Screening of Human Gut Bacterial Culture Collection Identifies Species That Biotransform Quercetin into Metabolites with Anticancer Properties.

We previously demonstrated that flavonoid metabolites inhibit cancer cell proliferation through both CDK-dependent and -independent mechanisms. The existing evidence suggests that gut microbiota is capable of flavonoid biotransformation to generate bioactive metabolites including 2,4,6-trihydroxybenzoic acid (2,4,6-THBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), 3,4,5-trihyroxybenzoic acid (3,4,5-THBA) and 3,4-dihydroxyphenylacetic acid (DOPAC). In this study, we screened 94 human gut bacterial species for their ability to biotransform flavonoid quercetin into different metabolites. We demonstrated that five of these species were able to degrade quercetin including Bacillus glycinifermentans, Flavonifractor plautii, Bacteroides eggerthii, Olsenella scatoligenes and Eubacterium eligens. Additional studies showed that B. glycinifermentans could generate 2,4,6-THBA and 3,4-DHBA from quercetin while F. plautii generates DOPAC. In addition to the differences in the metabolites produced, we also observed that the kinetics of quercetin degradation was different between B. glycinifermentans and F. plautii, suggesting that the pathways of degradation are likely different between these strains. Similar to the antiproliferative effects of 2,4,6-THBA and 3,4-DHBA demonstrated previously, DOPAC also inhibited colony formation ex vivo in the HCT-116 colon cancer cell line. Consistent with this, the bacterial culture supernatant of F. plautii also inhibited colony formation in this cell line. Thus, as F. plautii and B. glycinifermentans generate metabolites possessing antiproliferative activity, we suggest that these strains have the potential to be developed into probiotics to improve human gut health.

Gut microbes from the phylogenetically diverse genus Eubacterium and their various contributions to gut health.

Over the last two decades our understanding of the gut microbiota and its contribution to health and disease has been transformed. Among a new 'generation' of potentially beneficial microbes to have been recognized are members of the genus Eubacterium, who form a part of the core human gut microbiome. The genus consists of phylogenetically, and quite frequently phenotypically, diverse species, making Eubacterium a taxonomically unique and challenging genus. Several members of the genus produce butyrate, which plays a critical role in energy homeostasis, colonic motility, immunomodulation and suppression of inflammation in the gut. Eubacterium spp. also carry out bile acid and cholesterol transformations in the gut, thereby contributing to their homeostasis. Gut dysbiosis and a consequently modified representation of Eubacterium spp. in the gut, have been linked with various human disease states. This review provides an overview of Eubacterium species from a phylogenetic perspective, describes how they alter with diet and age and summarizes its association with the human gut and various health conditions.

MtcB, a member of the MttB superfamily from the human gut acetogen Eubacterium limosum, is a cobalamin-dependent carnitine demethylase.

The trimethylamine methyltransferase MttB is the first described member of a superfamily comprising thousands of microbial proteins. Most members of the MttB superfamily are encoded by genes that lack the codon for pyrrolysine characteristic of trimethylamine methyltransferases, raising questions about the activities of these proteins. The superfamily member MtcB is found in the human intestinal isolate Eubacterium limosum ATCC 8486, an acetogen that can grow by demethylation of l-carnitine. Here, we demonstrate that MtcB catalyzes l-carnitine demethylation. When growing on l-carnitine, E. limosum excreted the unusual biological product norcarnitine as well as acetate, butyrate, and caproate. Cellular extracts of E. limosum grown on l-carnitine, but not lactate, methylated cob-(I)alamin or tetrahydrofolate using l-carnitine as methyl donor. MtcB, along with the corrinoid protein MtqC and the methylcorrinoid:tetrahydrofolate methyltransferase MtqA, were much more abundant in E. limosum cells grown on l-carnitine than on lactate. Recombinant MtcB methylates either cob(I)alamin or Co(I)-MtqC in the presence of l-carnitine and, to a much lesser extent, γ-butyrobetaine. Other quaternary amines were not substrates. Recombinant MtcB, MtqC, and MtqA methylated tetrahydrofolate via l-carnitine, forming a key intermediate in the acetogenic Wood-Ljungdahl pathway. To our knowledge, MtcB methylation of cobalamin or Co(I)-MtqC represents the first described mechanism of biological l-carnitine demethylation. The conversion of l-carnitine and its derivative γ-butyrobetaine to trimethylamine by the gut microbiome has been linked to cardiovascular disease. The activities of MtcB and related proteins in E. limosum might demethylate proatherogenic quaternary amines and contribute to the perceived health benefits of this human gut symbiont.

Breastfeeding may have a long-term effect on oral microbiota: results from the Fin-HIT cohort.

BACKGROUND: Breastfeeding contributes to gastrointestinal microbiota colonization in early life, but its long-term impact is inconclusive. We aimed to evaluate whether the type of feeding during the first six months of life was associated with oral microbiota in adolescence. METHODS: This is a cross-sectional sub-study using baseline information of 423 adolescents from the Finnish Health in Teens (Fin-HIT) cohort. Type of feeding was recalled by parents and dichotomized as (i) No infant formula; (ii) Infant formula (breastmilk + formula or only formula). Saliva microbiota was analysed using 16S rRNA (V3-V4) sequencing. Alpha diversity and beta diversity were compared between feeding type groups using ANCOVA and PERMANOVA, respectively. Differential bacteria abundance was tested using appropriate general linear models. RESULTS: Mean age and body mass index were 11.7 years and 18.0 kg/m2, respectively. The No formula group contained 41% of the participants. Firmicutes (51.0%), Bacteroidetes (19.1%), and Proteobacteria (16.3%) were the most abundant phyla among all participants. Alpha and beta diversity indices did not differ between the two feeding groups. Three Operational Taxonomic Units (OTUs) belonging to Eubacteria and Veillonella genera (phylum Firmicutes) were more abundant in the No formula than in the Infant formula group (log2fold changes/ p - values - 0.920/ < 0.001, - 0.328/ 0.001, - 0.577/ 0.004). CONCLUSION: Differences exist in abundances of some OTUs in adolescence according to feeding type during the first six months of life, but our findings do not support diversity and overall oral microbiota composition in adolescents being affected by early feeding type.

Open microbiome dominated by Clostridium and Eubacterium converts methanol into i-butyrate and n-butyrate.

Isobutyrate (i-butyrate) is a versatile platform chemical, whose acid form is used as a precursor of plastic and emulsifier. It can be produced microbially either using genetically engineered organisms or via microbiomes, in the latter case starting from methanol and short-chain carboxylates. This opens the opportunity to produce i-butyrate from non-sterile feedstocks. Little is known on the ecology and process conditions leading to i-butyrate production. In this study, we steered i-butyrate production in a bioreactor fed with methanol and acetate under various conditions, achieving maximum i-butyrate productivity of 5.0 mM day-1, with a concurrent production of n-butyrate of 7.9 mM day-1. The production of i-butyrate was reversibly inhibited by methanogenic inhibitor 2-bromoethanesulfonate. The microbial community data revealed the co-dominance of two major OTUs during co-production of i-butyrate and n-butyrate in two distinctive phases throughout a period of 54 days and 28 days, respectively. The cross-comparison of product profile with microbial community composition suggests that the relative abundance of Clostridium sp. over Eubacterium sp. is correlated with i-butyrate productivity over n-butyrate productivity.

Inclusion of Soluble Fiber in the Gestation Diet Changes the Gut Microbiota, Affects Plasma Propionate and Odd-Chain Fatty Acids Levels, and Improves Insulin Sensitivity in Sows.

The transition from pregnancy to lactation is characterized by a progressive decrease in insulin sensitivity. Propionate increases with dietary fiber consumption and has been shown to improve insulin sensitivity. Recent studies suggest that plasma odd-chain fatty acids [OCFAs; pentadecanoic acid (C15:0) and heptadecanoic acid (C17:0)] that inversely correlated with insulin resistance are synthesized endogenously from gut-derived propionate. The present study investigated the effects of soluble fiber during gestation on gut microbiota, plasma non-esterified fatty acids and insulin sensitivity in sows. Sows were allocated to either control or 2.0% guar gum plus pregelatinized waxy maize starch (SF) dietary treatment during gestation. The SF addition changes the structure and composition of gut microbiota in sows. Genus Eubacterium increased by SF addition may promote intestinal propionate production. Moreover, the dietary SF increased circulating levels of plasma OCFAs, especially C17:0. The SF-fed sows had a higher insulin sensitivity and a lower systemic inflammation level during perinatal period. Furthermore, the plasma C15:0 and C17:0 was negatively correlated with the area under curve of plasma glucose after meal and plasma interleukin-6. In conclusion, dietary SF improves insulin sensitivity and alleviates systemic inflammation in perinatal sows, potentially related to its stimulating effect on propionate and OCFAs production.

Changes in Microbiota and Development of Nonspecific Inflammation of Genitals in Female C57Bl/6 Mice after Aerosol Infection with Mycobacterium tuberculosis.

Infectious process even at the initial stage after aerosol infection with Mycobacterium tuberculosis induced rapid changes in vaginal microbiota in mice. Rapid decrease in both the quantity and diversity of microbiota was noted, and then, partial recovery of normal flora was observed. Changes in vaginal microbiota was detected as soon as in 3-7 days after lung infection, while inflammatory changes appeared by day 35. At the early stage of infection, no signs of inflammation were observed, neither M. tuberculosis nor its DNA were detected in mouse genital organs.

Dose Effects of Orally Administered Spirulina Suspension on Colonic Microbiota in Healthy Mice.

Oral supplemented nutraceuticals derived from food sources are surmised to improve the human health through interaction with the gastrointestinal bacteria. However, the lack of fundamental quality control and authoritative consensus (e.g., formulation, route of administration, dose, and dosage regimen) of these non-medical yet bioactive compounds are one of the main practical issues resulting in inconsistent individual responsiveness and confounded clinical outcomes of consuming nutraceuticals. Herein, we studied the dose effects of widely used food supplement, microalgae spirulina (Arthrospira platensis), on the colonic microbiota and physiological responses in healthy male Balb/c mice. Based on the analysis of 16s rDNA sequencing, compared to the saline-treated group, oral administration of spirulina once daily for 24 consecutive days altered the diversity, structure, and composition of colonic microbial community at the genus level. More importantly, the abundance of microbial taxa was markedly differentiated at the low (1.5 g/kg) and high (3.0 g/kg) dose of spirulina, among which the relative abundance of Clostridium XIVa, Desulfovibrio, Eubacterium, Barnesiella, Bacteroides, and Flavonifractor were modulated at various degrees. Evaluation of serum biomarkers in mice at the end of spirulina intervention showed reduced the oxidative stress and the blood lipid levels and increased the level of appetite controlling hormone leptin in a dose-response manner, which exhibited the significant correlation with differentially abundant microbiota taxa in the cecum. These findings provide direct evidences of dose-related modulation of gut microbiota and physiological states by spirulina, engendering its future mechanistic investigation of spirulina as potential sources of prebiotics for beneficial health effects via the interaction with gut microbiota.

Dysbiosis of oral microbiota and its association with salivary immunological biomarkers in autoimmune liver disease.

The gut microbiota has recently been recognized to play a role in the pathogenesis of autoimmune liver disease (AILD), mainly primary biliary cholangitis (PBC) and autoimmune hepatitis (AIH). This study aimed to analyze and compare the composition of the oral microbiota of 56 patients with AILD and 15 healthy controls (HCs) and to evaluate its association with salivary immunological biomarkers and gut microbiota. The subjects included 39 patients with PBC and 17 patients with AIH diagnosed at our hospital. The control population comprised 15 matched HCs. Salivary and fecal samples were collected for analysis of the microbiome by terminal restriction fragment length polymorphism of 16S rDNA. Correlations between immunological biomarkers measured by Bio-Plex assay (Bio-Rad) and the oral microbiomes of patients with PBC and AIH were assessed. Patients with AIH showed a significant increase in Veillonella with a concurrent decrease in Streptococcus in the oral microbiota compared with the HCs. Patients with PBC showed significant increases in Eubacterium and Veillonella and a significant decrease in Fusobacterium in the oral microbiota compared with the HCs. Immunological biomarker analysis showed elevated levels of inflammatory cytokines (IL-1ß, IFN-γ, TNF-α, IL-8) and immunoglobulin A in the saliva of patients with AILD. The relative abundance of Veillonella was positively correlated with the levels of IL-1ß, IL-8 and immunoglobulin A in saliva and the relative abundance of Lactobacillales in feces. Dysbiosis of the oral microbiota is associated with inflammatory responses and reflects changes in the gut microbiota of patients with AILD. Dysbiosis may play an important role in the pathogenesis of AILD.

Mucin Cross-Feeding of Infant Bifidobacteria and Eubacterium hallii.

Mucus production is initiated before birth and provides mucin glycans to the infant gut microbiota. Bifidobacteria are the major bacterial group in the feces of vaginally delivered and breast milk-fed infants. Among the bifidobacteria, only Bifidobacterium bifidum is able to degrade mucin and to release monosaccharides which can be used by other gut microbes colonizing the infant gut. Eubacterium hallii is an early occurring commensal that produces butyrate and propionate from fermentation metabolites but that cannot degrade complex oligo- and polysaccharides. We aimed to demonstrate that mucin cross-feeding initiated by B. bifidum enables growth and metabolite formation of E. hallii leading to short-chain fatty acid (SCFA) formation. Growth and metabolite formation of co-cultures of B. bifidum, of Bifidobacterium breve or Bifidobacterium infantis, which use mucin-derived hexoses and fucose, and of E. hallii were determined. Growth of E. hallii in the presence of lactose and mucin monosaccharides was tested. In co-culture fermentations, the presence of B. bifidum enabled growth of the other strains. B. bifidum/B. infantis co-cultures yielded acetate, formate, and lactate while co-cultures of B. bifidum and E. hallii formed acetate, formate, and butyrate. In three-strain co-cultures, B. bifidum, E. hallii, and B. breve or B. infantis produced up to 16 mM acetate, 5 mM formate, and 4 mM butyrate. The formation of propionate (approximately 1 mM) indicated cross-feeding on fucose. Lactose, galactose, and GlcNAc were identified as substrates of E. hallii. This study shows that trophic interactions of bifidobacteria and E. hallii lead to the formation of acetate, butyrate, propionate, and formate, potentially contributing to intestinal SCFA formation with potential benefits for the host and for microbial colonization of the infant gut. The ratios of SCFA formed differed depending on the microbial species involved in mucin cross-feeding.

Eubacterium moniliforme Bacteremia in a Woman with Fractures.

E. moniliforme infections in humans have not been reported previously. We firstly described blood-stream infections caused by E. moniliforme in an elder woman with fractures of her left thigh. This study highlights the strategies to detect this anaerobic pathogen and the importance of investigating its molecular epidemiology in humans.

Caecibacterium sporoformans gen. nov., sp. nov., an anaerobic, butyrate-producing, spore-forming bacterium isolated from chicken caecum.

Strains of a Gram-stain-negative, rod-shaped and immotile bacterium were isolated from broiler chicken caecal content. The isolates required strict anaerobic conditions for growth, formed spores, were catalase-positive and oxidase-negative. They produced butyrate as the major metabolic end product in reinforced clostridial medium broth. The genomic DNA G+C content of the isolated strains was 32.5-34.6 mol%. The major cellular fatty acids were C16 : 0 FAME, C14 : 0 FAME, C19 : 0CYC 9,10DMA and C16 : 0DMA. The fatty acid composition of the cell wall showed no similarity to any strain in the midi database. 16S rRNA gene sequence analysis showed that the nearest phylogenetic neighbours were Anaerostipes hadrus and Clostridium populeti (92 % sequence similarity) within Clostridium cluster XIVa of the phylum Firmicutes. Therefore, a novel genus is proposed, with the name Caecibacterium sporoformans gen. nov., sp. nov. The type strain of Caecibacterium sporoformans is LMG 27730T=DSM 26959T.

The Association between Cardiorespiratory Fitness and Gut Microbiota Composition in Premenopausal Women.

The aim of this study was to investigate the association between cardiorespiratory fitness and gut microbiota composition in premenopausal women. The participants consisted of 71 premenopausal Finnish women (aged 19-49 years). Gut microbiota were analyzed using flow cytometry, 16S rRNA gene hybridization and DNA-staining. Maximum oxygen uptake (VO2max) was assessed by respiratory gas analyzer and body composition by Bioimpdance. We found that participants with low VO2max had lower Bacteroides, but higher Eubacterium rectale-Clostridium coccoides than the high VO2max group (p < 0.05 for all). VO2max was inversely associated with EreC (r = -0.309, p = 0.01) but not with other bacteria. VO2max also negatively correlated with fat% (r = -0.755, p < 0.001), triglycerides (r = -0.274, p = 0.021) and leptin (r = -0.574, p < 0.001). By contrast, EreC was positively associated with fat% (r = 0.382, p = 0.002), dietary fat intake (r = 0.258, p = 0.034), triglycerides (r = 0.390, p = 0.002) and leptin (r = 0.424, p = 0.001), but negatively with carbohydrate intake (r = -0.252, p = 0.034) and HDL (r = -0.26, p = 0.028). After adjusting for age and dietary intake, all the significant associations remained. However, after adjusting for fat%, the associations between VO2max and EreC disappeared. Our results suggest that cardiorespiratory fitness is associated with gut microbiota composition, independent of age and carbohydrate or fat intake. The association between VO2max and EreC, however, appears to be mediated by body fatness.

Description of Absiella argi gen. nov., sp. nov., and transfer of Eubacterium dolichum and Eubacterium tortuosum to the genus Absiella as Absiella dolichum comb. nov. and Absiella tortuosum comb. nov.

Gram-positive, straight or slightly curved rod-shaped bacteria, designated as strains N6H1-5T and N6H1-3, were isolated from fecal samples of old dog. The analysis of 16S rRNA gene sequences indicated that the isolates belonged to the Clostridium cluster XVI and were closely related to Eubacterium dolichum KCTC 5832T, Eubacterium tortuosum DSM 3987T, Clostridium innocuum KCTC 5183T, Allobaculum stecoricanis DSM 13633T, Eubacterium limosum KCTC 3266T, and Clostridium butyricum KCTC 1871T, with 94.0%, 93.8%, 92.0%, 84.9%, 80.7%, and 80.0% sequence similarity, respectively. Chemotaxonomic data supported placement of the strains N6H1-5T and N6H1-3 in the new taxon. The strains contained m-diaminopimelic acid cell wall peptidoglycan; the major polar lipids were diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), and glycolipids (GL); and the major fatty acids were C18:1cis 9 (30.7%) and C16:0 (17.1%). The predominant metabolic end product was lactic acid. The G + C content was 35.8 mol%. The most closely related species, E. dolichum and E. tortuosum, were also assigned to the new taxon, based on the phylogenetic analysis and phenotypic data. Thus, the type strain N6H1-5T (=KCTC 15422 = JCM 30884) represents a novel genus and species, for which the name Absiella argi gen. nov., sp. nov is proposed. It is also proposed that E. dolichum KCTC 5832T and E. tortuosum DSM 3987T be transferred to this new genus, and named Absiella dolichum comb. nov. and Absiella tortuosum comb. nov., respectively.

Microbial strain-level population structure and genetic diversity from metagenomes.

Among the human health conditions linked to microbial communities, phenotypes are often associated with only a subset of strains within causal microbial groups. Although it has been critical for decades in microbial physiology to characterize individual strains, this has been challenging when using culture-independent high-throughput metagenomics. We introduce StrainPhlAn, a novel metagenomic strain identification approach, and apply it to characterize the genetic structure of thousands of strains from more than 125 species in more than 1500 gut metagenomes drawn from populations spanning North and South American, European, Asian, and African countries. The method relies on per-sample dominant sequence variant reconstruction within species-specific marker genes. It identified primarily subject-specific strain variants (<5% inter-subject strain sharing), and we determined that a single strain typically dominated each species and was retained over time (for >70% of species). Microbial population structure was correlated in several distinct ways with the geographic structure of the host population. In some cases, discrete subspecies (e.g., for Eubacterium rectale and Prevotella copri) or continuous microbial genetic variations (e.g., for Faecalibacterium prausnitzii) were associated with geographically distinct human populations, whereas few strains occurred in multiple unrelated cohorts. We further estimated the genetic variability of gut microbes, with Bacteroides species appearing remarkably consistent (0.45% median number of nucleotide variants between strains), whereas P. copri was among the most plastic gut colonizers. We thus characterize here the population genetics of previously inaccessible intestinal microbes, providing a comprehensive strain-level genetic overview of the gut microbial diversity.

Reduced Mucosa-associated Butyricicoccus Activity in Patients with Ulcerative Colitis Correlates with Aberrant Claudin-1 Expression.

BACKGROUND AND AIMS: Butyricicoccus is a butyrate-producing clostridial cluster IV genus whose numbers are reduced in the stool of ulcerative colitis [UC] patients. Conditioned medium of Butyricicoccus [B.] pullicaecorum prevents tumour necrosis factor alpha [TNFα]-induced increase in epithelial permeability in vitro. Since butyrate influences intestinal barrier integrity, we further investigated the relationship between the abundance of mucosa-associated Butyricicoccus and the expression of butyrate-regulated tight junction [TJ] genes. METHODS: Tight junction protein 1 [TJP1], occludin [OCLN], claudin-1 [CLDN1], and Butyricicoccus 16S rRNA expression was analysed in a collection of colonic biopsies of healthy controls and UC patients with active disease. The effect of butyrate and B. pullicaecorum conditioned medium on TJ gene expression was investigated in TNFα-stimulated Caco-2 monolayers and inflamed mucosal biopsies of UC patients. RESULTS: TJP1 expression was significantly decreased in inflamed UC mucosa, whereas CLDN1 mRNA levels were increased. OCLN did not differ significantly between the groups. Mucosa-associated Butyricicoccus 16S rRNA transcripts were reduced in active UC patients compared with healthy controls. Interestingly, Butyricicoccus activity negatively correlated with CLDN1 expression. Butyrate reversed the inflammation-induced increase of CLDN1 protein levels, and stimulation of inflamed UC biopsies with B. pullicaecorum conditioned medium normalized CLDN1 mRNA levels. CONCLUSIONS: Butyricicoccus is a mucosa-associated bacterial genus under-represented in colonic mucosa of patients with active UC, whose activity inversely correlates with CLDN1 expression. Butyrate and B. pullicaecorum conditioned medium reduce CLDN1 expression, supporting its use as a pharmabiotic preserving epithelial TJ integrity.

ENDOMETRIAL POLYPS IN WOMEN OF REPRODUCTIVE AGE: CLINICAL AND PATHOGENE-TIC VARIATIONS.

The aim of the study was to study the relationship between the morphofunctional characteristics of the endometrium, hormonal homeostasis and microbiocenosis of the reproductive system in patients with endometrial polyps. The study involved 130 patients aged 18-35 years: 34 patients with endometrial polyps, 30 patients with micropolyps, 36 patients with endometrial polyps and micropolyps, 30 healthy women of the control group. Hysteroscopy was performed for women who had been suspected for endometrial polyps and who had infertility or repeated recurrent miscarriages. Endometrial samples from healthy women were obtained by aspiration biopsy. The endometrial sections were immunostained with monoclonal antibodies against the specific markers of plasmacytes (CD138), NK cells (CD56, CD16), pan-leukocytes (CD45), macrophages (CD68), cellular marker for proliferation (Ki-67), ER, PR. Bacteriological examination of the endometrium was performed by PCR and by cultivating aerobic and anaerobic microorganisms on special growth media. In all groups of women the content in blood serum for 3-5 day of a menstrual cycle of gonadotropic hormones (FSH, LH) and sex steroid hormones (estradiol, prolactin) was studied, for 21 days of a cycle estimated the content of progesterone. Level of an expression of receptors of progesterone and estrogen estimated in endometrium and at EP, also in І a cycle phase. Highlighted are separate clinical and pathogenetic variations of endometrial polyps: isolated polyps, micropolyps, polyps in conjunction with micropolyps. In the course of study, it was found that progesterone deficiency and local immune imbalance with severe hypofunctional NK cells against viral and fungal infestations result in excessive endometrial cell proliferation and development of an isolated polyp. The case of a polyp merging with micropolyps potentiates an active inflammatory process alongside all of the mechanisms mentioned above. Micropolyps as a macroscopic manifestation of an active inflammatory process in chronic endometritis are characterized by focal infiltrates of leukocytes (CD45), macrophages (CD68), plasmacells (CD138) and NK (CD56) cells, whose activity leads to excess abnormal proliferation of endometrium, even in the absence of hormone receptor disorders.

Effect of smokeless tobacco products on human oral bacteria growth and viability.

To evaluate the toxicity of smokeless tobacco products (STPs) on oral bacteria, seven smokeless tobacco aqueous extracts (STAEs) from major brands of STPs and three tobacco-specific N-nitrosamines (TSNAs) were used in a growth and viability test against 38 oral bacterial species or subspecies. All seven STAEs showed concentration-dependent effects on the growth and viability of tested oral bacteria under anaerobic culture conditions, although there were strain-to-strain variations. In the presence of 1 mg/ml STAEs, the growth of 4 strains decreased over 0.32-2.14 log10 fold, while 14 strains demonstrated enhanced growth of 0.3-1.76 log10 fold, and the growth of 21 strains was not significantly affected. In the presence of 10 mg/ml STAEs, the growth of 17 strains was inhibited 0.3-2.11 log10 fold, 18 strains showed enhanced growth of 0.3-0.97 log10 fold, and 4 strains were not significantly affected. In the presence of 50 mg/ml STAEs, the growth of 32 strains was inhibited 0.3-2.96 log10 fold, 8 strains showed enhanced growth of 0.3-1.0 log10 fold, and 2 strains were not significantly affected. All seven STAEs could promote the growth of 4 bacterial strains, including Eubacterium nodatum, Peptostreptococcus micros, Streptococcus anginosus, and Streptococcus constellatus. Exposure to STAEs modulated the viability of some bacterial strains, with 21.1-66.5% decrease for 4 strains at 1 mg/ml, 20.3-85.7% decrease for 10 strains at 10 mg/ml, 20.0-93.3% decrease for 27 strains at 50 mg/ml, and no significant effect for 11 strains at up to 50 mg/ml. STAEs from snuffs inhibited more tested bacterial strains than those from snus indicating that the snuffs may be more toxic to the oral bacteria than snus. For TSNAs, cell growth and viability of 34 tested strains were not significantly affected at up to 100 µg/ml; while the growth of P. micros was enhanced 0.31-0.54 log10 fold; the growth of Veillonella parvula was repressed 0.33-0.36 log10 fold; and the cell viabilities of 2 strains decreased 56.6-69.9%. The results demonstrate that STAEs affected the growth of some types of oral bacteria, which may affect the healthy ecological balance of oral bacteria in humans. On the other hand, TSNAs did not significantly affect the growth of the oral bacteria.