Immunological Stability of Clostridium difficile Toxins in Clinical Specimens

Clostridioides difficile infection: history, epidemiology, risk factors, prevention, clinical manifestations, treatment, and future options

SUMMARYClostridioides difficile infection (CDI) is one of the major issues in nosocomial infections. This bacterium is constantly evolving and poses complex challenges for clinicians, often encountered in real-life scenarios. In the face of CDI, we are increasingly equipped with new therapeutic strategies, such as monoclonal antibodies and live biotherapeutic products, which need to be thoroughly understood to fully harness their benefits. Moreover, interesting options are currently under study for the future, including bacteriophages, vaccines, and antibiotic inhibitors. Surveillance and prevention strategies continue to play a pivotal role in limiting the spread of the infection. In this review, we aim to provide the reader with a comprehensive overview of epidemiological aspects, predisposing factors, clinical manifestations, diagnostic tools, and current and future prophylactic and therapeutic options for C. difficile infection.

Pragmatic Strategy for Fecal Specimen Storage and the Corresponding Test Methods for Clostridioides difficile Diagnosis

The quality of fecal specimens is one of the factors responsible for successful Clostridioides difficile infection (CDI) diagnosis. The quality depends largely on the storage conditions, including the temperature and time period. In this study, we organized the outputs of previous studies, filled experimental gaps in the knowledge of storage conditions, and introduced a pragmatic strategy for fecal storage for CDI diagnosis. A 5-step pathway was adopted to develop the fecal specimen storage strategy as follows: step 1, bibliomic analysis; step 2, experimental gap-filling; step 3, comparative evaluation; step 4, strategy development; step 5, internal review. Step 1 identified eight articles providing experimental information on the effects of fecal specimen storage conditions on the effectiveness of C. difficile detection methods. Step 2 provided additional quantitative data on C. difficile vegetative and spore cell viability and DNA stability. All previous and current results were compared (step 3). In step 4, fir general and nine special strategies were developed, followed by an internal review of the overall approaches (step 5). It is recommended to separate fecal samples into aliquots before testing and storing them. It is particularly recommended that fecal specimen samples be stored for CDI diagnosis at 4 °C for up to 60 days for all test methods.

Clostridioides difficile Infection: The Challenge, Tests, and Guidelines

Clostridioides difficile is a dangerous human pathogen because it can grow to high numbers in the intestine, cause colitis with its potent toxins, and persist as spores. C. difficile infection (CDI) is the primary hospital-acquired infection in North America and Europe, and it now is a global disease. Even with newer laboratory tests, there still is confusion on accurately diagnosing this disease. Three guidelines from three different healthcare-affiliated societies have recently been published. Consensus consolidated recommendations from these guidelines should be recognized by healthcare professionals, who need to understand why this disease continues to be difficult to diagnose and need a clear understanding of the advantages and limitations of current tests. Hopefully, these combined efforts will lead to an improvement in the recognition of this pathogen and a reduction in the suffering and economic loss caused by CDI.

Prospective Evaluation of the mariPOC Test for Detection of Clostridioides difficile Glutamate Dehydrogenase and Toxins A/B

The objective of this study was to evaluate a novel automated random-access test, mariPOC CDI (ArcDia Ltd., Finland), for the detection of Clostridioides difficile glutamate dehydrogenase (GDH) and toxins A and B directly from fecal specimens. The mariPOC test was compared with both the GenomEra C. difficile PCR assay (Abacus Diagnostica Oy, Finland) and the TechLab C. diff Quik Chek Complete (Alere Inc.; now Abbot) membrane enzyme immunoassay (MEIA). Culture and the Xpert C. difficile assay (Cepheid Inc., USA) were used to resolve discrepant results. In total, 337 specimens were tested with the mariPOC CDI test and GenomEra PCR. Of these specimens, 157 were also tested with the TechLab MEIA. The sensitivity of the mariPOC test for GDH was slightly lower (95.2%) than that obtained with the TechLab assay (100.0%), but no toxin-positive cases were missed. The sensitivity of the mariPOC test for the detection of toxigenic C. difficile by analyzing toxin expression was better (81.6%) than that of the TechLab assay (71.1%). The analytical specificities for the mariPOC and the TechLab tests were 98.3% and 100.0% for GDH and 100.0% and 99.2% for toxin A/B, respectively. The analytical specificity of the GenomEra method was 100.0%. The mariPOC and TechLab GDH tests and GenomEra PCR had high negative predictive values of 99.3%, 98.3%, and 99.7%, respectively, in excluding infection with toxigenic C. difficile The mariPOC toxin A/B test and GenomEra PCR had an identical analytical positive predictive value of 100%, providing highly reliable information about toxin expression and the presence of toxin genes, respectively.

Ultrasensitive Detection of Clostridioides difficile Toxins in Stool by Use of Single-Molecule Counting Technology: Comparison with Detection of Free Toxin by Cell Culture Cytotoxicity Neutralization Assay

Laboratory tests for Clostridioides difficile infection (CDI) rely on the detection of free toxin or molecular detection of toxin genes. The Singulex Clarity C. diff toxins A/B assay is a rapid, automated, and ultrasensitive assay that detects C. difficile toxins A and B in stool. We compared CDI assays across two prospective multicenter studies to set a cutoff for the Clarity assay and to independently validate the performance compared with that of a cell culture cytotoxicity neutralization assay (CCCNA). The cutoff was set by two sites testing fresh samples from 897 subjects with suspected CDI and then validated at four sites testing fresh samples from 1,005 subjects with suspected CDI. CCCNA testing was performed at a centralized laboratory. Samples with discrepant results between the Clarity assay and CCCNA were retested with CCCNA when the Clarity result agreed with that of at least one comparator method; toxin enzyme immunoassays (EIA), glutamate dehydrogenase (GDH) detection, and PCR were performed on all samples. The cutoff for the Clarity assay was set at 12.0 pg/ml. Compared to results with CCCNA, the Clarity assay initially had 85.2% positive agreement and 92.4% negative agreement. However, when samples with discrepant results between the Clarity assay and CCCNA in the validation study were retested by CCCNA, 13/17 (76.5%) Clarity-negative but CCCNA-positive samples (Clarity⁺/CCCNA^-) became CCCNA^-, and 5/26 (19.2%) Clarity⁺/CCCNA^- samples became CCCNA⁺, resulting in a 96.3% positive agreement and 93.0% negative agreement between Clarity and CCCNA results. The toxin EIA had 59.8% positive agreement with CCCNA. The Clarity assay was the most sensitive free-toxin immunoassay, capable of providing CDI diagnosis in a single-step solution. A different CCCNA result was reported for 42% of retested samples, increasing the positive agreement between Clarity and CCCNA from 85.2% to 96.3% and indicating the challenges of comparing free-toxin results to CCCNA results as a reference standard.

Increased Clinical Specificity with Ultrasensitive Detection of Clostridioides difficile Toxins: Reduction of Overdiagnosis Compared to Nucleic Acid Amplification Tests

Clostridioides difficile infection (CDI) is one of the most common health care-associated infections, resulting in significant morbidity, mortality, and economic burden. Diagnosis of CDI relies on the assessment of clinical presentation and laboratory tests. We evaluated the clinical performance of ultrasensitive single-molecule counting technology for detection of C. difficile toxins A and B. Stool specimens from 298 patients with suspected CDI were tested with the nucleic acid amplification test (NAAT; BD MAX Cdiff assay or Xpert C. difficile assay) and Singulex Clarity C. diff toxins A/B assay. Specimens with discordant results were tested with the cell cytotoxicity neutralization assay (CCNA), and the results were correlated with disease severity and outcome. There were 64 NAAT-positive and 234 NAAT-negative samples. Of the 32 NAAT⁺/Clarity^- and 4 NAAT^-/Clarity⁺ samples, there were 26 CCNA^- and 4 CCNA^- samples, respectively. CDI relapse was more common in NAAT⁺/toxin⁺ patients than in NAAT⁺/toxin^- and NAAT^-/toxin^- patients. The clinical specificity of Clarity and NAAT was 97.4% and 89.0%, respectively, and overdiagnosis was more than three times more common in NAAT⁺/toxin^- than in NAAT⁺/toxin⁺ patients. The Clarity assay was superior to NAATs for the diagnosis of CDI, by reducing overdiagnosis and thereby increasing clinical specificity, and the presence of toxins was associated with negative patient outcomes.

Storage procedures and time influence the detectability of Clostridium difficile toxin A but not toxin B in porcine fecal specimens

Storage procedures are known to affect the detectability of Clostridium difficile toxins in equine and human feces. We assessed the impact of different storage conditions on the detectability of C. difficile toxins in swine feces. Specimens were inoculated with toxins, 112 ng/g of toxin A (TcdA) and 16 ng/g of toxin B (TcdB) and subjected to the following 3 storage treatments: 4°C, −30°C, repetitive freezing at −30°C and thawing. Toxin determination was assessed at 1, 2, 7, 14, and 21 d with ELISA. A decrease in concentrations of TcdA with time was observed for samples stored at 4°C and repetitive freezing–thawing (p ≤0.05). On day 14, storage at 4°C resulted in decreased TcdA concentration as opposed to storage at −30°C and repetitive freezing–thawing (p ≤0.05). On day 21, storage at 4°C resulted in decreased TcdA detectability compared with storage at −30°C (p ≤0.05). The TcdB concentration was unaffected. These results on toxin detectability in swine feces should be carefully considered in in vitro studies on toxigenic C. difficile. Our results also offer valuable information for microbiologists and veterinarians monitoring the presence of virulent C. difficile in pigs.

Ultrasensitive Detection of Clostridioides difficile Toxins A and B by Use of Automated Single-Molecule Counting Technology

Current tests for the detection of Clostridioides (formerly Clostridium) difficile free toxins in feces lack sensitivity, while nucleic acid amplification tests lack clinical specificity. We have evaluated the Singulex Clarity C. diff toxins A/B assay (currently in development), an automated and rapid ultrasensitive immunoassay powered by single-molecule counting technology, for detection of C. difficile toxin A (TcdA) and toxin B (TcdB) in stool. The analytical sensitivity, analytical specificity, repeatability, and stability of the assay were determined. In a clinical evaluation, frozen stool samples from 311 patients with suspected C. difficile infection were tested with the Clarity C. diff toxins A/B assay, using an established cutoff value. Samples were tested with the Xpert C. difficile/Epi assay, and PCR-positive samples were tested with an enzyme immunoassay (EIA) (C. Diff Quik Chek Complete). EIA-negative samples were further tested with a cell cytotoxicity neutralization assay. The limits of detection for TcdA and TcdB were 0.8 and 0.3 pg/ml in buffer and 2.0 and 0.7 pg/ml in stool, respectively. The assay demonstrated reactivity to common C. difficile strains, did not show cross-reactivity to common gastrointestinal pathogens, was robust against common interferents, allowed detection in fresh and frozen stool samples and in samples after three freeze-thaw cycles, and provided results with high reproducibility. Compared to multistep PCR and toxin-testing procedures, the Singulex Clarity C. diff toxins A/B assay yielded 97.7% sensitivity and 100% specificity. The Singulex Clarity C. diff toxins A/B assay is ultrasensitive and highly specific and may offer a standalone solution for rapid detection and quantitation of free toxins in stool.