Identification and screening for antimicrobial activity against Clostridium difficile of Bifidobacterium and Lactobacillus species isolated from healthy infant faeces

Rational Design of Live Biotherapeutic Products for the Prevention of Clostridioides difficile Infection

Clostridioides difficile infection (CDI) is one of the leading causes of healthcare- and antibiotic-associated diarrhea. While fecal microbiota transplantation (FMT) has emerged as a promising therapy for recurrent CDI, its exact mechanisms of action and long-term safety are not fully understood. Defined consortia of clonal bacterial isolates, known as live biotherapeutic products (LBPs), have been proposed as an alternative therapeutic option. However, the rational design of LBPs remains challenging. Here, we employ a computational pipeline and three independent metagenomic datasets to systematically identify microbial strains that have the potential to inhibit CDI. We first constructed the CDI-related microbial genome catalog, comprising 3,741 non-redundant metagenome-assembled genomes (nrMAGs) at the strain level. We then identified multiple potential protective nrMAGs that can be candidates for the design of microbial consortia targeting CDI, including strains from Dorea formicigenerans, Oscillibacter welbionis, and Faecalibacterium prausnitzii. Importantly, some of these potential protective nrMAGs were found to play an important role in the success of FMT, and the majority of the top protective nrMAGs can be validated by various previously reported findings. Our results demonstrate a computational framework for the rational selection of microbial strains targeting CDI, paving the way for the computational design of microbial consortia against other enteric infections.

Gut Microbiome Analysis and Screening of Lactic Acid Bacteria with Probiotic Potential in Anhui Swine

With the widespread promotion of the green feeding concept of "substitution and resistance", there is a pressing need for alternative products in feed and breeding industries. Employing lactic acid bacteria represents one of the most promising antimicrobial strategies to combat infections caused by pathogenic bacteria. As such, we analyzed the intestinal tract of Anhui local pig breeds, including LiuBai Pig, YueHei Pig, and HuoShou Pig, to determine the composition and diversity of intestinal microbiota using 16S rRNA. Further, the functionality of the pigs' intestinal microbiota was studied through metagenomic sequencing. This study revealed that lactic acid bacteria were the primary contributors to the functional composition, as determined through a species functional contribution analysis. More specifically, the functional contribution of lactic acid bacteria in the HuoShou Pig group was higher than that of the LiuBai Pig and YueHei Pig. Subsequently, the intestinal contents of the HuoShou Pig group were selected for the screening of the dominant lactic acid bacteria strains. Out of eight strains of lactic acid bacteria, the acid-production capacity, growth curve, and tolerance to a simulated intestinal environment were assessed. Additional assessments included surface hydrophobicity, the self-aggregation capability, co-agglutination of lactic acid bacteria with pathogenic bacteria, and an in vitro bacteriostatic activity assay. Lactobacillus johnsonii L5 and Lactobacillus reuteri L8 were identified as having a strong overall performance. These findings serve as a theoretical basis for the further development of pig-derived probiotics, thereby promoting the application of lactic acid bacteria to livestock production.

Gastrointestinal Microbiome and Multiple Health Outcomes: Umbrella Review

In recent years, there has been growing concern about the impact of the gastrointestinal microbiome on human health outcomes. To clarify the evidence for a link between the gastrointestinal microbiome and a variety of health outcomes in humans, we conducted an all-encompassing review of meta-analyses and systematic reviews that included 195 meta-analyses containing 950 unique health outcomes. The gastrointestinal microbiome is related to mortality, gastrointestinal disease, immune and metabolic outcomes, neurological and psychiatric outcomes, maternal and infant outcomes, and other outcomes. Existing interventions for intestinal microbiota (such as probiotics, fecal microbiota transplant, etc.) are generally safe and beneficial to a variety of human health outcomes, but the quality of evidence is not high, and more detailed and well-designed randomized controlled trials are necessary.

Probiotics, Prebiotics, and Synbiotics: Implications and Beneficial Effects against Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is still a common functional gastrointestinal disease that presents chronic abdominal symptoms but with a pathophysiology that is not yet fully elucidated. Moreover, the use of the synergistic combination of prebiotics and probiotics, known as synbiotics, for IBS therapy is still in the early stages. Advancements in technology led to determining the important role played by probiotics in IBS, whereas the present paper focuses on the detailed review of the various pathophysiologic mechanisms of action of probiotics, prebiotics, and synbiotics via multidisciplinary domains involving the gastroenterology (microbiota modulation, alteration of gut barrier function, visceral hypersensitivity, and gastrointestinal dysmotility) immunology (intestinal immunological modulation), and neurology (microbiota–gut–brain axis communication and co-morbidities) in mitigating the symptoms of IBS. In addition, this review synthesizes literature about the mechanisms involved in the beneficial effects of prebiotics and synbiotics for patients with IBS, discussing clinical studies testing the efficiency and outcomes of synbiotics used as therapy for IBS.

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.

Bifidobacteriumlongum subsp. infantis CECT7210 (B. infantis IM-1®) Displays In Vitro Activity against Some Intestinal Pathogens

Certain non-digestible oligosaccharides (NDO) are specifically fermented by bifidobacteria along the human gastrointestinal tract, selectively favoring their growth and the production of health-promoting metabolites. In the present study, the ability of the probiotic strain Bifidobacterium longum subsp. infantis CECT7210 (herein referred to as B. infantis IM-1^®) to utilize a large range of oligosaccharides, or a mixture of oligosaccharides, was investigated. The strain was able to utilize all prebiotics screened. However, galactooligosaccharides (GOS), and GOS-containing mixtures, effectively increased its growth to a higher extent than the other prebiotics. The best synbiotic combination was used to examine the antimicrobial activity against Escherichia coli, Cronobacter sakazakii, Listeria monocytogenes and Clostridium difficile in co-culture experiments. C. difficile was inhibited by the synbiotic, but it failed to inhibit E. coli. Moreover, Cr. sakazakii growth decreased during co-culture with B. infantis IM-1^®. Furthermore, adhesion experiments using the intestinal cell line HT29 showed that the strain IM-1^® was able to displace some pathogens from the enterocyte layer, especially Cr. sakazakii and Salmonella enterica, and prevented the adhesion of Cr. sakazakii and Shigella sonnei. In conclusion, a new synbiotic (probiotic strain B. infantis IM-1^® and GOS) appears to be a potential effective supplement for maintaining infant health. However, further studies are needed to go more deeply into the mechanisms that allow B.infantis IM-1^® to compete with enteropathogens.

Bacteria producing antimicrobials against Clostridium difficile isolated from human stool

Clostridium difficile infection (CDI) is a common cause of morbidity and mortality in hospitalized patients worldwide. The major problem facing current treatment is multiple recurrences, prompting the need for alternative therapies. In this study we isolated bacterial species, from Egyptian individuals' stool, with antimicrobial activity against clinical isolates of C. difficile and tried to examine the nature of the produced antimicrobials. In vitro antibacterial activity against C. difficile was initially screened in 123 fecal samples cultures using an agar overlay method. The isolates with antimicrobial activity against C. difficile in addition to Clostridium isolates were identified using partial 16S rDNA gene sequencing analysis. The isolates acting against C. difficile belonged to Lactobacillus, Enterococcus and Clostridium genera. The concentrated cell-free supernatants (CFSs) from these bacterial isolates were examined for antimicrobial activity against C. difficile growth by broth dilution method. 10 x concentrated CFSs of five isolates showed inhibition for C. difficile growth which was significantly different (p < 0.001) from control. Lactobacillus agilis T99A and Clostridium butyricum T58A isolates were selected for further evaluation of the produced antimicrobials. The antimicrobial activity of 10x CFSs of the two isolates was stable after enzymatic treatment with proteinase K or heating treatments up to 90 °C or neutralizing pH. The spectrum of activity of the two isolates was evaluated using different gram-positive and gram-negative bacterial species and did not show antimicrobial activity against these species. Our results showed two unconventional bacterial isolates: L. agilis T99A and C. butyricum T58A producing extracellular thermo stable antimicrobial agents against C. difficile clinical isolates.

At-hatch administration of probiotic to chickens can introduce beneficial changes in gut microbiota

Recent advances in culture-free microbiological techniques bring new understanding of the role of intestinal microbiota in heath and performance. Intestinal microbial communities in chickens assume a near-stable state within the week which leaves a very small window for permanent microbiota remodelling. It is the first colonisers that determine the fate of microbial community in humans and birds alike, and after the microbiota has matured there are very small odds for permanent modification as stable community resists change. In this study we inoculated broiler chicks immediately post hatch, with 3 species of Lactobacillus, identified by sequencing of 16S rRNA and pheS genes as L. ingluviei, L. agilis and L. reuteri. The strains were isolated from the gut of healthy chickens as reproducibly persistent Lactobacillus strains among multiple flocks. Birds inoculated with the probiotic mix reached significantly higher weight by 28 days of age. Although each strain was able to colonise when administered alone, administering the probiotic mix at-hatch resulted in colonisation by only L. ingluviei. High initial abundance of L. ingluviei was slowly reducing, however, the effects of at-hatch administration of the Lactobacillus mix on modifying microbiota development and structure remained persistent. There was a tendency of promotion of beneficial and reduction in pathogenic taxa in the probiotic administered group.

Biochanin A improves fibre fermentation by cellulolytic bacteria

AIMS

The objective was to determine the effect of the isoflavone biochanin A (BCA) on rumen cellulolytic bacteria and consequent fermentative activity.

METHODS AND RESULTS

When bovine microbial rumen cell suspensions (n = 3) were incubated (24 h, 39°C) with ground hay, cellulolytic bacteria proliferated, short-chain fatty acids were produced and pH declined. BCA (30 μg ml^-1 ) had no effect on the number of cellulolytic bacteria or pH, but increased acetate, propionate and total SCFA production. Addition of BCA improved total digestibility when cell suspensions (n = 3) were incubated (48 h, 39°C) with ground hay, Avicel, or filter paper. Fibrobacter succinogenes S85, Ruminococcus flavefaciens 8 and Ruminococcus albus 8 were directly inhibited by BCA. Synergistic antimicrobial activity was observed with BCA and heat killed cultures of cellulolytic bacteria, but the effects were species dependent.

CONCLUSIONS

These results indicate that BCA improves fibre degradation by influencing cellulolytic bacteria competition and guild composition.

SIGNIFICANCE AND IMPACT OF THE STUDY

BCA could serve as a feed additive to improve cellulosis when cattle are consuming high-fibre diets. Future research is needed to evaluate the effect of BCA on fibre degradation and utilization in vivo.

Antagonistic Characteristics Against Food-borne Pathogenic Bacteria of Lactic Acid Bacteria and Bifidobacteria Isolated from Feces of Healthy Thai Infants

Background:

Food-borne pathogens are among the most significant problems in maintaining the health of people. Many probiotics have been widely reported to alleviate and protect against gastrointestinal infections through antibacterial secretion. However, the majority of them cannot always play antagonistic roles under gut conditions. Probiotic bacteria of human origin must possess other protective mechanisms to survive, out-compete intestinal flora and to successfully establish in their new host at a significant level.

Objectives:

Probiotic characteristics of Lactic Acid Bacteria (LAB) and bifidobacteria isolated from the feces of Thai infants were primarily investigated in terms of gastric acid and bile resistances, antibacterial activity and mucin adhesion ability. Antagonistic interaction through secretion of antibacterial compounds and competitive exclusion against food-borne pathogens were also evaluated.

Materials and Methods:

Culturable LAB and bifidobacteria were isolated from feces of Thai infants. Their ability to withstand gastric acid and bile were then evaluated. Acid and bile salt tolerant LAB and bifidobacteria were identified. They were then further assessed according to their antagonistic interactions through antibacterial secretion, mucin adhesion and competitive mucin adhesion against various food-borne pathogenic bacteria.

Results:

Gastric acid and bile tolerant LAB and bifidobacteria isolated from healthy infant feces were identified and selected according to their antagonistic interaction against various food-borne pathogenic bacteria. These antagonistic probiotics included four strains of Lactobacillus rhamnosus, two strains of L. casei, five strains of L. plantarum, two strains of Bifidobacterium longum subsp. longum and three strains of B. bifidum. All strains of the selected LAB inhibited all pathogenic bacteria tested through antibacterial secretion, while bifidobacteria showed high level of competitive exclusion against the pathogenic bacteria.

Conclusions:

These human-derived LAB and bifidobacteria exhibited different mechanisms involved in pathogenic inhibition. Therefore a combination of these probiotic strains could be a great promise and possibility for the development of probiotic products to effectively prevent and control food-borne infection in humans.

Fucosyltransferase 2 (FUT2) non-secretor status is associated with Crohn's disease

Genetic variation in both innate and adaptive immune systems is associated with Crohn's disease (CD) susceptibility, but much of the heritability to CD remains unknown. We performed a genome-wide association study (GWAS) in 896 CD cases and 3204 healthy controls all of Caucasian origin as defined by multidimensional scaling. We found supportive evidence for 21 out of 40 CD loci identified in a recent CD GWAS meta-analysis, including two loci which had only nominally achieved replication (rs4807569, 19p13; rs991804, CCL2/CCL7). In addition, we identified associations with genes involved in tight junctions/epithelial integrity (ASHL, ARPC1A), innate immunity (EXOC2), dendritic cell biology [CADM1 (IGSF4)], macrophage development (MMD2), TGF-beta signaling (MAP3K7IP1) and FUT2 (a physiological trait that regulates gastrointestinal mucosal expression of blood group A and B antigens) (rs602662, P=3.4x10(-5)). Twenty percent of Caucasians are 'non-secretors' who do not express ABO antigens in saliva as a result of the FUT2 W134X allele. We demonstrated replication in an independent cohort of 1174 CD cases and 357 controls between the four primary FUT2 single nucleotide polymorphisms (SNPs) and CD (rs602662, combined P-value 4.90x10(-8)) and also association with FUT2 W143X (P=2.6x10(-5)). Further evidence of the relevance of this locus to CD pathogenesis was demonstrated by the association of the original four SNPs and CD in the recently published CD GWAS meta-analysis (rs602662, P=0.001). These findings strongly implicate this locus in CD susceptibility and highlight the role of the mucus layer in the development of CD.

Selective growth inhibitory effect of biochanin A against intestinal tract colonizing bacteria

Both bifidobacteria and clostridia are part of the natural gut microflora and while clostridia may be responsible for severe intestinal infections, bifidobacteria are probiotic microorganisms belonging to the most important prospective bacteria in the bowel. The antimicrobial activity of biochanin A was tested in vitro against six Bifidobacterium spp., and eight Clostridium spp. using the broth microdilution method. Biochanin A showed an inhibition against all clostridia in the range of minimum inhibitory concentrations (MIC) from 64 microg/mL (for Cl. clostridioforme, strains DSM 933 and I3) to 1,024 microg/mL (for Cl. perfringens, DSM 11778). No bifidobacteria were suppressed at four-fold higher concentration (MICs > 4,096) than MIC of Cl. perfringens. These results indicate selective growth inhibition of biochanin A and its potential use in antimicrobial prevention and/or protection.

Molecular microbial analysis of lactobacillus strains isolated from the gut of calves for potential probiotic use

The intestinal microbiota has an influence on the growth and health status of the hosts. This is of particular interest in animals reared using intensive farming practices. Hence, it is necessary to know more about complexity of the beneficial intestinal microbiota. The use of molecular methods has revolutionized microbial identification by improving its quality and effectiveness. The specific aim of the study was to analyze predominant species of Lactobacillus in intestinal microbial ecosystem of young calves. Forty-two lactic acid bacteria (LAB) isolated from intestinal tract of young calves were characterized by: Amplified Ribosomal DNA Restriction Analysis (ARDRA), by using Hae III, Msp I, and Hinf I restriction enzymes, and 16S rDNA gene sequencing. ARDRA screening revealed nine unique patterns among 42 isolates, with the same pattern for 29 of the isolates. Gene fragments of 16S rDNA of 19 strains representing different patterns were sequenced to confirm the identification of these species. These results confirmed that ARDRA is a good tool for identification and discrimination of bacterial species isolated from complex ecosystem and between closely related groups. This paper provides information about the LAB species predominant in intestinal tract of young calves that could provide beneficial effects when administered as probiotic.

New functional probiotic Lactobacillus sakei probio 65 alleviates atopic symptoms in the mouse

The purpose of this study was to investigate the improvement of allergic dermatitis in chemical allergen-induced mice by Lactobacillus sakei probio 65. L. sakei probio-65 was isolated from kimchi, a traditional Korean fermented food. This strain was resistant to gastric acidity, bile, and several antibiotics and possessed antimicrobial activity against several pathogenic microorganisms. To investigate whether the probiotic activity of L. sakei probio 65 was effective for treating allergic dermatitis, the organism was supplied to mice triggered by allergen (1-chloro-2,4-dinitrobenzene). Mice that received L. sakei probio 65 showed a more rapid recovery compared to control mice, as assessed by visual evaluation of the severity of allergic dermatitis and levels of immunoglobulin (Ig) E and interleukin (IL)-4. L. sakei probio 65 exhibited good probiotic properties in vitro and in mice and was effective in reducing allergen-induced skin inflammation through the regulation of both elevated IgE and IL-4 in sensitized mice.

Oral probiotics prevent necrotizing enterocolitis in very low birth weight preterm infants: a multicenter, randomized, controlled trial

OBJECTIVE

The goal was to investigate the efficacy of orally administered probiotics in preventing necrotizing enterocolitis for very low birth weight preterm infants.

METHODS

A prospective, blinded, randomized, multicenter controlled trial was conducted at 7 NICUs in Taiwan, to evaluate the beneficial effects of probiotics in necrotizing enterocolitis among very low birth weight infants (birth weight: <1500 g). Very low birth weight infants who survived to start enteral feeding were eligible and were assigned randomly to 2 groups after parental informed consent was obtained. Infants in the study group were given Bifidobacterium bifidum and Lactobacillus acidophilus, added to breast milk or mixed feeding (breast milk and formula), twice daily for 6 weeks. Infants in the control group were fed with breast milk or mixed feeding. The clinicians caring for the infants were blinded to the group assignment. The primary outcome measurement was death or necrotizing enterocolitis (Bell's stage >or=2).

RESULTS

Four hundred thirty-four infants were enrolled, 217 in the study group and 217 in the control group. The incidence of death or necrotizing enterocolitis (stage >or=2) was significantly lower in the study group (4 of 217 infants vs 20 of 217 infants). The incidence of necrotizing enterocolitis (stage >or=2) was lower in the study group, compared with the control group (4 of 217 infants vs 14 of 217 infants). No adverse effect, such as sepsis, flatulence, or diarrhea, was noted.

CONCLUSION

Probiotics, in the form of Bifidobacterium and Lactobacillus, fed enterally to very low birth weight preterm infants for 6 weeks reduced the incidence of death or necrotizing enterocolitis.

The adhesion of putative probiotic lactobacilli to cultured epithelial cells and porcine intestinal mucus

AIMS

To investigate the adhesion of lactobacilli and their subsequent competitive exclusion ability against pathogens.

METHODS AND RESULTS

Four species of putative probiotic lactobacilli were studied for their adhesion abilities. First, the adhesion to Caco-2 cells was examined by light and electron microscopy. The four species were then labelled by [methyl-(3)H] thymidine and their adhesion to porcine intestinal mucus was determined by radioactivity. The tested lactobacilli showed best adhesion on ileal mucus compared with duodenal and jejunal mucus. Oxidative compound pre-treatment (NaIO(3) and NaIO(4)) dramatically decreased the adhesion of the lactobacilli to mucus. Pre-treating mucus with proteolytic enzymes (proteinase K and trypsin) resulted in the increase of adhesion in Lactobacillus serotype Reuteri I2021, but the results in the other species were variable. Lactobacillus serotype Fermentum I5007 showed greatest adhesion potential and exerted the best competitive exclusion against Salmonella and Escherichia.

CONCLUSIONS

Adhesion ability in lactobacilli is species-specific. Lactobacilli with higher adhesion index have better competitive exclusion ability.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study suggests that there is a positive correlation between adhesion and competitive exclusion ability of lactobacilli. Additionally, the in vitro adhesion assay is a feasible way to screen unknown lactobacilli, potentially for future industrial applications.

Genetic and phenotypic diversity of Bifidobacterium thermacidophilum fecal isolates from newborns

This study was undertaken to genetically identify and phenotypically characterize 14 bifidobacteria isolated from 20 breast-fed newborns. These isolates showed 98%–99% similarity to Bifidobacterium thermacidophilum subsp. suis based on 16S rDNA. Further analysis by pulsed-field gel electrophoresis of chromosomal DNA digested with XbaI revealed 4 distinct restriction patterns. The predominant pattern, shared by 8 (57%) isolates, produced a macro-restriction profile with about 13 large fragments ranging in size from >242.5 to 23.1 kb, whereas the other 6 displayed 3 distinct restriction profiles all characterized by more micro- than macro-restriction, with fragments ranging in size from 97 to 9.4 kb. Phenotypic characteristics, including carbohydrate fermentation profile, maximal growth temperature, and antibiotic susceptibility, varied widely even among strains showing the same restriction profile. The presence of B. thermacidophilum in stools of newborn infants may indicate the potential of these bacteria for aiding the development of the intestinal ecosystem.

Specific Bifidobacterium strains isolated from elderly subjects inhibit growth of Staphylococcus aureus

Cell-free, pH-controlled supernatants of thirty-eight Bifidobacterium strains isolated from healthy elderly subjects were subjected to antimicrobial activity assay. Bioluminescent indicator strains Staphylococcus aureus RN4220, Escherichia coli K-12, and Salmonella enterica serovar Typhimurium ATCC 14028 were used as targets of antimicrobial activity. The effect of nutrient depletion on the inhibition was eliminated with spent-culture controls. Three out of thirty-eight Bifidobacterium strains were capable of inhibiting the growth of S. aureus. The inhibition was equal to 23.2+/-19.1% to 50.4+/-26.7% of the inhibition caused by 50 IU/ml nisin. Reuterin-producing positive strain Lactobacillus reuteri SD2112 was capable of 86.0+/-24.6% inhibition, but Bifidobacterium lactis Bb-12, a known probiotic strain, showed no inhibition. None of the strains was capable of inhibiting the growth of E. coli or S. enterica. The observed inhibition by bifidobacteria was related to hydrogen peroxide formation and possible production of heat-stable proteinaceous compounds. The results suggest that production of antimicrobial substances other than organic acids is not common among Bifidobacterium strains typical of elderly subjects. However, specific strains were identified which showed considerable inhibitory activity against S. aureus.

Lactobacillus salivarius CECT 5713, a potential probiotic strain isolated from infant feces and breast milk of a mother-child pair

In this study, Lactobacillus salivarius CECT 5713 was originally isolated from feces of a one-month-old breast-fed infant. Since it has been suggested that the gut microbiota of breast-fed infants reflects that of the maternal breast milk, we investigated if this specific strain was present in breast milk of the respective mother. RAPD and PFGE analysis revealed the presence of the strain L. salivarius CECT 5713 in this biological fluid. To our knowledge, this is the first report of a L. salivarius strain isolated from breast milk. L. salivarius CECT 5713 produced l-lactate, acetate and hydrogen peroxide, which may be responsible for its antimicrobial activity against most of the indicator organisms used in this study; in addition, this strain showed a high survival rate after exposition to conditions simulating those found in the gastrointestinal tract. Finally, it was strongly adhesive to Caco-2 and HT-29 cells did not produce biogenic amines and were unable to degrade gastric mucin in vitro.

Comparison of antagonistic ability against enteropathogens by G+ and G− anaerobic dominant components of human fecal microbiota

To confirm if anaerobic G+-components are those responsible for the function of colonization resistance, obligate anaerobic G+- and G- -bacteria from normal dominant microbiota of human feces were isolated from three successive collections and then used in in vitro assays for antagonism against two enteropathogenic bacteria. The production of inhibitory diffusible compounds was determined on supplemented BHI agar and MRS agar media for G- - and G+-bacteria, respectively. Salmonella enterica subsp. enterica serovar Typhimurium and Shigella sonnei were used as indicators. G+-bacteria presented a higher overall antagonistic frequency against both pathogenic bacteria (57 and 64 % for S. enterica serovar Typhimurium and S. sonnei, respectively) when compared to G+-microorganisms but with a quite elevated variation between volunteers (0-100 %) and collection samples (40-72 and 40-80 % for S. enterica sv. Typhimurium and S. sonnei, respectively). On the other hand, only three among 143 G- -isolates tested showed antagonistic activity. The results showed that, at least in vitro, obligate anaerobic G+-components of the dominant human fecal microbiota present a higher potential for antagonism against the enteropathogenic models tested than do G- -bacteria.

A rapid method combining immunofluorescence and flow cytometry for improved understanding of competitive interactions between lactic acid bacteria (LAB) and methicillin-resistant S. aureus (MRSA) in mixed culture

The increasing frequency of methicillin-resistant Staphylococcus aureus (MRSA) infections in hospital and community settings highlights the need for effective anti-MRSA agents that will not contribute to the growing problem of antibiotic resistance. Lactic acid bacteria (LAB) are known to exclude various pathogens through multiple mechanisms. In vitro models studying interactions of pathogens and LAB in mixed cultures use selective agar plates to quantify changes in target populations. We applied commercially available S. aureus-specific polyclonal antibodies conjugated with fluorescein isothiocyanate (FITC) for this purpose, producing a bright green signal that clearly differentiates S. aureus from LAB species when mixed cultures are analyzed by flow cytometry and fluorescent microscopy. Flow cytometry of mixed cultures revealed a much larger population of MRSA cells than was detectable using selective agar plates. To our knowledge, this is the first time immunofluorescent flow cytometry has been applied to the study of competitive exclusion in mixed bacterial populations over time.

A randomized formula controlled trial of Bifidobacterium lactis and Streptococcus thermophilus for prevention of antibiotic-associated diarrhea in infants

GOALS

This clinical trial was carried out to determine whether oral treatment with a commercial probiotic formula containing Bifidobacterium lactis and Streptococcus thermophilus would reduce the frequency of antibiotic-associated diarrhea (AAD) in infants.

STUDY

In this double-bind formula controlled study, 80 infants, 6 to 36 months of age, were randomly assigned to receive a commercial formula containing 10 viable cells of B. lactis and 10 viable cells of S. thermophilus at the initiation of antibiotics for a duration of 15 days. The infants were assessed daily for formula intake, stool frequency, and stool consistency for a total duration of 30 days. Seventy-seven infants received nonsupplemented formula for the entire duration.

RESULTS

There was a significant difference in the incidence of AAD in the children receiving probiotic-supplemented formula (16%) than nonsupplemented formula (31%).

CONCLUSIONS

The present study shows that prevention against AAD in infants was obtained by oral treatment with daily dose of B. lactis and S. thermophilus.

Production of bacteriocin-like inhibitory compounds by human fecal Bifidobacterium strains

Acid- and bile-resistant Bifidobacterium strains were isolated from human feces and identified by genus-specific PCR and randomly amplified polymorphic DNA PCR. Twenty-four different strains were screened for possible production of proteinaceous antimicrobial compounds by assaying the inhibitory effects of their neutralized culture supernatants. Six Bifidobacterium strains (BIR-0304, BIR-0307, BIR-0312, BIR-0324, BIR-0326, and BIR-0349) were selected on the basis of their broad inhibitory spectra. These strains were active against gram-positive and gram-negative bacteria and yeasts relevant to food safety and human health. The antagonistic effects of the six selected Bifidobacterium strains were related to bacteriocin-like compounds, which were active at pH values between 3 and 10, stable at 100 degrees C for 10 min, resistant to alpha-amylase and lipase A, but sensitive to proteinases (trypsin, proteinase K, protease A, pepsin, and cathepsin B). The molecular masses of the antimicrobial compounds produced by Bifidobacterium BIR-0312 and BIR-0324 were in the range of 10 to 30 kDa, and those of the compounds produced by Bifidobacterium BIR-0304, BIR-0307, BIR-0326, and BIR-0349 were less than 10 kDa. All Bifidobacterium strains produced maximum antimicrobial activities in the late logarithmic phase of growth and in the presence of Tween 80. These results confirm that the synthesis of bacteriocin-like inhibitory compounds is a key factor in the in vitro inhibition of pathogen and spoilage bacteria by Bifidobacterium strains.

Antagonistic activities of lactobacilli and bifidobacteria against microbial pathogens

The gastrointestinal tract is a complex ecosystem that associates a resident microbiota and cells of various phenotypes lining the epithelial wall expressing complex metabolic activities. The resident microbiota in the digestive tract is a heterogeneous microbial ecosystem containing up to 1 x 10(14) colony-forming units (CFUs) of bacteria. The intestinal microbiota plays an important role in normal gut function and maintaining host health. The host is protected from attack by potentially harmful microbial microorganisms by the physical and chemical barriers created by the gastrointestinal epithelium. The cells lining the gastrointestinal epithelium and the resident microbiota are two partners that properly and/or synergistically function to promote an efficient host system of defence. The gastrointestinal cells that make up the epithelium, provide a physical barrier that protects the host against the unwanted intrusion of microorganisms into the gastrointestinal microbiota, and against the penetration of harmful microorganisms which usurp the cellular molecules and signalling pathways of the host to become pathogenic. One of the basic physiological functions of the resident microbiota is that it functions as a microbial barrier against microbial pathogens. The mechanisms by which the species of the microbiota exert this barrier effect remain largely to be determined. There is increasing evidence that lactobacilli and bifidobacteria, which inhabit the gastrointestinal microbiota, develop antimicrobial activities that participate in the host's gastrointestinal system of defence. The objective of this review is to analyze the in vitro and in vivo experimental and clinical studies in which the antimicrobial activities of selected lactobacilli and bifidobacteria strains have been documented.

Effect of Bifidobacterium longum ingestion on experimental salmonellosis in mice

AIMS

The effect of lactic acid bacteria on the immune system is well established under normal conditions and generally by in vivo determinations, but few data are available, in vivo, during an infectious challenge. The objective of this study was to obtain data on the putative protective role of bifidobacteria upon challenge with an intestinal pathogen.

METHODS AND RESULTS

The effect of oral treatment with Bifidobacterium longum Bb46 on intragastric challenge with Salmonella Typhimurium was studied. Faecal bacterial levels were determined in gnotobiotic (GN) mice and mortality, histopathology (intestines, liver), immunoglobulin levels (IgM, IgG, IgG1, IgG2a) and cytokine production (IFN-gamma, IL-10) were determined in conventional (CV) mice. Conventional mice received 0.1 ml probiotic milk (10(8) CFU) daily, 10 days before the oral pathogenic challenge (10(2) CFU). Then, probiotic treatment was continued until the end of the experiment. Probiotic treatment in germ-free mice consisted of a single dose at the beginning of the experiment. Control groups were treated with sterile skim milk and submitted to the same procedure. A higher survival (40%) was observed for probiotic-treated animals when compared with the control group (0%). This protective effect was confirmed by the histopathological and morphometric data. However, S. Typhimurium population levels in the faeces were similar among control and probiotic-treated groups. During the challenge with S. Typhimurium, a decrease in IFN-gamma and IgG2a productions was observed in probiotic-treated mice.

CONCLUSIONS

The protective effect against the pathogenic challenge may be due to a reduced inflammatory response, mediated by the probiotic treatment, but not to a population antagonism.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results suggest that dietary supplementation with B. longum could provide benefits against enteric infection.

Competitive inhibition of adherence of enterotoxigenic Escherichia coli, enteropathogenic Escherichia coli and Clostridium difficile to intestinal epithelial cell line Lovo by purified adhesin of Bifidobacterium adolescentis 1027

AIM: To observe competitive inhibition of adherence of enterotoxigenic Escherichia coli (ETEC), enteropathogenic Escherichia coli (EPEC) and Clostridium difficile (C. difficile) to intestinal epithelial cell line Lovo by purified adhesin of Bifidobacterium adolescentis 1027 (B. ado 1027).

METHODS: The binding of bacteria to intestinal epithelial cell line Lovo was counted by adhesion assay. The inhibition of adherence of ETEC, EPEC and C. difficile to intestinal epithelial cell line Lovo by purified adhesin of B. ado 1027 was evaluated quantitatively by flow cytometry.

RESULTS: The purified adhesin at the concentration of 10 µg/mL, 20 µg/mL and 30 µg/mL except at 1 µg/mL and 5 µg/mL could inhibit significantly the adhesion of ETEC, EPEC and C. difficile to intestinal epithelial cell line Lovo. Moreover, we observed that a reduction in bacterial adhesion was occurred with increase in the concentration of adhesin, and MFI (Mean fluorescent intensity) was decreased with increase in the concentration of adhesin.

CONCLUSION: The purified adhesin of B. ado 1027 can inhibit the adhesion of ETEC, EPEC and C. difficile to intestinal epithelial cell line Lovo in a dose-dependent manner.

Production of antibacterial substances by bifidobacterial isolates from infant stool active against Listeria monocytogenes

AIMS

This study aimed to characterize new isolates of human bifidobacteria, evaluate some of their probiotic potential and to screen these isolates for their effectiveness at inhibiting Listeria monocytogenes in vitro.

METHODS AND RESULTS

Thirty-four Bifidobacterium isolates from infant faeces were identified by fructose-6-phosphate phosphoketolase and PCR. Six isolates, coded RBL67, RBL68, RBL69, RBL70, RBL85 and RBL86, showed higher antagonistic activity against L. monocytogenes. Neutralized culture supernatants of these strains did not inhibit L. monocytogenes when tested by agar diffusion method. However, the concentration of supernatant by speed-vac resulted in the formation of an inhibitory effect with supernatants from strains RBL67, RBL68 and RBL70. This effect was shown to be related to heat-stable proteinaceous compound(s) which were resistant to heating at 100 degrees C for 5 min but not to pronase-E, proteinase-K or trypsin. The extraction of the inhibitory compounds by methanol-acetone extraction procedure indicated that four strains (RBL67, RBL68, RBL69 and RBL70) were mostly soluble in acetone. However, strain RBL85 produced inhibitory substances that were soluble in methanol.

CONCLUSION

Infant bifidobacterial isolates produce heat-stable proteinaceous compounds active against L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Production of antibacterial substances by bifidobacteria would improve intestinal bacterial ecology and inhibit intestinal pathogens.