Value of lysozyme agar incorporation and alkaline thioglycollate exposure for the environmental recovery of Clostridium difficile

Hypervirulent R20291 Clostridioides difficile spores show disinfection resilience to sodium hypochlorite despite structural changes

BACKGROUND

Clostridioides difficile is a spore forming bacterial species and the major causative agent of nosocomial gastrointestinal infections. C. difficile spores are highly resilient to disinfection methods and to prevent infection, common cleaning protocols use sodium hypochlorite solutions to decontaminate hospital surfaces and equipment. However, there is a balance between minimising the use of harmful chemicals to the environment and patients as well as the need to eliminate spores, which can have varying resistance properties between strains. In this work, we employ TEM imaging and Raman spectroscopy to analyse changes in spore physiology in response to sodium hypochlorite. We characterize different C. difficile clinical isolates and assess the chemical's impact on spores' biochemical composition. Changes in the biochemical composition can, in turn, change spores' vibrational spectroscopic fingerprints, which can impact the possibility of detecting spores in a hospital using Raman based methods.

RESULTS

We found that the isolates show significantly different susceptibility to hypochlorite, with the R20291 strain, in particular, showing less than 1 log reduction in viability for a 0.5% hypochlorite treatment, far below typically reported values for C. difficile. While TEM and Raman spectra analysis of hypochlorite-treated spores revealed that some hypochlorite-exposed spores remained intact and not distinguishable from controls, most spores showed structural changes. These changes were prominent in B. thuringiensis spores than C. difficile spores.

CONCLUSION

This study highlights the ability of certain C. difficile spores to survive practical disinfection exposure and the related changes in spore Raman spectra that can be seen after exposure. These findings are important to consider when designing practical disinfection protocols and vibrational-based detection methods to avoid a false-positive response when screening decontaminated areas.

Investigating the transient and persistent effects of heat on Clostridium difficile spores

Purpose. Clostridium difficile spores are extremely resilient to high temperatures. Sublethal temperatures are associated with the 'reactivation' of dormant spores, and are utilized to maximize C. difficile spore recovery. Spore eradication is of vital importance to the food industry. The current study seeks to elucidate the transient and persisting effects of heating C. difficile spores at various temperatures.Methods. Spores of five C. difficile strains of different ribotypes (001, 015, 020, 027 and 078) were heated at 50, 60 and 70-80 °C for 60 min in phosphate-buffered saline (PBS) and enumerated at 0, 15, 30, 45 and 60 min. GInaFiT was used to model the kinetics of spore inactivation. In subsequent experiments, spores were transferred to enriched brain heart infusion (BHI) broths after 10 min of 80 °C heat treatment in PBS; samples were enumerated at 90 min and 24 h.Results. The spores of all strains demonstrated log-linear inactivation with tailing when heated for 60 min at 80 °C [(x̄=7.54±0.04 log₁₀ vs 4.72±0.09 log₁₀ colony-forming units (c.f.u.) ml^{- 1}; P<0.001]. At 70 °C, all strains except 078 exhibited substantial decline in recovery over 60 min. Interestingly, 50 °C heat treatment had an inhibitory effect on 078 spore recovery at 0 vs 60 min (7.61±0.06 log₁₀ c.f.u. ml^{- 1} vs 6.13±0.05 log₁₀ c.f.u. ml^{- 1}; P<0.001). Heating at 70/80 °C inhibited the initial germination and outgrowth of both newly produced and aged spores in enriched broths. This inhibition appeared to be transient; after 24 h vegetative counts were higher in heat-treated vs non-heat-treated spores (x̄=7.65±0.04 log₁₀ c.f.u. ml^{- 1} vs 6.79±0.06 log₁₀ c.f.u. ml^{- 1}; P<0.001).Conclusions. The 078 spores were more resistant to the inhibitory effects of higher temperatures. Heat initially inhibits spore germination, but the subsequent outgrowth of vegetative populations accelerates after the initial inhibitory period.

Clostridium difficile infection in pregnant and postpartum women in 2 hospitals and a review of literature

BACKGROUND

Healthcare-associated Clostridium difficile infection (CDI) in pregnant/postpartum women is underreported, especially outside of North America. We report a cluster of cases in 2 neighboring secondary care hospitals in South-East England. The objective of this study was to identify the epidemiology and risk factors for infection.

METHODS

An investigation into a cluster of cases of confirmed CDI in pregnant/postpartum women was performed over a 12-month period, from June 2016 to June 2017.

RESULTS

Eleven cases, in 10 patients, were identified, including 1 patient who had a relapse. Eight of 10 patients developed symptoms after hospital discharge. All patients had received broad-spectrum antibiotics prior to CDI onset. Environmental vectors, such as labor room mattresses, that were found difficult to effectively decontaminate after heavy contamination with blood, feces, and other body fluids may have been possible reservoirs. An infection control care bundle was successful in preventing further cases.

CONCLUSIONS

Antibiotic use and exposure to the organism in a contaminated labor room environment are likely risk factors for healthcare-associated CDI in postpartum women. Active surveillance is necessary to prevent these infections, as these cases often present after hospital discharge.

Antimicrobial susceptibility and ribotypes of Clostridium difficile isolates from a Phase 2 clinical trial of ridinilazole (SMT19969) and vancomycin

Objectives

We evaluated the antimicrobial susceptibility and ribotypes of Clostridium difficile isolates from participants in a Phase 2 study of ridinilazole, a novel targeted-spectrum agent for treatment of C. difficile infection.

Methods

Participants received ridinilazole (200 mg twice daily) or vancomycin (125 mg four times daily) for 10 days (ClinicalTrials.gov: NCT02092935). The MICs of ridinilazole and comparators for C. difficile isolates from stool samples were determined by agar dilution. Toxin gene profiling was performed by multiplex PCR and ribotype identification by capillary electrophoresis.

Results

Eighty-nine isolates were recovered from 88/100 participants (one participant had two strains at baseline). The median colony count (cfu/g stool) was 1.9 × 104 (range: 2.5 × 102-7.0 × 106). Twelve participants (three received ridinilazole and nine received vancomycin) experienced recurrence, confirmed by immunoassays for free toxin in stool samples. The ribotype of eight out of nine isolates obtained at recurrence matched those of the initial isolates. All isolates, including those obtained at recurrence, were susceptible to ridinilazole within the expected range [median (range) MIC: 0.12 (0.06-0.5) mg/L]. The median (range) vancomycin MIC was 1 (0.5-4.0) mg/L. At baseline, 13.6% and 13.3% of samples in the ridinilazole and vancomycin groups were positive for VRE, increasing to 23.7% and 29.7% by day 40, respectively. Common ribotypes included 014-20 (14 isolates), 027 (13), 106 (7), 002 (7), 078-126 (4), 001 (4), 087 (3) and 198 (3). Toxin gene profiling of nearly all baseline isolates (98.9%) revealed a binary toxin gene (cdtA/cdtB) prevalence of 35%.

Conclusions

Ridinilazole potently inhibited recovered C. difficile isolates. Recurrence was not associated with altered susceptibility.

Development and Validation of a New Protocol for Detecting and Recovering Clostridium difficile from Meat Samples

There is no recommended protocol for detecting and isolating Clostridium difficile present in food samples. Here, we have evaluated the recovery of C. difficile in meat samples after incubating them in various enrichment broths. The media were as follows: cycloserine-cefoxitin fructose broth supplemented with taurocholic acid, d-cycloserine, cefoxitin, and lysozyme; cycloserine-cefoxitin mannitol broth with taurocholate and lysozyme; and cycloserine-cefoxitin fructose broth supplemented with taurocholic acid, C. difficile moxalactam norfloxacin selective supplement, and lysozyme. Samples were inoculated with various strains and quantities of C. difficile and then enriched in the different broths for 1, 4, and 7 days. C. difficile was isolated on agar plates and detected with quantitative real-time PCR (qPCR). The procedure using enrichment in cycloserine-cefoxitin fructose broth supplemented with taurocholic acid, d-cycloserine, cefoxitin, and lysozyme and incubation for 4 days for qPCR detection and 7 days for isolation (plating on C. difficile agar base with added C. difficile selective supplement and 7% [v/v] defibrinated horse blood after alcoholic shock and centrifugation) was validated. Samples of different kinds of meat and meat preparation were contaminated and used for validation of the chosen protocol. The sensitivity of detection with qPCR was 100%, and the sensitivity of the isolation method was 96%.

Investigating the effect of supplementation on Clostridioides (Clostridium) difficile spore recovery in two solid agars

BACKGROUND

A variety of supplemented solid media are used within Clostridium difficile research to optimally recover spores. Our study sought to investigate different media and additives, providing a method of optimised C. difficile spore recovery. Additionally, due to the results observed in the initial experiments, the inhibitory effects of three amino acids (glycine, l-histidine &l-phenylalanine) on C. difficile spore outgrowth were investigated.

METHODS

Spores of five C. difficile strains (PCR ribotypes 001,015,020,027,078) were recovered on two commonly used solid media (BHI & CCEY, or cycloserine-cefoxitin egg yolk) supplemented with various concentrations of germinants (taurocholate, glycine & lysozyme). Agar-incorporation minimum inhibitory concentration (MIC) testing was carried out for glycine and taurocholate on vegetative cells and spores of all five strains. Additionally a BHI broth microassay method was utilised to test the growth of C. difficile in the presence of increasing concentrations (0,1,2,3,4%) of three amino acids (glycine,l-histidine,l-phenyalanine).

RESULTS

CCEY agar alone and BHI supplemented with taurocholate (0.1/1%) provided optimal recovery for C. difficile spores. Glycine was inhibitory to spore recovery at higher concentrations, although these varied between the two media used. In agar-incorporated MIC testing, glycine concentrations higher than 2% (20 g/L) were inhibitory to both C. difficile spore and vegetative cell growth versus the control (mean absorbance = 0.33 ± 0.02 vs 0.12 ± 0.01) (P < 0.001). This indicates a potential mechanism whereby glycine interferes with vegetative cell growth. Further microbroth testing provided evidence of inhibition by two amino acids other than glycine, l-histidine and l-phenylalanine.

CONCLUSIONS

We provide two media for optimal recovery of C. difficile spores (CCEY alone and BHI supplemented with 0.1/1% taurocholate). CCEY is preferred for isolation from faecal samples. For pure cultures, either CCEY or supplemented BHI agar are appropriate. The inhibitory nature of three amino acids (glycine,l-histidine,l-phenylalanine) to C. difficile vegetative cell proliferation is also highlighted.

A Decade of Development of Chromogenic Culture Media for Clinical Microbiology in an Era of Molecular Diagnostics

In the last 25 years, chromogenic culture media have found widespread application in diagnostic clinical microbiology. In the last decade, the range of media available to clinical laboratories has expanded greatly, allowing specific detection of additional pathogens, including Pseudomonas aeruginosa, group B streptococci, Clostridium difficile, Campylobacter spp., and Yersinia enterocolitica. New media have also been developed to screen for pathogens with acquired antimicrobial resistance, including vancomycin-resistant enterococci, carbapenem-resistant Acinetobacter spp., and Enterobacteriaceae with extended-spectrum β-lactamases and carbapenemases. This review seeks to explore the utility of chromogenic media in clinical microbiology, with particular attention given to media that have been commercialized in the last decade. The impact of laboratory automation and complementary technologies such as matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is also assessed. Finally, the review also seeks to demarcate the role of chromogenic media in an era of molecular diagnostics.

A Novel Quantitative Sampling Technique for Detection and Monitoring of Clostridium difficile Contamination in the Clinical Environment

The horizontal transmission of Clostridium difficile in the hospital environment is difficult to establish. Current methods to detect C. difficile spores on surfaces are not quantitative, lack sensitivity, and are protracted. We propose a novel rapid method to detect and quantify C. difficile contamination on surfaces. Sponge swabbing was compared to contact plate sampling to assess the in vitro recovery of C. difficile ribotype 027 contamination (∼10(0), 10(1), or 10(2) CFU of spores) from test surfaces (a bed rail, a stainless steel sheet, or a polypropylene work surface). Sponge swab contents were concentrated by vacuum filtration, and the filter membrane was plated onto selective agar. The efficacy of each technique for the recovery of C. difficile from sites in the clinical environment that are touched at a high frequency was evaluated. Contact plates recovered 19 to 32% of the total contamination on test surfaces, whereas sponge swabs recovered 76 to 94% of the total contamination, and contact plates failed to detect C. difficile contamination below a detection limit of 10 CFU/25 cm(2) (0.4 CFU/cm(2)). In use, contact plates failed to detect C. difficile contamination (0/96 contact plates; 4 case wards), while sponge swabs recovered C. difficile from 29% (87/301) of the surfaces tested in the clinical environment. Approximately 74% (36/49) of the area in the vicinity of the patient was contaminated (∼1.34 ± 6.88 CFU/cm(2) C. difficile spores). Reservoirs of C. difficile extended to beyond the areas near the patient: a dirty utility room sink (2.26 ± 5.90 CFU/cm(2)), toilet floor (1.87 ± 2.40 CFU/cm(2)), and chair arm (1.33 ± 4.69 CFU/cm(2)). C. difficile was present on floors in ∼90% of case wards. This study highlights that sampling with a contact plate may fail to detect C. difficile contamination and result in false-negative reporting. Our sponge sampling technique permitted the rapid and quantitative measurement of C. difficile contamination on surfaces with a sensitivity (limit, 0 CFU) greater than that which is otherwise possible. This technique could be implemented for routine surface hygiene monitoring for targeted cleaning interventions and as a tool to investigate routes of patient-patient transmission in the clinical environment.

Isolation and Identification of Clostridium difficile Using ChromID C. difficile Medium Combined With Gram Staining and PRO Disc Testing: A Proposal for a Simple Culture Process

Background

ChromID C. difficile agar (CDIF; bioMérieux, France), a chromogenic medium, allows for the isolation and identification of Clostridium difficile strains within 24 hr regardless of pretreatment of stool specimens with heat or alcohol shock. In the present study, we designed and evaluated a simple procedure for the implementation C. difficile cultures using CDIF medium in a tertiary hospital setting.

Methods

We designed a simple protocol for untreated stool specimens using CDIF medium followed by Gram staining and PRO disc (PRO disc K1532B, Key Scientific Products, USA) testing for the identification of C. difficile in colonies produced on CDIF agar. A total of 1,402 prospectively collected stool specimens from patients with suspected C. difficile infection were tested. The protocol was evaluated by phenotypic or molecular identification of C. difficile using Vitek 2 ANC card (bioMérieux) or 16S rDNA/tpi gene sequencing, respectively.

Results

Of 1,402 stool specimens, 650 isolates were cultured in CDIF. Overall, 235 (36.2%, 235/650) strains could be presumptively identified as C. difficile by using Gram staining and PRO disc testing. Of those, 231 (98.3%, 231/235) isolates were confirmed as true C. difficile by molecular assays.

Conclusions

The use of CDIF combined with Gram staining and PRO disc testing of untreated stool specimens would allow for isolation and accurate identification of C. difficile strains and would be advantageous in reducing the multistep process for C. difficile culture.

Strategies to prevent Clostridium difficile infections in acute care hospitals: 2014 update

Previously published guidelines are available that provide comprehensive recommendations for detecting and preventing healthcare-associated infections (HAIs). The intent of this document is to highlight practical recommendations in a concise format designed to assist acute care hospitals in implementing and prioritizing their Clostridium difficile infection (CDI) prevention efforts. This document updates “Strategies to Prevent Clostridium difficile Infections in Acute Care Hospitals,” published in 2008. This expert guidance document is sponsored by the Society for Healthcare Epidemiology of America (SHEA) and is the product of a collaborative effort led by SHEA, the Infectious Diseases Society of America (IDSA), the American Hospital Association (AHA), the Association for Professionals in Infection Control and Epidemiology (APIC), and The Joint Commission, with major contributions from representatives of a number of organizations and societies with content expertise. The list of endorsing and supporting organizations is presented in the introduction to the 2014 updates.

A possible route for foodborne transmission of Clostridium difficile?

Spores of toxigenic Clostridium difficile and spores of food-poisoning strains of Clostridium perfringens show a similar prevalence in meats. Spores of both species are heat resistant and can survive cooking of foods. C. perfringens is a major cause of foodborne illness; studies are needed to determine whether C. difficile transmission by a similar route is a cause of infection.

Clinical Practice Guidelines for Clostridium difficile Infection in Adults: 2010 Update by the Society for Healthcare Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA)

Since publication of the Society for Healthcare Epidemiology of America position paper onClostridium difficileinfection in 1995, significant changes have occurred in the epidemiology and treatment of this infection.C. difficileremains the most important cause of healthcare-associated diarrhea and is increasingly important as a community pathogen. A more virulent strain ofC. difficilehas been identified and has been responsible for more-severe cases of disease worldwide. Data reporting the decreased effectiveness of metronidazole in the treatment of severe disease have been published. Despite the increasing quantity of data available, areas of controversy still exist. This guideline updates recommendations regarding epidemiology, diagnosis, treatment, and infection control and environmental management.

Efficacy of Hospital Cleaning Agents and Germicides Against EpidemicClostridium difficileStrains

Objective.

To compare the effects of hospital cleaning agents and germicides on the survival of epidemicClostridium difficilestrains.

Methods.

We compared the activity of and effects of exposure to 5 cleaning agents and/or germicides (3 containing chlorine, 1 containing only detergent, and 1 containing hydrogen peroxide) on vegetative and spore forms of epidemic and non-epidemicC. difficilestrains (3 of each). We carried out in vitro exposure experiments using a human fecal emulsion to mimic conditions found in situ.

Results.

Cleaning agent and germicide exposure experiments yielded very different results forC. difficilevegetative cells, compared with those for spores. Working-strength concentrations of all of the agents inhibited the growth ofC. difficilein culture. However, when used at recommended working concentrations, only chlorine-based germicides were able to inactivateC. difficilespores.C. difficileepidemic strains had a greater sporulation rate than nonepidemic strains. The mean sporulation rate, expressed as the proportion of a cell population that is in spore form, was 13% for all strains not exposed to any cleaning agent or germicide, and it was significantly increased by exposure to cleaning agents or germicides containing detergent alone (34%), a combination of detergent and hypochlorite (24%), or hydrogen peroxide (33%). By contrast, the mean sporulation rate did not change substantially after exposure to germicides containing either a combination of detergent and dichloroisocyanurate (9%) or dichloroisocyanurate alone (15%).

Conclusions.

These results highlight differences in the activity of cleaning agents and germicides againstC. difficilespores and the potential for some of these products to promote sporulation.

Evaluation of the illumigene C. difficile assay for toxigenic Clostridium difficile detection: a prospective study of 302 consecutive clinical fecal samples

Toxigenic Clostridium difficile is a major pathogen causing nosocomial diarrhea. Consequently, rapid detection of toxigenic C. difficile is very important in clinical laboratories. The illumigene C. difficile DNA amplification assay (illumigene; Meridian Bioscience, Inc.) is a rapid method that detects the toxin A gene (tcdA) by loop-mediated isothermal amplification. In the present study, we evaluated the diagnostic performance of the illumigene assay using 302 consecutive stool specimens in comparison with the VIDAS C. difficile A&B enzyme-linked fluorescent immunoassay (VIDAS-CDAB; bioMérieux). Toxigenic culture was used as the reference method. The sensitivity, specificity, positive predictive value, and negative predictive value of the illumigene assay were 88.1%, 96.7%, 86.7%, and 97.1%, respectively, while those of the VIDAS-CDAB assay were 40.4%, 98.8%, 87.5%, and 88.5%, respectively. It is of note that use of a combination of the illumigene and VIDAS-CDAB assays did not improve any of the 4 evaluated parameters (88.1%, 95.5%, 82.5%, and 97.1%, respectively). The illumigene assay showed limits of detection of 250 and 11,467 CFU/mL for ATCC 9688 (tcdA+, tcdB+, cdtB-) and ATCC 43598 (tcdA-, tcdB+, cdtB-) reference strains, respectively, and there was no cross-reactivity with 8 frequently isolated bacterial species. In conclusion, the illumigene assay might be a useful method for rapid detection of toxigenic C. difficile in clinical laboratories. Additionally, the VIDAS-CDAB assay seems unnecessary if the illumigene assay is used.

Comparison of culture based methods for the isolation of Clostridium difficile from stool samples in a research setting

Effective isolation of Clostridium difficile from stool samples is important in the research setting, especially where low numbers of spores/vegetative cells may be present within a sample. In this study, three protocols for stool culture were investigated to find a sensitive, cost effective and timely method of C. difficile isolation. For the initial enrichment step, the effectiveness of two different rich media, cycloserine-cefoxitin fructose broth (CCFB) and cycloserine-cefoxitin mannitol broth with taurocholate and lysozyme (CCMB-TAL) were compared. For the comparison of four different, selective solid media; Cycloserine-cefoxitin fructose agar (CCFA), Cycloserine-cefoxitin egg yolk agar (CCEY), ChromID C. difficile and tryptone soy agar (TSA) with 5% sheep's blood with and without preceding broth enrichment were used. As a means to enable differentiation between C. difficile and other fecal flora, the effectiveness of the inclusion of a pH indictor (1% Neutral Red), was also evaluated. The data derived indicated that CCFB is more sensitive than CCMB-TAL, however, the latter had an improved recovery rate. A broth enrichment step had a reduced sensitivity over direct plating. ChromID C. difficile showed the best recovery rate whereas CCEY egg yolk agar was the most sensitive of the four. The addition of 1% Neutral Red did not show sufficient colour change when added to CCEY egg yolk agar to be used as a differential medium. For a low cost, timely and sensitive method of isolating C. difficile from stool samples we recommend direct plating onto CCEY egg yolk agar after heat shock.

Detecting Clostridium difficile spores from inanimate surfaces of the hospital environment: which method is best?

The recovery of Clostridium difficile spores from hospital surfaces was assessed using rayon swabs, flocked swabs, and contact plates. The contact plate method was less laborious, achieved higher recovery percentages, and detected spores at lower inocula than swabs. Rayon swabs were the least efficient method. However, further studies are required in health care settings.

Diagnosis of Clostridium difficile infection: the molecular approach

Diagnosis of Clostridium difficile infection is based on clinical presentation and laboratory tests. Although numerous laboratory methods are now available, the diagnosis of C. difficile infection remains challenging. Nucleic acid amplification tests (NAATs) are the most recent marketed methods. These methods detect genes for toxins A and/or B. They are very sensitive compared with the reference method (toxigenic culture) and are thus very promising, despite their cost. However, a positive NAAT result must be interpreted with caution owing to the possible detection of asymptomatic carriers of toxigenic strains who may have diarrhea for other reasons. The place of NAATs in current diagnostic strategies needs to be better defined, but the rapidity of the result is interesting for early recognition of the disease.

Sensitive and selective culture medium for detection of environmental Clostridium difficile isolates without requirement for anaerobic culture conditions

Effective and easy-to-use methods for detecting Clostridium difficile spore contamination would be useful for identifying environmental reservoirs and monitoring the effectiveness of room disinfection. Culture-based detection methods are sensitive for detecting C. difficile, but their utility is limited due to the requirement of anaerobic culture conditions and microbiological expertise. We developed a low-cost selective broth medium containing thioglycolic acid and l-cystine, termed C. difficile brucella broth with thioglycolic acid and l-cystine (CDBB-TC), for the detection of C. difficile from environmental specimens under aerobic culture conditions. The sensitivity and specificity of CDBB-TC (under aerobic culture conditions) were compared to those of CDBB (under anaerobic culture conditions) for the recovery of C. difficile from swabs collected from hospital room surfaces. CDBB-TC was significantly more sensitive than CDBB for recovering environmental C. difficile (36/41 [88%] versus 21/41 [51%], respectively; P = 0.006). C. difficile latex agglutination, an enzyme immunoassay for toxins A and B or glutamate dehydrogenase, and a PCR for toxin B genes were all effective as confirmatory tests. For 477 total environmental cultures, the specificity of CDBB-TC versus that of CDBB based upon false-positive yellow-color development of the medium without recovery of C. difficile was 100% (0 false-positive results) versus 96% (18 false-positive results), respectively. False-positive cultures for CDBB were attributable to the growth of anaerobic non-C. difficile organisms that did not grow in CDBB-TC. Our results suggest that CDBB-TC provides a sensitive and selective medium for the recovery of C. difficile organisms from environmental samples, without the need for anaerobic culture conditions.

Diagnosis of Clostridium difficile infection: an ongoing conundrum for clinicians and for clinical laboratories

Clostridium difficile is a formidable nosocomial and community-acquired pathogen, causing clinical presentations ranging from asymptomatic colonization to self-limiting diarrhea to toxic megacolon and fulminant colitis. Since the early 2000s, the incidence of C. difficile disease has increased dramatically, and this is thought to be due to the emergence of new strain types. For many years, the mainstay of C. difficile disease diagnosis was enzyme immunoassays for detection of the C. difficile toxin(s), although it is now generally accepted that these assays lack sensitivity. A number of molecular assays are commercially available for the detection of C. difficile. This review covers the history and biology of C. difficile and provides an in-depth discussion of the laboratory methods used for the diagnosis of C. difficile infection (CDI). In addition, strain typing methods for C. difficile and the evolving epidemiology of colonization and infection with this organism are discussed. Finally, considerations for diagnosing C. difficile disease in special patient populations, such as children, oncology patients, transplant patients, and patients with inflammatory bowel disease, are described. As detection of C. difficile in clinical specimens does not always equate with disease, the diagnosis of C. difficile infection continues to be a challenge for both laboratories and clinicians.

Potential use of inhibitors of bacteria spore germination in the prophylactic treatment of anthrax andClostridium difficile-associated disease

Spore germination is the first step in establishing Bacillus and Clostridium infections. Germination is triggered by the binding of small molecules by the resting spore. Subsequently, the activated spore secretes dipicolinic acid and calcium, the spore core is rehydrated and spore structures are degraded. Inhibition of any of the germination-related events will prevent development to the vegetative stage. Inhibition of spore germination has been studied intensively in the prevention of food spoilage. In this perspective, we propose that similar approaches could be used in the prophylactic control of Bacillus anthracis and Clostridium difficile infections. Inhibition of B. anthracis spore germination could protect military and first-line emergency personnel at high risk for anthrax exposure. Inhibition of C. difficile could prevent human C. difficile-associated disease during antibiotic treatment of immunocompromised patients.

Evaluation of cycloserine-cefoxitin fructose agar (CCFA), CCFA with horse blood and taurocholate, and cycloserine-cefoxitin mannitol broth with taurocholate and lysozyme for recovery of Clostridium difficile isolates from fecal samples

Cycloserine-cefoxitin fructose agar (CCFA), CCFA with horse blood and taurocholate (CCFA-HT), and cycloserine-cefoxitin mannitol broth with taurocholate and lysozyme (CCMB-TAL) were compared for recovery of Clostridium difficile from 120 stool specimens. Compared to CCFA, CCFA-HT enhanced C. difficile growth and improved recovery by 4%. In a separate study, 9% (8/91) of stool samples previously C. difficile negative on plate medium were C. difficile positive when cultured in CCMB-TAL.

Evaluation of the chromogenic agar chromID C. difficile

Three selective media (chromID C. difficile agar, taurocholate cycloserine cefoxitin agar [TCCA; homemade], and CLO medium) were compared from 406 stool samples of patients suspected of having Clostridium difficile infection. The sensitivities of chromID C. difficile agar at 24 h and 48 h, CLO medium, and TCCA were 74.1%, 87%, 85.2%, and 70.4%, respectively.

A systematic evaluation of methods to optimize culture-based recovery of Clostridium difficile from stool specimens

With the increasing prevalence of Clostridium difficile infection among hospitalized patients, a clear understanding of C. difficile epidemiology is needed to evaluate current prevention policies, and to create new and effective policies. To determine the epidemiology of C. difficile, the most sensitive methods for detection of C. difficile are required. The purpose of this study was to systematically assess multiple methods to determine the most sensitive method to recover C. difficile from stool and rectal swabs. Stool samples from healthy asymptomatic individuals that were collected and confirmed to be culture negative for C. difficile were spiked with known concentrations of C. difficile ranging from 10(4) CFU of C. difficile per ml of stool to 10 CFU per ml. Two sets of experiments (A and B) were performed and each involved multiple combinations of untreated and treated stool/rectal swab specimens and selective and non-selective broth and agar. Overall, recovery of C. difficile was increased with the use of an initial broth enrichment followed by plating to solid medium. The most sensitive method of C. difficile detection for both stools and swab specimens was heat shock prior to inoculation of cycloserine-cefoxitin mannitol broth with taurocholate lysozyme cysteine (CCMB, Anaerobe Systems, Morgan Hill, CA) followed by isolation from pre-reduced TSA II with 5% sheep blood (BAP, BBL BD and Co., Sparks, MD). Identifying the most sensitive method of recovery will allow for further study of asymptomatic C. difficile carriers and their role in the epidemiology of C. difficile.

Comparison of two selective media for the recovery of Clostridium difficile from environmental surfaces

Two culture media were compared for their ability to isolate Clostridium difficile from environmental sites within a UK hospital. The media were cefoxitin-cycloserine-egg yolk agar plus lysozyme (CCEY/L) and chromID C. difficile. A wide range of environmental surfaces was sampled using sterile sponges (Polywipes) and these were inoculated on to both media. C. difficile was recovered from 105 of 496 sites (21%) using a combination of both media. The sensitivity of chromID C. difficile was 87.6% compared with 26.6% for CCEY/L (P < 0.0001). chromID C. difficile performed significantly better than CCEY/L for the recovery of C. difficile from the environment.

Clostridium difficile isolation and culture techniques

Clostridium difficile infection (CDI) occurs as a disease with a spectrum of severity ranging from mild, self-limiting diarrhoea to a severe colitis, pseudomembraneous colitis or toxic megacolon. The disease arises as a major complication of antibiotic therapy and is most commonly acquired in hospital. The laboratory investigation of faecal samples is supportive of a clinical suspicion that a patient has the disease. Currently the mainstay of diagnosis is the demonstration of C. difficile toxins in a diarrhoeal sample; only a few laboratories set up cultures for the organism. However, toxin tests should not be used as stand alone tests since some patients with disease do not have detectable levels of toxin in their faeces. Furthermore, other patients may have large amounts of toxin in the faeces and yet remain well. A combination of tests, therefore, should be used to help the physician to establish a diagnosis of CDI. This combination of tests should include culture (with toxin testing of the isolate), demonstration of toxin direct from the faeces and the detection of C. difficile antigen. This chapter outlines the methods used to establish the laboratory diagnosis of CDI and also includes the investigation of environmental samples when it is required to monitor them for the presence of C. difficile.

Evaluation of a chromogenic culture medium for isolation of Clostridium difficile within 24 hours

Rapid and effective methods for the isolation of Clostridium difficile from stool samples are desirable to obtain isolates for typing or to facilitate accurate diagnosis of C. difficile-associated diarrhea. We report on the evaluation of a prototype chromogenic medium (ID C. difficile prototype [IDCd]) for isolation of C. difficile. The chromogenic medium was compared using (i) 368 untreated stool samples that were also inoculated onto CLO medium, (ii) 339 stool samples that were subjected to alcohol shock and also inoculated onto five distinct selective agars, and (iii) standardized suspensions of 10 C. difficile ribotypes (untreated and alcohol treated) that were also inoculated onto five distinct selective agars. Two hundred thirty-six isolates of C. difficile were recovered from 368 untreated stool samples, and all but 1 of these strains (99.6%) were recovered on IDCd within 24 h, whereas 74.6% of isolates were recovered on CLO medium after 48 h. Of 339 alcohol-treated stool samples cultured onto IDCd and five other selective agars, C. difficile was recovered from 218 samples using a combination of all media. The use of IDCd allowed recovery of 96.3% of isolates within 24 h, whereas 51 to 83% of isolates were recovered within 24 h using the five other media. Finally, when they were challenged with pure cultures, all 10 ribotypes of C. difficile generated higher colony counts on IDCd irrespective of alcohol pretreatment or duration of incubation. We conclude that IDCd is an effective medium for isolation of C. difficile from stool samples within 24 h.

Multilocus sequence typing of Clostridium difficile

A robust high-throughput multilocus sequence typing (MLST) scheme for Clostridium difficile was developed and validated using a diverse collection of 50 reference isolates representing 45 different PCR ribotypes and 102 isolates from recent clinical samples. A total of 49 PCR ribotypes were represented overall. All isolates were typed by MLST and yielded 40 sequence types (STs). A web-accessible database was set up (http://pubmlst.org/cdifficile/) to facilitate the dissemination and comparison of C. difficile MLST genotyping data among laboratories. MLST and PCR ribotyping were similar in discriminatory abilities, having indices of discrimination of 0.90 and 0.92, respectively. Some STs corresponded to a single PCR ribotype (32/40), other STs corresponded to multiple PCR ribotypes (8/40), and, conversely, the PCR ribotype was not always predictive of the ST. The total number of variable nucleotide sites in the concatenated MLST sequences was 103/3,501 (2.9%). Concatenated MLST sequences were used to construct a neighbor-joining tree which identified four phylogenetic groups of STs and one outlier (ST-11; PCR ribotype 078). These groups apparently correlate with clades identified previously by comparative genomics. The MLST scheme was sufficiently robust to allow direct genotyping of C. difficile in total stool DNA extracts without isolate culture. The direct (nonculture) MLST approach may prove useful as a rapid genotyping method, potentially benefiting individual patients and informing hospital infection control.

Clostridium difficile ribotypes 027 and 106: clinical outcomes and risk factors

The present study investigates risk factors for onset of Clostridium difficile-associated diarrhoea, specific ribotype and environmental spore contamination in a District General Hospital in South East England. C. difficile isolates were ribotyped from 97 diarrhoeal cases, following detection of C. difficile toxin from faecal specimens by enzyme immunoassay (Health Protection Agency, Southampton). The isolates were tested for various antimicrobial susceptibilities by E-test. Cases were assessed for prior antibiotic use and followed up for clinical outcomes. Controls were matched for age, sex, ward, length of stay and comorbidity to identify any antibiotic risk factors using conditional logistic regression analysis. Environmental sampling on wards was performed with cycloserine-cefoxitin-egg yolk agar. Forty-five percent C.difficile isolates ribotyped as 027, 39% as 106 and 10% as 001. All ribotypes were resistant to ciprofloxacin, erythromycin and cefotaxime but remained susceptible to metronidazole and vancomycin. The crude (death within 28 days) and early (death within 72h) mortalities were 23% and 11% for the 027 strain, whereas for the 106 ribotype they were 11% and 3%, respectively. The case-control study identified ciprofloxacin usage for >7 days as a significant risk factor (adjusted odds ratios of 3.72; 95% CI: 1.38-10.02; P=0.019). Environmental sampling revealed the presence of spores on faecally contaminated equipment such as commodes and bedpan shells, which persisted after cleaning. Ciprofloxacin appears to encourage C.difficile-associated diarrhoea and should be restricted to short courses. Cleaning agents for clinical equipment must have sporicidal activity to prevent cross-transmission.

Effective and reduced-cost modified selective medium for isolation of Clostridium difficile

Both for epidemiologic studies and for diagnostic testing, there is a need for effective, economical, and readily available selective media for the culture of Clostridium difficile. We have developed a reduced-cost substitute for cycloserine-cefoxitin-fructose agar (CCFA), which is an effective but expensive selective medium for C. difficile. The modified medium, called C. difficile brucella agar (CDBA), includes an enriched brucella base as a substitute for proteose peptone no. 2, and the concentration of sodium taurocholate has been reduced from 0.1% to 0.05%. To compare the sensitivities and selectivities of CDBA and CCFA, cultures for C. difficile were performed using stool samples from patients with C. difficile-associated disease. CDBA was as sensitive as CCFA for the recovery of C. difficile, with a similar frequency of breakthrough growth of stool microflora (25% versus 31%, respectively). A liquid formulation of the modified medium, termed C. difficile brucella broth (CDBB), stimulated rapid germination and outgrowth of C. difficile spores, at a rate comparable to that in cycloserine-cefoxitin-fructose broth. Our results suggest that CDBA and CDBB are sensitive, selective, and reduced-cost media for the recovery of C. difficile from stool samples.

Treatment of Clostridium difficile infection

Recent outbreaks of Clostridium difficile infection (CDI) in North America have been due to a more virulent, possibly more resistant strain that causes more-severe disease, making prompt recognition of cases and optimal management of infection essential for a successful therapeutic outcome. Treatment algorithms are presented to help guide the management of patients with CDI. Metronidazole has been recommended as initial therapy since the late 1990s and continues to be the first choice for all but seriously ill patients and those with complicated or fulminant infections or multiple recurrences of CDI, for whom vancomycin is recommended. Other options for recurrent CDI, such as probiotics and currently available anion-exchange resins, have limited efficacy and are potentially harmful. Intravenous immunoglobulin may benefit patients with refractory, recurrent, or severe disease, but no controlled data are available. Two antimicrobials available in the United States for other indications, nitazoxanide and rifaximin, have been used successfully for CDI treatment but, like metronidazole, lack United States Food and Drug Administration approval for this indication. Experimental treatments currently in clinical development include a toxin-binding polymer, tolevamer; 2 poorly absorbed antimicrobials, OPT-80 (formerly known as Difimicin) and ramoplanin; monoclonal antibodies; and a C. difficile vaccine.

Aerial dissemination of Clostridium difficile spores

BACKGROUND

Clostridium difficile-associated diarrhoea (CDAD) is a frequently occurring healthcare-associated infection, which is responsible for significant morbidity and mortality amongst elderly patients in healthcare facilities. Environmental contamination is known to play an important contributory role in the spread of CDAD and it is suspected that contamination might be occurring as a result of aerial dissemination of C. difficile spores. However previous studies have failed to isolate C. difficile from air in hospitals. In an attempt to clarify this issue we undertook a short controlled pilot study in an elderly care ward with the aim of culturing C. difficile from the air.

METHODS

In a survey undertaken during February (two days) 2006 and March (two days) 2007, air samples were collected using a portable cyclone sampler and surface samples collected using contact plates in a UK hospital. Sampling took place in a six bedded elderly care bay (Study) during February 2006 and in March 2007 both the study bay and a four bedded orthopaedic bay (Control). Particulate material from the air was collected in Ringer's solution, alcohol shocked and plated out in triplicate onto Brazier's CCEY agar without egg yolk, but supplemented with 5 mg/L of lysozyme. After incubation, the identity of isolates was confirmed by standard techniques. Ribotyping and REP-PCR fingerprinting were used to further characterise isolates.

RESULTS

On both days in February 2006, C. difficile was cultured from the air with 23 samples yielding the bacterium (mean counts 53 - 426 cfu/m3 of air). One representative isolate from each of these was characterized further. Of the 23 isolates, 22 were ribotype 001 and were indistinguishable on REP-PCR typing. C. difficile was not cultured from the air or surfaces of either hospital bay during the two days in March 2007.

CONCLUSION

This pilot study produced clear evidence of sporadic aerial dissemination of spores of a clone of C. difficile, a finding which may help to explain why CDAD is so persistent within hospitals and difficult to eradicate. Although preliminary, the findings reinforce concerns that current C. difficile control measures may be inadequate and suggest that improved ward ventilation may help to reduce the spread of CDAD in healthcare facilities.

Asymptomatic Carriers Are a Potential Source for Transmission of Epidemic and Nonepidemic Clostridium difficile Strains among Long-Term Care Facility Residents

BACKGROUND

Asymptomatic fecal carriage of Clostridium difficile is common in patients staying in health care facilities, but the importance of asymptomatic carriers with regard to disease transmission is unclear.

METHODS

We prospectively examined the prevalence of asymptomatic carriage of epidemic North American pulsed-field gel electrophoresis type 1 and nonepidemic toxigenic C. difficile strains among long-term care patients in the context of an outbreak of C. difficile-associated disease and evaluated the frequency of skin and environmental contamination. Molecular typing was performed by pulsed-field gel electrophoresis. Logistic regression was used to assess factors associated with asymptomatic carriage, and a sensitive and specific prediction rule was developed to identify high-risk patients.

RESULTS

Thirty-five (51%) of 68 asymptomatic patients were carriers of toxigenic C. difficile, and 13 (37%) of these patients carried epidemic strains. Compared with noncarriers, asymptomatic carriers had higher percentages of skin (61% vs. 19%; P=.001) and environmental contamination (59% vs. 24%; P=.004). Eighty-seven percent of isolates found in skin samples and 58% of isolates found in environmental samples were identical to concurrent isolates found in stool samples. Spores on the skin of asymptomatic patients were easily transferred to investigators' hands. Previous C. difficile-associated disease (P<.001) and previous antibiotic use (P=.017) were associated with asymptomatic carriage, and the combination of these 2 variables was predictive of asymptomatic carriage (sensitivity, 77%; specificity, 58%; positive predictive value, 66%; negative predictive value, 70%).

CONCLUSIONS

Our findings suggest that asymptomatic carriers of epidemic and nonepidemic C. difficile strains have the potential to contribute significantly to disease transmission in long-term care facilities. Clinical factors, such as previous C. difficile-associated disease and recent antibiotic use, may be predictive of asymptomatic carriage.

Vegetative Clostridium difficile survives in room air on moist surfaces and in gastric contents with reduced acidity: a potential mechanism to explain the association between proton pump inhibitors and C. difficile-associated diarrhea?

Proton pump inhibitors (PPIs) have been identified as a risk factor for Clostridium difficile-associated diarrhea (CDAD), though the mechanism is unclear because gastric acid does not kill C. difficile spores. We hypothesized that the vegetative form of C. difficile, which is killed by acid, could contribute to disease pathogenesis if it survives in room air and in gastric contents with elevated pH. We compared the numbers of C. difficile spores and vegetative cells in stools of patients prior to and during the treatment of CDAD. We assessed the survival of vegetative cells on moist or dry surfaces in room air versus anaerobic conditions and in human gastric contents, in pH-adjusted gastric contents, and in gastric contents from individuals receiving PPI therapy. Stool samples obtained from patients prior to the initiation of antibiotic treatment for C. difficile contained approximately 10-fold more vegetative cells than spores. On dry surfaces, vegetative C. difficile cells died rapidly, whereas they remained viable for up to 6 h on moist surfaces in room air. Vegetative C. difficile cells had only marginal survival in gastric contents at low pH; adjustment to a pH of >5 resulted in survival similar to that in the phosphate-buffered saline control. The survival of vegetative C. difficile in gastric contents obtained from patients receiving PPIs was also increased at a pH of >5. The ability of the vegetative form of C. difficile to survive on moist surfaces and in gastric contents with an elevated pH suggests a potential mechanism by which PPI therapy could increase the risk of acquiring C. difficile.

Prevalence of Clostridium difficile environmental contamination and strain variability in multiple health care facilities

BACKGROUND

Clostridium difficile spores can contaminate the hospital environment. Little is known about the prevalence and strain variability of C. difficile environmental contamination in health care facilities. The objective of this study was to assess C. difficile environmental contamination at various health care facilities in a metropolitan area and determine if the North American pulsed field gel electrophoresis type 1 (NAP1) strain was present.

METHODS

A cross-sectional pilot survey was conducted. Forty-eight environmental samples were collected from six health care facilities. Samples were cultured for the presence of C. difficile, and positive samples underwent pulsed field gel electrophoresis, toxinotyping, and detection of binary toxin and/or tcdC deletion.

RESULTS

C. difficile was cultured from 13 of 48 (27%) samples. Rooms housing a patient with C. difficile-associated disease (CDAD) were more likely to be culture positive than non-CDAD patient rooms (100% vs. 33%; P < 0.01); C. difficile was not isolated outside of patient rooms (0 of 12 samples). The NAP1 epidemic strain was found in 5 out of 6 facilities.

CONCLUSION

C. difficile spores frequently contaminated the hospital environment. Rooms with a CDAD patient were more likely to be contaminated than rooms without a CDAD patient. The NAP1 strain was prevalent throughout the metropolitan area.

Evaluation of real-time PCR and conventional diagnostic methods for the detection of Clostridium difficile-associated diarrhoea in a prospective multicentre study

In this prospective multicentre study, an enzyme-linked fluorescent assay (VIDAS CDA2; bioMérieux), an enzyme-linked assay [Premier Toxins A and B (PTAB); Meridian] and an in-house real-time PCR amplifying the tcdB gene were compared with the cell cytotoxicity assay used as the ‘gold standard’ for diagnosis of Clostridium difficile-associated diarrhoea (CDAD). Faecal samples from patients with a request for C. difficile diagnosis and samples from patients with diarrhoea hospitalized for at least 72 h were collected for 3 consecutive months from four university medical centres in The Netherlands. In total, 547 faecal samples were obtained from 450 patients. Of 540 samples available for all of the assays, 84 (15.6 %) showed a positive result in one or more assays. The cell cytotoxicity assay was positive in 31 samples (5.7 %) from 28 patients. A diagnosis of CDAD was not considered by the physician in 5 (23.8 %) of 21 patients with CDAD who were hospitalized for at least 72 h. Compared with the cell cytotoxicity assay, the sensitivity of VIDAS, PTAB and PCR was 83.9, 96.8 and 87.1 %, respectively. The specificity of VIDAS, PTAB and PCR was 97.1, 94.3 and 96.5 %, respectively. The positive and negative predictive values for VIDAS, PTAB and PCR were 63.4 and 99.0 %, 50.9 and 99.8 %, and 60.0 and 99.2 %, respectively. Of 61 samples that were positive in one, two or three of the assays, 56 were available for discordance analysis. Discordance analysis was performed by culture of toxinogenic strains. The concordance of VIDAS, PTAB and PCR with culture was 53.6 % (30/56), 55.4 % (31/56) and 71.4 % (40/56), respectively. It was concluded that real-time PCR had the highest concordance with toxinogenic culture and is therefore the preferred method for diagnosing CDAD in faecal samples. It was also concluded that diagnosis of patients with diarrhoea who have been hospitalized for more than 72 h should focus mainly on the detection of C. difficile, irrespective of the physician's request.

Comparative analysis of prevalence, risk factors, and molecular epidemiology of antibiotic-associated diarrhea due to Clostridium difficile, Clostridium perfringens, and Staphylococcus aureus

We prospectively studied the comparative epidemiology and risk factors for Clostridium difficile, Clostridium perfringens, and Staphylococcus aureus antibiotic-associated diarrhea (AAD). Four thousand six hundred fifty-nine inpatient fecal specimens (11 months) were tested for C. difficile cytotoxin, C. perfringens enterotoxin, and S. aureus by Vero cell assay, enzyme-linked immunosorbent assay, and growth on fresh blood agar, respectively. Two distinct age-, sex-, and location-matched control patient groups were used for multivariate logistic regression risk factor analyses: symptomatic patients who were AAD pathogen negative and asymptomatic patients with histories of recent antimicrobial therapy. All AAD pathogen isolates were DNA fingerprinted. In AAD cases, the prevalences of C. difficile cytotoxin, C. perfringens enterotoxin, and S. aureus were 12.7%, 3.3%, and 0.2%, respectively (15.8% overall). Age of >70 years was a common risk factor. Other risk factors for infective AAD and C. difficile AAD included length of hospital stay and use of feeding tubes (length of stay odds ratios [OR], 1.017 and 1.012; feeding tube OR, 1.864 and 2.808). Female gender and use of antacids were significantly associated with increased risk of C. perfringens AAD (OR, 2.08 and 2.789, respectively), but unlike what was found for C. difficile AAD, specific antibiotic classes were not associated with increased risk. A limited number of genotypes caused the majority of C. difficile and C. perfringens AAD cases. Similar to what was found for C. difficile AAD, there was epidemiological evidence of C. perfringens AAD case clustering and reinfection due to different strains. C. difficile AAD was approximately 4 and 60 times more common than C. perfringens AAD and S. aureus AAD, respectively. Risk factors for these AAD pathogens differed, highlighting the need to define specific control measures. There is evidence of nosocomial transmission in cases of C. perfringens AAD.

Increased rate of DNA recovery from United Kingdom epidemic Clostridium difficile PCR ribotype 1 strains stored cryogenically

We noted that some Clostridium difficile isolates are nonrecoverable after frozen storage and so used molecular typing analysis to characterize DNA from these strains. The recovery rate of C. difficile PCR ribotype 1 was statistically significantly greater than that of other strains. This observation has implications for C. difficile epidemiological studies.

Comparison of the effect of detergent versus hypochlorite cleaning on environmental contamination and incidence of Clostridium difficile infection

To determine how best to decontaminate the hospital environment of Clostridium difficile, we carried out a cross-over study on two elderly medicine wards to determine whether cleaning with a hypochlorite disinfectant was better than using neutral detergent in reducing the incidence of C. difficile infection (CDI). We examined 1128 environmental samples in two years, 35% of which grew C. difficile. There was a significant decrease of CDI incidence on ward X, from 8.9 to 5.3 cases per 100 admissions (P<0.05) using hypochlorite, but there was no significant effect on ward Y. On ward X the incidence of CDI was significantly associated with the proportion of culture-positive environmental sites (P<0.05). On ward Y the only significant correlation between CDI and C. difficile culture-positive environmental sites was in patient side-rooms (r=0.41, P<0.05). The total daily defined doses of cefotaxime, cephradine and aminopenicillins were similar throughout the trial. These results provide some evidence that use of hypochlorite for environmental cleaning may significantly reduce incidence of CDI, but emphasize the potential for confounding factors.

The effects of storage conditions on viability of Clostridium difficile vegetative cells and spores and toxin activity in human faeces

AIMS

Clostridium difficile is a common nosocomial pathogen and as such diagnostic and research methods may necessitate storage of faecal specimens for long periods, followed by subsequent re-examination. This study investigated the effects of storage conditions upon the viability of this organism and its toxin.

METHODS

Three genotypically distinct strains of C difficile (two clinical isolates including the UK epidemic strain, and an environmental isolate) were grown anaerobically at 37 degrees C for 72 hours in a pool of five faecal emulsions. Aliquots of each emulsion were stored at either -20 degrees C (frozen) or 4 degrees C (refrigerated). Emulsions were assayed for viable cells, spores, and cytotoxin titre before storage and at days 1, 3, 5, 7, 14, 28, and 56. An aliquot of each emulsion was also removed, assayed, and replaced in storage at each time point to investigate the effects of multiple freezing/refrigeration/thawing.

RESULTS

Neither storage temperature nor multiple cycles of refrigeration/freezing and thawing adversely affected the viability of C difficile vegetative cells or spores. Single and multiple exposures of samples to 4 degrees C had little effect upon the C difficile toxin titre. Toxin titres of multiply frozen and thawed faeces became significantly lower than for refrigerated faeces (p < 0.01) by day 5 of the experiment in two of the three strains, and in all strains by day 28. Toxin titres of singly frozen faeces became significantly lower than for refrigerated faeces (p < 0.01) by day 56 of the experiment in two of the three strains.

CONCLUSION

Storage temperature and multiple cycles of freezing (refrigeration)/thawing had minimal effects upon the viability of C difficile or its spores. Storage at 4 degrees C has no discernible effect on C difficile cytotoxin. However, storage at -20 degrees C has a detrimental effect upon C difficile cytotoxin, and multiple cycles of freezing and thawing may further adversely effect toxin titres.