Assessment of the in vitro bioactive properties of lactic acid bacteria isolated from native ecological niches of Ecuador

Transcriptomic Analysis Revealed Antimicrobial Mechanisms of Lactobacillus rhamnosus SCB0119 against Escherichia coli and Staphylococcus aureus

Lactic acid bacteria were reported as a promising alternative to antibiotics against pathogens. Among them, Lactobacillus rhamnosus could be used as probiotics and inhibit several pathogens, but its antibacterial mechanisms are still less known. Here, L. rhamnosus SCB0119 isolated from fermented pickles could inhibit bacterial growth or even cause cell death in Escherichia coli ATCC25922 and Staphylococcus aureus ATCC6538, which was mainly attributed to the cell-free culture supernatant (CFS). Moreover, CFS induced the accumulation of reactive oxygen species and destroyed the structure of the cell wall and membrane, including the deformation in cell shape and cell wall, the impairment of the integrity of the cell wall and inner membrane, and the increases in outer membrane permeability, the membrane potential, and pH gradient in E. coli and S. aureus. Furthermore, the transcriptomic analysis demonstrated that CFS altered the transcripts of several genes involved in fatty acid degradation, ion transport, and the biosynthesis of amino acids in E. coli, and fatty acid degradation, protein synthesis, DNA replication, and ATP hydrolysis in S. aureus, which are important for bacterial survival and growth. In conclusion, L. rhamnosus SCB0119 and its CFS could be used as a biocontrol agent against E. coli and S. aureus.

Antagonistic activity and mechanism of Lactobacillus rhamnosus SQ511 against Salmonella enteritidis

Salmonella enteritidis is an important food-borne pathogen. The use of antibiotics is a serious threat to animal and human health, owing to the existence of resistant strains and drug residues. Lactic acid bacteria, as a new alternative to antibiotics, has attracted much attention. In this study, we investigated the antibacterial potential and underlying mechanism of Lactobacillus rhamnosus SQ511 against S. enteritidis ATCC13076. The results revealed that L. rhamnosus SQ511 significantly inhibited S. enteritidis ATCC13076 growth or even caused death. Laser confocal microscopic imaging revealed that the cell-free supernatant (CFS) of L. rhamnosus SQ511 elevated the reactive oxygen species level and bacterial membrane depolarization in S. enteritidis ATCC13076, leading to cell death. Furthermore, L. rhamnosus SQ511 CFS had severely deleterious effects on S. enteritidis ATCC13076, causing membrane destruction and the release of cellular materials. In addition, L. rhamnosus SQ511 CFS significantly reduced the expression of virulence, motility, adhesion, and invasion genes in S. enteritidis ATCC13076 (P < 0.05), and considerably inhibited motility and biofilm formation capacity (P < 0.05). Thus, antimicrobial compounds produced by L. rhamnosus SQ511 strongly inhibited S. enteritidis growth, mobility, biofilm formation, membrane disruption, and reactive oxygen species generation, and regulated virulence-related gene expressions, presenting promising applications as a probiotic agent.

Probiotic Characteristics and Antimicrobial Potential of a Native Bacillus subtilis Strain Fa17.2 Rescued from Wild Bromelia sp. Flowers

In the present study, we identified the Bacillus subtilis strain annotated Fa17.2 isolated from Bromelia flower inflorescences collected from the subtropical humid mesothermal region, Santo Domingo de Los Tsachilas Province, Ecuador. The probiotic capacity and antimicrobial potential against four foodborne pathogens were assessed. The cell culture of Fa17.2 is highly resistant to synthetic gastric acid (pH 2.5, 3.0, and 3.5), bile salts (0.3%), tolerating different sodium chloride concentrations (1, 3, and 5%), and growth conditions (15 °C and 45 °C), suggesting its potential probiotic features. The isolate showed no antibiotic resistance and was considered safe as no hemolysis was detected on sheep blood agar. The optimum medium for bacterial growth and the release of antimicrobial compounds was MRS with 10% glucose. The active components released in the neutralized crude extract (NCE) were insensitive to organic solvents, surfactants, and nonproteolytic enzymes and sensitive to proteolytic enzymes suggesting their proteinaceous nature. The antimicrobial activity was enhanced by heat and maintained active over a wide range of pH (2.0–8.0). Moreover, the crude extract (CE) showed inhibitory activity against several Gram-negative and Gram-positive bacteria. The molecular weight of partially purified precipitated bacteriocin-like substances (BLISs) was about 14 kDa in 20% Tricine-SDS-PAGE. The CE obtained from Fa17.2 inhibits the growth of four foodborne pathogens, Staphylococcus aureus, Escherichia coli, Kosaconia cowanii, and Shigella dysenteriae, which implies its potential as an antimicrobial producer strain.

Decoding the Gene Variants of Two Native Probiotic Lactiplantibacillus plantarum Strains through Whole-Genome Resequencing: Insights into Bacterial Adaptability to Stressors and Antimicrobial Strength

In this study, whole-genome resequencing of two native probiotic Lactiplantibacillus plantarum strains—UTNGt21A and UTNGt2—was assessed in order to identify variants and perform annotation of genes involved in bacterial adaptability to different stressors, as well as their antimicrobial strength. A total of 21,906 single-nucleotide polymorphisms (SNPs) were detected in UTNGt21A, while 17,610 were disclosed in the UTNGt2 genome. The comparative genomic analysis revealed a greater number of deletions, transversions, and transitions within the UTNGt21A genome, while a small difference in the number of insertions was detected between the strains. A divergent number of types of variant annotations were detected in both strains, and categorized in terms of low, moderate, and high modifier impact on the protein effectiveness. Although both native strains shared common specific genes involved in the stress response to the gastrointestinal environment, which may qualify as a putative probiotic (bile salt, acid, temperature, osmotic stress), they were different in their antimicrobial gene cluster organization, with UTNGt21A displaying a complex bacteriocin gene arrangement and dissimilar gene variants that might alter their defense mechanisms and overall inhibitory capacity. The genome comparison revealed 34 and 9 genomic islands (GIs) in the UTNGt21A and UTNGt2 genomes, respectively, with the overrepresentation of genes involved in defense mechanisms and carbohydrate utilization. In addition, pan-genome analysis disclosed the presence of various strain-specific genes (shell genes), suggesting a high genome variation between strains. This genome analysis illustrates that the bacteriocin signature and gene variants reflect a niche-inherent pattern. These extensive genomic datasets will guide us to understand the potential benefits of the native strains and their utility in the food or pharmaceutical sectors.

First characterization of the probiotic potential of lactic acid bacteria isolated from Costa Rican pineapple silages

Background

Agro-industrial waste from tropical environments could be an important source of lactic acid bacteria (LAB) with probiotic potential.

Methods

Twelve LAB isolates were isolated from pineapple silages. The species identification was carried out considering 16S rRNA and pheS genes. Experiments to evaluate the probiotic potential of the isolates included survival under simulated gastrointestinal environment, in vitro antagonistic activity (against Salmonella spp. and Listeria monocytogenes), auto-aggregation assays, antibiotic susceptibility, presence of plasmids, adhesiveness to epithelial cells, and antagonistic activity against Salmonella in HeLa cells.

Results

Lacticaseibacillus paracasei, Lentilactobacillus parafarraginis, Limosilactobacillus fermentum, and Weissella ghanensis were identified. Survival of one of the isolates was 90% or higher after exposure to acidic conditions (pH: 2), six isolates showed at least 61% survival after exposure to bile salts. The three most promising isolates, based on survivability tests, showed a strong antagonistic effect against Salmonella. However, only L. paracasei_6714 showed a strong Listeria inhibition pattern; this isolate showed a good auto-aggregation ability, was resistant to some of the tested antibiotics but was not found to harbor plasmids; it also showed a high capacity for adhesion to epithelial cells and prevented the invasion of Salmonella in HeLa cells. After further in vivo evaluations, L. paracasei_6714 may be considered a probiotic candidate for food industry applications and may have promising performance in acidic products due to its origin.

The probiotic potential of Lactobacillus plantarum strain RW1 isolated from canine faeces

AIM

To evaluation the probiotic potential of Lactobacillus plantarum strain RW1 isolated from healthy dogs for its further utilization as a dietary supplement for dogs.

METHODS AND RESULTS

This study aimed to evaluate the probiotic potential of L. plantarum strain RW1 isolated from canine faeces. After confirming by conventional and then by 16S rRNA sequencing, the identified strain RW1 was in vitro screened for its survivability in simulated gastrointestinal conditions, low pH, bile salts and adhesion to gut epithelial tissues, growth inhibitory effects on common pathogens and anti-inflammatory potential by measuring the mRNA expression level of IL-6, IL-8, IL-1ꞵ in Salmonella-infected MODE-K cells. Furthermore, the effects on epithelial barrier function and host defensin peptide (beta-defensin 3) was studied by measuring the mRNA expression level of tight junction protein (occludin) and beta-defensin 3 in MODE-K cells. The strain RW1 showed a considerable potential to survive in simulated gastrointestinal environmental conditions, low pH and high bile salt concentrations along with good adhesion to MODE-K cell line. Pathogenic bacterial growth and their adhesion to MODE-K cell line were significantly inhibited by the strain RW1. Real-time PCR analyses demonstrated that the strain RW1 inhibited Salmonella-induced pro-inflammatory cytokines (IL-6, IL-8 and IL-1ꞵ) production and reinforced the expression of tight junction protein (occludin). The strain RW1 did not induce mRNA expression of beta-defensin 3.

CONCLUSION

Based on in vitro results, the strain RW1 has the potential to be used as a probiotic supplement in dogs. However, further study involving in vivo health effects is needed.

SIGNIFICANCE AND IMPACT OF THE STUDY

Antibiotics have many side effects and nowadays the probiotics are considered as a potential alternative to antibiotics. This study evaluates the probiotic potential of dog isolated L. plantarum strain RW1 to use it as a dietary supplement in dogs feeding to control infectious diseases.

Evaluation of the probiotic and functional potential of Lactobacillus agilis 32 isolated from pig manure

Escherichia coli is a symbiotic bacterium in humans and animals and an important pathogen of humans and animals. Prevention and suppression of E. coli infection is of great concern. In this study, we isolated a strain of Lactobacillus agilis 32 from pig manure and evaluated its biological characteristics, and found that its bacterial survival rate was 25% after 4 h of treatment at pH 2, and under the condition of 0·5% bile concentration, its survival rate exceeds 30%. In addition, L. agilis 32 has a cell surface hydrophobicity of 77·8%, and exhibits 67·1% auto-aggregation and 63·2% aggregation with Enterotoxigenic E. coli 10 (ETEC 10). FITC fluorescence labelling showed that the fluorescence intensity of cecum was significantly higher than that of duodenum, jejunum or colon (P < 0·05), but no significant difference from ileum. Lactobacillus agilis 32 bacterial culture and CFS showed average inhibition zone diameters of 14·2 and 15·4 mm respectively. Lactobacillus agilis 32 CFS treatment can significantly reduce the pathogenicity of ETEC 10. These results show that L. agilis 32 is an active and potential probiotic, and it has a good antibacterial effect on ETEC10, which provides basic research for probiotics to prevent and treat intestinal diarrhoea pathogen infection.

A Novel Weissella cibaria Strain UTNGt21O Isolated from Wild Solanum quitoense Fruit: Genome Sequence and Characterization of a Peptide with Highly Inhibitory Potential toward Gram-Negative Bacteria

A novel Weissella cibaria strain UTNGt21O from the fruit of the Solanum quitoense (naranjilla) shrub produces a peptide that inhibits the growth of both Salmonella enterica subsp. enterica ATCC51741 and Escherichia coli ATCC25922 at different stages. A total of 31 contigs were assembled, with a total length of 1,924,087 bases, 20 contig hits match the core genome of different groups within Weissella, while for 11 contigs no match was found in the database. The GT content was 39.53% and the genome repeats sequences constitute around 186,760 bases of the assembly. The UTNGt21O matches the W. cibaria genome with 83% identity and no gaps (0). The sequencing data were deposited in the NCBI Database (BioProject accessions: PRJNA639289). The antibacterial activity and interaction mechanism of the peptide UTNGt21O on target bacteria were investigated by analyzing the growth, integrity, and morphology of the bacterial cells following treatment with different concentrations (1×, 1.5× and 2× MIC) of the peptide applied alone or in combination with chelating agent ethylenediaminetetraacetic acid (EDTA) at 20 mM. The results indicated a bacteriolytic effect at both early and late target growth at 3 h of incubation and total cell death at 6 h when EDTA was co-inoculated with the peptide. Based on BAGEL 4 (Bacteriocin Genome Mining Tool) a putative bacteriocin having 33.4% sequence similarity to enterolysin A was detected within the contig 12. The interaction between the peptide UTNGt21O and the target strains caused permeability in a dose-, time- response manner, with Salmonella (3200 AU/mL) more susceptible than E. coli (6400 AU/mL). The results indicated that UTNGt21O may damage the integrity of the cell target, leading to release of cytoplasmic components followed by cell death. Differences in membrane shape changes in target cells treated with different doses of peptide were observed by transmission electronic microscopy (TEM). Spheroplasts with spherical shapes were detected in Salmonella while larger shaped spheroplasts with thicker and deformed membranes along with filamentous cells were observed in E. coli upon the treatment with the UTNGt21O peptide. These results indicate the promising potential of the putative bacteriocin released by the novel W. cibaria strain UTNGt21O to be further tested as a new antimicrobial substance.

Probiotic Potential and Technological Properties of Bacteriocinogenic Lactococcus lactis Subsp. Lactis UTNGt28 from a Native Amazonian Fruit as a Yogurt Starter Culture

A native Lactococcus lactis subsp. lactis UTNGt28 (GenBank accession no: MG675576.1) isolated from Amazonian fruit of the tropical Caimitillo (Chrysophyllum oliviforme) tree and the commercial strain Lactococcus lactis subsp lactis ATCC11454 (LacAT) were targeted ex vitro in whole milk in combination with Streptococcus thermophilus ATCC19258 to obtain a fermented probiotic beverage. Concomitant with cell viability determination during storage (28 days), the pH, titratable acidity, syneresis, protein and fat were evaluated. The results indicated that neither UTNGt28 nor LacAT displayed a high capacity to ferment whole milk and survive during storage; a statistically significant difference (p < 0.05) in cell viability was registered for UTNGt28 compared with LacAT when inoculated alone or in combination with S. thermophilus. A principal component analysis showed a clear difference between the yogurt formulations at day 1 and 28 of storage. The PC 1 explained 46.8% of the total variance (day 28), was loaded in the negative (-) direction with titratable acidity (% lactic acid), while the PC 2 explained 22.5% (day 1) with pH. PC 1 was loaded in the positive (+) direction with pH, cell viability, syneresis, fat and protein. Overall results indicated that UTNGt28 has the technological properties for further development of a new probiotic product.

Inhibitory Substances Produced by NativeLactobacillus plantarumUTNCys5-4 Control Microbial Population Growth in Meat

Microbial contamination is the cause of extensive economic loss in the food sector. Previously, the wide-range antimicrobial capacity of inhibitory substances secreted by theLactobacillus plantarumUTNCys5-4 strain was demonstratedin vitro; however, its mechanism of action in the food matrix remains unclear. This study was aimed to evaluate the effect of antimicrobials produced by the Cys5-4 strain in raw meat applied as pure cell cultures, cell-free supernatant (CFS), and partially purified peptides. The bacteriological results indicated the presence of commensal microbes exhibiting resistance to several antibiotics in meat samples purchased from the local market. Dipping solutions containing antimicrobial substances produced by Cys5-4 resulted in a decrease by 1.91,1.69, and 1.55 log10in cell counts upon addition of CFS, peptides and respectively pure cell culture in raw meat at day 9 of storage with refrigeration. The microbial population was maintained in the untreated meat samples during storage. An increase in pH and a concentration of released ammonia was detected in nontreated meat, indicating protein degradation. The Cys5-4 peptides exerted their bacteriolytic mode of action inducing damage in the cell membrane of the target bacteria, allowing the leaching of DNA/RNA content. The results indicate that coating meat with CFS containing Cys5-4 is a promising approach to protect against further contamination by microorganism spoilage, as well as an alternative for increasing the shelf life of raw meat.

Characterization of Bacteriocin-Producing Lactic Acid Bacteria Isolated from Native Fruits of Ecuadorian Amazon

Tropical, wild-type fruits are considered biodiverse "hotspots" of microorganisms with possible functional characteristics to be investigated. In this study, several native lactic acid bacteria (LAB) of Ecuadorian Amazon showing highly inhibitory potential were identified and characterized. Based on carbohydrate fermentation profile and 16S rRNA gene sequencing, seven strains were assigned as Lactobacillus plantarum and one strain as Weissella confusa. Using agar-well diffusion method the active synthetized components released in the neutralized and hydroxide peroxide eliminated cell-free supernatant were inhibited by proteolytic enzymes, while the activity was maintained stable after the treatment with catalase, lysozyme, α-amylase and lipase suggesting their proteinaceous nature. The inhibitory activity was stimulated by acidic conditions, upon exposure to high heat and maintained stable at different ranges of sodium chloride (4-10%). The DNA sequencing analysis confirmed the presence of plw structural gene encoding for plantacirin W in the selected L. plantarum strains. Moreover, we showed that the active peptides of Cys5-4 strains contrast effectively, in a bactericidal manner, the growth of food borne E. coli UTNEc1 and Salmonella UTNSm2, with about tree fold reduction of viable counts at the early stage of the target cell growth. The results indicated that the bacteriocin produced by selected native lactic acid bacteria strains has elevated capacity to suppress several pathogenic microorganisms implying their potential as antimicrobial agents or food preservatives.

Inhibitory Effect of Substances Produced by Native Lactococcus lactis Strains of Tropical Fruits towards Food Pathogens

The use of peptides produced by lactic acid bacteria (LAB) as antimicrobial agents in food emerged from the increasing need of replacing chemicals with natural substances to ensure their safety and quality. A total of 30 LAB belonging to the genus Lactococcus sp. (10) and Enterococcus sp. (20) were isolated from native fruits of Ecuador subtropical rainforest. Among Lactococcus species, the isolates assigned Gt28, Gt29, and Ella8, identified as Lactococcus lactis subsp. lactis with 99% identity, showing highly inhibitory potential against four food pathogens were further characterized. The treatment of cell-free supernatant with proteolytic enzymes indicated the protein nature of released components, which displayed a broad antimicrobial activity against Gram-positive and -negative bacteria. Polymerase chain reaction analysis indicated the presence of lacticin 3147 gene in all isolates, lactococcin M gene in Gt28 and Gt29 but not in Ella8 and lactococcin A gene in Gt28 only. The antimicrobial activity was not linked to the presence of structural nisin gene as no amplification product was obtained. Treatment of Salmonella enterica ATCC 51741 and Escherichia coli ATCC 25922 at both vegetative and exponential phase of growth with the cell-free supernatant of Gt28 resulted in complete inactivation upon 3 h suggesting its bactericidal mode of action. An increment on inhibitory activity occurred when partial purified bacteriocin Gt28 was combined with ethylenediaminetetraacetic acid rather than bacteriocin only, indicating that the cells were sensitized in vitro by the chelator agent acting synergistically to induce the killing of pathogenic cells.

Swine-Derived Probiotic Lactobacillus plantarum Inhibits Growth and Adhesion of Enterotoxigenic Escherichia coli and Mediates Host Defense

Weaning stress renders piglets susceptible to pathogen infection, which leads to post-weaning diarrhea, a severe condition characterized by heavy diarrhea and mortality in piglets. Enterotoxigenic Escherichia coli (ETEC) is one of typical strains associated with post-weaning diarrhea. Thus, prevention and inhibition of ETEC infection are of great concern. Probiotics possess anti-pathogenic activity and can counteract ETEC infection; however, their underlying mechanisms and modes of action have not yet been clarified. In the present study, the direct and indirect protective effects of Lactobacillus plantarum ZLP001 against ETEC infection were investigated by different methods. We found that bacterial culture and culture supernatant of L. plantarum ZLP001 prevented ETEC growth by the Oxford cup method, and ETEC growth inhibition was observed in a co-culture assay as well. This effect was suggested to be caused mainly by antimicrobial metabolites produced by L. plantarum ZLP001. In addition, adhesion capacity of L. plantarum ZLP001 to IPEC-J2 cells were observed using microscopy and counting. L. plantarum ZLP001 also exhibited a concentration-dependent ability to inhibit ETEC adhesion to IPEC-J2 cells, which mainly occurred via exclusion and competition mode. Furthermore, quantitative real time polymerase chain reaction (qPCR) analysis showed that L. plantarum ZLP001 upregulated the expression of host defense peptides (HDPs) but did not trigger an inflammatory response. In addition, L. plantarum ZLP001 induced HDP secretion, which enhanced the potential antimicrobial activity of IPEC-J2 cell-culture supernatant after incubation with L. plantarum ZLP001. Our findings demonstrate that L. plantarum ZLP001, an intestinal Lactobacillus species associated with piglet health, possesses anti-ETEC activity. L. plantarum ZLP001 might prevent ETEC growth, inhibit ETEC adhesion to the intestinal mucosa, and activate the innate immune response to secret antimicrobial peptides. L. plantarum ZLP001 is worth investigation as a potential probiotics.

Indigenous Probiotic Lactobacillus Isolates Presenting Antibiotic like Activity against Human Pathogenic Bacteria

Background: Indigenous lactic acid bacteria are well known probiotics having antibacterial activity against potentially pathogenic bacteria. This study aims to characterize the curd lactobacilli for their probiotic potentiality and antagonistic activity against clinical bacteria. Methods: Four curd samples were processed microbiologically for the isolation of lactic acid bacteria (LAB). The LAB strains obtained were identified by conventional methods: cultural aspect, gram-staining, biochemical and sugar fermentation tests. The probiotic properties were justified with tolerance to low-pH, bile salt and sodium chloride, and the antagonistic activity of the lactobacilli against human pathogenic bacteria (Escherichia coli, Proteus vulgaris, Acinetobacter baumannii and Salmonella enterica serovar Typhi) was assessed. Hemolytic activity and antibiotic susceptibility were determined for the lactobacilli isolates, and the cumulative probiotic potential (CPP) values were recorded. Result: Four lactobacilli isolates, L. animalis LMEM6, L. plantarum LMEM7, L. acidophilus LMEM8 and L. rhamnosus LMEM9, procured from the curd samples, survived in low-pH and high bile salt conditions, and showed growth inhibitory activity against the indicator bacteria by agar-well (zone diameter of inhibition; ZDIs: 13.67 ± 0.58–29.50 ± 2.10 mm) and agar overlay (ZDIs: 11.33 ± 0.58–35.67 ± 2.52 mm) methods; the average growth inhibitory activity of lactobacilli ranged 233.34 ± 45.54–280.56 ± 83.67 AU/mL, against the test bacterial pathogens. All the lactobacilli were non-hemolytic and sensitive to most of the test antibiotics. The CPP values of the isolated LAB were recorded as 80–100%. Conclusion: The curd lactobacilli procured might be used as the valid candidates of probiotics, and bio-therapeutics against bacterial infection to humans.

Antibacterial effects of Lactobacillus isolates of curd and human milk origin against food-borne and human pathogens

This study was undertaken to assess the antibacterial efficacy of lactobacilli isolated from curd and human milk samples. Identities of thirty-one different lactobacilli (20 from curd and 11 from human milk) were confirmed by genus-specific PCR and 16S rRNA-based sequencing. These strains belonged to five species, Lactobacillus casei, L. delbrueckii, L. fermentum, L. plantarum, and L. pentosus. Antibacterial activities of cell-free supernatants (CFSs) of all the Lactobacillus isolates were estimated through standard agar-well diffusion assay, against commonly occurring food-borne and clinically important human pathogens. None of the lactobacilli cell-free supernatant (CFS) exhibited inhibitory activity against four pathogens, namely Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Klebsiella pneumoniae. Bacillus cereus, Salmonella enterica serovar Typhi, and Shigella flexneri were moderately inhibited by majority of CFSs, whereas, weak activity was observed against Pseudomonas aeruginosa and Proteus mirabilis. CFS of some of the curd isolates displayed antagonistic activity against Streptococcus mutans; however, human milk lactobacilli did not displayed any inhibitory activity against them. As expected, Nisin (Nisaplin^®) showed inhibitory activity against Gram-positive, S. aureus, B. cereus, and L. monocytogenes. Interestingly, few of the examined CFSs exhibited inhibitory activities against both Gram-positive and Gram-negative pathogens. Findings from this study support the possibility to explore the tested lactobacilli and their CFSs as natural bio-preservatives, alone or in combination with approved bacteriocins in food and pharma formulations after validating their safety.