-free supernatant (CFS) of L. paracasei LPH01 demonstrated a strong inhibitory effect, with an inhibition zone diameter of 24.65 ± 0.27 mm and a minimum inhibitory concentration of 12.5 mg/mL. Among the CFS, the fraction over 10 kDa (CFS-10) revealed the best antibacterial effect. Confocal laser scanning microscopes and flow cytometry showed that CFS-10 could reduce cell metabolic activity and cell viability and destroy the integrity and permeability of the cell membrane. A scanning electron microscope revealed that bacterial cells exhibited obvious morphological and ultrastructural changes, which further confirmed the damage of CFS-10 to the cell membrane and cell wall. Findings demonstrated that CFS-10 inhibited the conversion of triglycerides, decreased the production of free fatty acids, and down-regulated the extracellular expression of the lipase gene. This study provides a theoretical basis for the metabolite of L. paracasei LPH01 as a potential antibiotic alternative in cosmeceutical skincare products.

Lacticaseibacillus paracasei fermentation broth identified peptide, Y2Fr, and its antibacterial activity on Vibrio parahaemolyticus

Although Vibrio parahaemolyticus infections cause severe diseases of large yellow croaker (Larimichthys crocea), using antibiotics and other chemical agents to treat these infections could result in antimicrobial resistance, environmental pollution, and other associated problems. This study identified seven peptides from Lacticaseibacillus paracasei fermentation broth using ultra-high-performance liquid chromatography-mass spectrometry and screened antimicrobial peptide Y2Fr (VEIKNGLLKLNGKPLLIR) through its net charge, hydrophobicity and predicted secondary structure. Antibacterial activity analysis revealed that Y2Fr had a minimum inhibitory concentration (MIC) of 125 μg/mL, minimum bactericidal concentration (MBC) of 250 μg/mL against V. parahaemolyticus and a time-kill of 3 h. In a bacterial membrane environment, the secondary structure of peptide Y2Fr changed from a random coil to a β-sheet to enhance its membrane permeability and binding to bacteria DNA to exert its antibacterial effect. Further molecular docking analysis revealed that peptide Y2Fr could bind to the membrane protein KKI11460.1 and DNA polymerase A0A0L8TVA4 of V. parahaemolyticus through hydrogen bonds. Meanwhile, treatment of Y2Fr with mammalian red blood cells and plasma revealed that it was noncytotoxic, nonhemolytic, and stable under physiological conditions. Thus, peptide Y2Fr has great potential use in treating and preventing infections caused by V. parahaemolyticus or similar bacteria in aquatic animals.

In Vitro and In Situ Characterization of Psychrotrophic Spoilage Bacteria Recovered from Chilled Chicken

Spoilage bacteria play a remarkable role in the spoilage of chilled chicken. In this paper, a total of 42 isolates belonging to 16 species of four genera were isolated from chilled chicken and displayed different characterizations of psychrotrophic spoilage. Six isolates of J7, J8, Q20, Q23, R1, and R9 with differences in proteolytic capabilities were further characterized for in situ spoilage potential evaluation. Pseudomonas lundensis J8 exhibited the strongest spoilage potential in situ, displaying a fast growth rate, increased pH velocity, high total volatile basic nitrogen, and high peptide content in the chicken samples. The volatile flavor analysis of chicken samples via electronic nose indicated that the content of characteristic odors representing spoilage, including sulfides, organic sulfide, and hydride, increased during storage. Additionally, the principle component and correlation analyses revealed that the spoilage odors produced by different species of bacteria were significantly different and positively correlated with the results of protease activity in vitro. The characteristics of spoilage bacteria in chilled chicken provided a comprehensive insight into microbial assessment during storage.

Antimicrobial activities and mechanism of sturgeon spermary protein extracts against Escherichia coli

This study aimed to evaluate the antimicrobial activities and mechanism of sturgeon spermary protein extracts (SSPE) against Escherichia coli. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined. Cell structural change was analyzed using scanning electron microscopy-energy dispersive X-ray spectrometry and transmission electron microscope. Moreover, pH, zeta potential, membrane potential, intracellular ATP concentrations and the interaction of SSPE with genomic DNA were analyzed. Results showed that molecular weight of SSPE is 13.4 kDa, the content of basic amino acids is the highest, in which arginine accounts for 73.2%. The MIC and MBC of SSPE for E. coli were 0.05 and 5 mg/mL, respectively. After SSPE treatment, cell membrane permeability changes, zeta potential decrease and genomic DNA lysis occurred in E. coli, which indicated it exerted bacteriostatic effects either independently or simultaneously by destroying the cell membrane and genomic DNA. These findings indicated that SSPE has potential to be a natural antiseptic.

Antibacterial Mechanism of Dellaglioa algida against Pseudomonas fluorescens and Pseudomonas fragi

Pseudomonas fluorescens (P. fluorescens) and Pseudomonas fragi (P. fragi), two kinds of psychrotrophic Pseudomonas species with pathogenicity, are likely to contaminate foods and cause diseases even in fairly cold environments, an outcome which should be suppressed. This paper investigates the antibacterial mechanisms of Dellaglioa algida (D. algida), a new type of low-temperature-resistant Lactobacillus, on two such Pseudomonas. By the enzyme treatment approach, the antibacterial substance existing in the cell-free supernatant (CFS) of D. algida is preliminarily determined as organic acid or protein; then, its inhibition effects are assessed under various culture environments, including pH value, salinity, and culture time, where the best antibacterial performance is achieved at pH = 6.00, S = 0%, and culture time = 48 h. A series of experiments on biofilms indicate that D. algida is not only able to inhibit the generation or damage the integrality of the biofilm of the two mentioned Pseudomonas, but also can reduce the motility, including swarming and swimming, of P. fragi and restrain the swarming of P. fluorescens. The aformentioned developed antibacterial mechanisms show the possibility of using D. algida in applications as an inhibitor for psychrotrophic Pseudomonas in the food industry, by virtue of its strong suppression capability, especially in cold environments.

The Complex Role of Lactic Acid Bacteria in Food Detoxification

Toxic ingredients in food can lead to serious food-related diseases. Such compounds are bacterial toxins (Shiga-toxin, listeriolysin, Botulinum toxin), mycotoxins (aflatoxin, ochratoxin, zearalenone, fumonisin), pesticides of different classes (organochlorine, organophosphate, synthetic pyrethroids), heavy metals, and natural antinutrients such as phytates, oxalates, and cyanide-generating glycosides. The generally regarded safe (GRAS) status and long history of lactic acid bacteria (LAB) as essential ingredients of fermented foods and probiotics make them a major biological tool against a great variety of food-related toxins. This state-of-the-art review aims to summarize and discuss the data revealing the involvement of LAB in the detoxification of foods from hazardous agents of microbial and chemical nature. It is focused on the specific properties that allow LAB to counteract toxins and destroy them, as well as on the mechanisms of microbial antagonism toward toxigenic producers. Toxins of microbial origin are either adsorbed or degraded, toxic chemicals are hydrolyzed and then used as a carbon source, while heavy metals are bound and accumulated. Based on these comprehensive data, the prospects for developing new combinations of probiotic starters for food detoxification are considered.

Bioactive Compounds from Kefir and Their Potential Benefits on Health: A Systematic Review and Meta-Analysis

Despite evidence of health benefits from kefir administration, a systematic review with meta-analysis on bioactive compounds associated with these benefits is still absent in the literature. Kefir is fermented milk resulting from the metabolism of a complex microbiota in symbiosis. Recent researches have investigated the bioactive compounds responsible for the preventive and therapeutic effects attributed to kefir. However, differences in functional potential between industrial and artisanal kefir are still controversial. Firstly, we identified differences in the microbial composition among both types of kefir. Available evidence concerning the action of different bioactive compounds from kefir on health, both from in vitro and in vivo studies, was subsequently summarized to draw a primary conclusion of the dose and the intervention time for effect, the producer microorganisms, the precursor in the milk, and the action mechanism. Meta-analysis was performed to investigate the statistically significant differences (P < 0.05) between intervention and control and between both types of kefir for each health effect studied. In summary, the bioactive compounds more commonly reported were exopolysaccharides, including kefiran, bioactive peptides, and organic acids, especially lactic acid. Kefir bioactive compounds presented antimicrobial, anticancer, and immune-modulatory activities corroborated by the meta-analysis. However, clinical evidence is urgently needed to strengthen the practical applicability of these bioactive compounds. The mechanisms of their action were diverse, indicating that they can act by different signaling pathways. Still, industrial and artisanal kefir may differ regarding functional potential-OR of 8.56 (95% CI: 2.27-32.21, P ≤ .001)-according to the observed health effect, which can be associated with differences in the microbial composition between both types of kefir.

Health-Promoting Properties of Lacticaseibacillus paracasei: A Focus on Kefir Isolates and Exopolysaccharide-Producing Strains

Among artisanal fermented beverages, kefir (fermented milk drink) and water kefir (fermented nondairy beverage) are of special interest because their grains can be considered natural reservoirs of safe and potentially probiotic strains. In the last years, several reports on Lacticaseibacillus paracasei (formerly Lactobacillus paracasei) isolated from both artisanal fermented beverages were published focusing on their health-promoting properties. Although this is not the predominant species in kefir or water kefir, it may contribute to the health benefits associated to the consumption of the fermented beverage. Since the classification of L. paracasei has been a difficult task, the selection of an adequate method for identification, which is essential to avoid mislabeling in products, publications, and some publicly available DNA sequences, is discussed in the present work. The last findings in health promoting properties of L. paracasei and the bioactive compounds are described and compared to strains isolated from kefir, providing a special focus on exopolysaccharides as effector molecules. The knowledge of the state of the art of Lacticaseibacillus paracasei from kefir and water kefir can help to understand the contribution of these microorganisms to the health benefits of artisanal beverages as well as to discover new probiotic strains for applications in food industry.