Beyond bacteria: Role of non-bacterial gut microbiota species in inflammatory bowel disease and colorectal cancer progression.

This letter emphasizes the need to expand discussions on gut microbiome's role in inflammatory bowel disease (IBD) and colorectal cancer (CRC) by including the often-overlooked non-bacterial components of the human gut flora. It highlights how viral, fungal and archaeal inhabitants of the gut respond towards gut dys-biosis and contribute to disease progression. Viruses such as bacteriophages target certain bacterial species and modulate the immune system. Other viruses found associated include Epstein-Barr virus, human papillomavirus, John Cunningham virus, cytomegalovirus, and human herpes simplex virus type 6. Fungi such as Candida albicans and Malassezia contribute by forming tissue-invasive filaments and producing inflammatory cytokines, respectively. Archaea, mainly metha-nogens are also found altering the microbial fermentation pathways. This corres-pondence, thus underscores the significance of considering the pathological and physiological mechanisms of the entire spectrum of the gut microbiota to develop effective therapeutic interventions for both IBD and CRC.

Role of diet in development of non-communicable diseases: focus on gut microbiome.

OBJECTIVES: The dietary composition is able to rapidly and significantly influence the diversity of the gut microbiome. This article focuses on how various types of diet affect the composition of the gut microbiome and how dietary changes are able to prevent or slow down the development of non-communicable diseases including obesity, type 2 diabetes mellitus, cardiovascular diseases, and low-grade inflammation. METHODS: A review in PubMed and a hand search using references in identified articles were performed. Studies published in English from 2000 to 2024 were included. RESULTS: The studies showed the significant effect of diet on the development of non-communicable diseases dependent on the state of the gut microbiota and molecules it produces. The Western diet that continues to gain in popularity for Czech people, leads to dysbiosis and production of bacterial lipopolysaccharide or trimethylamine N-oxide causing systemic chronic inflammation in the body and thus promoting the development of non-communicable diseases. CONCLUSIONS: Findings from this review emphasize the importance of healthy eating habits in the prevention of intestinal dysbiosis and still increasing prevalence and incidence of obesity and other non-communicable diseases.

Microbiome as an endocrine organ and its relationship with eye diseases: Effective factors and new targeted approaches.

Microbiome is an endocrine organ that refers to both the complicated biological system of microbial species that colonize our bodies and their genomes and surroundings. Recent studies confirm the connection between the microbiome and eye diseases, which are involved in the pathogenesis of eye diseases, including age-related macular disorders, diabetic retinopathy, glaucoma, retinitis pigmentosa, dry eye, and uveitis. The aim of this review is to investigate the microbiome in relation to eye health. First, a brief introduction of the characteristics of the gut microorganisms terms of composition and work, the role of dysbiosis, the gut microbiome and the eye microbiome in the progression of eye illnesses are highlighted, then the relationship among the microbiome and the function of the immune system and eye diseases, the role of inflammation and aging and the immune system, It has been reviewed and finally, the control and treatment goals of microbiome and eye diseases, the role of food factors and supplements, biotherapy and antibiotics in relation to microbiome and eye health have been reviewed.

Alteration in gut microbiota after colonoscopy: proposed mechanisms and the role of probiotic interventions.

Colonoscopy, a widely used procedure for diagnosing and treating colonic diseases, induces transient gastrointestinal symptoms and alterations in the gut microbiota. This review comprehensively examines the evidence on alterations in the gut microbiota following colonoscopy and their possible mechanisms. Factors such as rapid colonic evacuation, increased osmolality, and mucus thinning caused by bowel preparation and exposure to oxygen during the procedure contribute to these alterations. Typically, the alterations revert to the baseline within a short time. However, their long-term implications remain unclear, necessitating further investigation. Split-dose bowel preparation and CO2 insufflation during the procedure result in fewer alterations in the gut microbiota. Probiotic administration immediately after colonoscopy shows promise in reducing alterations and gastrointestinal symptoms. However, the widespread use of probiotics remains controversial due to the transient nature of the symptoms and microbiobial alterations in the microbiota. Probiotics may offer greater benefits to individuals with preexisting gastrointestinal symptoms. Thus, probiotic administration may be a viable option for selected patients.

Intestinal Dysbiosis: Exploring Definition, Associated Symptoms, and Perspectives for a Comprehensive Understanding - a Scoping Review.

Dysbiosis is a clinical condition marked by altered gut microbiota resulting from external and internal host factors. It is strongly associated with gastrointestinal and extraintestinal alterations, so its symptomatology is broad and nonspecific. To date, gaps remain that limit professionals from making a timely diagnosis and prescribing the appropriate treatment. We aim to synthesize existing literature regarding clinical parameters for the early detection of patients with intestinal dysbiosis and the clinical events in which the use of probiotics as adjuvant therapy is most frequently reported. A scoping review of the literature was conducted in PubMed, Embase, Cochrane, and BVS (Biblioteca Virtual en Salud in Spanish) databases for articles published in the last 5 years. Primary studies and literature reviews related to clinical presentation, dysbiosis screening, and probiotics as adjuvant therapy for adult and pediatric patients were included. Twenty-three articles were retrieved in which the most frequently reported symptoms were abdominal distension, abdominal pain, and diarrhea. Chronic and metabolic diseases where the conditions most strongly associated with dysbiosis. Depending on symptomatology and etiology, dysbiosis is often treated with probiotics. Dysbiosis, often linked to diarrhea, should be considered with other symptoms like abdominal distension and pain, along with predisposing conditions and patient risk factors. Probiotics are commonly used as co-adjuvant treatments for antibiotic-associated diarrhea, irritable bowel syndrome, and childhood allergic diseases. The most commonly used probiotics were Weizmannia coagulans (formerly B. coagulans), Alkalihalobacillus clausii (formerly Bacillus clausii), Lacticaseibacillus rhamnosus, Limosilactobacillus reuteri, and Saccharomyces boulardii.

Reduction of butyrate-producing bacteria in the gut microbiome of Japanese patients with pancreatic cancer.

BACKGROUND: The incidence of pancreatic cancer is on the rise, and its prognosis remains poor. Recent reports have established a link between the gut and oral microbiome and pancreatic cancer. However, the intricacies of this association within the Japanese population remain unclear. In this study, we investigated the gut and oral microbiomes of Japanese patients with pancreatic cancer, comparing them with those of healthy individuals. METHODS: We recruited 30 patients with untreated pancreatic cancer and 18 healthy controls at Kyoto University Hospital (2018-2022). We performed a comprehensive 16S rRNA gene sequencing to analyze their gut and oral microbiomes. RESULTS: Analysis revealed that the diversity of the gut and oral microbiomes of patients with pancreatic cancer was reduced compared to that of the healthy controls. Specifically, we observed an increase in the genus Streptococcus in both the gut and oral microbiomes and a significant decrease in several butyrate-producing bacteria in fecal samples. Moreover, bacteria such as Streptococcus mitis and Holdemanella biformis were present in pancreatic cancer tissues, suggesting that they might influence the carcinogenesis and progression of pancreatic cancer. CONCLUSIONS: The gut and oral microbiome differed between patients with pancreatic cancer and healthy controls, with a notable decrease in butyrate-producing bacteria in the gut microbiome of the patients. This suggests that there may be a distinct microbial signature associated with pancreatic cancer in the Japanese population. Further studies are required to elucidate the microbiome's causal role in this cancer and help develop prognostic markers or targeted therapies.

Dermatological Health in the Light of Skin Microbiome Evolution.

BACKGROUND: The complex ecosystem of the skin microbiome is essential for skin health by acting as a primary defense against infections, regulating immune responses, and maintaining barrier integrity. This literature review aims to consolidate existing information on the skin microbiome, focusing on its composition, functionality, importance, and its impact on skin aging. METHODS: An exhaustive exploration of scholarly literature was performed utilizing electronic databases including PubMed, Google Scholar, and ResearchGate, focusing on studies published between 2011 and 2024. Keywords included "skin microbiome," "skin microbiota," and "aging skin." Studies involving human subjects that focused on the skin microbiome's relationship with skin health were included. Out of 100 initially identified studies, 70 met the inclusion criteria and were reviewed. RESULTS: Studies showed that aging is associated with a reduction in the variety of microorganisms of the skin microbiome, leading to an increased susceptibility to skin conditions. Consequently, this underlines the interest in bacteriotherapy, mainly topical probiotics, to reinforce the skin microbiome in older adults, suggesting improvements in skin health and a reduction in age-related skin conditions. Further exploration is needed into the microbiome's role in skin health and the development of innovative, microbe-based skincare products. Biotherapeutic approaches, including the use of phages, endolysins, probiotics, prebiotics, postbiotics, and microbiome transplantation, can restore balance and enhance skin health. This article also addresses regulatory standards in the EU and the USA that ensure the safety and effectiveness of microbial skincare products. CONCLUSION: This review underscores the need to advance research on the skin microbiome's role in cosmetic enhancements and tailored skincare solutions, highlighting a great interest in leveraging microbial communities for dermatological benefits.

Fecal let-7b and miR-21 directly modulate the intestinal microbiota, driving chronic inflammation.

Inflammatory bowel diseases (IBD) etiology is multifactorial. Luminal microRNAs (miRNAs) have been suspected to play a role in the promotion of chronic inflammation, but the extent to which fecal miRNAs are interacting with the intestinal ecosystem in a way that contribute to diseases, including IBD, remains unknown. Here, fecal let-7b and miR-21 were found elevated, associated with inflammation, and correlating with multiple bacteria in IBD patients and IL-10-/- mice, model of spontaneous colitis. Using an in vitro microbiota modeling system, we revealed that these two miRNAs can directly modify the composition and function of complex human microbiota, increasing their proinflammatory potential. In vivo investigations revealed that luminal increase of let-7b drastically alters the intestinal microbiota and enhances macrophages' associated proinflammatory cytokines (TNF, IL-6, and IL-1ß). Such proinflammatory effects are resilient and dependent on the bacterial presence. Moreover, we identified that besides impairing the intestinal barrier function, miR-21 increases myeloperoxidase and antimicrobial peptides secretion, causing intestinal dysbiosis. More importantly, in vivo inhibition of let-7b and miR-21 with anti-miRNAs significantly improved the intestinal mucosal barrier function and promoted a healthier host-microbiota interaction in the intestinal lining, which altogether conferred protection against colitis. In summary, we provide evidence of the functional significance of fecal miRNAs in host-microbiota communication, highlighting their therapeutic potential in intestinal inflammation and dysbiosis-related conditions, such as IBD.

The signatures and crosstalk of gut microbiome, mycobiome, and metabolites in decompensated cirrhotic patients.

Background: Numerous studies have confirmed that gut microbiota plays a crucial role in the progression of cirrhosis. However, the contribution of gut fungi in cirrhosis is often overlooked due to the relatively low abundance. Methods: We employed 16S ribosomal RNA sequencing, internal transcribed spacer sequencing, and untargeted metabolomics techniques to investigate the composition and interaction of gut bacteria, fungi, and metabolites in cirrhotic patients. Results: Cirrhotic patients exhibited significant differences in the diversity and composition of gut microbiota and their metabolites in cirrhotic patients compared to healthy individuals. Increase in pathogenic microbial genera and a decrease in beneficial microbial genera including bacteria and fungi were observed. Various clinical indexes were closely connected with these increased metabolites, bacteria, fungi. Additionally, endoscopic treatment was found to impact the gut microbiota and metabolites in cirrhotic patients, although it did not significantly alter the gut ecology. Finally, we constructed a cirrhosis diagnostic model based on different features (bacteria, fungi, metabolites, clinical indexes) with an AUC of 0.938. Conclusion: Our findings revealed the characteristics of gut microbial composition and their intricate internal crosstalk in cirrhotic patients, providing cutting-edge explorations of potential roles of gut microbes in cirrhosis.

Dysbiosis of pro-inflammatory and anti-inflammatory salivary cytokines during psoriasis providing a therapeutic window and a valuable diagnostic aid in future.

The objective of this article is to evaluate the salivary levels of tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin-2 (IL-2), and IL-10 in patients with active psoriasis and compare them with those in healthy control subjects. This study included 60 subjects who were clinically diagnosed cases with active psoriasis (categorized further into 33 mild to moderate and 27 severe cases based on the Psoriasis Area Severity Index score) and 60 age- and gender-matched healthy control subjects. Levels of TNF-α, IFN-γ, IL-2, and IL-10 in the unstimulated saliva of subjects were determined via enzyme-linked immunosorbent assay (BT Lab). The salivary levels of TNF-α, IFN-γ, and IL-2 were significantly higher, whereas IL-10 concentration was significantly reduced in psoriatic patients in comparison to controls, and the difference increased with the progressing severity of the disease. Assessment of cytokine profiles in psoriasis patients is significant for diagnostic validation and monitoring the disease severity. Saliva offers an alternate, noninvasive, and readily available biological sample for evaluating cytokine levels. Extensive research in this field has been recommended for better scientifically proven conclusions.

Correlation of gut microbial diversity to sight-threatening diabetic retinopathy.

PURPOSE: To determine the association of gut microbiome diversity and sight-threatening diabetic retinopathy (STDR) amongst patients with pre-existing diabetes. METHODS: A cross-sectional study was performed, wherein 54 participants selected in total were placed into cases cohort if diagnosed with STDR and those without STDR but had a diagnosis of diabetes mellitus of at least 10-year duration were taken as controls. Statistical analysis comparing the gut microbial alpha diversity between cases and control groups as well as patients differentiated based on previously hypothesized Bacteroidetes/Firmicutes(B/F) ratio with an optimal cut-off 1.05 to identify patients with STDR were performed. RESULTS: Comparing gut microbial alpha diversity did not show any difference between cases and control groups. However, statistically significant difference was noted amongst patients with B/F ratio ≥1.05 when compared to B/F ratio < 1.05; ACE index [Cut-off < 1.05:773.83 ± 362.73; Cut-off > 1.05:728.03 ± 227.37; p-0.016]; Chao1index [Cut-off < 1.05:773.63 ± 361.88; Cut-off > 1.05:728.13 ± 227.58; p-0.016]; Simpson index [Cut-off < 1.05:0.998 ± 0.001; Cut-off > 1.05:0.997 ± 0.001; p-0.006]; Shannon index [Cut-off < 1.05:6.37 ± 0.49; Cut-off > 1.05:6.10 ± 0.43; p-0.003]. Sub-group analysis showed that cases with B/F ratio ≥ 1.05, divided into proliferative diabetic retinopathy (PDR) and clinically significant macular edema (CSME), showed decreased diversity compared to controls (B/F ratio < 1.05). For PDR, all four diversity indices significantly decreased (p < 0.05). However, for CSME, only Shannon and Simpson indices showed significant decrease in diversity (p < 0.05). CONCLUSIONS: Based on clinical diagnosis, decreasing gut microbial diversity was observed among patients with STDR, although not statistically significant. When utilizing B/F ratio, the decreasing gut microbial diversity in STDR patients seems to be associated due to species richness and evenness in PDR when compared to decreasing species richness in CSME.

The Impact of Oral Microbiome Dysbiosis on the Aetiology, Pathogenesis, and Development of Oral Cancer.

Oral squamous cell carcinoma (OSCC) is the most common head and neck cancer. Although the oral cavity is an easily accessible area for visual examination, the OSCC is more often detected at an advanced stage. The global prevalence of OSCC is around 6%, with increasing trends posing a significant health problem due to the increase in morbidity and mortality. The oral cavity microbiome has been the target of numerous studies, with findings highlighting the significant role of dysbiosis in developing OSCC. Dysbiosis can significantly increase pathobionts (bacteria, viruses, fungi, and parasites) that trigger inflammation through their virulence and pathogenicity factors. In contrast, chronic bacterial inflammation contributes to the development of OSCC. Pathobionts also have other effects, such as the impact on the immune system, which can alter immune responses and contribute to a pro-inflammatory environment. Poor oral hygiene and carbohydrate-rich foods can also increase the risk of developing oral cancer. The risk factors and mechanisms of OSCC development are not yet fully understood and remain a frequent research topic. For this reason, this narrative review concentrates on the issue of dysbiosis as the potential cause of OSCC, as well as the underlying mechanisms involved.

A Comprehensive Review of the Triangular Relationship among Diet-Gut Microbiota-Inflammation.

The human gastrointestinal tract hosts a complex and dynamic community of microorganisms known as the gut microbiota, which play a pivotal role in numerous physiological processes, including digestion, metabolism, and immune function. Recent research has highlighted the significant impact of diet on the gut microbiota composition and functionality, and the consequential effects on host health. Concurrently, there is growing evidence linking the gut microbiota to inflammation, a key factor in many chronic diseases such as inflammatory bowel disease (IBD), obesity, diabetes, and cardiovascular diseases (CVDs). This review explores how dietary components influence the gut microbiota composition, how these microbial changes affect inflammatory pathways, and the therapeutic implications of modulating this axis for chronic inflammatory disease prevention and management. Beneficial dietary patterns, such as the Mediterranean diet (MD) and plant-based diets, promote a diverse and balanced gut microbiota composition, supporting anti-inflammatory pathways. Conversely, the Western diet (WD), high in saturated fats and refined sugars, is associated with dysbiosis and increased inflammation. With all the links between the three variables considered, this review attempts to offer a thorough examination of the triangle formed by inflammation, the gut microbiota, and food.

A Novel Microbial Dysbiosis Index and Intestinal Microbiota-Associated Markers as Tools of Precision Medicine in Inflammatory Bowel Disease Paediatric Patients.

Recent evidence indicates that the gut microbiota (GM) has a significant impact on the inflammatory bowel disease (IBD) progression. Our aim was to investigate the GM profiles, the Microbial Dysbiosis Index (MDI) and the intestinal microbiota-associated markers in relation to IBD clinical characteristics and disease state. We performed 16S rRNA metataxonomy on both stools and ileal biopsies, metabolic dysbiosis tests on urine and intestinal permeability and mucosal immunity activation tests on the stools of 35 IBD paediatric patients. On the GM profile, we assigned the MDI to each patient. In the statistical analyses, the MDI was correlated with clinical parameters and intestinal microbial-associated markers. In IBD patients with high MDI, Gemellaceae and Enterobacteriaceae were increased in stools, and Fusobacterium, Haemophilus and Veillonella were increased in ileal biopsies. Ruminococcaceae and WAL_1855D were enriched in active disease condition; the last one was also positively correlated to MDI. Furthermore, the MDI results correlated with PUCAI and Matts scores in ulcerative colitis patients (UC). Finally, in our patients, we detected metabolic dysbiosis, intestinal permeability and mucosal immunity activation. In conclusion, the MDI showed a strong association with both severity and activity of IBD and a positive correlation with clinical scores, especially in UC. Thus, this evidence could be a useful tool for the diagnosis and prognosis of IBD.

The Latest Data Concerning the Etiology and Pathogenesis of Irritable Bowel Syndrome.

Globally, irritable bowel syndrome (IBS) is present in approximately 10% of the population. While this condition does not pose a risk of complications, it has a substantial impact on the patient's quality of life. Moreover, this disease has a significant financial impact on healthcare systems. This includes the direct costs associated with the diagnosis and treatment of these patients, as well as the indirect costs that arise from work absenteeism and reduced productivity. In light of these data, recent research has focused on elucidating the pathophysiological basis of this condition in order to improve the quality of life for affected individuals. Despite extensive research to date, we still do not fully understand the precise mechanisms underlying IBS. Numerous studies have demonstrated the involvement of the gut-brain axis, visceral hypersensitivity, gastrointestinal dysmotility, gut microbiota dysbiosis, food allergies and intolerances, low-grade mucosal inflammation, genetic factors, and psychosocial factors. The acquisition of new data is crucial for the advancement of optimal therapeutic approaches aimed at enhancing the general health of these patients while simultaneously reducing the financial burden associated with this ailment.

Intrauterine Shaping of Fetal Microbiota.

Mechanisms resulting from the physiological immaturity of the digestive system in children delivered before 32 weeks of gestation and, in particular, different interactions between the microbiome and the body have not been fully elucidated yet. Next-generation sequencing methods demonstrated the presence of bacterial DNA in the placenta and amniotic fluid, which may reflect bacterial populations that initiate intestinal colonization in utero. Numerous studies confirmed the hypothesis stating that intestinal bacteria played an important role in the pathogenesis of necrotizing enterocolitis (NEC) early- and late-onset neonatal sepsis (EONS and LONS). The model and scale of disorders within the intestinal microbiome are the subject of active research in premature infants. Neonatal meconium was primarily used as an indicator defining the environment in utero, as it is formed before birth. Metagenomic results and previous data from microbiological bacterial cultures showed a correlation between the time from birth to sample collection and the detection of bacteria in the neonatal meconium. Therefore, it may be determined that the colonization of the newborn's intestines is influenced by numerous factors, which may be divided into prenatal, perinatal, and postnatal, with particular emphasis put on the mode of delivery and contact with the parent immediately after birth. Background: The aim of this review was to collect available data on the intrauterine shaping of the fetal microbiota. Methods: On 13 March 2024, the available literature in the PubMed National Library of Medicine search engine was reviewed using the following selected keywords: "placental microbiome", "intestinal bacteria in newborns and premature infants", and "intrauterine microbiota". Results: After reviewing the available articles and abstracts and an in-depth analysis of their content, over 100 articles were selected for detailed elaboration. We focused on the origin of microorganisms shaping the microbiota of newborns. We also described the types of bacteria that made up the intrauterine microbiota and the intestinal microbiota of newborns. Conclusions: The data presented in the review on the microbiome of both term newborns and those with a body weight below 1200 g indicate a possible intrauterine colonization of the fetus depending on the duration of pregnancy. The colonization occurs both via the vaginal and intestinal route (hematogenous route). However, there are differences in the demonstrated representatives of various types of bacteria, phyla Firmicutes and Actinobacteria in particular, taking account of the distribution in their abundance in the individual groups of pregnancy duration. Simultaneously, the distribution of the phyla Actinobacteria and Proteobacteria is consistent. Considering the duration of pregnancy, it may also be concluded that the bacterial flora of vaginal origin dominates in preterm newborns, while the flora of intestinal origin dominates in term newborns. This might explain the role of bacterial and infectious factors in inducing premature birth with the rupture of fetal membranes.

The 3 Ds: Depression, Dysbiosis, and Clostridiodes difficile.

This paper explores the intricate relationship between depression, gut dysbiosis, and Clostridioides difficile infections, collectively termed "The 3 Ds". Depression is a widespread mental disorder increasing in prevalence. It is recognized for its societal burden and complex pathophysiology, encompassing genetic, environmental, and microbiome-related factors. The consequent increased use of antidepressants has led to growing concerns about their effects on the gut microbiome. Various classes of antidepressants and antipsychotics show antimicrobial activity, potentially leading to shifts in the gut microbiome and contributing to the development of dysbiosis. Dysbiosis, in turn, can predispose individuals to opportunistic infections like C. difficile, a significant healthcare concern due to its high recurrence rates and severe impact on patients' quality of life. Further, the link between antidepressant use and an increased risk of C. difficile infection (CDI) is explored and, finally, the emergence of live biotherapeutic products as novel treatment options for recurrent CDI is discussed.

Probiotic treatment improves post-traumatic stress disorder outcomes in mice.

Post-traumatic stress disorder (PTSD) is a mental disorder resulting from traumatic events which are characterized primarily by anxiety and depressive disorder. In this study, we determine the role of gut bacteria in PTSD. PTSD-like symptoms were produced by single prolonged stress (SPS). SPS animals showed increased levels of anxiety as measured by the elevated plus maze test, while depressive behaviour was confirmed using sucrose preference, force swim, and tail suspension tests. Gut dysbiosis was confirmed in PTSD animals by next-generation sequencing of 16 s RNA of faecal samples, while these animals also showed increased intestinal permeability and altered intestinal ultrastructure. Probiotic treatment increases beneficial microbiota, improves intestinal health and reduces PTSD-associated anxiety and depression. We also found a decrease in cortical BDNF levels in PTSD animals, which was reversed after probiotic administration. Here, we establish the link between gut dysbiosis and PTSD and show that probiotic treatment may improve the outcome of PTSD like symptoms in mice.

Obesity, dysbiosis and inflammation: interactions that modulate the efficacy of immunotherapy.

Recent years have seen an outstanding growth in the understanding of connections between diet-induced obesity, dysbiosis and alterations in the tumor microenvironment. Now we appreciate that gut dysbiosis can exert important effects in distant target tissues via specific microbes and metabolites. Multiple studies have examined how diet-induced obese state is associated with gut dysbiosis and how gut microbes direct various physiological processes that help maintain obese state in a bidirectional crosstalk. Another tightly linked factor is sustained low grade inflammation in tumor microenvironment that is modulated by both obese state and dysbiosis, and influences tumor growth as well as response to immunotherapy. Our review brings together these important aspects and explores their connections. In this review, we discuss how obese state modulates various components of the breast tumor microenvironment and gut microbiota to achieve sustained low-grade inflammation. We explore the crosstalk between different components of tumor microenvironment and microbes, and how they might modulate the response to immunotherapy. Discussing studies from multiple tumor types, we delve to find common microbial characteristics that may positively or negatively influence immunotherapy efficacy in breast cancer and may guide future studies.