Glycans are sugar molecules located on the surface of cells and in human secretions (including cervicovaginal fluid). They are specifically recognized by antibodies, lectins (sidenote: Lectins The term lectin (from the Latin word lectus, “chosen”) was coined by William C. Boyd and Elizabeth Shapeleigh in 1954 to refer to a heterogeneous class of (glyco)proteins, mainly of plant origin. Despite their wide range of physicochemical properties and biological activities, lectins share a common characteristic that is responsible for their various biological, biochemical, and immunochemical effects: they bind with high affinity and specificity to mono- and oligosaccharides of complex carbohydrates (including glycans) in solutions, on cell surfaces, subcellular organelles, and tissue sections. Source : Vierbuchen, M. (1991). Lectin Receptors. In: Seifert, G. (eds) Cell Receptors. Current Topics in Pathology, vol 83. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-75515-6_10 ) , and carbohydrate binding proteins. For example, in the vagina, host glycans modulate microbial colonization, acting as both binding and adhesion sites and sources of nutrients.

To better understand the interactions between these human glycans and the main pathogenic vaginal bacteria implicated in reproductive health, the researchers constructed glycan “chips” and tested the adhesion of bacteria in vitro under acidic (pH = 4) to neutral (pH = 7) conditions to reflect the reality of vaginal pH gradients observed in women.

A range of glycan-binding proteins

The results showed that the various bacteria tested could bind, to varying degrees, to several types of glycan. Moreover, according to previous work by the same team, pathogens appear to have a broader range of proteins that bind to these glycans than commensal species.

Some of the bonds are shared by different bacteria: with the exception of a few glycans, the binding profiles of the commensal bacteria Lactobacillus crispatus and L. iners and those of potentially pathogenic bacteria such as Gardnerella vaginalis and Streptococcus agalactiae overlapped, which could reflect competitive binding.

In contrast, other bonds are very specific: Fusobacterium nucleatum shows a preference for galactose-terminating glycans, while S. agalactiae is one of the few bacteria to bind to hyaluronic acid-terminating glycans.

Towards glycan-based therapies?

These results pave the way for the development of glycan-based therapies which block the adhesion of pathogens or promote colonization by probiotics. The aim is to one day reduce the incidence of bacterial vaginosis, preterm birth, and associated neonatal complications.

In assisted reproductive technology (ART), embryo implantation failures remain difficult to explain, probably because they involve multiple factors. Among these, a vaginal microbiota dominated by Lactobacillus seems to enhance the success of embryo transfers. However, results can sometimes be contradictory, and the ethnic origin of women is rarely considered.

A prospective single-site observational study¹ (Phoenix, USA) has therefore analyzed the vaginal microbiota of 87 American women during frozen embryo transfers, including 15 women of Hispanic origin. Its goal: to better understand the impact of vaginal flora on pregnancy rates after frozen embryo transfer, highlighting the protective role of Lactobacillus, while considering ethnic diversity.

More Lactobacillus, more pregnancies

Of the 55 patients who became pregnant, two-thirds (67%, or 37 women) exhibited a microbiota dominated by Lactobacillus at the time of insemination. These women had a 52% higher chance of becoming pregnant compared with those whose flora was not dominated by lactobacilli. Patients who did not become pregnant had more opportunistic pathogens, notably species of Enterobacteriaceae and Streptococcus.

In contrast, the richness or diversity of the vaginal flora was unrelated to ART outcome. Thus, the vaginal microbiota appears to interact with female fertility and the outcome of frozen embryo transfer: vaginal microbiomes dominated by Lactobacillus, especially those where the species L. crispatus or L. gasseri are prevalent, are positively associated with pregnancy. 

Explaining ethnic disparities?

The study also examined ethnic disparities. Hispanic women, who made up 18.3% of the cohort’s women (and about 19% of the US population), had lower clinical pregnancy rates following embryo transfer, a trend also observed nationally.

Moreover, a smaller proportion of them had a vaginal microbiota dominated by lactobacilli (compared with non-Hispanic white women), an observation already reported in previous studies. Could this lower prevalence of Lactobacillus dominance among Hispanic women partly explain the lower success of embryo transfer in this population? That is indeed the researchers’ hypothesis.

With 1.1 million deaths each year, preterm birth is the leading cause of death among young children under the age of five. Sadly, misfortune never comes alone, the risk of giving birth to another preterm baby being high, ranging from 15% to over 50%. The earlier in the pregnancy the previous preterm birth (sidenote: Preterm bitrh Babies born alive before 37 weeks of pregnancy are completed. There are sub-categories of preterm birth, based on gestational age: - Extremely preterm (less than 28 weeks). - Very preterm (28 to less than 32 weeks). - Moderate to late preterm (32 to 37 weeks). https://www.who.int/news-room/fact-sheets/detail/preterm-birth ) , the higher the risk of recurrence.

Medical science is searching for solutions, but a lack of knowledge about what causes these recurrences, which are probably multifactorial, limits the effectiveness of the treatments on offer (progesterone (sidenote: Progesterone Female sex hormone secreted after ovulation and during pregnancy. ) , cervical cerclage (sidenote: Cervical cerclage A surgical procedure performed during pregnancy whereby a thread is placed around the cervix when there is a risk it may open too easily. ) ,etc.). Could the solution lie partly in the vaginal flora?

This was the hypothesis of a group of researchers who followed 152 pregnant Chinese women at high risk of miscarriage, and their vaginal microbiota, sampled with a cotton swab during early pregnancy (before 16 weeks) and then between 16 and 24 weeks.

Risk linked to L. Iners.

Follow-up of these women showed that a vaginal microbiota dominated by Lactobacillus iners before 16 weeks of gestation is associated with an increased risk of premature birth. What explains this link? According to the authors, a vaginal flora dominated by L. iners is less stable than one dominated by L. crispatus: the former tends to evolve easily into a flora in which beneficial strains of Lactobacillus no longer reign supreme. In other words, it is less effective at keeping pathogenic bacteria at bay, as has already been shown in the case of Group B Streptococcus.

However, between 16 and 24 weeks of gestation the link between L. iners and preterm birth is no longer evident, highlighting that early pregnancy is the crucial period, perhaps one day even for intervention on the vaginal microbiota to reduce the risk of recurrent preterm birth. It should be noted that this type of intervention is no longer the stuff of science fiction: one 30-year-old mother who suffered a series of miscarriages after her first child was able to become a mother again after a vaginal microbiota transplant.

Vaginal microbiota is a complex ecosystem of bacteria inhabiting the vagina which plays a crucial role in women’s health, including during pregnancy. As an example, a higher concentration of lactobacilli appears to reduce the risk of miscarriage.

Among the various lactobacilli in the vaginal flora, Lactobacillus iners is particularly interesting as this bacterium is found in both healthy and pathological microbiota, raising questions about its exact role. A study conducted on 91 Chinese women in the third trimester of pregnancy provides new insights.

Higher levels of L. iners in healthy women

The study shows that one in two healthy women harbors a vaginal flora dominated by L. iners, whereas fewer than one in three women in the “unhealthy” group (gestational diabetes (sidenote: Gestational diabetes Gestational diabetes can develop during pregnancy in women who don't already have diabetes, usually around the 24th week. Testing is typically done between 24 and 28 weeks. It occurs when the body can't produce enough insulin during pregnancy—a hormone that allows blood sugar (glucose) to enter the cells to be used for energy. As a result, blood sugar levels (glycemia) become higher than normal. Every year, 5% to 9% of pregnancies in the U.S. are affected by gestational diabetes. Proper management of gestational diabetes helps ensure a healthy pregnancy and a healthy baby. CDC ) , pregnancy complications, etc.) have this type of microbiota. Conversely, a flora dominated by L. crispatus is more frequent among expectant mothers with health issues.

For example, this type of microbiota is present in 57% of women with gestational diabetes.

Could the higher frequency and abundance of L. iners explain the good health of pregnant women? Researchers believe this could be true. This is because a higher presence of L. iners means an enhanced production of beneficial microbial molecules by this bacterium. This includes an increased biosynthesis of a compound with the intimidating name “tetrahydrofolate” which helps maintain moderate inflammation in late pregnancy.

Different strains of L. iners

However, not all L. iners strains are the same. Among the seven strains identified in pregnant women, three strains associated with bacterial vaginosis (sidenote: Bacterial vaginosis Bacterial vaginosis (BV) is a type of vaginal inflammation caused by an imbalance of the bacterial species that are normally present in the vagina. ) were particularly adept at forming feared biofilms, which serve as shelters where pathogens can multiply. Four other strains (some associated with vaginosis, others not) appeared capable of inhibiting the growth of the pathogen Gardnerella vaginalis. In short, each L. iners strain has its own characteristics—and likely several tricks up its “bacterial” sleeve. But some strains could help maintain the stability of the vaginal ecosystem in pregnant women.

Diversity in vaginal microbiota profiles

Vaginal microbiota is made up of five different community state types (CSTs), including three protective CSTs (respectively dominated by Lactobacillus crispatus, Lactobacillus gasseri or Lactobacillus jensenii), one disruptive CST, and one—CST III—dominated by L. iners, whose role in vaginal health remains debated. This is because the bacterium may be protective or disruptive—while it seems to be an integral part of a healthy vaginal microbiome, it is paradoxically also abundant in pathological and dysbiotic conditions and has even been implicated in colonization by Group B Streptococcus during pregnancy.

More L. iners in healthy expectant mothers

To better understand the relationship between microbial flora and vaginal health, Chinese researchers focused on the particular case of pregnant women in their third trimester—either healthy (34 women) or not (61 women with gestational diabetes, complications, infection, etc.). Their results highlight the persistence of lactobacilli predominance and the maintenance of alpha diversity across all expectant mothers.

Most notably, the type dominated by L. iners was less common in the group of sick women (31.15%) than in the group of healthy women (50%). In addition, L. iners was relatively more abundant (as a percentage of the species present) in healthy women.

Altered metabolic pathways

The increased abundance of L. iners in healthy pregnant women was associated with the overexpression of metabolic pathways favorable to a healthy pregnancy—for example, tetrahydrofolate (sidenote: Tetrahydrofolate a coenzyme derived from folic acid, primarily involved in the synthesis of nucleic acid bases (purines and pyrimidines), which constitute the DNA and RNA of genetic material. Tetrahydrofolate (THF) is also involved in the synthesis of amino acids, including methionine, histidine, and serine. ) biosynthesis, which may play various roles (microbial folate synthesis, a slightly pro-inflammatory state).

But the higher abundance of this bacterium in healthy women was also associated with glycosyltransferase (sidenote: Glycosyltransferase a membrane-associated enzyme that catalyzes the transfer of a sugar moiety onto a protein, resulting in the formation of a glycoprotein. In pathogenic bacteria, these glycoproteins have been implicated at various stages of the infection process.

Explore: Tomás JM, Fulton KM, Twine SM et al. Generation of Null Mutants to Elucidate the Role of Bacterial Glycosyltransferases in Bacterial Motility. J Vis Exp. 2022 Mar 11;(181). ) synthesis routes and antibiotic resistance, compared with women suffering from pathologies. These mechanisms may reflect the dynamic adaptation of the microbiota to the immune and hormonal environment characteristic of the third trimester of pregnancy.
 

Seven very different strains of L. iners

More in-depth analyses show that not all L. iners are alike. Among the seven strains of L. iners identified by the authors, three strains associated with bacterial vaginosis (versus four strains associated with good health) proved to be more efficient at forming biofilms, thanks to genes coding for the proteins involved. The team also showed that five of the seven identified strains (whether associated with bacterial vaginosis or not) inhibited the growth of the pathogen G. vaginalis, which is implicated in preterm birth.

These results suggest that L. iners may exert a protective influence depending on environmental conditions and the strains involved. A microbiota dominated by certain strains of L. iners could therefore contribute to the prevention of complications linked to persistent dysbiosis.

Explore the latest insights on the conditions that promote a balanced vaginal microbiota: 

For years, the scientific community has been gathering evidence that our gut and brain are in constant communication, a concept known as the gut-brain axis. ^{1, 2}  We’ve seen that the composition of the gut microbiota is different in patients with Alzheimer’s disease ³, and that this dysbiosis might contribute to the neuroinflammation that fuels the disease ^{4, 5}.

But the precise details have been blurry. We’ve been looking at the forest, but a groundbreaking new study ⁶ zooms in on the individual trees, and what it reveals could fundamentally change how we approach this Alzheimer devastating neurodegenerative disease.

Beyond the brain: not overall diversity, but specific microbial identity

What if the first whispers of Alzheimer’s disease weren’t cognitive, but compositional? A landmark study published in Alzheimer's Research & Therapy provides compelling evidence that the key to understanding, and perhaps one day diagnosing, the cognitive decline in the lives of patients affected by Alzheimer’s disease may lie within the specific species of bacteria residing in our gut.

Using high-resolution shotgun metagenomics (sidenote: Shotgun Metagenomics This is a high-resolution sequencing method that analyzes all the genetic material from every microbe in a sample. Unlike older techniques that just identify bacterial families, it allows for precise identification down to the species level and reveals the functional genes those bacteria possess. ) on patients with Mild Cognitive Impairment (MCI) (sidenote: Mild Cognitive Impairment (MCI) MCI is a clinical stage between the expected cognitive decline of normal aging and the more severe decline of dementia. Individuals with MCI have noticeable memory or thinking problems but can still perform most daily activities, representing a critical window for intervention and study. ) , a critical intermediate stage, the researchers found that there was no significant difference in the overall diversity of the gut microbiota compared to healthy controls. Instead, the crucial difference was the identity of the players. The study pinpointed 59 specific microbial species whose presence or absence was directly correlated with MCI, amyloid plaques, and tau protein (sidenote: Tau Protein Tau is a protein that normally stabilizes the internal transport system, or microtubules, within the brain's nerve cells. In Alzheimer's disease, it becomes abnormally phosphorylated and aggregates into neurofibrillary tangles inside the neurons, leading to cellular dysfunction and death. ) levels, the core pathological hallmarks of Alzheimer's disease. This tells us it’s not about the size of the microbial army, but which specific soldiers are on the front lines.

The surprising role of two Bacteroides: why species-level detail is a game-changer

Here is where the findings about gut biomarkers become truly paradigm-shifting. The study revealed that different species within the very same genus can have opposite effects on brain health. For example, the presence of the species Bacteroides eggerthii was associated with a reduced risk of MCI. Yet, another species, Bacteroides thetaiotaomicron, was linked to a higher risk.

This is a critical discovery because it demonstrates that previous studies relying on lower-resolution sequencing, which could only identify bacteria at the genus level, may have missed the most important part of the story. It’s like knowing someone is a "mammal" without knowing if it's a mouse or a lion. This species-specific activity is a fundamental insight that will force the field to adopt more precise methods.

Toward functional biomarkers: the protective role of Akkermansia

The study moves beyond mere correlation, identifying bacteria that are not just present, but are functionally tied to brain health. One of the beneficial species identified, Akkermansia muciniphila, was negatively correlated with amyloid burden. This is significant because Akkermansia is known to produce metabolites that strengthen the gut barrier and have anti-inflammatory effects. ⁷  This research suggests its role may be even more direct, potentially influencing the brain's energy metabolism and protecting against the buildup of toxic proteins, such as tau protein.

The identification of specific pro- and anti-inflammatory species tied directly to amyloid and tau levels opens the door for developing highly sensitive metabolic biomarkers, ^{8, 9, 10} potentially allowing for a diagnosis at the MCI stage, long before irreversible damage to the central nervous system occurs.

Anorexia nervosa is a psychiatric disorder classified as an eating disorder. It can have serious health consequences and carries a significant risk of becoming chronic or even fatal. Anorexia nervosa is characterized by voluntary food restriction that leads to severe weight loss and is often linked to bulimia, anxiety and behavioral disorders that can contribute to other health problems.

Psychotherapy combined with nutritional rehabilitation is the recommended approach for reestablishing normal eating habits. However, patient responses vary and some eating disorder symptoms such as bulimia and anxiety may persist.

How the microbiota impacts cognitive functions

In 2023, psychiatrists at the University of Graz in Austria identified an alteration in implicit learning (the unconscious acquisition of knowledge) that may partly explain the lack of response to treatment. In a new study, the same team suggests that this impairment could be linked… to the microbiota!²

It is known that the gut microbiota influences cognitive functions through the gut–brain axis (sidenote: Gut-brain axis Two-way communication network between the gut and the brain, which allows the gut and brain to communicate via three different pathways: 
1. the neuronal pathway (neurons), mainly via the vagus nerve and the enteric nervous system,
2. the endocrine pathway, by secreting hormones such as cortisol, adrenaline and serotonin
3. the immune system pathway, by modulating cytokines The gut-brain axis influences our behavior, cognition (memory), emotions, moods, desires, perception... and pain, among other things. ) . This axis modulates the neuroendocrine system, particularly the hypothalamic–pituitary–adrenal axis, which regulates stress responses and cortisol production. The enteric nervous system is also involved in bidirectional communication with the autonomic nervous system and the vagus nerve, as are neurotransmitters (GABA, dopamine, serotonin, etc.) produced by the microbiota.

Based on this observation, the Austrian scientists compared memory and implicit learning abilities as well as the microbiota of 15 patients with anorexia nervosa to those of 13 healthy control women.

Lower learning scores linked to less diverse microbiota

The results show that in the anorexia group:

• implicit learning scores are lower than those of healthy controls, while memory scores are similar;
• the gut microbiota shows an increased abundance of Akkermansia muciniphila, whereas in the control group, short-chain fatty acid (SCFA (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) )-producing bacteria such as Faecalibacterium are more prevalent.

Overall, higher implicit learning scores are linked to greater microorganism diversity and a higher number of distinct species:

• a high score was associated with an increase in Actinobacteria, especially Bifidobacteria, key microorganisms in gut–brain communication that may reduce anxiety via vagal pathways and thereby influence learning processes;
• a low score, in contrast, was associated with an increase in Lachnospiraceae, which several studies have linked to depressive disorders that may impair brain function and implicit learning.

Toward new treatment approaches

Despite certain limitations (small sample size, lack of dietary and educational data, absence of male participants), this study shows promise. It opens the door to potential new treatment strategies for managing disorders such as anorexia nervosa.

Food restriction, intense fear of gaining weight, calorie obsession, body dysmorphia, bulimia, anxiety, depression, etc. Anorexia nervosa is a serious eating disorder that significantly affects a patient's health, impacting both behavior and the body. It is also particularly difficult to manage (read inset).

People affected by the condition often experience impaired cognitive function, particularly in certain learning abilities essential for behavioral adaptation, which may slow recovery.

A new study suggests the disorder could be linked to changes taking place in the gut microbiota. ⁴

A less diverse microbiota 

The authors, researchers from the University of Graz in Austria, enrolled 15 patients with anorexia nervosa and 13 healthy female controls. All participants underwent tests to assess their implicit learning ability (see inset). At the same time, their stools were analyzed to determine the composition of their gut microbiota.

The researchers’ findings confirm that patients with anorexia nervosa show lower implicit learning scores than healthy volunteers. What is more interesting, however, is that these scores are linked to microbiota composition: the higher the scores, the more diverse the microorganisms. 

When the gut microbiota scrambles the brain

How can this finding be explained? It’s well known that the gut microbiota influences brain function via the gut–brain axis. For example, it can alter stress responses or produce brain messengers (dopamine, serotonin, etc.) that can affect learning abilities.

In this study:

A high learning score was, for instance, linked to an increase in Bifidobacteria, bacteria that are key to gut–brain communication.These bacteria can help reduce anxiety and in turn influence learning processes.

Conversely, a low score was associated with an increase in Lachnospiraceae, bacteria that have been linked in several studies to depressive disorders that may impair brain function and implicit learning. These effects suggest a strong connection between the microbiota, behavior and mental health in conditions such as anorexia.

Toward a probiotic-based treatment for anorexia?

This discovery is particularly intriguing as it may help explain why psychotherapy which partly relies on implicit learning is not always effective in treating anorexia. If confirmed, it could one day be possible to use probiotics containing Bifidobacteria to improve the management of anorexia nervosa. By stabilizing the gut–brain axis, these probiotics could help women return to normal eating habits.

For years, we've known that our gut and our brain are in constant conversation. This "gut-brain axis" is why you might feel "butterflies" when you're nervous. Now, a groundbreaking new study ¹ suggests this connection is far more important than we ever imagined, revealing that the earliest clues to Alzheimer's disease may not be in the brain at all, but hidden among the trillions of bacteria living in our gut.

It’s not the size of the crowd, but who's in it

Scientists used to think that in Alzheimer's, the problem was a general loss of different types of gut bacteria, like a garden becoming less diverse. But this new research found something completely different. In people with early memory loss,(those diagnosed with mild cognitive impairment (MCI) (sidenote: Mild Cognitive Impairment (MCI) MCI is a clinical stage between the expected cognitive decline of normal aging and the more severe decline of dementia. Individuals with MCI have noticeable memory or thinking problems but can still perform most daily activities, representing a critical window for intervention and study. ) the overall number of bacterial types was fine.

The real problem was a shift in which specific bacteria were present. The study identified 59 precise types of bacteria, potential biomarkers that were either more or less common in people on the path to Alzheimer's. This tells us it's not about having fewer bacteria, but about having the wrong ones in charge.

The gut's heroes and villains can look alike

This is where the story gets truly fascinating. The study revealed that two bacteria from the exact same family can have completely opposite effects. Think of it like a family with a "good twin" and an "evil twin". One bacterium, named Bacteroides eggerthii, was linked to a lower risk of memory problems, acting like a hero for the brain. But its close relative, Bacteroides thetaiotaomicron, was linked to a higher risk, acting like a villain. This is a critical discovery because it means previous science, which couldn't tell these bacterial "relatives" apart, was missing the most important details in understanding the disease.

What are the stages of Alzheimer's disease?

Toward a new future for early detection

So, what does this all mean for you? This research is paving the way for a revolutionary new approach to diagnosis of Alzheimer’s disease. By identifying a "good guy" bacterium called Akkermansia muciniphila, which was linked to less of the toxic amyloid protein (sidenote: Toxic amyloid protein Amyloids are aggregates of proteins that fold together. In certain neurodegenerative diseases such as Alzheimer's disease, amyloid plaques form from aggregates of misfolded proteins, composed mainly of beta-amyloid protein. These plaques form around neurons and prevent them from functioning properly.

https://emedicine.medscape.com/article/335414-overview ) found in Alzheimer's patients brains, scientists are creating a "fingerprint" of a healthy gut.

One day, we might be able to use a simple stool sample to check for these specific bacterial heroes and villains. This could help spot a person's risk for Alzheimer's years earlier than we can now, opening a crucial window to protect brain health through diet and lifestyle.

Colorectal cancer (CRC) is the third most common type of tumor and also the second deadliest cancer. The gut microbiome appears to play a crucial role in carcinogenesis. However, research is still too limited to use microbiota as a clinical screening tool, even though early detection would increase the chances for survival. 

This is why studies published in 2025 in Nature Medicine are so important. They are based on the analysis of 18 datasets: 12 from pre-existing databases including 2,116 individuals (930 patients with CRC, 210 with adenomas and 976 healthy controls) and 6 from new cohorts (1,625 individuals) providing information on both the cancer’s stage and the tumor’s location in the body. In total, the study included 3,741 individuals, providing strong statistical power and potentially accurate results

Species involved, including oral bacteria

The authors detected 3,866 bacterial species, 15 eukaryotes and 23 archaea. The microbiota of healthy controls differ markedly from that of CRC patients, confirming results from previous studies: 125 species are more abundant in patients (106 known and 19 unknown) and 83 in controls (53 known and 30 unknown).

Five subspecies of F. nucleatum were among those more abundant in patients, namely, F. nucleatum subsp. animalis, vincentii (two different subspecies), nucleatum, polymorphum. Other bacteria previously associated with CRC, such as P. micra and B. fragilis, were also identified.

The gut microbiota may be involved in regulating ammonia in the CRC tumor micro-environment.

A significant portion of CRC-specific gut bacteria are typically oral species, with 21 of the 125 species more abundant in patients (16.8%) being oral in origin, including 11 commonly found in dental plaque.

Predicting colorectal cancer

Above all, this large dataset has improved the accuracy of colorectal cancer (CRC) prediction based on a simple stool sample: the area under the curve (AUC), a measure of model performance, now reaches 0.85 —an improvement over previous studies, which achieved a maximum of 0.81. A large part of this predictive power relies on bacteria that are typically oral in origin.

The authors also show that:

• microbial biomarkers are linked to the presence of a tumor,
• they vary according to disease stage: the abundance of P. micra and F. nucleatum increases as early as stage I CRC, while Akkermansia muciniphila and Parabacteroides distasonis rise in advanced stages, suggesting that microbiota changes occur continuously and intensify as cancer progresses (adenoma–carcinoma sequence).
• they also differ depending on tumor’s location: for example, three oral species were significantly more abundant in proximal colorectal cancer.

Previous studies had implicated ammonia in the tumor micro-environment in T-cell depletion and cancer progression.