Effects of beta-lactam antibiotics on intestinal microflora and bile acid metabolism in rats

Perturbation and resilience of the gut microbiome up to 3 months after β-lactams exposure in healthy volunteers suggest an important role of microbial β-lactamases

BACKGROUND

Antibiotics notoriously perturb the gut microbiota. We treated healthy volunteers either with cefotaxime or ceftriaxone for 3 days, and collected in each subject 12 faecal samples up to day 90. Using untargeted and targeted phenotypic and genotypic approaches, we studied the changes in the bacterial, phage and fungal components of the microbiota as well as the metabolome and the β-lactamase activity of the stools. This allowed assessing their degrees of perturbation and resilience.

RESULTS

While only two subjects had detectable concentrations of antibiotics in their faeces, suggesting important antibiotic degradation in the gut, the intravenous treatment perturbed very significantly the bacterial and phage microbiota, as well as the composition of the metabolome. In contrast, treatment impact was relatively low on the fungal microbiota. At the end of the surveillance period, we found evidence of resilience across the gut system since most components returned to a state like the initial one, even if the structure of the bacterial microbiota changed and the dynamics of the different components over time were rarely correlated. The observed richness of the antibiotic resistance genes repertoire was significantly reduced up to day 30, while a significant increase in the relative abundance of β-lactamase encoding genes was observed up to day 10, consistent with a concomitant increase in the β-lactamase activity of the microbiota. The level of β-lactamase activity at baseline was positively associated with the resilience of the metabolome content of the stools.

CONCLUSIONS

In healthy adults, antibiotics perturb many components of the microbiota, which return close to the baseline state within 30 days. These data suggest an important role of endogenous β-lactamase-producing anaerobes in protecting the functions of the microbiota by de-activating the antibiotics reaching the colon. Video Abstract.

Impact of Primary and Secondary Bile Acids on Clostridioides difficile Infection

Primary bile acids (BAs), synthesized from cholesterol in the liver, after their secretion with bile into the intestinal lumen, are transformed by gut microbiota to secondary BAs. As natural detergents, BAs play a key role in the digestion and absorption of lipids and liposoluble vitamins. However, they have also been recognized as important signaling molecules involved in numerous metabolic processes. The close bidirectional interactions between BAs and gut microbiota occur since BAs influence microbiota composition, whereas microbiota determines BA metabolism. In particular, it is well established that BAs modulate Clostridioides difficile life cycle in vivo. C. difficile is a cause of common nosocomial infections that have become a growing concern. The aim of this review is to summarize the current knowledge regarding the impact of BAs on the pathogenesis, prevention, and treatment of C. difficile infection.

Gut microbiome and Clostridioides difficile infection: a closer look at the microscopic interface

The pathogenesis of Clostridioides difficile infection (CDI) was recognized with its link to the use of antimicrobials. Antimicrobials significantly alter gut microbiota structure and composition, which led to the discovery of the association of this gut perturbation with the development of CDI. A number of factors implicated in its pathogenesis, such as advancing age, proton-pump inhibitors, and gastrointestinal diseases, are linked to gut microbiota perturbations. In an effort to better understand CDI, a multitude of studies have tried to ascertain protective and predictive microbial footprints linked with CDI. It has further been realized that CDI in itself can alter the gut microbiome. Its spore-forming capability poses as an impediment in the management of the infection and contributes to its recurrence. Antibiotic therapies used for its management have also been linked to gut microbiota changes, making its treatment a little more challenging. In an effort to exploit and utilize this association, gut microbial restoration therapies, particularly in the form of fecal microbial transplant, are increasingly being put to use and are proving to be beneficial. In this review, we summarize the association of the gut microbiome and microbial perturbation with initial and recurrent CDI.

The Route to Palatable Fecal Microbiota Transplantation

The community of symbiotic microorganisms that reside in our gastrointestinal tract is integral to human health. Fecal microbiota transplantation (FMT) has been shown to be highly effective in treating recurrent Clostridioides difficile infection (rCDI) and is now recommended by medical societies for patients suffering from rCDI who have failed to respond to conventional therapy. The main challenges with FMT are its accessibility, acceptability, lack of standardization, and regulatory complexity, which will be discussed in this review. Access to FMT is being addressed through the development of frozen and lyophilized FMT preparations that can be prepared at stool banks and shipped to the point of care. Both access and patient acceptance would be enhanced by oral FMT capsules, and there is potential to reduce capsule burden by utilizing colonic release capsules, targeting the site of disease. This review compares the efficacy of different FMT routes of administration: capsules, nasal feeding tubes, enemas, and colonoscopic infusions. FMT is considered investigational by the Food and Drug Administration. In effort to improve access to FMT, physicians may perform FMT outside of an investigational new drug application for treating CDI infections not responsive to standard therapies. The majority of FMT studies report only minor adverse effects; however, there is risk of transmission of infections.

Strategies to prevent adverse outcomes following Clostridioides difficile infection in the elderly

Introduction: Clostridioides difficile remains the most common cause of healthcare-associated infections in the US, and it disproportionately affects the elderly. Older patients are more susceptible and have a greater risk of adverse outcomes from C. difficile infection (CDI), despite advances in treatment and prevention.Areas covered: The epidemiology and pathogenesis of CDI, as well as risk factors in the aging host, will be reviewed. The importance of antimicrobial stewardship and infection prevention in order to avoid acquisition and transmission will be discussed, as well as strategies to prevent adverse outcomes and recurrent CDI, through optimization of CDI treatment s,election.Expert opinion: Appropriate CDI-prevention strategies to avoid adverse outcomes in this susceptible population involve antimicrobial stewardship and methods to prevent C. difficile transmission in healthcare settings. Management strategies to prevent adverse outcomes include initiation of supportive therapy and proper selection of CDI specific treatments. Many patients may also benefit from adjunctive therapies or additional procedures.

Potential biomarkers to predict outcome of faecal microbiota transfer for recurrent Clostridioides difficile infection

BACKGROUND & AIMS

Faecal microbiota transplantation (FMT) has proven high clinical efficacy in the management of recurrent Clostridioides difficile infection (rCDI) with cure rates of over 80% after a single treatment. Nevertheless, the reasons for failure in the remaining 20% remain elusive. The aim of the present study was to investigate different potential predictors of response to FMT.

METHODS

Faecal specimens of sixteen patients undergoing FMT for rCDI, as well as samples from the respective donors were collected and analyzed by 16S rRNA gene profiling, bile acid-inducible (baiCD) gene specific qPCR, and liquid chromatography tandem-mass spectrometry (LC-MS/MS) to quantify the concentrations of primary and secondary bile acids.

RESULTS

Using the faecal concentration of the secondary bile acid lithocholic acid (LCA)within the patient specimens, we were able to predict response to FMT (accuracy 95.2%, sensitivity 100%, specificity 90.9%). By combining the faecal LCA concentration with the urinary pCS concentration, an accuracy of 100% was achieved.

CONCLUSION

LCA appears to be a promising marker candidate for prediction of clinical response to FMT. Other makers, such as urinary concentration of pCS, but not 3-IS, might be used to improve accuracy of prediction. Further studies are warranted to validate these candidate markers.

BaiCD gene cluster abundance is negatively correlated with Clostridium difficile infection

BACKGROUND

Clostridium difficile infection (CDI) is a major cause of hospital-acquired diarrhea. Secondary bile acids were shown to confer resistance to colonization by C. difficile. 7α-dehydroxylation is a key step in transformation of primary to secondary bile acids and required genes have been located in a single bile acid-inducible (bai) operon in C. scindens as well as in C. hiranonis, two Clostridium sp. recently reported to protect against C. difficile colonization.

AIM

To analyze baiCD gene abundance in C. difficile positive and negative fecal samples.

MATERIAL & METHODS

A species-specific qPCR for detecting baiCD genes was established. Fecal samples of patients with CDI, asymptomatic toxigenic C. difficile colonization (TCD), non-toxigenic C. difficile colonization (NTCD), of C. difficile negative (NC) patients, and of two patients before and after fecal microbiota transplantation (FMT) for recurrent CDI (rCDI) were tested for the presence of the baiCD genes.

RESULTS

The prevalence of the baiCD gene cluster was significantly higher in C. difficile negative fecal samples than in samples of patients diagnosed with CDI (72.5% (100/138) vs. 35.9% (23/64; p<0.0001). No differences in baiCD gene cluster prevalence were seen between NC and NTCD or NC and TCD samples. Both rCDI patients were baiCD-negative at baseline, but one of the two patients turned positive after successful FMT from a baiCD-positive donor.

CONCLUSION

Fecal samples of CDI patients are less frequently baiCD-positive than samples from asymptomatic carriers or C. difficile-negative individuals. Furthermore, we present a case of baiCD positivity observed after successful FMT for rCDI.

Proton pump inhibitors and risk of Clostridium difficile infection: association or causation?

PURPOSE OF REVIEW

The rising burden of Clostridium difficile infection (CDI) requires urgent identification of preventable risk factors. Observational studies suggest an association between proton-pump inhibitor (PPI) use and CDI risk.

RECENT FINDINGS

Key historical literature on PPI and CDI associations is reviewed as a prelude to evaluating the plausibility of a causative association. Impactful literature from the past 18 months is examined in detail and critically appraised through the lens of the Bradford Hill Criteria for determination of causality. The PPI and CDI association has been studied extensively and is valid. Nonetheless, causality is not proven due to extensive and difficult to control confounding in observational studies of CDI patient populations with complex comorbidities.

SUMMARY

In the authors' opinion, systematic discontinuation of PPIs in patients at risk for CDI is not warranted based on current evidence. Well controlled prospective human studies are needed. Careful and repeated consideration should be given to all PPI prescriptions to avoid potential adverse effects.

Lithocholic acid controls adaptive immune responses by inhibition of Th1 activation through the Vitamin D receptor

Bile acids are established signaling molecules next to their role in the intestinal emulsification and uptake of lipids. We here aimed to identify a potential interaction between bile acids and CD4+ Th cells, which are central in adaptive immune responses. We screened distinct bile acid species for their potency to affect T cell function. Primary human and mouse CD4+ Th cells as well as Jurkat T cells were used to gain insight into the mechanism underlying these effects. We found that unconjugated lithocholic acid (LCA) impedes Th1 activation as measured by i) decreased production of the Th1 cytokines IFNγ and TNFαα, ii) decreased expression of the Th1 genes T-box protein expressed in T cells (T-bet), Stat-1 and Stat4, and iii) decreased STAT1α/β phosphorylation. Importantly, we observed that LCA impairs Th1 activation at physiological relevant concentrations. Profiling of MAPK signaling pathways in Jurkat T cells uncovered an inhibition of ERK-1/2 phosphorylation upon LCA exposure, which could provide an explanation for the impaired Th1 activation. LCA induces these effects via Vitamin D receptor (VDR) signaling since VDR RNA silencing abrogated these effects. These data reveal for the first time that LCA controls adaptive immunity via inhibition of Th1 activation. Many factors influence LCA levels, including bile acid-based drugs and gut microbiota. Our data may suggest that these factors also impact on adaptive immunity via a yet unrecognized LCA-Th cell axis.

Recurrent Clostridium difficile infection associates with distinct bile acid and microbiome profiles

BACKGROUND

The healthy microbiome protects against the development of Clostridium difficile infection (CDI), which typically develops following antibiotics. The microbiome metabolises primary to secondary bile acids, a process if disrupted by antibiotics, may be critical for the initiation of CDI.

AIM

To assess the levels of primary and secondary bile acids associated with CDI and associated microbial changes.

METHODS

Stool and serum were collected from patients with (i) first CDI (fCDI), (ii) recurrent CDI (rCDI) and (iii) healthy controls. 16S rRNA sequencing and bile salt metabolomics were performed. Random forest regression models were constructed to predict disease status. PICRUSt analyses were used to test for associations between predicted bacterial bile salt hydrolase (BSH) gene abundances and bile acid levels.

RESULTS

Sixty patients (20 fCDI, 19 rCDI and 21 controls) were enrolled. Secondary bile acids in stool were significantly elevated in controls compared to rCDI and fCDI (P < 0.0001 and P = 0.0007 respectively). Primary bile acids in stool were significantly elevated in rCDI compared to controls (P < 0.0001) and in rCDI compared to fCDI (P = 0.02). Using random forest regression, we distinguished rCDI and fCDI patients 84.2% of the time using bile acid ratios. Stool deoxycholate to glycoursodeoxycholate ratio was the single best predictor. PICRUSt analyses found significant differences in predicted abundances of bacterial BSH genes in stool samples across the groups.

CONCLUSIONS

Primary and secondary bile acid composition in stool was different in those with rCDI, fCDI and controls. The ratio of stool deoxycholate to glycoursodeoxycholate was the single best predictor of disease state and may be a potential biomarker for recurrence.

Transmissible microbial and metabolomic remodeling by soluble dietary fiber improves metabolic homeostasis

Dietary fibers are increasingly appreciated as beneficial nutritional components. However, a requisite role of gut microbiota in fiber function and the overall impact of fibers on metabolomic flux remain unclear. We herein showed enhancing effects of a soluble resistant maltodextrin (RM) on glucose homeostasis in mouse metabolic disease models. Remarkably, fecal microbiota transplantation (FMT) caused pronounced and time-dependent improvement in glucose tolerance in RM recipient mice, indicating a causal relationship between microbial remodeling and metabolic efficacy. Microbial 16S sequencing revealed transmissible taxonomic changes correlated with improved metabolism, notably enrichment of probiotics and reduction of Alistipes and Bacteroides known to associate with high fat/protein diets. Metabolomic profiling further illustrated broad changes, including enrichment of phenylpropionates and decreases in key intermediates of glucose utilization, cholesterol biosynthesis and amino acid fermentation. These studies elucidate beneficial roles of RM-dependent microbial remodeling in metabolic homeostasis, and showcase prevalent health-promoting potentials of dietary fibers.

Clostridium difficile infection: molecular pathogenesis and novel therapeutics

The Gram-positive anaerobic bacterium Clostridium difficile produces toxins A and B, which can cause a spectrum of diseases from pseudomembranous colitis to C. difficile-associated diarrhea. A limited number of C. difficile strains also produce a binary toxin that exhibits ADP ribosyltransferase activity. Here, the structure and the mechanism of action of these toxins as well as their role in disease are reviewed. Nosocomial C. difficile infection is often contracted in hospital when patients treated with antibiotics suffer a disturbance in normal gut microflora. C. difficile spores can persist on dry, inanimate surface for months. Metronidazole and oral vancomycin are clinically used for treatment of C. difficile infection but clinical failure and concern about promotion of resistance are motivating the search for novel non-antibiotic therapeutics. Methods for controlling both toxins and spores, replacing gut microflora by probiotics or fecal transplant, and killing bacteria in the anaerobic gut by photodynamic therapy are discussed.

Microbiota transplantation restores normal fecal bile acid composition in recurrent Clostridium difficile infection

Fecal microbiota transplantation (FMT) has emerged as a highly effective therapy for refractory, recurrent Clostridium difficile infection (CDI), which develops following antibiotic treatments. Intestinal microbiota play a critical role in the metabolism of bile acids in the colon, which in turn have major effects on the lifecycle of C. difficile bacteria. We hypothesized that fecal bile acid composition is altered in patients with recurrent CDI and that FMT results in its normalization. General metabolomics and targeted bile acid analyses were performed on fecal extracts from patients with recurrent CDI treated with FMT and their donors. In addition, 16S rRNA gene sequencing was used to determine the bacterial composition of pre- and post-FMT fecal samples. Taxonomic bacterial composition of fecal samples from FMT recipients showed rapid change and became similar to the donor after the procedure. Pre-FMT fecal samples contained high concentrations of primary bile acids and bile salts, while secondary bile acids were nearly undetectable. In contrast, post-FMT fecal samples contained mostly secondary bile acids, as did non-CDI donor samples. Therefore, our analysis showed that FMT resulted in normalization of fecal bacterial community structure and metabolic composition. Importantly, metabolism of bile salts and primary bile acids to secondary bile acids is disrupted in patients with recurrent CDI, and FMT corrects this abnormality. Since individual bile salts and bile acids have pro-germinant and inhibitory activities, the changes suggest that correction of bile acid metabolism is likely a major mechanism by which FMT results in a cure and prevents recurrence of CDI.

Microbiota transplantation restores normal fecal bile acid composition in recurrent Clostridium difficile infection

Fecal microbiota transplantation (FMT) has emerged as a highly effective therapy for refractory, recurrent Clostridium difficile infection (CDI), which develops following antibiotic treatments. Intestinal microbiota play a critical role in the metabolism of bile acids in the colon, which in turn have major effects on the lifecycle of C. difficile bacteria. We hypothesized that fecal bile acid composition is altered in patients with recurrent CDI and that FMT results in its normalization. General metabolomics and targeted bile acid analyses were performed on fecal extracts from patients with recurrent CDI treated with FMT and their donors. In addition, 16S rRNA gene sequencing was used to determine the bacterial composition of pre- and post-FMT fecal samples. Taxonomic bacterial composition of fecal samples from FMT recipients showed rapid change and became similar to the donor after the procedure. Pre-FMT fecal samples contained high concentrations of primary bile acids and bile salts, while secondary bile acids were nearly undetectable. In contrast, post-FMT fecal samples contained mostly secondary bile acids, as did non-CDI donor samples. Therefore, our analysis showed that FMT resulted in normalization of fecal bacterial community structure and metabolic composition. Importantly, metabolism of bile salts and primary bile acids to secondary bile acids is disrupted in patients with recurrent CDI, and FMT corrects this abnormality. Since individual bile salts and bile acids have pro-germinant and inhibitory activities, the changes suggest that correction of bile acid metabolism is likely a major mechanism by which FMT results in a cure and prevents recurrence of CDI.

Defects in gallbladder emptying and bile Acid homeostasis in mice with cystic fibrosis transmembrane conductance regulator deficiencies

BACKGROUND & AIMS

Patients with cystic fibrosis (CF) have poorly defined defects in biliary function. We evaluated the effects of cystic fibrosis transmembrane conductance regulator (CFTR) deficiency on the enterohepatic disposition of bile acids (BAs).

METHODS

Bile secretion and BA homeostasis were investigated in Cftr(tm1Unc) (Cftr-/-) and CftrΔF508 (ΔF508) mice.

RESULTS

Cftr-/- and ΔF508 mice did not grow to normal size, but did not have liver abnormalities. The gallbladders of Cftr-/- mice were enlarged and had defects in emptying, based on (99m)technetium-mebrofenin scintigraphy or post-prandial variations in gallbladder volume; gallbladder contraction in response to cholecystokinin-8 was normal. Cftr-/- mice had abnormal gallbladder bile and duodenal acidity, and overexpressed the vasoactive intestinal peptide-a myorelaxant factor for the gallbladder. The BA pool was larger in Cftr-/- than wild-type mice, although there were no differences in fecal loss of BAs. Amounts of secondary BAs in portal blood, liver, and bile of Cftr-/- mice were much lower than normal. Expression of genes that are induced by BAs, including fibroblast growth factor-15 and BA transporters, was lower in the ileum but higher in the gallbladders of Cftr-/- mice, compared with wild-type mice, whereas enzymes that synthesize BA were down-regulated in livers of Cftr-/- mice. This indicates that BAs underwent a cholecystohepatic shunt, which was confirmed using cholyl-(Ne-NBD)-lysine as a tracer. In Cftr-/- mice, cholecystectomy reversed most changes in gene expression and partially restored circulating levels of secondary BAs. The ΔF508 mice overexpressed vasoactive intestinal peptide and had defects in gallbladder emptying and in levels of secondary BAs, but these features were less severe than in Cftr-/- mice.

CONCLUSIONS

Cftr-/- and CftrΔF508 mice have defects in gallbladder emptying that disrupt enterohepatic circulation of BAs. These defects create a shunt pathway that restricts the amount of toxic secondary BAs that enter the liver.

Metabolism of bile salts in mice influences spore germination in Clostridium difficile

Clostridium difficile, a spore-forming bacterium, causes antibiotic-associated diarrhea. In order to produce toxins and cause disease, C. difficile spores must germinate and grow out as vegetative cells in the host. Although a few compounds capable of germinating C. difficile spores in vitro have been identified, the in vivo signal(s) to which the spores respond were not previously known. Examination of intestinal and cecal extracts from untreated and antibiotic-treated mice revealed that extracts from the antibiotic-treated mice can stimulate colony formation from spores to greater levels. Treatment of these extracts with cholestyramine, a bile salt binding resin, severely decreased the ability of the extracts to stimulate colony formation from spores. This result, along with the facts that the germination factor is small, heat-stable, and water-soluble, support the idea that bile salts stimulate germination of C. difficile spores in vivo. All extracts able to stimulate high level of colony formation from spores had a higher proportion of primary to secondary bile salts than extracts that could not. In addition, cecal flora from antibiotic-treated mice was less able to modify the germinant taurocholate relative to flora from untreated mice, indicating that the population of bile salt modifying bacteria differed between the two groups. Taken together, these data suggest that an in vivo-produced compound, likely bile salts, stimulates colony formation from C. difficile spores and that levels of this compound are influenced by the commensal gastrointestinal flora.

Bile acids, fibre and colon cancer: the story unfolds

Are the changes in faecal bile acid concentrations the cause of colorectal cancer or one of its effects? This is an area of controversy mainly due to the lack of a clear explanation as to how the bile acid concentrations are controlled under different circumstances. This review presents an outline of the evidence that bile acids are both a causal factor in colorectal cancer and that their concentrations are affected by it in a synergistic manner. It also offers an explanation of how some dietary fibre protects against colorectal cancer.