Lactobacillus probiotics in the prevention of diarrhea associated with Clostridium difficile: a systematic review and Bayesian hierarchical meta-analysis

Probiotics for Prevention and Treatment of Clostridium difficile Infection

Probiotics have been claimed as a valuable tool to restore the balance in the intestinal microbiota following a dysbiosis caused by, among other factors, antibiotic therapy. This perturbed environment could favor the overgrowth of Clostridium difficile, and in fact, the occurrence of C. difficile-associated infections (CDI) is increasing in recent years. In spite of the high number of probiotics able to in vitro inhibit the growth and/or toxicity of this pathogen, its application for treatment or prevention of CDI is still scarce since there are not enough well-defined clinical studies supporting efficacy. Only a few strains, such as Lactobacillus rhamnosus GG and Saccharomyces boulardii, have been studied in more extent. The increasing knowledge about the probiotic mechanisms of action against C. difficile, some of them reviewed here, makes promising the application of these live biotherapeutic agents against CDI. Nevertheless, more effort must be paid to standardize the clinical studies conducted to evaluate probiotic products, in combination with antibiotics, in order to select the best candidate for C. difficile infections.

<i>Clostridioides difficile</i> infection: diagnosis, treatment, and prevention Clinical guidelines of the Russian Scientific Medical Society of Internal Medicine, the Gastroenterological Scientific Society of Russia, and the North- West Society of Gastroenterologists and Hepatologists

   Clostridioides difficile infection (CDI) is the most common cause of antibiotic-associated diarrhea, and an important cause of nosocomial infection. Since the publication of the National Guidelines (2016, 2017), new data have been accumulated on the genetic structure and pathogenic properties of the most common causative agent of severe forms of antibiotic- associated diarrhea, which has led to the reclassifi cation of the pathogen, formerly known as Clostridium diffi cile, to Clostridioides difficile. Laboratory algorithms have been developed to diagnose CDI and determine the toxigenicity of strains reliably. New data on the effectiveness of antibacterials  have been published, monoclonal antibodies to toxin B (bezlotoxumab) have been introduced into clinical practice to prevent CDI recurrence, and fecal microbiota transplantation has been proposed. Over the past 5 years, many international guidelines on the management of adult patients with CDI have also been updated (USA, EU). In the last decade, including due to the COVID-19 pandemic, there has been an increase in CDI incidence. Considering therelevance of CDI, new data on the pathogen, and domestic features, the Russian Scientific Medical Society of Internal Medicine, the Gastroenterological Scientific Society of Russia, and the North-West Society of Gastroenterologists and Hepatologists developed these clinical guidelines.

Prescribed probiotic usage to prevent Clostridioides difficile infection among older patients receiving antibiotics: A retrospective cohort study

OBJECTIVES

Clostridioides difficile infection (CDI) is a leading cause of antimicrobial-associated colitis and is a global clinical concern. Probiotics are considered a CDI-preventive measure; however, highly inconsistent data have been previously reported. Thus, we evaluated the CDI-preventive effect of prescribed probiotics in high-risk older patients receiving antibiotics.

METHODS

Older patients (aged ≥65 years) admitted to the emergency department who received antibiotics between 2014 and 2017 were enrolled in this single-center retrospective cohort study. Propensity score-matched analysis was used to compare the CDI incidence in patients who took the prescribed probiotics within 2 days of receiving antibiotics for at least 7 days with those who did not. The rates of severe CDI and associated hospital mortality were also evaluated.

RESULTS

Among 6148 eligible patients, 221 were included in the prescribed probiotic group. A propensity score-matched (221 matched pairs) well-balanced for patient characteristics was obtained. The incidence of primary nosocomial CDI did not differ significantly between the prescribed and non-prescribed probiotic groups (0% [0/221] vs. 1.0% [2/221], p = 0.156). Of the 6148 eligible patients, 0.5% (30/6148) developed CDI, with a severe CDI rate of 33.3% (10/30). Furthermore, no CDI-associated in-hospital mortality was observed in the study cohort.

CONCLUSIONS

The evidence from this study does not support recommendations for the routine use of prescribed probiotics to prevent primary CDI in older patients receiving antibiotics in situations where the CDI is infrequent.

A Case of Lactobacillus casei Endocarditis Associated With Probiotic Intake in an Immunocompromised Patient

Probiotics are microorganisms, typically bacteria, similar to beneficial microbiota found in the human gut, usually consumed as dietary supplements or fermented foods. Although probiotics are generally safe, several cases of bacteremia, sepsis, and endocarditis associated with probiotics have been reported. Here we report a rare case of Lactobacillus casei endocarditis in a 71-year-old female, immunocompromised due to chronic steroid intake, who presented with a productive cough and low-grade fever. Blood cultures grew L. casei resistant to vancomycin and meropenem. Transesophageal echocardiography showed mitral and aortic vegetations; valve replacement was done after successfully removing vegetations. She was treated with a six-week course of daptomycin and recovered.

A Single-Center, Retrospective Cohort Study Evaluating the Use of Probiotics for the Prevention of Hospital-Onset Clostridioides difficile Infection in Hospitalized Patients Receiving Intravenous Antibiotics

Background

Exposure to antimicrobials is a known risk factor for Clostridioides difficile infection (CDI). Antimicrobials cause collateral damage by disrupting the natural intestinal microbiota allowing for C. difficile to thrive and production of C. difficile toxins. Probiotics could modulate the onset and course of CDI. However, the data on probiotics for the prevention of CDI is conflicting.

Objective

To evaluate the rates of hospital-onset Clostridioides difficile infection (HO-CDI) among patients who received intravenous (IV) antibiotics plus probiotics versus IV antibiotics alone.

Design

Retrospective, single-center cohort study.

Methods

We included adult patients that received at least 1 dose of IV antibiotics and had a hospital length of stay of at least 3 days between August 2017 and July 2020. Patients were separated into 2 cohorts, either receipt of probiotics or non-receipt of probiotics. Patients with positive C. difficile toxin test prior to antibiotic therapy, or receipt of only C. difficile active treatment were excluded. The primary outcome was incidence of HO-CDI in patients who received IV antibiotics plus probiotics compared to those that received IV antibiotics alone. Logistic regression was performed to account for confounding variables.

Results

We identified 17 598 patients that received IV antibiotics alone and 2659 patients received IV antibiotics plus probiotics. HO-CDI occurred in 46 (0.26%) of those that received antibiotics alone compared to 5 (0.19%) of those that received probiotics with IV antibiotics (OR 0.72, 95% CI 0.28-1.81). ICU admission (OR 1.81, 95% CI 1.02-3.19) and history of CDI (OR 3.37, 95% CI 1.07-10.97) in the past 12 months were associated with a higher incidence of HO-CDI.

Conclusion

The addition of probiotics did not reduce the incidence of HO-CDI among inpatients receiving IV antibiotics.

The role of the gut microbiome in colonization resistance and recurrent Clostridioides difficile infection

The species composition of the human gut microbiota is related to overall health, and a healthy gut microbiome is crucial in maintaining colonization resistance against pathogens. Disruption of gut microbiome composition and functionality reduces colonization resistance and has been associated with several gastrointestinal and non-gastrointestinal diseases. One prime example is Clostridioides difficile infection (CDI) and subsequent recurrent infections that occur after the development of systemic antibiotic-related dysbiosis. Standard-of-care antibiotics used for both acute and recurrent infections do not address dysbiosis and often worsen the condition. Moreover, monoclonal antibodies, recommended in conjunction with standard-of-care antibiotics for the prevention of recurrent CDI in patients at high risk of recurrence, reduce recurrences but do not address the underlying dysbiosis. Fecal microbiota transplantation (FMT) is an evolving therapeutic strategy in which microbes are harvested from healthy donor stool and transplanted into the gut of a recipient to restore the gut microbiome. Although effective in the prevention of recurrent CDI, some existing challenges include screening and the standardization of stool acquisition and processing. Recent safety alerts by the US Food and Drug Administration raised concern about the possibility of transmission of multidrug-resistant organisms or severe acute respiratory syndrome coronavirus 2 via FMT. Increased knowledge that microbes are beneficial in restoring the gut microbiome has led to the clinical development of several newer biotherapeutic formulations that are more regulated than FMT, which may allow for improved restoration of the gut microbiome and prevention of CDI recurrence. This review focuses on mechanisms by which gut microbiome restoration could influence colonization resistance against the pathogen C. difficile.

Plain language summary

The Role of the Gut Microbiome in Clostridioides difficile Infection Introduction: A rich and diverse gut microbiome is key to immune system regulation and colonization resistance against pathogens.A disruption in the gut microbiome composition can make the gut more vulnerable to diseases such as Clostridioides difficile infection (CDI), caused by the bacterium C. difficile.CDI management presents a therapeutic dilemma, as it is usually treated with antibiotics that can treat the infection but also can damage the microbiome.Treatment of CDI using antibiotics can further reduce microbial diversity and deplete beneficial bacteria from the gut leading to a condition called dysbiosis.Antibiotic treatment can be followed by therapies that restore the gut microbiota, boost colonization resistance, and prevent the development of antimicrobial resistance.It is important to evaluate treatment options to determine their safety and effectiveness. Methods: The researchers provided an overview of the mechanisms that the gut microbiome uses to prevent colonization of the gut by pathogens.They subsequently reviewed the efficacy and shortcomings of the following treatments for CDI: - Antibiotics- Monoclonal antibodies- Fecal microbiota transplantation (FMT) Results: Commensal intestinal bacteria prevent colonization of the gut by pathogens using mechanisms such as: - Competition for key nutrients- Production of inhibitory bile acids- Short-chain fatty acid production- Lowering the luminal pH- Production of bacteriocinsAntibiotic therapy is recommended as a standard treatment for CDI. However, patients are vulnerable to recurrent CDI after discontinuation of the therapy.Monoclonal antibodies that inactivate C. difficile toxins may be recommended along with antibiotics to prevent recurrent CDI. However, this approach does not restore the microbiome.FMT is one method of microbial restoration, where stool is harvested from a healthy donor and transplanted into a patient's colon.Although FMT has shown some efficacy in the treatment of recurrent CDI, the procedure is not standardized.Safety concerns have been raised about the possibility of transmission of multidrug-resistant pathogens via FMT. Conclusion: Treatment methods that can efficiently restore the diversity of the gut microbiome are crucial in preventing recurrence of CDI.

Risk factors of first recurrence of Clostridioides difficile infection

OBJECTIVES

Clostridioides difficile infection (CDI) often recurs. Approximately 25% of patients have recurrences after the initial treatment, and patients who have relapsed once are more likely to relapse. We aimed to identify the risk factors for initial CDI recurrence.

METHODS

We performed a retrospective survey of patient backgrounds and treatment-related factors. Risk factors were analyzed using single and multiple logistic regression analyses.

RESULTS

A total of 134 patients were included in the study. Prophylactic probiotic use and nasogastric tube feeding were independent risk factors for the initial recurrence of CDI. Patients using prophylactic probiotics had significantly higher recurrence rates than those not using prophylactic probiotics.

CONCLUSION

Prophylactic probiotic use and nasogastric tube placement may be risk factors for the initial recurrence of CDI. It is noteworthy that CDI that occurs during the use of prophylactic probiotics may be prone to recurrence.

Diagnosis and management of Clostridioides difficile infection in patients with inflammatory bowel disease

PURPOSE OF REVIEW

Clostridioides difficile infection (CDI) may complicate the course of ulcerative colitis and Crohn's disease. The clinical presentation of CDI in this population is often atypical, and patients may experience exacerbations of their underlying inflammatory bowel disease (IBD) secondary to C. difficile. In this review, we aim to review the risk factors, diagnosis, and management of CDI in the context of IBD.

RECENT FINDINGS

Patients with colonic involvement of their IBD are at higher risk for CDI and colonization may be more common than in the general population. Therefore, CDI is confirmed using a two-step approach to stool testing. Oral vancomycin or fidaxomicin are the preferred agents for nonfulminant disease, and oral metronidazole is no longer recommended as first-line therapy. For all patients with CDI recurrence, fecal microbiota transplant (FMT) should be considered, as this has been shown to be safe and effective. Among those who have worsening of their underlying IBD, retrospective research suggest that outcomes are improved for those who undergo escalation of immunosuppression with appropriate antimicrobial treatment of C. difficile, however prospective data are needed.

SUMMARY

CDI may complicate the course of IBD, however the presentation may not be typical. Therefore, all patients with worsening gastrointestinal symptoms should be evaluated for both CDI and IBD exacerbation. Providers should consider FMT for all patients with recurrent CDI as well as escalation of immunosuppression for patients who fail to improve with appropriate antimicrobial therapy.

Efficacy of oral vancomycin prophylaxis for prevention of Clostridioides difficile infection: a systematic review and meta-analysis

BACKGROUND

Prevention of recurrent Clostridioides difficile infection (CDI) is a challenge in clinical practice, particularly in patients who need systemic antimicrobial therapy. We aimed to evaluate the role of oral vancomycin prophylaxis (OVP) in prevention of primary or future CDI in patients on systemic antimicrobial therapy.

METHODS

A systematic search of MEDLINE, Embase, and Web of Science was performed from 2000 to January 2020. We included case-control or cohort studies that included patients on systemic antimicrobial therapy who did or did not receive oral vancomycin prophylaxis (OVP) and were evaluated for development of CDI. Odds ratio (OR) estimates with 95% confidence intervals (CI) were calculated.

RESULTS

Four studies including 1352 patients evaluated OVP for primary CDI prevention, with CDI occurring in 29/402 patients on OVP (7.4%) compared with 10.4% (99/950) without OVP. Meta-analysis revealed no significant decrease in risk of CDI in patients who received OVP (OR, 0.18; 95% CI, 0.03-1.03; p = 0.06). There was significant heterogeneity with I 2 = 76%. Ten studies including 9258 patients evaluated OVP for secondary CDI prevention. Future CDI occurred in 91/713 patients on OVP (13.3%) compared with 21.9% (1875/8545) who did not receive OVP. Meta-analysis revealed a statistically significant decreased risk of future CDI (OR, 0.34; 95% CI, 0.20-0.59; p < 0.00001). Significant heterogeneity was seen with I 2 = 59%.

DISCUSSION

Based on observational data, OVP appears to decrease the risk of future CDI in patients with prior CDI who require systemic antimicrobial therapy. However, OVP was not effective for primary prevention of CDI.

Effects of heat-killed Enterococcus faecalis T-110 supplementation on gut immunity, gut flora, and intestinal infection in naturally aged hamsters

Infectious diseases are a threat to elderly individuals, whose immune systems weaken with age. Among the various infectious diseases, Clostridium difficile infection is associated with a high rate of mortality in elderly individuals and is a serious health problem worldwide, owing to the increasing infection rates. Probiotic use has been proposed as an effective countermeasure for C. difficile infection. The aim of this study was to evaluate the effects of heat-killed Enterococcus faecalis T-110 on intestinal immunity, intestinal flora, and intestinal infections, especially C. difficile infections, in naturally ageing animals, for extrapolating the results to elderly human subjects. Twenty female hamsters were randomly distributed into two groups. Group 1 was fed a basal diet and group 2 was fed a basal diet supplemented with heat-killed E. faecalis for 7 days. Heat-killed E. faecalis T-110 improved the gut immunity and microflora, especially Clostridium perfringens and C. difficile, in naturally aged hamsters. Therefore, heat-killed E. faecalis T-110 use may be a countermeasure against age-related immune dysfunction and intestinal infections, especially C. difficile infection, in elderly humans. However, further investigation in this regard is needed in humans.

Prevention of Clostridium difficile Infection and Associated Diarrhea: An Unsolved Problem

For many years, it has been known that Clostridium difficile (CD) is the primary cause of health-care-associated infectious diarrhea, afflicting approximately 1% of hospitalized patients. CD may be simply carried or lead to a mild disease, but in a relevant number of patients, it can cause a very severe, potentially fatal, disease. In this narrative review, the present possibilities of CD infection (CDI) prevention will be discussed. Interventions usually recommended for infection control and prevention can be effective in reducing CDI incidence. However, in order to overcome limitations of these measures and reduce the risk of new CDI episodes, novel strategies have been developed. As most of the cases of CDI follow antibiotic use, attempts to rationalize antibiotic prescriptions have been implemented. Moreover, to reconstitute normal gut microbiota composition and suppress CD colonization in patients given antimicrobial drugs, administration of probiotics has been suggested. Finally, active and passive immunization has been studied. Vaccines containing inactivated CD toxins or components of CD spores have been studied. Passive immunization with monoclonal antibodies against CD toxins or the administration of hyperimmune whey derived from colostrum or breast milk from immunized cows has been tried. However, most advanced methods have significant limitations as they cannot prevent colonization and development of primary CDI. Only the availability of vaccines able to face these problems can allow a resolutive approach to the total burden due to this pathogen.

Lactobacillus Protects Against S. Typhimurium-Induced Intestinal Inflammation by Determining the Fate of Epithelial Proliferation and Differentiation

SCOPE

The influence of the intestinal microbiota, such as Lactobacillus, on the intestinal mucosa, particularly intestinal stem cells, remains incompletely understood. In this study, mice and intestinal organoids are used to explore the regulatory effect of Lactobacillus on the proliferation and differentiation of intestinal epithelial cells.

METHODS AND RESULTS

This study demonstrates that S. typhimurium causes intestinal epithelial damage and affected growth of intestinal organoids. S. typhimurium also colonizes the intestine and then causes pathological changes to the intestinal epithelium, intestinal inflammation, and even death. However, L. acidophilus alleviates damage to intestinal organoids, increases the survival ratio of mice infected with S. typhimurium, and reduces tumor necrosis factor-α (TNF-α) secretion. Moreover, L. acidophilus affects the differentiation of epithelial cells through inhibition of the excessive expansion of goblet cells and Paneth cells induced by S. typhimurium to avoid over-exhaustion. Finally, it is also demonstrated that L. acidophilus ameliorates overactivation of Wnt/β-catenin pathway by Salmonella, depending on the contact with toll-like receptor 2 (TLR2), to affect the proliferation of the intestinal epithelium.

CONCLUSIONS

This study demonstrates that L. acidophilus protects the intestinal mucosa against S. typhimurium infection through not only the inhibition of pathogen invasion but also determination of the fate of the intestinal epithelium.

Lactobacillus sp as a Probiotic for the Prevention of Clostridium difficile Associated Diarrhea

Background: Antibiotic treatment can disturb the resistance of the gastrointestinal flora to colonization. This may result in complications, the most serious of which is Clostridium difficile associated diarrhea (CDAD). The aim of this study was to determine the effectiveness of probiotics for the prevention of CDAD.Method: The databases used were Scopus, Proquest, CINAHL, Medline, Pubmed and ScienceDirect, limited to having been published in the last 5 years. A literature review followed the keyword search. The keywords used were probiotics, Clostridium difficile, associated, diarrhea, randomized, control and trial using "AND" and “OR”. Twelve trials with 5102 participants were included. Eight trials reported a preventive effect for CDAD using a mixture of 2 strains of lactobacillus, a mixture of 4 combination strains, a mixture of lactobacillus and Saccharomyces or a mixture of Bifidobacterium, Lactobacillus and Saccharomyces.Result: Our findings indicate that probiotics may prevent CDAD. Most probiotics contain a singular strain. The combination with lactobacillus sp was the most effective at preventing CDAD.Conclusion: In addition, 6 out of 8 trials had an in relation to preventing CDAD containing lactobacillus sp. Four studies said that there were some factors that meant that the probiotic could not reduce or prevent the CDAD.

A Surface Protein From Lactobacillus plantarum Increases the Adhesion of Lactobacillus Strains to Human Epithelial Cells

Adhesion to epithelial cells is considered important for Lactobacillus to exert probiotic effects. In this study, we found that trypsin treatment decreased the adhesion ability of Lactobacillus plantarum AR326 and AR269, which exhibit good adhesion ability, and surface proteins extracts increased the adhesion of the strains with poor adhesion ability. By SDS–polyacrylamide gel electrophoresis and mass spectrometry analysis, the main component of the surface proteins was detected and identified as a protein of approximately 37 kDa. It was 100% homologous with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from L. plantarum WCFS1. The adhesion of AR326 and AR269 was decreased significantly by blocking with the anti-GAPDH antibody, and GAPDH restored the adhesion of AR326 and AR269 treated with trypsin. In addition, purified GAPDH significantly increased the adhesion of the strains with poor adhesion ability. These results indicated that GAPDH mediates the adhesion of these highly adhesive lactobacilli to epithelial cells and can be used to improve the adhesion ability of probiotics or other bacteria of interest.

Probiotics for Prevention and Treatment of Clostridium difficile Infection

Probiotics have been claimed as a valuable tool to restore the balance in the intestinal microbiota following a dysbiosis caused by, among other factors, antibiotic therapy. This perturbed environment could favor the overgrowth of Clostridium difficile and, in fact, the occurrence of C. difficile-associated infections (CDI) is being increasing in recent years. In spite of the high number of probiotics able to in vitro inhibit the growth and/or toxicity of this pathogen, its application for treatment or prevention of CDI is still scarce since there are not enough well-defined clinical studies supporting efficacy. Only a few strains, such as Lactobacillus rhamnosus GG and Saccharomyces boulardii have been studied in more extent. The increasing knowledge about the probiotic mechanisms of action against C. difficile, some of them reviewed here, makes promising the application of these live biotherapeutic agents against CDI. Nevertheless, more effort must be paid to standardize the clinical studied conducted to evaluate probiotic products, in combination with antibiotics, in order to select the best candidate for C. difficile infections.

Systematic review: probiotics in the management of lower gastrointestinal symptoms - an updated evidence-based international consensus

BACKGROUND

In 2013, a systematic review and Delphi consensus reported that specific probiotics can benefit adult patients with irritable bowel syndrome (IBS) and other gastrointestinal (GI) problems.

AIM

To update the consensus with new evidence.

METHODS

A systematic review identified randomised, placebo-controlled trials published between January 2012 and June 2017. Evidence was graded, previously developed statements were reassessed by an 8-expert panel, and agreement was reached via Delphi consensus.

RESULTS

A total of 70 studies were included (IBS, 34; diarrhoea associated with antibiotics, 13; diarrhoea associated with Helicobacter pylori eradication therapy, 7; other conditions, 16). Of 15 studies that examined global IBS symptoms as a primary endpoint, 8 reported significant benefits of probiotics vs placebo. Consensus statements with 100% agreement and "high" evidence level indicated that specific probiotics help reduce overall symptom burden and abdominal pain in some patients with IBS and duration/intensity of diarrhoea in patients prescribed antibiotics or H. pylori eradication therapy, and have favourable safety. Statements with 70%-100% agreement and "moderate" evidence indicated that, in some patients with IBS, specific probiotics help reduce bloating/distension and improve bowel movement frequency/consistency.

CONCLUSIONS

This updated review indicates that specific probiotics are beneficial in certain lower GI problems, although many of the new publications did not report benefits of probiotics, possibly due to inclusion of new, less efficacious preparations. Specific probiotics can relieve lower GI symptoms in IBS, prevent diarrhoea associated with antibiotics and H. pylori eradication therapy, and show favourable safety. This study will help clinicians recommend/prescribe probiotics for specific symptoms.

Institutional review of the implementation and use of a Clostridium difficile infection bundle and probiotics in adult trauma patients

BACKGROUND

Clostridium difficile infection (CDI) is a common cause of healthcare associated infections contributing to morbidity and mortality. Our objective was to evaluate the impact of the implementation of a CDI bundle along with probiotic utilization.

METHODS

A retrospective review of trauma admissions from 2008 to 2014 was performed. The CDI bundle was implemented in stages from 2009 through 2014 with probiotics initiated in 2010. The bundle included changes in cleaning practices, education, screening, and contact precautions.

RESULTS

4632 (49%) patients received antibiotics with 21% receiving probiotics. Probiotic use was associated with increased age, male sex, more severely injured, and antibiotic use. CDI incidence decreased from 11.2 to 4.8 per 1000 admissions, p = .03. Among patients who received antibiotics CDI incidence decreased from 2.2% to 0.7%, p = .01.

CONCLUSIONS

We report the largest series of a CDI bundle implementation including probiotics. During the period of adoption of these interventions, the incidence of CDI decreased significantly.

Next-Generation Probiotics Targeting Clostridium difficile through Precursor-Directed Antimicrobial Biosynthesis

Integration of antibiotic and probiotic therapy has the potential to lessen the public health burden of antimicrobial-associated diseases. Clostridium difficile infection (CDI) represents an important example where the rational design of next-generation probiotics is being actively pursued to prevent disease recurrence. Because intrinsic resistance to clinically relevant antibiotics used to treat CDI (vancomycin, metronidazole, and fidaxomicin) is a desired trait in such probiotic species, we screened several bacteria and identified Lactobacillus reuteri to be a promising candidate for adjunct therapy. Human-derived L. reuteri bacteria convert glycerol to the broad-spectrum antimicrobial compound reuterin. When supplemented with glycerol, strains carrying the pocR gene locus were potent reuterin producers, with L. reuteri 17938 inhibiting C. difficile growth at a level on par with the level of growth inhibition by vancomycin. Targeted pocR mutations and complementation studies identified reuterin to be the precursor-induced antimicrobial agent. Pathophysiological relevance was demonstrated when the codelivery of L. reuteri with glycerol was effective against C. difficile colonization in complex human fecal microbial communities, whereas treatment with either glycerol or L. reuteri alone was ineffective. A global unbiased microbiome and metabolomics analysis independently confirmed that glycerol precursor delivery with L. reuteri elicited changes in the composition and function of the human microbial community that preferentially targets C. difficile outgrowth and toxicity, a finding consistent with glycerol fermentation and reuterin production. Antimicrobial resistance has thus been successfully exploited in the natural design of human microbiome evasion of C. difficile, and this method may provide a prototypic precursor-directed probiotic approach. Antibiotic resistance and substrate bioavailability may therefore represent critical new determinants of probiotic efficacy in clinical trials.