Antibiotic-induced alterations in taurocholic acid levels promote gastrointestinal colonization of Candida albicans

Interplay between Bile Acids and Intestinal Microbiota: Regulatory Mechanisms and Therapeutic Potential for Infections

Bile acids (BAs) play a crucial role in the human body's defense against infections caused by bacteria, fungi, and viruses. BAs counteract infections not only through interactions with intestinal bacteria exhibiting bile salt hydrolase (BSH) activity but they also directly combat infections. Building upon our research group's previous discoveries highlighting the role of BAs in combating infections, we have initiated an in-depth investigation into the interactions between BAs and intestinal microbiota. Leveraging the existing literature, we offer a comprehensive analysis of the relationships between BAs and 16 key microbiota. This investigation encompasses bacteria (e.g., Clostridioides difficile (C. difficile), Staphylococcus aureus (S. aureus), Escherichia coli, Enterococcus, Pseudomonas aeruginosa, Mycobacterium tuberculosis (M. tuberculosis), Bacteroides, Clostridium scindens (C. scindens), Streptococcus thermophilus, Clostridium butyricum (C. butyricum), and lactic acid bacteria), fungi (e.g., Candida albicans (C. albicans) and Saccharomyces boulardii), and viruses (e.g., coronavirus SARS-CoV-2, influenza virus, and norovirus). Our research found that Bacteroides, C. scindens, Streptococcus thermophilus, Saccharomyces boulardii, C. butyricum, and lactic acid bacteria can regulate the metabolism and function of BSHs and 7α-dehydroxylase. BSHs and 7α-dehydroxylase play crucial roles in the conversion of primary bile acid (PBA) to secondary bile acid (SBA). It is important to note that PBAs generally promote infections, while SBAs often exhibit distinct anti-infection roles. In the antimicrobial action of BAs, SBAs demonstrate antagonistic properties against a wide range of microbiota, with the exception of norovirus. Given the intricate interplay between BAs and intestinal microbiota, and their regulatory effects on infections, we assert that BAs hold significant potential as a novel approach for preventing and treating microbial infections.

Immune response to colonization of Candida albicans in mice treated with Cefoperazone

Candida species are a normal human flora in humans' digestive and reproductive systems, oral cavity, skin, and mucosal surfaces. This study aimed to detect the immunological role of Candida infection by using some immunological markers. The results of levels in serum showed high concentrations of IgA (56.20 ± 12 pg/ml,29.55 ± 4.5 pg/ml respectively) and IgG (12.05 ± 3.218 pg/ml, 3.836 ± 1.23 pg/ml respectively) in mice infected with C. albicans and mice treated with Cefoperazone and infected with Candida with significant differences (P value < 0.05). The results showed high serum levels of IL-17(191.5 ± 42.81 pg/ml) and TLR2(7.651 ± 1.5 pg/ml) in group mice infected with C. albicans compared with negative control and group mice treated with Cefoperazone. Also, high levels of IL-17 (91.33 ± 4.816 pg/ml) and TLR2 (2.630 ± 0.5 pg/ml) in group mice treated with Cefoperazone and infected with Candida compared with negative control and group mice treated with Cefoperazone (P value < 0.05). The results of antibodies and immunological markers in the intestine showed high levels of IgA and IgG in mice infected with C.albicans (55.7 ± 4.9 pg/ml, 18.19 ± 0.63 pg/ml respectively).Also,IgA and IgG in mice treated with Cefoperazone and infected with Candida were high level (43.04 ± 2.1 pg/ml, 2.927 ± 0.2 pg/ml respectively) in mice infected with C. albicans with significant differences (P value < 0.05). The results levels of IL-17 and TLR2 were increased in mice infected with C. albicans (191.5 ± 42.81 pg/ml, 7.651 ± 1.5 pg/ml respectively) and mice treated with Cefoperazone and infected with Candida (91.33 ± 4.816 pg/ml,2.630 ± 0.5 pg/ml respectively) with significant differences (P < 0.05). In conclusion, this study demonstrated that cefoperazone treatment and infection by Candida albicans changed the microbiome components in the gut and finally can change host immune responses. It was observed that elevated levels of the antibodies production (IgA and IgG) and immunological markers (IL-17, and TLR2) in serum and the gut.

Candida albicans and Candida glabrata: global priority pathogens

SUMMARYA significant increase in the incidence of Candida-mediated infections has been observed in the last decade, mainly due to rising numbers of susceptible individuals. Recently, the World Health Organization published its first fungal pathogen priority list, with Candida species listed in medium, high, and critical priority categories. This review is a synthesis of information and recent advances in our understanding of two of these species-Candida albicans and Candida glabrata. Of these, C. albicans is the most common cause of candidemia around the world and is categorized as a critical priority pathogen. C. glabrata is considered a high-priority pathogen and has become an increasingly important cause of candidemia in recent years. It is now the second most common causative agent of candidemia in many geographical regions. Despite their differences and phylogenetic divergence, they are successful as pathogens and commensals of humans. Both species can cause a broad variety of infections, ranging from superficial to potentially lethal systemic infections. While they share similarities in certain infection strategies, including tissue adhesion and invasion, they differ significantly in key aspects of their biology, interaction with immune cells, host damage strategies, and metabolic adaptations. Here we provide insights on key aspects of their biology, epidemiology, commensal and pathogenic lifestyles, interactions with the immune system, and antifungal resistance.

The Intricate Connection between Bacterial α-Diversity and Fungal Engraftment in the Human Gut of Healthy and Impaired Individuals as Studied Using the In Vitro SHIME® Model

From the estimated 2.2 to 3.8 million fungal species existing on Earth, only a minor fraction actively colonizes the human gastrointestinal tract. In fact, these fungi only represent 0.1% of the gastrointestinal biosphere. Despite their low abundance, fungi play dual roles in human health-both beneficial and detrimental. Fungal infections are often associated with bacterial dysbiosis following antibiotic use, yet our understanding of gut fungi-bacteria interactions remains limited. Here, we used the SHIME® gut model to explore the colonization of human fecal-derived fungi across gastrointestinal compartments. We accounted for the high inter-individual microbial diversity by using fecal samples from healthy adults, healthy babies, and Crohn's disease patients. Using quantitative Polymerase Chain Reaction and targeted next-generation sequencing, we demonstrated that SHIME®-colonized mycobiomes change upon loss of transient colonizers. In addition, SHIME® reactors from Crohn's disease patients contained comparable bacterial levels as healthy adults but higher fungal concentrations, indicating unpredictable correlations between fungal levels and total bacterial counts. Our findings rather link higher bacterial α-diversity to limited fungal growth, tied to colonization resistance. Hence, while healthy individuals had fewer fungi engrafting the colonic reactors, low α-diversity in impaired (Crohn's disease patients) or immature (babies) microbiota was associated with greater fungal abundance. To validate, antibiotic-treated healthy colonic microbiomes demonstrated increased fungal colonization susceptibility, and bacterial taxa that were negatively correlated with fungal expansion were identified. In summary, fungal colonization varied individually and transiently, and bacterial resistance to fungal overgrowth was more related with specific bacterial genera than total bacterial load. This study sheds light on fungal-bacterial dynamics in the human gut.

The Nonbacterial Microbiome: Fungal and Viral Contributions to the Preterm Infant Gut in Health and Disease

The intestinal microbiome is frequently implicated in necrotizing enterocolitis (NEC) pathogenesis. While no particular organism has been associated with NEC development, a general reduction in bacterial diversity and increase in pathobiont abundance has been noted preceding disease onset. However, nearly all evaluations of the preterm infant microbiome focus exclusively on the bacterial constituents, completely ignoring any fungi, protozoa, archaea, and viruses present. The abundance, diversity, and function of these nonbacterial microbes within the preterm intestinal ecosystem are largely unknown. Here, we review findings on the role of fungi and viruses, including bacteriophages, in preterm intestinal development and neonatal intestinal inflammation, with potential roles in NEC pathogenesis yet to be determined. In addition, we highlight the importance of host and environmental influences, interkingdom interactions, and the role of human milk in shaping fungal and viral abundance, diversity, and function within the preterm intestinal ecosystem.

Evaluation of Candida spp. and Other Fungi in Feces from Dogs with Naturally Occurring Diabetes Mellitus

Simple Summary

Diabetes mellitus is a common endocrine disorder in dogs that is similar to type 1 diabetes mellitus (T1DM) in humans. Candida spp. is a common non-pathogenic fungi that is identified more commonly and in higher amounts in humans with T1DM, including the gastrointestinal tract. This change to the distribution of microorganisms that inhabit the intestine has potential to affect glycemic control and even spread to other organs and cause severe illness. There are no studies that have investigated whether diabetic dogs, like humans, have alterations to the intestinal mycobiome. Therefore, our study sought to determine whether differences exist in the types of fungi cultured from feces in diabetic dogs and non-diabetic healthy control dogs. In addition, we wanted to find out if there were variables associated with fungi colonization. Diabetic dogs had more quantitative fungal growth than controls and females were more likely to yield growth than males. Diabetic dogs were also more likely to have Candida spp. colonized from feces. Glycemic control was also seemingly associated with growth of Candida spp. in diabetic dogs. Our results indicate that the intestinal mycobiome is altered in diabetic dogs with increased prevalence of Candida spp. and quantitative growth of fungi.

Abstract

Diabetes mellitus is a common endocrinopathy in dogs and in most cases is analogous to type 1 diabetes mellitus (T1DM) in humans. Candida spp. is a common commensal fungi with higher prevalence and magnitude of growth in humans with T1DM. There is currently no published information about the fungal microbiome in diabetic dogs. Therefore, the objectives of this study were to (i) determine whether diabetic dogs were more likely to have Candida spp. or other types of fungi from feces compared to non-diabetic controls, and (ii) identify variables associated with fungi colonization. Fourteen diabetic dogs and 14 age, sex, and breed matched non-diabetic healthy control dogs were included in this prospective case–control study. Matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used for fungal identification. Diabetic dogs had greater quantitative fungal growth compared to controls (p = 0.004). Moreover, female dogs were more likely to have fungi colonization than males (p = 0.02). All instances of Candida spp. and Aspergillus spp. colonization were exclusively identified in diabetic dogs. Serum fructosamine concentration was higher in diabetic dogs with fecal colonization of Candida spp. compared to diabetic dogs without growth (p = 0.03). Our results indicate that the fungal microbiome in feces is altered in diabetic dogs, which seem to favor an increased prevalence of Candida spp. and higher quantitative fungal growth. Moreover, female sex and glycemic control could affect the intestinal mycobiome.

Interactions between Candida albicans and the resident microbiota

Candida albicans is a prevalent, opportunistic human fungal pathogen. It usually dwells in the human body as a commensal, however, once in its pathogenic state, it causes diseases ranging from debilitating superficial to life-threatening systemic infections. The switch from harmless colonizer to virulent pathogen is, in most cases, due to perturbation of the fungus-host-microbiota interplay. In this review, we focused on the interactions between C. albicans and the host microbiota in the mouth, gut, blood, and vagina. We also highlighted important future research directions. We expect that the evaluation of these interplays will help better our understanding of the etiology of fungal infections and shed new light on the therapeutic approaches.

Kefir microbiota and metabolites stimulate intestinal mucosal immunity and its early development

Kefir consists of a large number of probiotics, which can regulate or shape the balance of intestinal microbiota, and enhance the host's immune response. Kefir microbiota can shape the mucosal immunity of the body through SCFAs, EPS, polypeptides, lactic acid, and other metabolites and microbial antigens themselves, and this shaping may have time windows and specific pathways. Kefir can regulate antibody SIgA and IL-10 levels to maintain intestinal homeostasis, and its secreted SIgA can shape the stable microbiota system by wrapping and binding different classes of microorganisms. The incidence of intestinal inflammation is closely linked to the development and maturation of intestinal mucosal immunity. Based on summarizing the existing research results on Kefir, its metabolites, and immune system development, this paper proposes to use Kefir, traditional fermented food with natural immune-enhancing components and stable functional microbiota, as an intervention method. Early intervention in the immune system may seize the critical window period of mucosal immunity and stimulate the development and maturation of intestinal mucosal immunity in time.

Lactobacillus rhamnosus colonisation antagonizes Candida albicans by forcing metabolic adaptations that compromise pathogenicity

Intestinal microbiota dysbiosis can initiate overgrowth of commensal Candida species - a major predisposing factor for disseminated candidiasis. Commensal bacteria such as Lactobacillus rhamnosus can antagonize Candida albicans pathogenicity. Here, we investigate the interplay between C. albicans, L. rhamnosus, and intestinal epithelial cells by integrating transcriptional and metabolic profiling, and reverse genetics. Untargeted metabolomics and in silico modelling indicate that intestinal epithelial cells foster bacterial growth metabolically, leading to bacterial production of antivirulence compounds. In addition, bacterial growth modifies the metabolic environment, including removal of C. albicans' favoured nutrient sources. This is accompanied by transcriptional and metabolic changes in C. albicans, including altered expression of virulence-related genes. Our results indicate that intestinal colonization with bacteria can antagonize C. albicans by reshaping the metabolic environment, forcing metabolic adaptations that reduce fungal pathogenicity.

Bile Acid Regulates the Colonization and Dissemination of Candida albicans from the Gastrointestinal Tract by Controlling Host Defense System and Microbiota

Candida albicans (CA), a commensal and opportunistic eukaryotic organism, frequently inhabits the gastrointestinal (GI) tract and causes life-threatening infections. Antibiotic-induced gut dysbiosis is a major risk factor for increased CA colonization and dissemination from the GI tract. We identified a significant increase of taurocholic acid (TCA), a major bile acid in antibiotic-treated mice susceptible to CA infection. In vivo findings indicate that administration of TCA through drinking water is sufficient to induce colonization and dissemination of CA in wild-type and immunosuppressed mice. Treatment with TCA significantly reduced mRNA expression of immune genes ang4 and Cxcr3 in the colon. In addition, TCA significantly decreased the relative abundance of three culturable species of commensal bacteria, Turicibacter sanguinis, Lactobacillus johnsonii, and Clostridium celatum, in both cecal contents and mucosal scrapings from the colon. Taken together, our results indicate that TCA promotes fungal colonization and dissemination of CA from the GI tract by controlling the host defense system and intestinal microbiota that play a critical role in regulating CA in the intestine.

A peptidoglycan storm caused by β-lactam antibiotic's action on host microbiota drives Candida albicans infection

The commensal fungus Candida albicans often causes life-threatening infections in patients who are immunocompromised with high mortality. A prominent but poorly understood risk factor for the C. albicans commensal‒pathogen transition is the use of broad-spectrum antibiotics. Here, we report that β-lactam antibiotics cause bacteria to release significant quantities of peptidoglycan fragments that potently induce the invasive hyphal growth of C. albicans. We identify several active peptidoglycan subunits, including tracheal cytotoxin, a molecule produced by many Gram-negative bacteria, and fragments purified from the cell wall of Gram-positive Staphylococcus aureus. Feeding mice with β-lactam antibiotics causes a peptidoglycan storm that transforms the gut from a niche usually restraining C. albicans in the commensal state to promoting invasive growth, leading to systemic dissemination. Our findings reveal a mechanism underlying a significant risk factor for C. albicans infection, which could inform clinicians regarding future antibiotic selection to minimize this deadly disease incidence.

Transcriptional control of hyphal morphogenesis in Candida albicans

Candida albicans is a multimorphic commensal organism and opportunistic fungal pathogen in humans. A morphological switch between unicellular budding yeast and multicellular filamentous hyphal growth forms plays a vital role in the virulence of C. albicans, and this transition is regulated in response to a range of environmental cues that are encountered in distinct host niches. Many unique transcription factors contribute to the transcriptional regulatory network that integrates these distinct environmental cues and determines which phenotypic state will be expressed. These hyphal morphogenesis regulators have been extensively investigated, and represent an increasingly important focus of study, due to their central role in controlling a key C. albicans virulence attribute. This review provides a succinct summary of the transcriptional regulatory factors and environmental signals that control hyphal morphogenesis in C. albicans.

Understanding Human Microbiota Offers Novel and Promising Therapeutic Options against Candida Infections

Human fungal pathogens particularly of Candida species are one of the major causes of hospital acquired infections in immunocompromised patients. The limited arsenal of antifungal drugs to treat Candida infections with concomitant evolution of multidrug resistant strains further complicates the management of these infections. Therefore, deployment of novel strategies to surmount the Candida infections requires immediate attention. The human body is a dynamic ecosystem having microbiota usually involving symbionts that benefit from the host, but in turn may act as commensal organisms or affect positively (mutualism) or negatively (pathogenic) the physiology and nourishment of the host. The composition of human microbiota has garnered a lot of recent attention, and despite the common occurrence of Candida spp. within the microbiota, there is still an incomplete picture of relationships between Candida spp. and other microorganism, as well as how such associations are governed. These relationships could be important to have a more holistic understanding of the human microbiota and its connection to Candida infections. Understanding the mechanisms behind commensalism and pathogenesis is vital for the development of efficient therapeutic strategies for these Candida infections. The concept of host-microbiota crosstalk plays critical roles in human health and microbiota dysbiosis and is responsible for various pathologies. Through this review, we attempted to analyze the types of human microbiota and provide an update on the current understanding in the context of health and Candida infections. The information in this article will help as a resource for development of targeted microbial therapies such as pre-/pro-biotics and microbiota transplant that has gained advantage in recent times over antibiotics and established as novel therapeutic strategy.

Antibiotic-induced gut metabolome and microbiome alterations increase the susceptibility to Candida albicans colonization in the gastrointestinal tract

Antibiotic-induced alterations in the gut ecosystem increases the susceptibility to Candida albicans, yet the mechanisms involved remains poorly understood. Here we show that mice treated with the broad-spectrum antibiotic cefoperazone promoted the growth, morphogenesis and gastrointestinal (GI) colonization of C. albicans. Using metabolomics, we revealed that the cecal metabolic environment of the mice treated with cefoperazone showed a significant alteration in intestinal metabolites. Levels of carbohydrates, sugar alcohols and primary bile acids increased, whereas carboxylic acids and secondary bile acids decreased in antibiotic treated mice susceptible to C. albicans. Furthermore, using in-vitro assays, we confirmed that carbohydrates, sugar alcohols and primary bile acids promote, whereas carboxylic acids and secondary bile acids inhibit the growth and morphogenesis of C. albicans. In addition, in this study we report changes in the levels of gut metabolites correlated with shifts in the gut microbiota. Taken together, our in-vivo and in-vitro results indicate that cefoperazone-induced metabolome and microbiome alterations favor the growth and morphogenesis of C. albicans, and potentially play an important role in the GI colonization of C. albicans.

The gut, the bad and the harmless: Candida albicans as a commensal and opportunistic pathogen in the intestine

Candida albicans is a regular member of the intestinal microbiota in the majority of the human population. This underscores C. albicans' adaptation to life in the intestine without inducing competitive interactions with other microbes, or immune responses detrimental to its survival. However, specific conditions such as a dysbalanced microbiome, a suppression of the immune system, and an impaired intestinal barrier can predispose for invasive, mostly nosocomial, C. albicans infections. Colonization of the intestine and translocation through the intestinal barrier are fundamental aspects of the processes preceding life-threatening systemic candidiasis. Insights into C. albicans' commensal lifestyle and translocation can thus help us to understand how patients develop candidiasis, and may provide leads for therapeutic strategies aimed at preventing infection. In this review, we discuss the commensal lifestyle of C. albicans in the intestine, the role of morphology for commensalism, the influence of diet, and the interactions with bacteria of the microbiota.

T Cell Antifungal Immunity and the Role of C-Type Lectin Receptors

Fungi can cause disease in humans, from mucocutaneous to life-threatening systemic infections. Initiation of antifungal immunity involves fungal recognition by pattern recognition receptors such as C-type lectin receptors (CLRs). These germline-encoded receptors trigger a multitude of innate responses including phagocytosis, fungal killing, and antigen presentation which can also shape the development of adaptive immunity. Recently, studies have shed light on how CLRs directly or indirectly modulate lymphocyte function. Moreover, CLR-mediated recognition of commensal fungi maintains homeostasis and prevents invasion from opportunistic commensals. We present an overview of current knowledge of antifungal T cell immune responses, with emphasis on the role of C-type lectins, and discuss how these receptors modulate these responses at different levels.

CLRs are essential pattern recognition receptors involved in fungal recognition and initiation of protective antifungal immunity.

CLRs promote the differentiation of mammalian T helper cell subsets essential for the control of systemic (Th1) and mucosal (Th17) fungal infections.

CLRs are involved in antigen presentation, the expression of co-stimulatory molecules, and cytokine secretion; therefore, they can regulate lymphocyte function and adaptive immune responses at different levels.

Fungal morphological changes, such as the transition from yeast to hyphae in Candida albicans during tissue invasion, affects recognition by CLRs and impacts on adaptive immune responses.

CLRs recognize the fungal component of the microbiome that can influence T cell responses during infection at intestinal and peripheral sites.

Antibiotic-induced decreases in the levels of microbial-derived short-chain fatty acids correlate with increased gastrointestinal colonization of Candida albicans

Candida albicans is the fourth most common cause of systemic nosocomial infections, posing a significant risk in immunocompromised individuals. As the majority of systemic C. albicans infections stem from endogenous gastrointestinal (GI) colonization, understanding the mechanisms associated with GI colonization is essential in the development of novel methods to prevent C. albicans-related mortality. In this study, we investigated the role of microbial-derived short-chain fatty acids (SCFAs) including acetate, butyrate, and propionate on growth, morphogenesis, and GI colonization of C. albicans. Our results indicate that cefoperazone-treated mice susceptible to C. albicans infection had significantly decreased levels of SCFAs in the cecal contents that correlate with a higher fungal load in the feces. Further, using in vivo concentration of SCFAs, we demonstrated that SCFAs inhibit the growth, germ tube, hyphae and biofilm development of C. albicans in vitro. Collectively, results from this study suggest that antibiotic-induced decreases in the levels of SCFAs in the cecum enhances the growth and GI colonization of C. albicans.