Insights into physiological and genetic mupirocin susceptibility in bifidobacteria

Genomic Characterization and Safety Assessment of Bifidobacterium breve BS2-PB3 as Functional Food

Our group had isolated Bifidobacterium breve strain BS2-PB3 from human breast milk. In this study, we sequenced the whole genome of B. breve BS2-PB3, and with a focus on its safety profile, various probiotic characteristics (presence of antibiotic resistance genes, virulence factors, and mobile elements) were then determined through bioinformatic analyses. The antibiotic resistance profile of B. breve BS2-PB3 was also evaluated. The whole genome of B. breve BS2-PB3 consisted of 2,268,931 base pairs with a G-C content of 58.89% and 2,108 coding regions. The average nucleotide identity and whole-genome phylogenetic analyses supported the classification of B. breve BS2-PB3. According to our in silico assessment, B. breve BS2-PB3 possesses antioxidant and immunomodulation properties in addition to various genes related to the probiotic properties of heat, cold, and acid stress, bile tolerance, and adhesion. Antibiotic susceptibility was evaluated using the Kirby-Bauer disk-diffusion test, in which the minimum inhibitory concentrations for selected antibiotics were subsequently tested using the Epsilometer test. B. breve BS2-PB3 only exhibited selected resistance phenotypes, i.e., to mupirocin (minimum inhibitory concentration/MIC >1,024 μg/ml), sulfamethoxazole (MIC >1,024 μg/ml), and oxacillin (MIC >3 μg/ml). The resistance genes against those antibiotics, i.e., ileS, mupB, sul4, mecC and ramA, were detected within its genome as well. While no virulence factor was detected, four insertion sequences were identified within the genome but were located away from the identified antibiotic resistance genes. In conclusion, B. breve BS2-PB3 demonstrated a sufficient safety profile, making it a promising candidate for further development as a potential functional food.

The Genome of Bifidobacterium longum subsp. infantis YLGB-1496 Provides Insights into Its Carbohydrate Utilization and Genetic Stability

Bifidobacterium longum subsp. infantis YLGB-1496 (YLGB-1496) is a probiotic strain isolated from human breast milk. The application of YLGB-1496 is influenced by carbohydrate utilization and genetic stability. This study used genome sequencing and morphology during continuous subculture to determine the carbohydrate utilization characteristics and genetic stability of YLGB-1496. The complete genome sequence of YLGB-1496 consists of 2,758,242 base pairs, 2442 coding sequences, and a GC content of 59.87%. A comparison of carbohydrate transport and metabolism genes of Bifidobacterium longum subsp. infantis (B. infantis) showed that YLGB-1496 was rich in glycosyl hydrolase 13, 20, 25, and 109 gene families. During continuous subculture, the growth characteristics and fermentation activity of the strain were highly stable. The bacterial cell surface and edges of the 1000th-generation strains were progressively smoother and well-defined, with no perforations or breaks in the cell wall. There were 20 SNP loci at the 1000th generation, fulfilling the requirement of belonging to the same strain. The presence of genes associated with cell adhesion and the absence of resistance genes supported the probiotic characteristics of the strain. The data obtained in this study provide insights into broad-spectrum carbohydrate utilization, genomic stability, and probiotic properties of YLGB-1496, which provide theoretical support to promote the use of YLGB-1496.

Abundant resistome determinants in rhizosphere soil of the wild plant Abutilon fruticosum

A metagenomic whole genome shotgun sequencing approach was used for rhizospheric soil micribiome of the wild plant Abutilon fruticosum in order to detect antibiotic resistance genes (ARGs) along with their antibiotic resistance mechanisms and to detect potential risk of these ARGs to human health upon transfer to clinical isolates. The study emphasized the potential risk to human health of such human pathogenic or commensal bacteria, being transferred via food chain or horizontally transferred to human clinical isolates. The top highly abundant rhizospheric soil non-redundant ARGs that are prevalent in bacterial human pathogens or colonizers (commensal) included mtrA, soxR, vanRO, golS, rbpA, kdpE, rpoB2, arr-1, efrA and ileS genes. Human pathogenic/colonizer bacteria existing in this soil rhizosphere included members of genera Mycobacterium, Vibrio, Klebsiella, Stenotrophomonas, Pseudomonas, Nocardia, Salmonella, Escherichia, Citrobacter, Serratia, Shigella, Cronobacter and Bifidobacterium. These bacteria belong to phyla Actinobacteria and Proteobacteria. The most highly abundant resistance mechanisms included antibiotic efflux pump, antibiotic target alteration, antibiotic target protection and antibiotic inactivation. antimicrobial resistance (AMR) families of the resistance mechanism of antibiotic efflux pump included resistance-nodulation-cell division (RND) antibiotic efflux pump (for mtrA, soxR and golS genes), major facilitator superfamily (MFS) antibiotic efflux pump (for soxR gene), the two-component regulatory kdpDE system (for kdpE gene) and ATP-binding cassette (ABC) antibiotic efflux pump (for efrA gene). AMR families of the resistance mechanism of antibiotic target alteration included glycopeptide resistance gene cluster (for vanRO gene), rifamycin-resistant beta-subunit of RNA polymerase (for rpoB2 gene) and antibiotic-resistant isoleucyl-tRNA synthetase (for ileS gene). AMR families of the resistance mechanism of antibiotic target protection included bacterial RNA polymerase-binding protein (for RbpA gene), while those of the resistance mechanism of antibiotic inactivation included rifampin ADP-ribosyltransferase (for arr-1 gene). Better agricultural and food transport practices are required especially for edible plant parts or those used in folkloric medicine.

A novel approach for combining the metagenome, metaresistome, metareplicome and causal inference to determine the microbes and their antibiotic resistance gene repertoire that contribute to dysbiosis

The use of whole metagenomic data to infer the relative abundance of all its microbes is well established. The same data can be used to determine the replication rate of all eubacterial taxa with circular chromosomes. Despite their availability, the replication rate profiles (metareplicome) have not been fully exploited in microbiome analyses. Another relatively new approach is the application of causal inferencing to analyse microbiome data that goes beyond correlational studies. A novel scalable pipeline called MeRRCI (Metagenome, metaResistome, and metaReplicome for Causal Inferencing) was developed. MeRRCI combines efficient computation of the metagenome (bacterial relative abundance), metaresistome (antimicrobial gene abundance) and metareplicome (replication rates), and integrates environmental variables (metadata) for causality analysis using Bayesian networks. MeRRCI was applied to an infant gut microbiome data set to investigate the microbial community's response to antibiotics. Our analysis suggests that the current treatment stratagem contributes to preterm infant gut dysbiosis, allowing a proliferation of pathobionts. The study highlights the specific antibacterial resistance genes that may contribute to exponential cell division in the presence of antibiotics for various pathogens, namely Klebsiella pneumoniae, Citrobacter freundii, Staphylococcus epidermidis, Veilonella parvula and Clostridium perfringens. These organisms often contribute to the harmful long-term sequelae seen in these young infants.

Different maturation of gut microbiome in Korean children

Introduction

Gut microbiome plays a crucial role in maintaining human health and is influenced by food intake, age, and other factors.

Methods

In this study based in Korea, we examined the bacterial taxonomic composition of the gut microbiota in infants (≤ 1 year), toddlers (1-<4 years), and school-aged children (4-13 years) and compared them with those of healthy adults to investigate the microbiota changes in early life and their association with the resistome. We used whole metagenome sequences obtained by Illumina HiSeq sequencing and clinical information of 53 healthy children, and sequence data of 61 adults from our previous study.

Results

Our results indicate that the bacterial proportion of the gut in the population ranging from infants to adults forms three clusters: the Ruminococcus-Eubacterium (G1), Bifidobacterium-Escherichia (G2), and Bacteroides-Faecalibacterium (G3) groups. The gut microbiota of infants and toddlers (100% of infants and 85% of toddlers) constituted mostly of G2 and G3 groups, whereas 90% of adults showed G1-type gut microbiota. School-aged children showed a transitional gut microbiota composition of both infants and adults (31%, 38%, and 31% in G1, G2, and G3, respectively). Notably, the three clusters of microbiota showed significantly different patterns of bacterial diversity (p < 0.001): G2 showed the lowest Shannon index, followed by G3 and G1 (1.41, 2.08, and 2.48, respectively; median Shannon index). When combined with the adult group, alpha diversity showed a positive correlation with age (R² = 0.3). Furthermore, clustering the composition of antibiotic resistance genes (ARG) identified two clusters (A1 and A2), and most of G1 (95%) and G3 (80%) belonged to A1. However, G2 showed the least diversity and the highest abundance of ARGs. Nine ARG families showed a significant difference among age groups; three tetracycline resistance genes, tet32, tetO, and tetW, showed a positive correlation, and six other genes, ampC, TEM, ileS, bacA, pmr transferase, and cepA, showed a negative correlation with age.

Discussion

In conclusion, our results highlighted that a delayed persistence of the Bifidobacterium-dominant enterotype with a lower bacterial diversity was observed in Korean children up to 13 years of age, which suggests a different maturation process with a delayed maturation time.

Gut colonisation by extended-spectrum β-lactamase-producing Escherichia coli and its association with the gut microbiome and metabolome in Dutch adults: a matched case-control study

BACKGROUND

Gut colonisation by extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is a risk factor for developing overt infection. The gut microbiome can provide colonisation resistance against enteropathogens, but it remains unclear whether it confers resistance against ESBL-producing E coli. We aimed to identify a potential role of the microbiome in controlling colonisation by this antibiotic-resistant bacterium.

METHODS

For this matched case-control study, we used faeces from 2751 individuals in a Dutch cross-sectional population study (PIENTER-3) to culture ESBL-producing bacteria. Of these, we selected 49 samples that were positive for an ESBL-producing E coli (ESBL-positive) and negative for several variables known to affect microbiome composition. These samples were matched 1:1 to ESBL-negative samples on the basis of individuals' age, sex, having been abroad or not in the past 6 months, and ethnicity. Shotgun metagenomic sequencing was done and taxonomic species composition and functional annotations (ie, microbial metabolism and carbohydrate-active enzymes) were determined. Targeted quantitative metabolic profiling (proton nuclear magnetic resonance spectroscopy) was done to investigate metabolomic profiles and combinations of univariate (t test and Wilcoxon test), multivariate (principal coordinates analysis, permutational multivariate analysis of variance, and partial least-squares discriminant analysis) and machine-learning approaches (least absolute shrinkage and selection operator and random forests) were used to analyse all the molecular data.

FINDINGS

No differences in diversity parameters or in relative abundance were observed between ESBL-positive and ESBL-negative groups based on bacterial species-level composition. Machine-learning approaches using microbiota composition did not accurately predict ESBL status (area under the receiver operating characteristic curve [AUROC]=0·41) when using either microbiota composition or any of the functional profiles. The metabolome also did not differ between ESBL groups, as assessed by various methods including random forest (AUROC=0·61).

INTERPRETATION

By combining multiomics and machine-learning approaches, we conclude that asymptomatic gut carriage of ESBL-producing E coli is not associated with an altered microbiome composition or function. This finding might suggest that microbiome-mediated colonisation resistance against ESBL-producing E coli is not as relevant as it is against other enteropathogens and antibiotic-resistant bacteria.

FUNDING

None.

Novel microaerobic agar plate method delivers highly selective and accurate enumeration of probiotic lactobacilli in freeze-dried blends containing bifidobacteria

The enumeration of viable bacteria is an essential metric in the dietary supplement and food industry to ensure quality of probiotic products. However, selective enumeration of lactobacilli in probiotic freeze-dried blends containing bifidobacteria is difficult to achieve with current Lactobacillus-specific agars (i.e., Rogosa and LAMVAB). Using a panel of Bifidobacterium and Lactobacillus commercial probiotic species, we found that Rogosa agar failed to inhibit all bifidobacteria while LAMVAB agar suppressed several lactobacilli. This prompted us to develop an alternative method of selection, hereby referred to as Lactobacillus Micro-Aerobic (LMA) method, which promotes growth under controlled microaerobic conditions (6-12% O₂, 5-8% CO₂) to leverage the different oxygen sensitivities of lactobacilli and bifidobacteria. Validation using pure cultures and multi-strain blends of 4 Bifidobacterium and 10 Lactobacillus species showed that LMA effectively suppressed all bifidobacteria and accurately enumerated all lactobacilli when compared to control methods. These results demonstrate the superior efficacy of modulating the redox environment to select for Lactobacillus within a Bifidobacterium-rich background, as opposed to applying acid and antibiotic pressures.

Mobile Antimicrobial Resistance Genes in Probiotics

Even though people worldwide tend to consume probiotic products for their beneficial health effects on a daily basis, recently, concerns were outlined regarding the uptake and potential intestinal colonisation of the bacteria that they carry. These bacteria are capable of executing horizontal gene transfer (HGT) which facilitates the movement of various genes, including antimicrobial resistance genes (ARGs), among the donor and recipient bacterial populations. Within our study, 47 shotgun sequencing datasets deriving from various probiotic samples (isolated strains and metagenomes) were bioinformatically analysed. We detected more than 70 ARGs, out of which rpoB mutants conferring resistance to rifampicin, tet(W/N/W) and potentially extended-spectrum beta-lactamase (ESBL) coding TEM-116 were the most common. Numerous ARGs were associated with integrated mobile genetic elements, plasmids or phages promoting the HGT. Our findings raise clinical and public health concerns as the consumption of probiotic products may lead to the transfer of ARGs to human gut bacteria.

Protocol to Select Bifidobacteria from Fecal and Environmental Samples

Bifidobacteria are commensal microorganisms able to colonize several ecological niches. Since their discovery, culture-dependent methods combined with the most modern next-generation sequencing techniques have contributed to shed light on the ecological, functional and genomic features of bifidobacteria, purporting them as microorganisms with probiotic traits. Thanks to their acclaimed health-promoting effects, several members of the Bifidobacterium genus have been included in a variety of functional foods and drugs. In this context, the functional relevance of bifidobacteria in the gut explains ongoing efforts to isolate novel and potentially beneficial strains. For this purpose, development of effective and selective isolation protocols in concert with knowledge on the physiological characteristics of bifidobacterial are fundamental requirements for their recovery and discovery from their natural environments, in particular from fecal samples.

Ruminal resistome of dairy cattle is individualized and the resistotypes are associated with milking traits

BACKGROUND

Antimicrobial resistance is one of the most urgent threat to global public health, as it can lead to high morbidity, mortality, and medical costs for humans and livestock animals. In ruminants, the rumen microbiome carries a large number of antimicrobial resistance genes (ARGs), which could disseminate to the environment through saliva, or through the flow of rumen microbial biomass to the hindgut and released through feces. The occurrence and distribution of ARGs in rumen microbes has been reported, revealing the effects of external stimuli (e.g., antimicrobial administrations and diet ingredients) on the antimicrobial resistance in the rumen. However, the host effect on the ruminal resistome and their interactions remain largely unknown. Here, we investigated the ruminal resistome and its relationship with host feed intake and milk protein yield using metagenomic sequencing.

RESULTS

The ruminal resistome conferred resistance to 26 classes of antimicrobials, with genes encoding resistance to tetracycline being the most predominant. The ARG-containing contigs were assigned to bacterial taxonomy, and the majority of highly abundant bacterial genera were resistant to at least one antimicrobial, while the abundances of ARG-containing bacterial genera showed distinct variations. Although the ruminal resistome is not co-varied with host feed intake, it could be potentially linked to milk protein yield in dairy cows. Results showed that host feed intake did not affect the alpha or beta diversity of the ruminal resistome or the abundances of ARGs, while the Shannon index (R² = 0.63, P < 0.01) and richness (R² = 0.67, P < 0.01) of the ruminal resistome were highly correlated with milk protein yield. A total of 128 significantly different ARGs (FDR < 0.05) were identified in the high- and low-milk protein yield dairy cows. We found four ruminal resistotypes that are driven by specific ARGs and associated with milk protein yield. Particularly, cows with low milk protein yield are classified into the same ruminal resistotype and featured by high-abundance ARGs, including mfd and sav1866.

CONCLUSIONS

The current study uncovered the prevalence of ARGs in the rumen of a cohort of lactating dairy cows. The ruminal resistome is not co-varied with host feed intake, while it could be potentially linked to milk protein yield in dairy cows. Our results provide fundamental knowledge on the prevalence, mechanisms and impact factors of antimicrobial resistance in dairy cattle and are important for both the dairy industry and other food animal antimicrobial resistance control strategies.

Literature-Based Phenotype Survey and In Silico Genotype Investigation of Antibiotic Resistance in the Genus Bifidobacterium

Bifidobacteria are typical commensals inhabiting the human intestine and are beneficial to the host because of their probiotic properties. One of the risks concerning probiotics is the potential of introducing antibiotic resistance genes (ARGs) to the host gut pathogens. This study was aimed to depict the general antibiotic resistance characteristics of the genus Bifidobacterium by combining the reported phenotype dataset and in silico genotype prediction. Bifidobacteria were mostly reported to be sensitive to beta-lactams, glycopeptides, chloramphenicol, and rifampicin, but resistant to aminoglycosides, polypeptides, quinolones, and mupirocin. Generally, the resistance phenotypes to erythromycin, tetracycline, fusidic acid, metronidazole, clindamycin, and trimethoprim were variable. Besides cmX and tetQ, characterized in bifidobacterial resident plasmids, 3520 putative ARGs were identified from 831 bifidobacterial genomes through BLASTP search. The identified ARGs matched thirty-eight reference ARGs, four of which seemed to be mutant housekeeping genes. The two high-abundant ARGs, tetW and ermX, were found to have different distribution traits. The predicted ARGs reasonably explained most of the corresponding resistant phenotypes in the published literature.

Antibiotic resistance propagation through probiotics

INTRODUCTION

The widespread use of probiotics globally has established an argument against their safety profile. Recent studies investigated the gastrointestinal tract (GIT) as a reservoir for antibiotic resistance genes and horizontal gene transfer (HGT) amongst opportunistic pathogens, probiotics, and the normal microbiota which might cause severe clinical implications.

AREAS COVERED

In this review, we aimed to discuss the potential role of probiotics in spreading antibiotic resistance. All relevant data were found through online/updated databases such as PubMed, Google Scholar, and Clinicaltrials.gov. This review is based on the studies undertaken over the past two decades (2000-2020).

EXPERT OPINION

Microorganisms are capable of transferring resistance genes to survive against antimicrobial medications. Transference of resistance genes among pathogens, probiotics, and gut microbiota in the GIT through HGT endow probiotics as a possible source for antimicrobial resistance genes, which is responsible for the development of the antibiotic resistance crisis. According to the expression of genes in mechanisms of antibiotics resistance and probiotics HGT, the hypothesis of the role of these microorganisms in personalized medicine and gene therapy could also be considered.

Human milk and mucosa-associated disaccharides impact on cultured infant fecal microbiota

Human milk oligosaccharides (HMOs) are a mixture of structurally diverse carbohydrates that contribute to shape a healthy gut microbiota composition. The great diversity of the HMOs structures does not allow the attribution of specific prebiotic characteristics to single milk oligosaccharides. We analyze here the utilization of four disaccharides, lacto-N-biose (LNB), galacto-N-biose (GNB), fucosyl-α1,3-GlcNAc (3FN) and fucosyl-α1,6-GlcNAc (6FN), that form part of HMOs and glycoprotein structures, by the infant fecal microbiota. LNB significantly increased the total levels of bifidobacteria and the species Bifidobacterium breve and Bifidobacterium bifidum. The Lactobacillus genus levels were increased by 3FN fermentation and B. breve by GNB and 3FN. There was a significant reduction of Blautia coccoides group with LNB and 3FN. In addition, 6FN significantly reduced the levels of Enterobacteriaceae family members. Significantly higher concentrations of lactate, formate and acetate were produced in cultures containing either LNB or GNB in comparison with control cultures. Additionally, after fermentation of the oligosaccharides by the fecal microbiota, several Bifidobacterium strains were isolated and identified. The results presented here indicated that each, LNB, GNB and 3FN disaccharide, might have a specific beneficial effect in the infant gut microbiota and they are potential prebiotics for application in infant foods.

Metagenomic analysis reveals antibiotic resistance genes in the bovine rumen

Metagenomics and network analysis were used to profile antibiotic resistance genes (ARGs) and their cooccurrence patterns in bovine rumen microbes. A total of 4941 ruminal microbial genomes and 20 metagenome samples were used in this study. In general, 103 ARG subtypes belonging to 20 ARG types in 79 candidate genomes were identified, showing the broad-spectrum profiles of ARGs in the bovine rumen environment. A wide distribution of genes encoding bacitracin resistance was found among the candidate genomes, suggesting the possibility that bovines might be one of the sources of bacitracin resistance genes. Cooccurrence patterns were found within or between the ARG types, and a positive correlation was found between some ARGs and bacteria, which revealed potential dominant hosts of ARGs. The investigation showed that bovine rumen systems are important ARG reservoirs, and our research might provide a theoretical basis for the evaluation of the harmfulness of ARGs and antibiotic-resistant bacteria (ARB) to food safety and human health.

Rapid MinION profiling of preterm microbiota and antimicrobial-resistant pathogens

The MinION sequencing platform offers near real-time analysis of DNA sequence; this makes the tool attractive for deployment in fieldwork or clinical settings. We used the MinION platform coupled to the NanoOK RT software package to perform shotgun metagenomic sequencing and profile mock communities and faecal samples from healthy and ill preterm infants. Using Nanopore data, we reliably classified a 20-species mock community and captured the diversity of the immature gut microbiota over time and in response to interventions such as probiotic supplementation, antibiotic treatment or episodes of suspected sepsis. We also performed rapid real-time runs to assess gut-associated microbial communities in critically ill and healthy infants, facilitated by NanoOK RT software package, which analysed sequences as they were generated. Our pipeline reliably identified pathogenic bacteria (that is, Klebsiella pneumoniae and Enterobacter cloacae) and their corresponding antimicrobial resistance gene profiles within as little as 1 h of sequencing. Results were confirmed using pathogen isolation, whole-genome sequencing and antibiotic susceptibility testing, as well as mock communities and clinical samples with known antimicrobial resistance genes. Our results demonstrate that MinION (including cost-effective Flongle flow cells) with NanoOK RT can process metagenomic samples to a rich dataset in < 5 h, which creates a platform for future studies aimed at developing these tools and approaches in clinical settings with a focus on providing tailored patient antimicrobial treatment options.

Antibiotic resistance genes in the Actinobacteria phylum

The Actinobacteria phylum is one of the oldest bacterial phyla that have a significant role in medicine and biotechnology. There are a lot of genera in this phylum that are causing various types of infections in humans, animals, and plants. As well as antimicrobial agents that are used in medicine for infections treatment or prevention of infections, they have been discovered of various genera in this phylum. To date, resistance to antibiotics is rising in different regions of the world and this is a global health threat. The main purpose of this review is the molecular evolution of antibiotic resistance in the Actinobacteria phylum.

River Ganges water as reservoir of microbes with antibiotic and metal ion resistance genes: High throughput metagenomic approach

The large scale usage of antibiotics and trace elements leads to their progressive release in the environment, and ultimately the spread of antibiotic resistance genes (ARGs) and metal ion resistance genes (MRGs) in bacteria. A high-throughput metagenomic sequencing of the microbial community in water and sediments in the river Ganges harboring resistance genes was performed. The results revealed that the river harbors a broad spectrum of resistance genes with high abundance in sediments. The highly dominant ARGs type was beta-lactam, multidrug/efflux and elfamycin. The ARGs such as (tuf, parY, ileS, mfd) were highly abundant in water and sediments. The MRGs subtype acn was the most abundant metal resistance gene in water and sediments. Majority of ARGs types showed significant (p ≤ 0.05) positive correlation with the MRGs types in the river environment suggesting their distribution and transfer to be possibly linked. Taxonomic classification revealed that Proteobacteria and Actinobacteria were the two most abundant phyla in water and sediments. Arcobacter, Terrimicrobium, Acidibacter and Pseudomonas were the most abundant genera. This study suggests that antibiotics and metals are the driving force for the emergence of resistance genes, and their subsequent propagation and accumulation in the environmental bacteria. The present metagenomic investigation highlights significance of such study, and attracts attention for the mitigation of pollutants associated with the propagation of ARGs and MRGs in the river environment.

Complementary Mechanisms for Degradation of Inulin-Type Fructans and Arabinoxylan Oligosaccharides among Bifidobacterial Strains Suggest Bacterial Cooperation

Inulin-type fructans (ITF) and arabinoxylan oligosaccharides (AXOS) are broken down to different extents by various bifidobacterial strains present in the human colon. To date, phenotypic heterogeneity in the consumption of these complex oligosaccharides at the strain level remains poorly studied. To examine mechanistic variations in ITF and AXOS constituent preferences present in one individual, ITF and AXOS consumption by bifidobacterial strains isolated from the simulator of the human intestinal microbial ecosystem (SHIME) after inoculation with feces from one healthy individual was investigated. Among the 18 strains identified, four species-independent clusters displaying different ITF and AXOS degradation mechanisms and preferences were found. Bifidobacterium bifidum B46 showed limited growth on all substrates, whereas B. longum B24 and B. longum B18 could grow better on short-chain-length fractions of fructooligosaccharides (FOS) than on fructose. B. longum B24 could cleave arabinose substituents of AXOS extracellularly, without using the AXOS-derived xylose backbones, whereas B. longum B18 was able to consume oligosaccharides (up to xylotetraose) preferentially and consumed AXOS to a limited extent. B. adolescentis B72 degraded all fractions of FOS simultaneously, partially degraded inulin, and could use xylose backbones longer than xylotetraose extracellularly. The strain-specific degradation mechanisms were suggested to be complementary and indicated resource partitioning. Specialization in the degradation of complex carbohydrates by bifidobacteria present on the individual level could have in vivo implications for the successful implementation of ITF and AXOS, aiming at bifidogenic and/or butyrogenic effects. Finally, this work shows the importance of taking microbial strain-level differences into account in gut microbiota research.IMPORTANCE It is well known that bifidobacteria degrade undigestible complex polysaccharides, such as ITF and AXOS, in the human colon. However, this process has never been studied for strains coexisting in the same individual. To examine strain-dependent mechanistic variations in ITF and AXOS constituent preferences present in one individual, ITF and AXOS consumption by bifidobacterial strains isolated from the SHIME after inoculation with feces from one healthy individual was investigated. Among the 18 bifidobacterial strains identified, four species-independent clusters displaying different ITF and AXOS degradation mechanisms and preferences were found, indicating that such strains can coexist in the human colon. Such specialization in the degradation of complex carbohydrates by bifidobacteria present on the individual level could have in vivo implications for the successful implementation of ITF and AXOS, aiming at bifidogenic and/or butyrogenic effects.

Unveiling bifidobacterial biogeography across the mammalian branch of the tree of life

Internally transcribed spacer (ITS) rRNA profiling is a novel tool for detailed analysis of microbial populations at low taxonomic ranks. Here we exploited this approach to explore species-level biogeography of the Bifidobacterium genus across 291 adult mammals. These include humans and 13 other primates, domesticated animals, such as dogs, cats, cows, sheep, goats, horses and pigs, and 46 additional species. The collected profiles revealed the presence of 89 putative novel bifidobacterial taxa in addition to 45 previously described species. Remarkably, in contrast to what is currently known for many gut commensals, we did not observe host-specialization among bifidobacterial species but rather their widespread distribution across mammals. Moreover, ITS rRNA profiling of wild relatives of domesticated dogs, rabbits and pigs clearly indicates that domestication and close contact with humans have impacted on the composition of the fecal bifidobacterial population. These data were complemented by analysis of bifidobacterial communities in milk of eight mammalian families, showing that bifidobacteria represent prototypical early gut microbiota members which are inherited by newborns from their lactating mother. Thus this study highlights the role of bifidobacteria as pioneering gut colonizers of a wide range of mammals.

Genomic Characteristics of Bifidobacterium thermacidophilum Pig Isolates and Wild Boar Isolates Reveal the Unique Presence of a Putative Mobile Genetic Element with tetW for Pig Farm Isolates

Genomic analysis was performed on seven strains of Bifidobacterium thermacidophilum, a Sus-associated Bifidobacterium. Three strains from the feces of domestic pigs (Sus scrofa domesticus) and four strains from the rectal feces of free-range Japanese wild boars (S. s. scrofa) were compared. The phylogenetic position of these isolates suggested by genomic analyses were not concordant with that suggested by 16S rRNA sequence. There was biased distribution of genes for virulence, phage, metabolism of aromatic compounds, iron acquisition, cell division, and DNA metabolism. In particular four wild boar isolates harbored fiber-degrading enzymes, such as endoglucanase, while two of the pig isolates obtained from those grown under an intensive feeding practice with routine use of antimicrobials, particularly tetracycline harbored a tetracycline resistance gene, which was further proved functional by disk diffusion test. The tetW gene is associated with a serine recombinase of an apparently non-bifidobacterial origin. The insertion site of the tetW cassette was precisely defined by analyzing the corresponding genomic regions in the other tetracycline-susceptible isolates. The cassette may have been transferred from some other bacteria in the pig gut.

Naturally Occurring Isoleucyl-tRNA Synthetase without tRNA-dependent Pre-transfer Editing

Isoleucyl-tRNA synthetase (IleRS) is unusual among aminoacyl-tRNA synthetases in having a tRNA-dependent pre-transfer editing activity. Alongside the typical bacterial IleRS (such as Escherichia coli IleRS), some bacteria also have the enzymes (eukaryote-like) that cluster with eukaryotic IleRSs and exhibit low sensitivity to the antibiotic mupirocin. Our phylogenetic analysis suggests that the ileS1 and ileS2 genes of contemporary bacteria are the descendants of genes that might have arisen by an ancient duplication event before the separation of bacteria and archaea. We present the analysis of evolutionary constraints of the synthetic and editing reactions in eukaryotic/eukaryote-like IleRSs, which share a common origin but diverged through adaptation to different cell environments. The enzyme from the yeast cytosol exhibits tRNA-dependent pre-transfer editing analogous to E. coli IleRS. This argues for the presence of this proofreading in the common ancestor of both IleRS types and an ancient origin of the synthetic site-based quality control step. Yet surprisingly, the eukaryote-like enzyme from Streptomyces griseus IleRS lacks this capacity; at the same time, its synthetic site displays the 10³-fold drop in sensitivity to antibiotic mupirocin relative to the yeast enzyme. The discovery that pre-transfer editing is optional in IleRSs lends support to the notion that the conserved post-transfer editing domain is the main checkpoint in these enzymes. We substantiated this by showing that under error-prone conditions S. griseus IleRS is able to rescue the growth of an E. coli lacking functional IleRS, providing the first evidence that tRNA-dependent pre-transfer editing in IleRS is not essential for cell viability.

Evaluation of culture media for selective enumeration of bifidobacteria and lactic acid bacteria

The purpose of this study was to test the suitability of Transgalactosylated oligosaccharides-mupirocin lithium salt (TOS-MUP) and MRS-clindamycin-ciprofloxacin (MRS-CC) agars, along with several other culture media, for selectively enumerating bifidobacteria and lactic acid bacteria (LAB) species commonly used to make fermented milks. Pure culture suspensions of a total of 13 dairy bacteria strains, belonging to eight species and five genera, were tested for growth capability under various incubation conditions. TOS-MUP agar was successfully used for the selective enumeration of both Bifidobacterium animalis subsp. lactis BB-12 and B. breve M-16 V. MRS-CC agar showed relatively good selectivity for Lactobacillus acidophilus, however, it also promoted the growth of Lb. casei strains. For this reason, MRS-CC agar can only be used as a selective medium for the enumeration of Lb. acidophilus if Lb. casei is not present in a product at levels similar to or exceeding those of Lb. acidophilus. Unlike bifidobacteria and coccus-shaped LAB, all the lactobacilli strains involved in this work were found to grow well in MRS pH 5.4 agar incubated under anaerobiosis at 37 °C for 72 h. Therefore, this method proved to be particularly suitable for the selective enumeration of Lactobacillus spp.

Bifidobacterium bifidum PRL2010 modulates the host innate immune response

Here, we describe data obtained from transcriptome profiling of human cell lines and intestinal cells of a murine model upon exposure and colonization, respectively, with Bifidobacterium bifidum PRL2010. Significant changes were detected in the transcription of genes that are known to be involved in innate immunity. Furthermore, results from enzyme-linked immunosorbent assays (ELISAs) showed that exposure to B. bifidum PRL2010 causes enhanced production of interleukin 6 (IL-6) and IL-8 cytokines, presumably through NF-κB activation. The obtained global transcription profiles strongly suggest that Bifidobacterium bifidum PRL2010 modulates the innate immune response of the host.

de los Reyes-Gavilán C, Margolles A. Antibiotic resistance in probiotic bacteria

Probiotics are live microorganisms which when administered in adequate amounts confer a health benefit on the host. The main probiotic bacteria are strains belonging to the genera Lactobacillus and Bifidobacterium, although other representatives, such as Bacillus or Escherichia coli strains, have also been used. Lactobacillus and Bifidobacterium are two common inhabitants of the human intestinal microbiota. Also, some species are used in food fermentation processes as starters, or as adjunct cultures in the food industry. With some exceptions, antibiotic resistance in these beneficial microbes does not constitute a safety concern in itself, when mutations or intrinsic resistance mechanisms are responsible for the resistance phenotype. In fact, some probiotic strains with intrinsic antibiotic resistance could be useful for restoring the gut microbiota after antibiotic treatment. However, specific antibiotic resistance determinants carried on mobile genetic elements, such as tetracycline resistance genes, are often detected in the typical probiotic genera, and constitute a reservoir of resistance for potential food or gut pathogens, thus representing a serious safety issue.

An efficient and reproducible method for transformation of genetically recalcitrant bifidobacteria

This study describes an efficient transformation system for the introduction of plasmid DNA into Bifidobacterium bifidum PRL2010 and Bifidobacterium asteroides PRL2011, for which to the best of our knowledge no transformation data have been reported previously. The method is based on electroporation of bifidobacterial cells, which were made competent by an optimized methodology based on varying media and growth conditions. Furthermore, the transformation protocol was applied in order to design a PRL2010-derivative, which carries antibiotic resistance against chloramphenicol and which was used to monitor PRL2010 colonization in a murine model.

Ability of Bifidobacterium breve to grow on different types of milk: exploring the metabolism of milk through genome analysis

We have investigated the occurrence of bifidobacteria in human milk samples, and we provide evidence regarding the predominance of members of the Bifidobacterium breve species in this environment. Moreover, evaluation of the growth capabilities and transcriptomic analyses of one representative isolate of this species, i.e., B. breve 4L, on different milk types were performed.