Fecal Pharmacokinetics and Gut Microbiome Effects of Oral Omadacycline Versus Vancomycin in Healthy Volunteers.

BACKGROUND: Clostridioides difficile infection (CDI) is a common healthcare-associated infection with limited treatment options. Omadacycline, an aminomethylcycline tetracycline, has potent in vitro activity against C difficile and a low propensity to cause CDI in clinical trials. We aimed to assess fecal pharmacokinetics and gut microbiome effects of oral omadacycline compared to oral vancomycin in healthy adults. METHODS: This was a phase 1, nonblinded, randomized clinical trial conducted in healthy volunteers aged 18-40 years. Subjects received a 10-day course of omadacycline or vancomycin. Stool samples were collected at baseline, daily during therapy, and at follow-up visits. Omadacycline and vancomycin stool concentrations were assessed, and microbiome changes were compared. RESULTS: Sixteen healthy volunteers with a mean age of 26 (standard deviation [SD], 5) years were enrolled; 62.5% were male, and participants' mean body mass index was 23.5 (SD, 4.0) kg/m2. Omadacycline was well tolerated with no safety signal differences between the 2 antibiotics. A rapid initial increase in fecal concentrations of omadacycline was observed compared to vancomycin, with maximum concentrations achieved within 48 hours. A significant difference in alpha diversity was observed following therapy in both the omadacycline and vancomycin groups (P < .05). Bacterial abundance and beta diversity analysis showed differing microbiome changes in subjects who received omadacycline versus vancomycin. CONCLUSIONS: Subjects given omadacycline had high fecal concentrations with a distinct microbiome profile compared to vancomycin. CLINICAL TRIALS REGISTRATION: NCT06030219.

Reduced Vancomycin Susceptibility in Clostridioides difficile Is Associated With Lower Rates of Initial Cure and Sustained Clinical Response.

BACKGROUND: Epidemiologic studies have shown decreasing vancomycin susceptibility among clinical Clostridioides difficile isolates, but the impact on patient outcomes is unknown. We hypothesized that reduced vancomycin susceptibility would be associated with decreased rates of sustained clinical response (SCR). METHODS: This multicenter cohort study included adults with C. difficile infection (CDI) treated with oral vancomycin between 2016 and 2021. Clostridioides difficile isolates underwent agar dilution vancomycin susceptibility testing, ribotyping, and Sanger sequencing of the vancomycin resistance vanR gene. Reduced susceptibility was defined as vancomycin minimum inhibitory concentration (MIC) >2 µg/mL. The primary outcome was 30-day SCR; secondary outcomes were 14-day initial cure, 30-day recurrence, and 30-day mortality. Exploratory analysis assessed the association between the VanR Thr115Ala polymorphism, susceptibility, and outcomes. RESULTS: A high proportion (34% [102/300]) of C. difficile isolates exhibited reduced vancomycin susceptibility (range, 0.5-16 µg/mL; MIC50/90 = 2/4 µg/mL). Ribotype 027 accounted for the highest proportion (77.4% [41/53]) of isolates with reduced vancomycin susceptibility. Overall, 83% (249) of patients achieved 30-day SCR. Reduced vancomycin susceptibility was associated with lower rates of 30-day SCR (76% [78/102]) than vancomycin-susceptible strains (86% [171/198]; P = .031). A significantly lower rate of 14-day initial cure was also observed among individuals infected with strains with reduced vancomycin susceptibility (89% vs 96%; P = .04). Reduced susceptibility remained an independent predictor of 30-day SCR in multivariable modeling (odds ratio, 0.52 [95% confidence interval, .28-.97]; P = .04). CONCLUSIONS: Reduced vancomycin susceptibility in C. difficile was associated with decreased odds of 30-day SCR and lower 14-day initial cure rates in the studied patient cohort.

Antibacterial activity of ibezapolstat against antimicrobial-resistant clinical strains of Clostridioides difficile.

Antimicrobial resistance is emerging in clinical strains of Clostridioides difficile. Ibezapolstat (IBZ) is a DNA polymerase IIIC inhibitor that has completed phase II clinical trials. IBZ has potent in vitro activity against wild-type, susceptible strains but its effect on C. difficile strains with reduced susceptibility to metronidazole (MTZ), vancomycin (VAN), or fidaxomicin (FDX) has not been tested. The primary objective of this study was to test the antibacterial properties of IBZ against multidrug-resistant C. difficile strains. The in vitro activity, bactericidal, and time-kill activity of IBZ versus comparators were evaluated against 100 clinical strains of which 59 had reduced susceptibility to other C. difficile antibiotics. Morphologic changes against a multidrug resistance strain were visualized by light and scanning electron microscopy. The overall IBZ MIC50/90 values (µg/mL) for evaluated C. difficile strains were 4/8, compared with 2/4 for VAN, 0.5/1 for FDX, and 0.25/4 for MTZ. IBZ MIC50/90 values did not differ based on non-susceptibility to antibiotic class or number of classes to which strains were non-susceptible. IBZ bactericidal activity was similar to the minimum inhibitory concentration (MIC) and maintained in wild-type and non-susceptible strains. Time-kill assays against two laboratory wild-type and two clinical non-susceptible strains demonstrated sustained IBZ activity despite reduced killing by comparator antibiotics for IBZ and VAN non-susceptible strains. Microscopy visualized increased cell lengthening and cellular damage in multidrug-resistant strains exposed to IBZ sub-MIC concentrations. This study demonstrated the potent antibacterial activity of IBZ against a large collection of C. difficile strains including multidrug-resistant strains. This study highlights the therapeutic potential of IBZ against multidrug-resistant strains of C. difficile.

Review Article: Safety of Live Biotherapeutic Products Used for the Prevention of Clostridioides difficile Infection Recurrence.

Live biotherapeutic products (LBPs) represent a new class of therapeutics indicated to prevent the recurrence of Clostridioides difficile infection (CDI) in adults. However, microbiota-based therapies have been used in CDI management before the Food and Drug Administration (FDA) designated this new drug class. The regulation of these microbiome-based therapies has varied, and several safety concerns have arisen over time. Requirements established by the FDA regarding the development of LBPs minimizes many of these prior concerns, and phase III trials have proven the safety and efficacy of 2 stool donor-derived LBPs: fecal microbiota, live-jslm (Rebyota™; formerly RBX2660) and fecal microbiota spores, live-brpk (Vowst™; formerly SER-109). Mild gastrointestinal side effects are common, but no severe drug-related adverse events have been reported with their use to date. A third LBP entering phase III clinical trials, VE303, follows a novel approach by sourcing bacterial strains from clonal cell banks and has demonstrated a similarly favorable safety profile.

Efficacy, Safety, Pharmacokinetics, and Microbiome Changes of Ibezapolstat in Adults with Clostridioides difficile Infection: A Phase 2a Multicenter Clinical Trial.

BACKGROUND: This study was the first human validation of the gram-positive bacterial DNA polymerase IIIC target in patients with Clostridioides difficile infection. The primary objectives were to assess clinical cure rates and adverse events (AEs). Secondary objectives were to evaluate plasma/fecal pharmacokinetics, microbiologic eradication, microbiome and bile acid effects, and sustained clinical cure (SCC) with ibezapolstat. METHODS: This single-arm, open-label, phase 2a study enrolled adults with C. difficile infection at 4 US centers. Patients received ibezapolstat 450 mg orally every 12 hours for 10 days and followed for an additional 28 days to assess study objectives. RESULTS: Ten patients with a mean (standard deviation [SD]) age of 49 [15] years were enrolled. Seven AEs were reported classified as mild-moderate. Plasma levels of ibezapolstat ranged from 233 to 578 ng/mL while mean (SD) fecal levels were 416 (494) µg/g stool by treatment day 3 and >1000 µg/g stool by days 8-10. A rapid increase in alpha diversity in the fecal microbiome was noted after starting ibezapolstat therapy, which was maintained after completion of therapy. A proportional decrease in Bacteroidetes phylum was observed (mean change [SD], -10.0% [4.8%]; P = .04) with a concomitantly increased proportion of Firmicutes phylum (+14.7% [5.4%]; P = .009). Compared with baseline, total primary bile acids decreased by a mean (SD) of 40.1 (9.6) ng/mg stool during therapy (P < .001) and 40.5 (14.1) ng/mg stool after completion of therapy (P = .007). Rates of both initial clinical cure and SCC at 28 days were 100% (10 of 10 patients). CONCLUSIONS: In this phase 2a study, 10 of 10 patients achieved SCC, demonstrated favorable pharmacokinetics, minimal AEs, and beneficial microbiome and bile acids results. These results support continued clinical development.

Ultrasensitive and Quantitative Toxin Measurement Correlates With Baseline Severity, Severe Outcomes, and Recurrence Among Hospitalized Patients With Clostridioides difficile Infection.

BACKGROUND: Stool toxin concentrations may impact Clostridioides difficile infection (CDI) severity and outcomes. We correlated fecal C difficile toxin concentrations, measured by an ultrasensitive and quantitative assay, with CDI baseline severity, attributable outcomes, and recurrence. METHODS: We enrolled 615 hospitalized adults (≥18 years) with CDI (acute diarrhea, positive stool nucleic acid amplification testing, and decision to treat). Baseline stool toxin A and B concentrations were measured by single molecule array. Subjects were classified by baseline CDI severity (4 scoring methods) and outcomes within 40 days (death, intensive care unit stay, colectomy, and recurrence). RESULTS: Among 615 patients (median, 68.0 years), in all scoring systems, subjects with severe baseline disease had higher stool toxin A+B concentrations than those without (P < .01). Nineteen subjects (3.1%) had a severe outcome primarily attributed to CDI (group 1). This group had higher median toxin A+B (14 303 pg/mL [interquartile range, 416.0, 141 967]) than subjects in whom CDI only contributed to the outcome (group 2, 163.2 pg/mL [0.0, 8423.3]), subjects with severe outcome unrelated to CDI (group 3, 158.6 pg/mL [0.0, 1795.2]), or no severe outcome (group 4, 209.5 pg/mL [0.0, 8566.3]) (P = .003). Group 1 was more likely to have detectable toxin (94.7%) than groups 2-4 (60.5%-66.1%) (P = .02). Individuals with recurrence had higher toxin A+B (2266.8 pg/mL [188.8, 29411]) than those without (154.0 pg/mL [0.0, 5864.3]) (P < .001) and higher rates of detectable toxin (85.7% versus 64.0%, P = .004). CONCLUSIONS: In CDI patients, ultrasensitive stool toxin detection and concentration correlated with severe baseline disease, severe CDI-attributable outcomes, and recurrence, confirming the contribution of toxin quantity to disease presentation and clinical course.

Higher In Vivo Fecal Concentrations of Clostridioides difficile Toxins A and B in Patients With North American Pulsed-Field Gel Electrophoresis Type 1/Ribotype 027 Strain Infection.

Ultrasensitive, quantitative Clostridioides difficile stool toxin measurement demonstrated significantly higher concentrations of toxins A and B in patients infected with the North American pulsed-field gel electrophoresis type 1/ribotype 027 (NAP-1/027) strain compared with other strains, providing in vivo confirmation of the in vitro association between NAP-1/027 and elevated toxin production.

Functional and Metagenomic Evaluation of Ibezapolstat for Early Evaluation of Anti-Recurrence Effects in Clostridioides difficile Infection.

Reduction of Clostridioides difficile infection (CDI) recurrence is an essential endpoint for CDI-directed antibiotic development that is often not evaluated until Phase III trials. The purpose of this project was to use a functional and metagenomic approach to predict the potential anti-CDI recurrence effect of ibezapolstat, a DNA polymerase IIIC inhibitor, in clinical development for CDI. As part of the Phase I ibezapolstat clinical study, stool samples were collected from 22 healthy volunteers, who were given either ibezapolstat or vancomycin. Stool samples were evaluated for microbiome changes and bile acid concentrations. Ibezapolstat 450 mg and vancomycin, but not ibezapolstat 300 mg, showed statistically significant changes in alpha diversity over time compared to that of a placebo. Beta diversity changes confirmed that microbiota were significantly different between study groups. Vancomycin had a more wide-ranging effect on the microbiome, characterized by an increased proportion of Gammaproteobacteria. Ibezapolstat demonstrated an increased proportion of Actinobacteria, including the Bifidobacteriaceae family. Using a linear regression analysis, vancomycin was associated with significant increases in primary bile acids as well as primary:secondary bile acid ratios. An overabundance of Enterobacteriaceae was most highly correlated with primary bile acid concentrations (r = 0.63; P < 0.0001). Using Phase I healthy volunteer samples, beneficial changes suggestive of a lower risk of CDI recurrence were associated with ibezapolstat compared to vancomycin. This novel omics approach may allow for better and earlier prediction of anti-CDI recurrence effects for antibiotics in the clinical development pipeline.

Development of the invasive candidiasis discharge [I Can discharge] model: a mixed methods analysis.

Patients with invasive candidiasis (IC) have complex medical and infectious disease problems that often require continued care after discharge. This study aimed to assess echinocandin use at hospital discharge and develop a transition of care (TOC) model to facilitate discharge for patients with IC. This was a mixed method study design that used epidemiologic assessment to better understand echinocandin use at hospital discharge TOC. Using grounded theory methodology focused on patients given echinocandins during their last day of hospitalization, a TOC model for patients with IC, the invasive candidiasis [I Can] discharge model was developed to better understand discharge barriers. A total of 33% (1405/4211) echinocandin courses were continued until the last day of hospitalization. Of 536 patients chosen for in-depth review, 220 (41%) were discharged home, 109 (20%) were transferred, and 207 (39%) died prior to discharge. Almost half (46%, 151/329) of patients discharged alive received outpatient echinocandin therapy. Independent predictors for outpatient echinocandin use were osteomyelitis (OR, 4.1; 95% CI, 1.1-15.7; p = 0.04), other deep-seated infection (OR, 4.4; 95% CI, 1.7-12.0; p = 0.003), and non-home discharge location (OR, 3.9, 95% CI, 2.0-7.7; p < 0.001). The I Can discharge model was developed encompassing four distinct themes which was used to identify potential barriers to discharge. Significant echinocadin use occurs at hospital discharge TOC. The I Can discharge model may help clinical, policy, and research decision-making processes to facilitate smoother and earlier hospital discharges.

Fulminant Clostridioides difficile Infection: A Review of Treatment Options for a Life-Threatening Infection.

Fulminant Clostridioides difficile infection (FCDI) encompasses 3 to 5% of all CDI cases with associated mortality rates between 30 and 40%. Major treatment modalities include surgery and medical management with antibiotic and nonantibiotic therapies. However, identification of patients with CDI that will progress to FCDI is difficult and makes it challenging to direct medical management and identify those who may benefit from surgery. Furthermore, since it is difficult to study such a critically ill population, data investigating treatment options are limited. Surgical management with diverting loop ileostomy (LI) instead of a total abdominal colectomy (TAC) with end ileostomy has several appealing advantages, and studies have not consistently demonstrated a clinical benefit with this less-invasive strategy, so both LI and TAC remain acceptable surgical options. Successful medical management of FCDI is complicated by pharmacokinetic changes that occur in critically ill patients, and there is an absence of high-quality studies that included patients with FCDI. Recommendations accordingly include a combination of antibiotics administered via multiple routes to ensure adequate drug concentrations in the colon: intravenous metronidazole, high-dose oral vancomycin, and rectal vancomycin. Although fidaxomicin is now recommended as first-line therapy for non-FCDI, there are limited clinical data to support its use in FCDI. Several nonantibiotic therapies, including fecal microbiota transplantation and intravenous immunoglobulin, have shown success as adjunctive therapies, but they are unlikely to be effective alone. In this review, we aim to summarize diagnosis and treatment options for FCDI.

Multi-country surveillance of Clostridioides difficile demonstrates high prevalence of spores in non-healthcare environmental settings.

BACKGROUND: C. difficile spores are frequently isolated from hospital and non-healthcare settings but a worldwide analysis has not been done. The study objectives were to assess C. difficile spore contamination in the hospital and non-healthcare environments across a variety of countries. METHODS: Field studies assessed hospital vs. non-healthcare C. difficile spore contamination in hospitals, non-healthcare buildings, outdoor environments, and shoes. Swabs were cultured anaerobically for C. difficile and typed using PCR-fluorescent ribotyping. C. difficile contamination by swabbing area and geographic locations were compared. FINDINGS: A total of 7,857 unique samples were collected primarily from the USA (89%) in addition to 9 other countries. The global prevalence of C difficile from environmental samples was 25.3% and did not differ between countries. In USA based studies, C. difficile contamination rates were similar for healthcare buildings (23.2%), non-healthcare buildings (23.4%), and outdoor spaces (24.7%). Floor samples had significantly higher (p < 0.001) C. difficile contamination rate (46.5%) followed by non-floor samples (21.1%), and bathrooms (15.3%). In a comparison of USA to other country samples, C. difficile contamination rates were similar for USA samples (21.5%) compared to rest of world samples (22.3%; p = 0.61). The most common ribotypes included F014-020 (15.7%), F106 (12.6%), F010 (8.9%), F027 (8.8%), and F002 (8.1%) and did not differ significantly between USA and non-USA samples. Finally, 546 of 1,218 (44.8%) shoe soles swabbed from the USA were contaminated with C. difficile spores. INTERPRETATION: This large surveillance study of several countries demonstrated high prevalence of toxigenic C. difficile in non-healthcare environments with high contamination rates from floors and shoe soles.

Clinical Practice Guideline by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA): 2021 Focused Update Guidelines on Management of Clostridioides difficile Infection in Adults.

This clinical practice guideline is a focused update on management of Clostridioides difficile infection (CDI) in adults specifically addressing the use of fidaxomicin and bezlotoxumab for the treatment of CDI. This guideline was developed by a multidisciplinary panel representing the Infectious Diseases Society of America (IDSA) and the Society for Healthcare Epidemiology of America (SHEA). This guideline is intended for use by healthcare professionals who care for adults with CDI, including specialists in infectious diseases, gastroenterologists, hospitalists, pharmacists, and any clinicians and healthcare providers caring for these patients. The panel's recommendations for the management CDI are based upon evidence derived from topic-specific systematic literature reviews. Summarized below are the recommendations for the management of CDI in adults. The panel followed a systematic process which included a standardized methodology for rating the certainty of the evidence and strength of recommendation using the GRADE approach (Grading of Recommendations Assessment, Development, and Evaluation). A detailed description of background, methods, evidence summary and rationale that support each recommendation, and knowledge gaps can be found online in the full text.

Clinical Practice Guideline by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA): 2021 Focused Update Guidelines on Management of Clostridioides difficile Infection in Adults.

This clinical practice guideline is a focused update on management of Clostridioides difficile infection (CDI) in adults specifically addressing the use of fidaxomicin and bezlotoxumab for the treatment of CDI. This guideline was developed by a multidisciplinary panel representing the Infectious Diseases Society of America (IDSA) and the Society for Healthcare Epidemiology of America (SHEA). This guideline is intended for use by healthcare professionals who care for adults with CDI, including specialists in infectious diseases, gastroenterologists, hospitalists, pharmacists, and any clinicians and healthcare providers caring for these patients. The panel's recommendations for the management CDI are based upon evidence derived from topic-specific systematic literature reviews. Summarized below are the recommendations for the management of CDI in adults. The panel followed a systematic process which included a standardized methodology for rating the certainty of the evidence and strength of recommendation using the GRADE approach (Grading of Recommendations Assessment, Development, and Evaluation). A detailed description of background, methods, evidence summary and rationale that support each recommendation, and knowledge gaps can be found online in the full text.

Recent developments in antimicrobial therapy for gastrointestinal infections.

PURPOSE OF REVIEW: This focused, narrative review summarizes human clinical trial data for direct-acting antimicrobials in development for the treatment of gastrointestinal infections that were published in the past 18 months (1 January 2019 to 30 June 2020). RECENT FINDINGS: Antimicrobial agents for Clostridioides difficile infection (n = 6), cryptosporidiosis (n = 1), cytomegalovirus infection (n = 3) and Helicobacter pylori infection (n = 1) have completed and/or are undergoing human clinical trials. SUMMARY: Although this review highlights significant advances in four disease states, many common gastrointestinal pathogens have no antimicrobials in human clinical trials, emphasizing the need for continued prioritization in this field of study.

Absence of Toxemia in Clostridioides difficile Infection: Results from Ultrasensitive Toxin Assay of Serum.

Clostridioides difficile infection (CDI) is caused by Toxins A and B, secreted from pathogenic strains of C. difficle. This infection can vary greatly in symptom severity and in clinical presentation. Current assays used to diagnose CDI may lack the required sensitivity to detect the exotoxins circulating in blood. The ultrasensitive single molecule array (Simoa) assay was modified to separately detect toxin A and toxin B in serum with a limit of detection at the low picogram level. When applied to a diverse cohort, Simoa was unable to detect toxins A or B in serum from patients with CDI, including many classified as having severe disease. The detection of toxin may be limited by the inference of antitoxin antibodies circulating in serum. This result does not support the hypothesis that toxemia occurs in C. difficile infection, conflicting with the findings of other published reports.

Comparative clinical outcomes evaluation of hospitalized patients infected with Clostridioides difficile ribotype 106 vs. other toxigenic strains.

BACKGROUND: Although Clostridioides difficile surveillance often identifies emerging strains, clinical outcome evaluations are rarely performed. Ribotype (RT) 106 is a commonly isolated C. difficile strain worldwide; however, studies investigating RT 106 clinical outcomes are limited. The purpose of this study was to investigate clinical outcomes of RT 106 infections compared with two other endemic strains of varying virulence. METHODS: This multicenter study evaluated adults hospitalized with C. difficile infection (CDI). C. difficile samples underwent PCR ribotyping and patients infected with RT 106 were compared to patients infected with a known hypervirulent strain (RT 027) and a strain associated with less virulence (RT 014-020). Electronic medical records were reviewed by blinded investigators to assess the primary outcome of poor clinical outcome (composite of initial clinical failure, discharge to a higher level of care, 90-day CDI recurrence, and CDI-contributable mortality). RESULTS: A total of 396 patients with CDI were identified (RT 106, 32.3%; RT 027, 29.3%; RT 014-020, 38.3%). Patients infected with RT 014-020 less often experienced a poor clinical outcome (40%) compared with RT 106 (56%) and RT 027 (65%) infection (P < 0.0001). After controlling for covariates and using RT 014-020 as a comparator, patients infected with RT 106 (OR, 2.25; 95% CI, 1.36-3.73) or RT 027 (OR, 2.56; 95% CI, 1.52-4.31) had higher odds of poor clinical outcome. Using RT 027 as the comparator, only RT 014-020 was associated with lower odds of poor clinical outcome (OR, 0.42; 95% CI, 0.27-0.65). CONCLUSION: This study demonstrated that the emergent C. difficile RT 106 was associated with increased rates of poor clinical outcomes compared to RT 014-020 and comparable poor clinical outcomes to RT 027. These findings can help to better understand the clinical significance of this and future emerging ribotypes.

Systems biology evaluation of refractory Clostridioides difficile infection including multiple failures of fecal microbiota transplantation.

BACKGROUND: Fecal microbiota transplantation (FMT) aims to cure Clostridioides difficile infection (CDI) through reestablishing a healthy microbiome and restoring colonization resistance. Although often effective after one infusion, patients with continued microbiome disruptions may require multiple FMTs. In this N-of-1 study, we use a systems biology approach to evaluate CDI in a patient receiving chronic suppressive antibiotics with four failed FMTs over two years. METHODS: Seven stool samples were obtained between 2016-18 while the patient underwent five FMTs. Stool samples were cultured for C. difficile and underwent microbial characterization and functional gene analysis using shotgun metagenomics. C. difficile isolates were characterized through ribotyping, whole genome sequencing, metabolic pathway analysis, and minimum inhibitory concentration (MIC) determinations. RESULTS: Growing ten strains from each sample, the index and first four recurrent cultures were single strain ribotype F078-126, the fifth was a mixed culture of ribotypes F002 and F054, and the final culture was ribotype F002. One single nucleotide polymorphism (SNP) variant was identified in the RNA polymerase (RNAP) ß-subunit RpoB in the final isolated F078-126 strain when compared to previous F078-126 isolates. This SNV was associated with metabolic shifts but phenotypic differences in fidaxomicin MIC were not observed. Microbiome differences were observed over time during vancomycin therapy and after failed FMTs. CONCLUSION: This study highlights the importance of antimicrobial stewardship in patients receiving FMT. Continued antibiotics play a destructive role on a transplanted microbiome and applies selection pressure for resistance to the few antibiotics available to treat CDI.

Toxin A-Predominant Pathogenic Clostridioides difficile: A Novel Clinical Phenotype.

BACKGROUND: Most Clostridioides difficile toxinogenic strains produce both toxins A and B (A+B+), but toxin A-negative, toxin B-positive (A-B+) variants also cause disease. We report the identification of a series of pathogenic clinical C. difficile isolates that produce high amounts of toxin A with low or nondetectable toxin B. METHODS: An ultrasensitive, quantitative immunoassay was used to measure toxins A and B in stool samples from 187 C. difficile infection (CDI) patients and 44 carriers. Isolates were cultured and assessed for in vitro toxin production and in vivo phenotypes (mouse CDI model). RESULTS: There were 7 CDI patients and 6 carriers who had stools with detectable toxin A (TcdA, range 23-17 422 pg/mL; 5.6% of samples overall) but toxin B (TcdB) below the clinical detection limit (<20 pg/mL; median TcdA:B ratio 17.93). Concentrations of toxin A far exceeded B in in vitro cultures of all 12 recovered isolates (median TcdA:B ratio 26). Of 8 toxin A>>B isolates tested in mice, 4 caused diarrhea, and 3 of those 4 caused lethal disease. Ribotyping demonstrated strain diversity. TcdA-predominant samples were also identified at 2 other centers, with similar frequencies (7.5% and 6.8%). CONCLUSIONS: We report the discovery of clinical pathogenic C. difficile strains that produce high levels of toxin A but minimal or no toxin B. This pattern of toxin production is not rare (>5% of isolates) and is consistently observed in vitro and in vivo in humans and mice. Our study highlights the significance of toxin A in human CDI pathogenesis and has important implications for CDI diagnosis, treatment, and vaccine development.

In Vitro Activity of Omadacycline, a New Tetracycline Analog, and Comparators against Clostridioides difficile.

Omadacycline is a potent aminomethylcycline with in vitro activity against Gram-positive, Gram-negative, and anaerobic bacteria. Preliminary data demonstrated that omadacycline has in vitro activity against Clostridioides difficile; however, large-scale in vitro studies have not been done. The purpose of this study was to assess the in vitro susceptibility of omadacycline and comparators on a large biobank of clinical C. difficile isolates. In vitroC. difficile susceptibility to omadacycline and comparators (fidaxomicin, metronidazole, and vancomycin) was assessed using the broth microdilution method. Minimum bactericidal concentrations (MBCs) and time-kill assays were assessed for pharmacodynamics analysis, and whole-genome sequencing was performed in a subset of isolates to assess distribution of MICs and resistance determinants. Two hundred fifty clinical C. difficile isolates collected between 2015 and 2018 were tested for in vitro susceptibility of omadacycline and comparators. Ribotypes included F001 (n = 5), F002 (n = 56), F014-020 (n = 66), F017 (n = 8), F027 (n = 53), F106 (n = 45), and F255 (n = 17). Omadacycline demonstrated potent in vitro activity with an MIC range of 0.016 to 0.13 µg/ml, an MIC50 of 0.031 µg/ml, and an MIC90 of 0.031 µg/ml. No difference was observed for omadacycline MIC50 and MIC90 values stratified by ribotype, disease severity, or vancomycin susceptibility. Bactericidal activity was confirmed in time-kill studies. No difference was observed in MIC based on C. difficile phylogeny. Further development of omadacycline as an intravenous and oral antibiotic directed toward C. difficile infection is warranted.

Utilizing antibiotics to prevent Clostridioides difficile infection: does exposure to a risk factor decrease risk? A systematic review.

BACKGROUND: Antibiotic use is a major risk factor for Clostridioides difficile infection (CDI). However, antibiotics recommended for CDI treatment are being utilized in clinical practice as prophylactic agents. OBJECTIVES: To comprehensively summarize and critically evaluate the published literature investigating the effectiveness of antibiotic CDI prophylaxis. METHODS: A systematic search for relevant literature was conducted in PubMed and ClinicalTrials.gov. Two investigators independently screened each article for inclusion, and the references of the included articles were studied to identify additional relevant articles. Data extraction and an assessment of risk of bias was completed for all included studies. Unadjusted risk ratios and 95% CI were calculated for each study, with CDI being the outcome variable and prophylaxis (prophylaxis versus control) representing the exposure. RESULTS: In total, 13 articles were identified in PubMed and 9 ongoing or unpublished trials were identified in ClinicalTrials.gov. The effect of antibiotic prophylaxis on CDI rates varied between studies; however, most favoured the use of antibiotic prophylaxis. CONCLUSIONS: The authors of this review conclude that the current literature carries a high risk of bias and the results should be interpreted with caution.