Enterococcus mundtii ST4SA and Lactobacillus plantarum 423 excludes Listeria monocytogenes from the GIT, as shown by bioluminescent studies in mice

Effect of encapsulated probiotic in Inulin-Maltodextrin-Sodium alginate matrix on the viability of Enterococcus mundtii SRBG1 and the rheological parameters of fermentedmilk

In the current research, Enterococcus mundtii SRBG1 newly isolated from Bat guano was encapsulated using spray drying technique to create a probiotic powder using six combinations of inulin, maltodextrin and sodium alginate. The encapsulation yield, moisture content, physical characteristics, and shape were investigated. Microcapsules yields ranged from 67 to 85 percent, which is consistent with typical B-290 spray-drier yields. The moisture content showed to increase (4 ± 0.15%) with the addition of sodium alginate to inulin and maltodextrin. In the gastrointestinal conditions (simulated gastric juice and bile salts), it was shown that the viability of probiotic cells in capsules was higher than that of free cells. This demonstrated the effectiveness of combining inulin and maltodextrin to encapsulate substances in surviving in gastro-intestinal conditions. Additionally, we evaluated the non-encapsulated and encapsulated SRBG1 by assessing their impact on the rheological parameters of fermented milk. The results showed that in the absence of sodium alginate the viscosity of milk was lower than with the other protectors, which was confirmed by the quick acidification of the fermented milk by microcapsules containing sodium alginate.

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Enterococcus mundtii SRBG1 isolated from Bat guano was encapsulated by spray drying.

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Six combinations of inulin, maltodextrin and sodium alginate were used.

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Microcapsules yields ranged from 67 to 85 percent.

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Inulin and maltodextrin were effective in protecting SRBG1.

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In the absence of sodium alginate the viscosity of fermented milk decreased.

Horses as a source of bioactive fecal strains Enterococcus mundtii

Bacteriocin-producing bacteria with probiotic character are known as nutritional supplements mainly for livestock. Among those beneficial bacteria we also found enterococci. Because the species strains Enterococcus mundtii also can produce bacteriocins, this study was focused on fecal strains E. mundtii from horses and their bioactivity with a view to their possible future use in breeding. Rectal removal from 47 horses (40 mares and 7 stallions), the Norik breed from Muráň were sampled in eastern Slovakia during November 2019 year. Horses age ranged from five months up to 23 years. Using MALDI-TOF mass spectrometry and 16S rRNA sequences analysis, 14 strains were allotted to the species E. mundtii. Bacteriocin substances produced by the strains EMKD 38/1, EMKD 40/2, EMKD 34/2 and EMKD 41/3 showed inhibitory activity against the most susceptible (principal) indicator strain Enterococcus avium EA5 and against listeriae as well (inhibitory activity from 100 up to 1 600 AU/mL). Only strain EMKD 41/3 possess Ent P and Mundticin KS genes and showed the broadest inhibitory activity. Ent B gene possessing strain EMKD 24/1 inhibited a growth of only indicator strain EA5. Identified E. mundtii tolerate low pH 3 and oxgall/bile. They were hemolysis, gelatinase and DNase negative and mostly susceptible to clinical antibiotics which are properties requested for application potential of strain. Substance from the strain with the broadest antimicrobial spectrum showed its practical/application potential, e.g. for optimizing the host microbiota which is important regarding the maintenance of animal`s health status.

Enterococcus spp.: Is It a Bad Choice for a Good Use-A Conundrum to Solve?

Since antiquity, the ubiquitous lactic acid bacteria (LAB) Enterococci, which are just as predominant in both human and animal intestinal commensal flora, have been used (and still are) as probiotics in food and feed production. Their qualities encounter several hurdles, particularly in terms of the array of virulence determinants, reflecting a notorious reputation that nearly prevents their use as probiotics. Additionally, representatives of the Enterococcus spp. genus showed intrinsic resistance to several antimicrobial agents, and flexibility to acquire resistance determinants encoded on a broad array of conjugative plasmids, transposons, and bacteriophages. The presence of such pathogenic aspects among some species represents a critical barrier compromising their use as probiotics in food. Thus, the genus neither has Generally Recognized as Safe (GRAS) status nor has it been included in the Qualified Presumption of Safety (QPS) list implying drastic legislation towards these microorganisms. To date, the knowledge of the virulence factors and the genetic structure of foodborne enterococcal strains is rather limited. Although enterococcal infections originating from food have never been reported, the consumption of food carrying virulence enterococci seems to be a risky path of transfer, and hence, it renders them poor choices as probiotics. Auspiciously, enterococcal virulence factors seem to be strain specific suggesting that clinical isolates carry much more determinants that food isolates. The latter remain widely susceptible to clinically relevant antibiotics and subsequently, have a lower potential for pathogenicity. In terms of the ideal enterococcal candidate, selected strains deemed for use in foods should not possess any virulence genes and should be susceptible to clinically relevant antibiotics. Overall, implementation of an appropriate risk/benefit analysis, in addition to the case-by-case assessment, the establishment of a strain's innocuity, and consideration for relevant guidelines, legislation, and regulatory aspects surrounding functional food development seem to be the crucial elements for industries, health-staff and consumers to accept enterococci, like other LAB, as important candidates for useful and beneficial applications in food industry and food biotechnology. The present review aims at shedding light on the world of hurdles and limitations that hampers the Enterococcus spp. genus and its representatives from being used or proposed for use as probiotics. The future of enterococci use as probiotics and legislation in this field are also discussed.

Molecular insights into probiotic mechanisms of action employed against intestinal pathogenic bacteria

Gastrointestinal (GI) diseases, and in particular those caused by bacterial infections, are a major cause of morbidity and mortality worldwide. Treatment is becoming increasingly difficult due to the increase in number of species that have developed resistance to antibiotics. Probiotic lactic acid bacteria (LAB) have considerable potential as alternatives to antibiotics, both in prophylactic and therapeutic applications. Several studies have documented a reduction, or prevention, of GI diseases by probiotic bacteria. Since the activities of probiotic bacteria are closely linked with conditions in the host's GI-tract (GIT) and changes in the population of enteric microorganisms, a deeper understanding of gut-microbial interactions is required in the selection of the most suitable probiotic. This necessitates a deeper understanding of the molecular capabilities of probiotic bacteria. In this review, we explore how probiotic microorganisms interact with enteric pathogens in the GIT. The significance of probiotic colonization and persistence in the GIT is also addressed.

Enterococcus faecalis Is a Better Competitor Than Other Lactic Acid Bacteria in the Initial Colonization of Colon of Healthy Newborn Babies at First Week of Their Life

Initial colonization of human gut by bacteria is an important step in controlling its microbiota and health status. This study followed the initial colonization by lactic acid bacteria (LAB) in colon of new born babies through following its occurrence in their stool at first week of their life. The LAB occurrence in the neonates' stool was followed on MRS agar medium. The isolated LAB from male and female newborn babies of normal birth and cesarean section surgical delivery were molecular biologically identified by phylogenetic analysis of 16S rRNA gene sequence. From the 24 investigated newborn babies, three LAB taxa, Lactobacillaceae, Enterococcus, and Streptococcus, were detected in their stool at first week of their life. Lactobacillaceae represented 20.8% of total colonized LAB in newborn babies in the culture-dependent approach used in this study and included three species namely Limosilactobacillus reuteri (previously known as Lactobacillus reuteri), Lacticaseibacillus rhamnosus (previously known as Lactobacillus rhamnosus) and Ligilactobacillus agilis (previously known as Lactobacillus agilis). Enterococcus faecalis and E. faecium were detected where E. faecalis was the highest dominant, representing 62.5% of total LAB colonizing newborn babies. This result suggests that this bacterium has high potency for colonization and might be important for controlling the initial settlement of microbiota in healthy newborn babies. Only one species of Streptococcus namely Streptococcus agalactiae was detected in 8.33% total of the investigated newborn babies indicating high competency by other LAB for colonization and that this bacteria, in spite of its pathogenicity, is commensal in its low existence in healthy babies. The explored potency of natural initial colonization of the LAB species E. faecalis, E. faecium, L. reuteri, L. rhamnosus, and L. agilis of which many health beneficial strains were previously reported, would be important for future applications. Despite the controversy in evaluating its health benefits, E. faecalis as a potent competitor to other LAB refers to its importance in initial colonization of healthy babies colon at first week of their life. Further future studies, with more number of samples and characterization, would be of importance for evaluating the potential use of beneficial Enterococcus strains which could improve intestinal ecosystem.

Fermented Seeds ("Zgougou") from Aleppo Pine as a Novel Source of Potentially Probiotic Lactic Acid Bacteria

Microorganisms inhabiting fermented foods represent the main link between the consumption of this food and human health. Although some fermented food is a reservoir of potentially probiotic microorganisms, several foods are still unexplored. This study aimed at characterizing the probiotic potential of lactic acid bacteria isolated from zgougou, a fermented matrix consisting of a watery mixture of Aleppo pine's seeds. In vitro methods were used to characterize the safety, survival ability in typical conditions of the gastrointestinal tract, and adherence capacity to surfaces, antimicrobial, and antioxidant activities. Strains belonged to the Lactobacillus plantarum group and Enterococcus faecalis showed no DNase, hemolytic, and gelatinase activities. In addition, their susceptibility to most of the tested antibiotics, satisfied some of the safety prerequisites for their potential use as probiotics. All the strains tolerated low pH, gastrointestinal enzymes, and bile salts. They displayed a good antibacterial activity and antibiofilm formation against 10 reference bacterial pathogens, especially when used as a cell-free supernatant. Furthermore, the lactic acid bacteria (LAB) strains inhibited the growth of Aspergillus flavus and Aspergillus carbonarius. Finally, they had good antioxidant activity, although depending on the strain. Overall, the results of this work highlight that zgougou represents an important reservoir of potentially probiotic LAB. Obviously, future studies should be addressed to confirm the health benefits of the LAB strains.

Migration of Bacteriocins Across Gastrointestinal Epithelial and Vascular Endothelial Cells, as Determined Using In Vitro Simulations

Little is known about the migration of bacteriocins across human cells. In this study, we report on migration of three bacteriocins nisin, plantaricin 423 and bacST4SA across colonic adenocarcinoma (Caco-2) cells and human umbilical vein endothelial cells (HUVECs). Bacteriocins were fluorescently labelled while still maintaining antimicrobial activity. Migration of fluorescently labelled bacteriocins across monolayers was assessed in vitro using transmigration well inserts. After 3 h, 75% of nisin, 85% of plantaricin 423 and 82% of bacST4SA migrated across the Caco-2 cell monolayer. Over the same time span, 88% nisin, 93% plantaricin 423 and 91% bacST4SA migrated across the HUVEC monolayer. The viability of both cell types remained unchanged when exposed to 50 µM of nisin, plantaricin 423 or bacST4SA. The effect of human plasma on bacteriocin activity was also assessed. Activity loss was dependent on bacteriocin type and concentration, with the class-IIa bacteriocins retaining more activity compared to nisin. This is the first report of bacteriocins migrating across simulated gastrointestinal- and vascular-barriers. This study provides some of the first evidence that bacteriocins are capable of crossing the gut-blood-barrier. However, in vivo studies need to be performed to confirm these findings and expand on the role of bacteriocin migration across cell barriers.

Enterococci: Between Emerging Pathogens and Potential Probiotics

Enterococci are ubiquitous microorganisms that could be found everywhere; in water, plant, soil, foods, and gastrointestinal tract of humans and animals. They were previously used as starters in food fermentation due to their biotechnological traits (enzymatic and proteolytic activities) or protective cultures in food biopreservation due to their produced antimicrobial bacteriocins called enterocins or as probiotics, live cells with different beneficial characteristics such as stimulation of immunity, anti-inflammatory activity, hypocholesterolemic effect, and prevention/treatment of some diseases. However, in the last years, the use of enterococci in foods or as probiotics caused an important debate because of their opportunistic pathogenicity implicated in several nosocomial infections due to virulence factors and antibiotic resistance, particularly the emergence of vancomycin-resistant enterococci. These virulence traits of some enterococci are associated with genetic transfer mechanisms. Therefore, the development of new enterococcal probiotics needs a strict assessment with regard to safety aspects for selecting the truly harmless enterococcal strains for safe applications. This review tries to give some data of the different points of view about this question.

Bacteriocin production and adhesion properties as mechanisms for the anti-listerial activity of Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA

Probiotics play an important role in maintaining a healthy and stable intestinal microbiota, primarily by preventing infection. Probiotic lactic acid bacteria (LAB) are known to be inhibitory to many bacterial enteric pathogens, including antibiotic-resistant strains. Whilst the positive role that probiotics have on human physiology, specifically in the treatment or prevention of specific infectious diseases of the gastro-intestinal tract (GIT) is known, the precise mechanistic basis of these effects remains a major research goal. In this study, molecular evidence to underpin the protective and anti-listerial effect of Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA against orally administered Listeria monocytogenes EGDe in the GIT of mice is provided. Bacteriocins plantaricin 423 and mundticin ST4SA, produced by L. plantarum 423 and E. mundtii ST4SA, respectively, inhibited the growth of L. monocytogenes in vitro and in vivo. Bacteriocin-negative mutants of L. plantarum 423 and E. mundtii ST4SA failed to exclude L. monocytogenes EGDe from the gastrointestinal tract (GIT) of mice. Furthermore, L. plantarum 423 and E. mundtii ST4SA failed to inhibit recombinant strains of L. monocytogenes EGDe in vivo that expressed the immunity proteins of the two bacteriocins. These results confirmed that bacteriocins plantaricin 423 and mundticin ST4SA acted as anti-infective mediators in vivo. Compared to wild type strains, mutants of L. plantarum 423 and E. mundtii ST4SA, in which the adhesion genes were knocked out, were less effective in the exclusion of L. monocytogenes EGDe from the GIT of mice. This work demonstrates the importance of bacteriocin and adhesion genes as probiotic anti-infective mechanisms.

In vivo bioluminescence imaging of the spatial and temporal colonization of lactobacillus plantarum 423 and enterococcus mundtii ST4SA in the intestinal tract of mice

Background

Lactic acid bacteria (LAB) are major inhabitants and part of the normal microflora of the gastrointestinal tract (GIT) of humans and animals. Despite substantial evidence supporting the beneficial properties of LAB, only a few studies have addressed the migration and colonization of probiotic bacteria in the GIT. The reason for this is mostly due to the limitations, or lack of, efficient reporter systems. Here we describe the development and application of a non-invasive in vivo bioluminescence reporter system to study, in real-time, the spatial and temporal persistence of Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA in the intestinal tract of mice.

Results

This study reports on the application of the firefly luciferase gene (ffluc) from Photinus pyralis to develop luciferase-expressing L. plantarum 423 and E. mundtii ST4SA, using a Lactococcus lactis NICE system on a high copy number plasmid (pNZ8048) and strong constitutive lactate dehydrogenase gene promoters (Pldh and STldh). The reporter system was used for in vivo and ex vivo monitoring of both probiotic LAB strains in the GIT of mice after single and multiple oral administrations. Enterococcus mundtii ST4SA reached the large intestine 45 min after gavage, while L. plantarum 423 reached the cecum/colon after 90 min. Both strains predominantly colonized the cecum and colon after five consecutive daily administrations. Enterococcus mundtii ST4SA persisted in faeces at higher numbers and for more days compared to L. plantarum 423.

Conclusions

Our findings demonstrate the efficiency of a high-copy number vector, constitutive promoters and bioluminescence imaging to study the colonization and persistence of L. plantarum 423 and E. mundtii ST4SA in the murine GIT. The system allowed us to differentiate between intestinal transit times of the two strains in the digestive tract. This is the first report of bioluminescence imaging of a luciferase-expressing E. mundtii strain to study colonization dynamics in the murine model. The bioluminescence system developed in this study may be used to study the in vivo colonization dynamics of other probiotic LAB.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1315-4) contains supplementary material, which is available to authorized users.

The Genus Enterococcus: Between Probiotic Potential and Safety Concerns-An Update

A considerable number of strains belonging to different species of Enterococcus are highly competitive due to their resistance to wide range of pH and temperature. Their competitiveness is also owed to their ability to produce bacteriocins recognized for their wide-range effectiveness on pathogenic and spoilage bacteria. Enterococcal bacteriocins have attracted great research interest as natural antimicrobial agents in the food industry, and as a potential drug candidate for replacing antibiotics in order to treat multiple drugs resistance pathogens. However, the prevalence of virulence factors and antibiotic-resistance genes and the ability to cause disease could compromise their application in food, human and animal health. From the current regulatory point of view, the genus Enterococcus is neither recommended for the QPS list nor have GRAS status. Although recent advances in molecular biology and the recommended methods for the safety evaluation of Enterococcus strains allowed the distinction between commensal and clinical clades, development of highly adapted methods and legislations are still required. In the present review, we evaluate some aspects of Enterococcus spp. related to their probiotic properties and safety concerns as well as the current and potential application in food systems and treatment of infections. The regulatory status of commensal Enterococcus candidates for food, feed, probiotic use, and recommended methods to assess and ensure their safety are also discussed.

In-vivo monitoring of infectious diseases in living animals using bioluminescence imaging

Traditional methods of localizing and quantifying the presence of pathogenic microorganisms in living experimental animal models of infections have mostly relied on sacrificing the animals, dissociating the tissue and counting the number of colony forming units. However, the discovery of several varieties of the light producing enzyme, luciferase, and the genetic engineering of bacteria, fungi, parasites and mice to make them emit light, either after administration of the luciferase substrate, or in the case of the bacterial lux operon without any exogenous substrate, has provided a new alternative. Dedicated bioluminescence imaging (BLI) cameras can record the light emitted from living animals in real time allowing non-invasive, longitudinal monitoring of the anatomical location and growth of infectious microorganisms as measured by strength of the BLI signal. BLI technology has been used to follow bacterial infections in traumatic skin wounds and burns, osteomyelitis, infections in intestines, Mycobacterial infections, otitis media, lung infections, biofilm and endodontic infections and meningitis. Fungi that have been engineered to be bioluminescent have been used to study infections caused by yeasts (Candida) and by filamentous fungi. Parasitic infections caused by malaria, Leishmania, trypanosomes and toxoplasma have all been monitored by BLI. Viruses such as vaccinia, herpes simplex, hepatitis B and C and influenza, have been studied using BLI. This rapidly growing technology is expected to continue to provide much useful information, while drastically reducing the numbers of animals needed in experimental studies.

High Doses of Halotolerant Gut-Indigenous Lactobacillus plantarum Reduce Cultivable Lactobacilli in Newborn Calves without Increasing Its Species Abundance

To elucidate the ecological effect of high oral doses of halotolerant (resistant to table salt) indigenous-gut bacteria on other commensals early in life, we conducted a culture-based study to quantify the effect of intestinal Lactobacillus plantarum strain of bovine origin (with remarkable aerobic growth capabilities and inhibitory activity against Escherichia coli O157:H7 and F5) on clinical health and gut lactobacilli/coliforms in newborn calves. In a double-blind placebo-randomized trial twelve colostrum-fed calves, consecutively born at a farm, were fed L. plantarum within 12 hours from birth at low (10^7-8 CFU/day) or high concentrations (10^10-11) or placebo (q24 h, 5 d; 10 d follow-up). We developed a 2.5% NaCl-selective culture strategy to facilitate the enumeration of L. plantarum-strain-B80, and tested 384 samples (>1,152 cultures). L. plantarum-B80-like colonies were detected in a large proportion of calves (58%) even before their first 24 hours of life indicating endemic presence of the strain in the farm. In contrast to studies where human-derived Lactobacillus LGG or rhamnosus had notoriously high, but short-lived, colonization, we found that L. plantarum colonized stably with fecal shedding of 6 ± 1 log₁₀·g⁻¹ (irrespective of dose, P > 0.2). High doses significantly reduced other fecal lactic acid bacteria (e.g., lactobacilli, P < 0.01) and slightly reduced body weight gain in calves after treatment. For the first time, a halotolerant strain of L. plantarum with inhibitory activity against a human pathogen has the ability to inhibit other lactobacilli in vivo without changing its species abundance, causing transintestinal translocation, or inducing clinical disease. The future selection of probiotics based on halotolerance may expand therapeutic product applicability.