Selective and differential medium for isolation of Clostridium difficile

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.

Optimizing the Laboratory Diagnosis of Clostridium difficile Infection

The best laboratory diagnostic approach to detect Clostridium difficile infection (CDI) is the subject of ongoing debate. In the United States, nucleic acid amplification tests (NAAT) have become the most widely used tests for making this diagnosis. Detection of toxin in stool may be a better predictor of CDI disease and severity. Laboratories that have switched from toxin-based to NAAT-based methods have significantly higher CDI detection rates. The important issue is whether all NAAT-positive patients have CDI or at least some of those patients are excretors of the organism and do not have clinical disease.

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.

Antimicrobial effects of virgin coconut oil and its medium-chain fatty acids on Clostridium difficile

Clostridium difficile is the leading cause of hospital-acquired antibiotic-associated diarrhea worldwide; in addition, the proliferation of antibiotic-resistant C. difficile is becoming a significant problem. Virgin coconut oil (VCO) has been shown previously to have the antimicrobial activity. This study evaluates the lipid components of VCO for the control of C. difficile. VCO and its most active individual fatty acids were tested to evaluate their antimicrobial effect on C. difficile in vitro. The data indicate that exposure to lauric acid (C12) was the most inhibitory to growth (P<.001), as determined by a reduction in colony-forming units per milliliter. Capric acid (C10) and caprylic acid (C8) were inhibitory to growth, but to a lesser degree. VCO did not inhibit the growth of C. difficile; however, growth was inhibited when bacterial cells were exposed to 0.15-1.2% lipolyzed coconut oil. Transmission electron microscopy (TEM) showed the disruption of both the cell membrane and the cytoplasm of cells exposed to 2 mg/mL of lauric acid. Changes in bacterial cell membrane integrity were additionally confirmed for VCO and select fatty acids using Live/Dead staining. This study demonstrates the growth inhibition of C. difficile mediated by medium-chain fatty acids derived from VCO.

Conserved oligopeptide permeases modulate sporulation initiation in Clostridium difficile

The anaerobic gastrointestinal pathogen Clostridium difficile must form a metabolically dormant spore to survive in oxygenic environments and be transmitted from host to host. The regulatory factors by which C. difficile initiates and controls the early stages of sporulation in C. difficile are not highly conserved in other Clostridium or Bacillus species. Here, we investigated the role of two conserved oligopeptide permeases, Opp and App, in the regulation of sporulation in C. difficile. These permeases are known to positively affect sporulation in Bacillus species through the import of sporulation-specific quorum-sensing peptides. In contrast to other spore-forming bacteria, we discovered that inactivating these permeases in C. difficile resulted in the earlier expression of early sporulation genes and increased sporulation in vitro. Furthermore, disruption of opp and app resulted in greater virulence and increased the amounts of spores recovered from feces in the hamster model of C. difficile infection. Our data suggest that Opp and App indirectly inhibit sporulation, likely through the activities of the transcriptional regulator SinR and its inhibitor, SinI. Taken together, these results indicate that the Opp and App transporters serve a different function in controlling sporulation and virulence in C. difficile than in Bacillus subtilis and suggest that nutrient availability plays a significant role in pathogenesis and sporulation in vivo. This study suggests a link between the nutritional status of the environment and sporulation initiation in C. difficile.

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.

A systematic review for pursuing the presence of antibiotic associated enterocolitis caused by methicillin resistant Staphylococcus aureus

BACKGROUND

Although it has received a degree of notoriety as a cause for antibiotic-associated enterocolitis (AAE), the role of methicillin resistant Staphylococcus aureus (MRSA) in the pathogenesis of this disease remains enigmatic despite a multitude of efforts, and previous studies have failed to conclude whether MRSA can cause AAE. Numerous cases of AAE caused by MRSA have been reported from Japan; however, due to the fact that these reports were written in the Japanese language and a good portion lacked scientific rigor, many of these reports went unnoticed.

METHODS

We conducted a systematic review of pertinent literatures to verify the existence of AAE caused by MRSA. We modified and applied methods in common use today and used a total of 9 criteria to prove the existence of AAE caused by Klebsiella oxytoca. MEDLINE/Pubmed, Excerpta Medica Database (EMBASE), the Cochrane Database of Systematic Reviews, and the Japan Medical Abstract Society database were searched for studies published prior to March 2013.

RESULTS

A total of 1,999 articles were retrieved for evaluation. Forty-five case reports/series and 9 basic studies were reviewed in detail. We successfully identified articles reporting AAE with pathological and microscopic findings supporting MRSA as the etiological agent. We also found comparative studies involving the use of healthy subjects, and studies detecting probable toxins. In addition, we found animal models in which enteritis was induced by introducing MRSA from patients. Although we were unable to identify a single study that encompasses all of the defined criteria, we were able to fulfill all 9 elements of the criteria by collectively analyzing multiple studies.

CONCLUSIONS

AAE caused by MRSA-although likely to be rarer than previous Japanese literatures have suggested-most likely does exist.

Premarket evaluations of the IMDx C. difficile for Abbott m2000 Assay and the BD Max Cdiff Assay

Clostridium difficile-associated diarrhea is a well-recognized complication of antibiotic use. Historically, diagnosing C. difficile has been difficult, as antigen assays are insensitive and culture-based methods require several days to yield results. Nucleic acid amplification tests (NAATs) are quickly becoming the standard of care. We compared the performance of two automated investigational/research use only (IUO/RUO) NAATs for the detection of C. difficile toxin genes, the IMDx C. difficile for Abbott m2000 Assay (IMDx) and the BD Max Cdiff Assay (Max). A prospective analysis of 111 stool specimens received in the laboratory for C. difficile testing by the laboratory's test of record (TOR), the BD GeneOhm Cdiff Assay, and a retrospective analysis of 88 specimens previously determined to be positive for C. difficile were included in the study. One prospective specimen was excluded due to loss to follow-up discrepancy analysis. Of the remaining 198 specimens, 90 were positive by all three methods, 9 were positive by TOR and Max, and 3 were positive by TOR only. One negative specimen was initially inhibitory by Max. The remaining 95 specimens were negative by all methods. Toxigenic C. difficile culture was performed on the 12 discrepant samples. True C. difficile-positive status was defined as either positive by all three amplification assays or positive by toxigenic culture. Based on this definition, the sensitivity and specificity were 96.9% and 95% for Max and 92.8% and 100% for IMDx. In summary, both highly automated systems demonstrated excellent performance, and each has individual benefits, which will ensure that they will both have a niche in clinical laboratories.

Spore formation and toxin production in Clostridium difficile biofilms

The ability to grow as a biofilm can facilitate survival of bacteria in the environment and promote infection. To better characterize biofilm formation in the pathogen Clostridium difficile, we established a colony biofilm culture method for this organism on a polycarbonate filter, and analyzed the matrix and the cells in biofilms from a variety of clinical isolates over several days of biofilm culture. We found that biofilms readily formed in all strains analyzed, and that spores were abundant within about 6 days. We also found that extracellular DNA (eDNA), polysaccharide and protein was readily detected in the matrix of all strains, including the major toxins A and/or B, in toxigenic strains. All the strains we analyzed formed spores. Apart from strains 630 and VPI10463, which sporulated in the biofilm at relatively low frequencies, the frequencies of biofilm sporulation varied between 46 and 65%, suggesting that variations in sporulation levels among strains is unlikely to be a major factor in variation in the severity of disease. Spores in biofilms also had reduced germination efficiency compared to spores obtained by a conventional sporulation protocol. Transmission electron microscopy revealed that in 3 day-old biofilms, the outermost structure of the spore is a lightly staining coat. However, after 6 days, material that resembles cell debris in the matrix surrounds the spore, and darkly staining granules are closely associated with the spores surface. In 14 day-old biofilms, relatively few spores are surrounded by the apparent cell debris, and the surface-associated granules are present at higher density at the coat surface. Finally, we showed that biofilm cells possess 100-fold greater resistance to the antibiotic metronidazole then do cells cultured in liquid media. Taken together, our data suggest that C. difficile cells and spores in biofilms have specialized properties that may facilitate infection.

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.

Development of a novel method for detection of Clostridium difficile using HS-SPME-GC-MS

AIMS

A novel method has been developed that allows successful differentiation between Clostridium difficile culture-positive and culture-negative stool samples based on volatile organic compound (VOC) evolution and detection by headspace solid-phase microextraction coupled with gas chromatography mass spectrometry (HS-SPME-GC-MS).

METHODS AND RESULTS

The method is based on the activation of p-hydroxyphenylacetate decarboxylase produced by Cl. difficile and the detection of a specific VOC, that is 2-fluoro-4-methylphenol from an enzyme substrate. In addition, other VOCs were good indicators for Cl. difficile, that is isocaproic acid and p-cresol, although they could not be used alone for identification purposes. One hundred stool samples were tested, of which 77 were positive by culture. Detection using HS-SPME-GC-MS allowed confirmation of the presence of Cl. difficile within 18 h with a sensitivity and specificity of 83·1 and 100%, respectively.

CONCLUSIONS

It is recommended that this new approach could be used alongside conventional methods for Cl. difficile detection, including toxin detection methods, which would allow any false-negative results to be eliminated.

SIGNIFICANCE AND IMPACT OF THE STUDY

The ability to identify Cl. difficile-positive stool samples by the analysis of VOCs could allow the development of a VOC detection device which could allow rapid diagnosis of disease and hence prompt treatment with appropriate antibiotics.

Comparison of ChromID agar and Clostridium difficile selective agar for effective isolation of C. difficile from stool specimens

Background

ChromID Clostridium difficile agar (IDCd; bioMérieux SA, France) is a recently developed chromogenic medium for rapid and specific isolation of C. difficile. We compared the performance of IDCd with that of Clostridium difficile Selective Agar (CDSA).

Methods

A total of 530 fresh stool specimens were collected from patients with clinical signs compatible with C. difficile infection, and cultures for C. difficile were performed on IDCd and CDSA. C. difficile colonies were identified by spore staining, odor, use of an ANI identification test kit (bioMérieux SA), and multiplex PCR for tcdA, tcdB, and tpi.

Results

The concordance rate between IDCd and CDSA was 90.6% (480/530). The positivity rates on IDCd on days 1 and 2 (55.6% and 85.0%, respectively) were significantly higher than those on CDSA (19.4% and 75.6%, respectively) (P<0.001 for day 1 and P=0.02 for day 2), but the detection rates on IDCd and CDSA on day 3 were not different (89.4% vs. 82.8%, P=0.0914). On day 3, the recovery rates for non-C. difficile isolates on IDCd and CDSA were 30.2% (160/530) and 22.1% (117/530), respectively (P=0.0075). Clostridium spp. other than C. difficile were the most prevalent non-C. difficile isolates on both media.

Conclusions

The culture positivity rates on IDCd and CDSA were not different on day 3 but IDCd may allow for rapid and sensitive detection of C. difficile within 2 days of cultivation.

The changing faces of Clostridium difficile: a personal reflection of the past 34 years

Late in 1978 my boss gave me a folder with "Clostridium difficile (diffikilé)" written on it. Inside were a few recent and now classic papers by Bartlett, Larson and co. It was suggested that this might be an interesting research topic. So began a continuing adventure which has resulted in at least 50 publications from my group. Over the years we have made several important contributions to the field. Beginning in 1982 we showed that C. difficile was a common cause of community-acquired infection! During the next few years we did extensive structural studies on the bacterium. This culminated in 1984 with a fingerprinting study (by immunoblotting surface antigens), on Swedish strains supplied by Carl-Erik Nord, which was probably the first study to demonstrate that C. difficile was really an infectious agent. This was later reinforced with strains sent from Amsterdam by Ed Kuijper. Later in the 1980s, in a study of recurrent disease, we showed that ca. 50% of recurrences were due to infection with a different strain. During my term as chair of the European Study Group for C. difficile, we began to define the status of C. difficile infection (CDI) in Europe and develop guidance for diagnosis and treatment. Recently we utilised our extensive culture collection, with isolates from the 1970s to the present, to observe how epidemiology has been driven largely by antibiotic usage. We have now come full circle: in the early years C. difficile infection was caused by many different strains. Then in the period beginning in the 1990s, characterised by often-large outbreaks and poor infection control, disease was caused by a few endemic strains highlighted by the 027/NAP1/BI pandemic. Now in a much-improved local situation, we are seeing again that the majority of cases (largely sporadic) is caused by multiple types. Current studies range from molecular studies on toxin and spore production, immune responses, novel observations on CDI in children, to what is the best way of decontaminating the anaerobe laboratory.

Aptamer biosensor for sensitive detection of toxin A of Clostridium difficile using gold nanoparticles synthesized by Bacillus stearothermophilus

A sensitive electrochemical biosensor was developed to detect toxin A (TOA) of Clostridium difficile based on an aptamer selected by the systematic evolution of ligands using exponential enrichment and gold nanoparticles (GNPS) synthesized by Bacillus stearothermophilus. The thiolated single-stranded DNA used as the capture probe (CP) was first self-assembled on a Nafion-thionine-GNPS-modified screen-printed electrode (SPE) through an Au-thiol interaction. The horseradish peroxidase (HRP)-labeled aptamer probe (AP) was then hybridized to the complementary oligonucleotide of CP to form an aptamer-DNA duplex. In the absence of TOA, the aptamer-DNA duplex modified the electrode surface with HRP, so that an amperometric response was induced based on the electrocatalytic properties of thionine. This was mediated by the electrons that were generated in the enzymatic reaction of hydrogen peroxide under HRP catalysis. After the specific recognition of TOA, an aptamer-TOA complex was produced rather than the aptamer-DNA duplex, forcing the HRP-labeled AP to dissociate from the electrode surface, which reduced the catalytic capacity of HRP and reduced the response current. The reduction in the response current correlated linearly with the concentration of TOA in the range of 0-200 ng/mL. The detection limit was shown to be 1 nM for TOA. This biosensor was applied to the analysis of TOA and showed good selectivity, reproducibility, stability, and accuracy.

Toxin-producing Clostridium difficile strains as long-term gut colonizers in healthy infants

Clostridium difficile is a colonizer of the human gut, and toxin-producing strains may cause diarrhea if the infectious burden is heavy. Infants are more frequently colonized than adults, but they rarely develop C. difficile disease. It is not known whether strains of C. difficile differ in the capacity to colonize and persist in the human gut microbiota. Here, we strain typed isolates of C. difficile that had colonized 42 healthy infants followed from birth to ≥12 months of age by using PCR ribotyping of the 16S-23S rRNA intergenic spacer region. The isolates were also characterized regarding carriage of the toxin genes tcdA, tcdB, and cdtA/B and the capacity to produce toxin B in vitro. Most strains (71%) were toxin producers, and 51% belonged to the 001 or 014 ribotypes, which often cause disease in adults. These ribotypes were significantly more likely than others to persist for ≥6 months in the infant micobiota, and they were isolated from 13/15 children carrying such long-term-colonizing strains. Ribotype 001 strains were often acquired in the first week of life and attained higher population counts than other C. difficile ribotypes in newborn infants' feces. Several toxin-negative ribotypes were identified, two of which (GI and GIII) were long-term colonizers, each found in one infant. Our results suggest that the toxin-producing C. difficile ribotypes 001 and 014 have special fitness in the infantile gut microbiota. Toxin-producing strains colonizing young children for long time periods may represent a reservoir for strains causing disease in adults.

The spore differentiation pathway in the enteric pathogen Clostridium difficile

Endosporulation is an ancient bacterial developmental program that culminates with the differentiation of a highly resistant endospore. In the model organism Bacillus subtilis, gene expression in the forespore and in the mother cell, the two cells that participate in endospore development, is governed by cell type-specific RNA polymerase sigma subunits. σ(F) in the forespore, and σ(E) in the mother cell control early stages of development and are replaced, at later stages, by σ(G) and σ(K), respectively. Starting with σ(F), the activation of the sigma factors is sequential, requires the preceding factor, and involves cell-cell signaling pathways that operate at key morphological stages. Here, we have studied the function and regulation of the sporulation sigma factors in the intestinal pathogen Clostridium difficile, an obligate anaerobe in which the endospores are central to the infectious cycle. The morphological characterization of mutants for the sporulation sigma factors, in parallel with use of a fluorescence reporter for single cell analysis of gene expression, unraveled important deviations from the B. subtilis paradigm. While the main periods of activity of the sigma factors are conserved, we show that the activity of σ(E) is partially independent of σ(F), that σ(G) activity is not dependent on σ(E), and that the activity of σ(K) does not require σ(G). We also show that σ(K) is not strictly required for heat resistant spore formation. In all, our results indicate reduced temporal segregation between the activities of the early and late sigma factors, and reduced requirement for the σ(F)-to-σ(E), σ(E)-to-σ(G), and σ(G)-to-σ(K) cell-cell signaling pathways. Nevertheless, our results support the view that the top level of the endosporulation network is conserved in evolution, with the sigma factors acting as the key regulators of the pathway, established some 2.5 billion years ago upon its emergence at the base of the Firmicutes Phylum.

Culturing and maintaining Clostridium difficile in an anaerobic environment

Clostridium difficile is a Gram-positive, anaerobic, sporogenic bacterium that is primarily responsible for antibiotic associated diarrhea (AAD) and is a significant nosocomial pathogen. C. difficile is notoriously difficult to isolate and cultivate and is extremely sensitive to even low levels of oxygen in the environment. Here, methods for isolating C. difficile from fecal samples and subsequently culturing C. difficile for preparation of glycerol stocks for long-term storage are presented. Techniques for preparing and enumerating spore stocks in the laboratory for a variety of downstream applications including microscopy and animal studies are also described. These techniques necessitate an anaerobic chamber, which maintains a consistent anaerobic environment to ensure proper conditions for optimal C. difficile growth. We provide protocols for transferring materials in and out of the chamber without causing significant oxygen contamination along with suggestions for regular maintenance required to sustain the appropriate anaerobic environment for efficient and consistent C. difficile cultivation.

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.

Epidemiology, diagnosis and treatment of Clostridium difficile infection

Clostridium difficile infection (CDI) is considered to be the main cause of bacterial infectious diarrhea in nosocomial settings. Since the beginning of the new century a continuous rise in the incidence of severe CDI has been observed worldwide. Even though some CDI cases are not associated with previous antibiotic exposure, this remains as the principal risk factor for the development of CDI. The rate of recurrences represents perhaps one the most challenging aspect on the management of CDI. There are several microbiological tests available, but glutamate dehydrogenase antigen test can be selected as the first screening step in a diagnostic algorithm, with positive samples then confirmed using a toxin(s) test, to distinguish toxinogenic from nontoxinogenic CDI. Although metronidazole and vancomycin are and have been the mainstay treatment options for CDI, there are some unmet medical and therapeutical needs. Usually oral metronidazole is recommended for initial treatment of nonsevere CDI and vancomycin for treatment of severe disease. Fidaxomicin may be considered in patients who cannot tolerate vancomycin, although more data are needed. For treatment of a nonsevere initial recurrence of CDI, oral metronidazole should be used, but for treatment of subsequent recurrences or more severe cases fidaxomicin may be helpful.

Isolation of Clostridium difficile from faecal specimens--a comparison of chromID C. difficile agar and cycloserine-cefoxitin-fructose agar

The culture of toxigenic Clostridium difficile from stool specimens is still seen as the gold standard for the laboratory diagnosis of C. difficile infection (CDI). bioMérieux have released ChromID Cdiff chromogenic agar (CDIF) for the isolation and identification of C. difficile in 24 h. In this study, we compared CDIF to pre-reduced cycloserine-cefoxitin-fructose agar with sodium taurocholate (TCCFA) in the examination of glutamate dehydrogenase-positive faecal specimens that were either GeneOhm positive or negative, using direct culture or culture following alcohol shock. Direct culture on CDIF had a sensitivity of 100 % and recovery of 94 % while for TCCFA these were 87 % and 82 %, respectively. For GeneOhm-positive alcohol-shocked faecal samples, sensitivity and recovery on CDIF was similar to direct culture while on TCCFA they were about 10 % higher. For direct culture, there was a significant difference between growth on CDIF at 24 h and TCCFA at 48 h (P = 0.001) and between the two media at 48 h (P<0.001). A total of 142 strains of C. difficile were recovered in pure culture from all GeneOhm-positive samples used in this study and 11 (7.7 %) of these were A(-)B(-)CDT(-) and may represent mixed infections of toxigenic and non-toxigenic C. difficile. The most dominant ribotype was UK 014 (14.7 %) followed by 002 (11.9 %) and 020 (11.9 %), and 36 % of toxigenic isolates, including an A(-)B(+)CDT(-) strain, could not be assigned a UK ribotype. CDIF outperformed pre-reduced TCCFA by negating the need for alcohol shock treatment and by giving a time saving of 24 h in the isolation of C. difficile. CDIF plates were also more selective than TCCFA and C. difficile colonies were easy to identify and subculture prior to strain typing.

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.

Improved recovery of Clostridium difficile spores with the incorporation of synthetic taurocholate in cycloserine-cefoxitin-fructose agar (CCFA)

AIM

Culture remains important for the detection and typing of Clostridium difficile. Culture of C. difficile spores can be enhanced on media supplemented with a germinant. Despite this, unsupplemented media continues to be used in some laboratories. The aim of this study was to quantify the effect of the known germinant sodium taurocholate on recovery of C. difficile spores and to determine if the supplement impacts on the recovery of vegetative C. difficile.

METHODS

The recovery on cycloserine-cefoxitin-fructose agar (CCFA) with and without taurocholate, of spore, vegetative, and total cell fractions of broth cultures of eight C. difficile isolates was compared.

RESULTS

Taurocholate in CCFA did not inhibit growth of vegetative C. difficile and significantly increased recovery of spores (p = 0.04).

CONCLUSIONS

The routine incorporation of taurocholate in CCFA is recommended for improved sensitivity in C. difficile culture from specimens.

Comparison of culture, cytotoxin assay and two EIA tests with clinical diagnosis of Clostridium difficile-associated diarrhea

OBJECTIVE

The most common etiology of infectious diarrhea in hospitalized patients is Clostridium difficile. No single laboratory test yields a definitive diagnosis. Four methods were evaluated for their sensitivity and specificity in patients who had clinically defined C difficile-associated diarrhea.

METHODS

Clinical criteria for C difficile-associated diarrhea were defined. All adult in-hospital patients whose stools were tested for C difficile were prospectively followed. Stools were examined with culture on a selective medium, a commercial cytotoxicity assay (cta), and two commercially available enzyme immunoassays (eias) for toxin A (Meridian) and toxin AB (cbc).

RESULTS

During the study period 235 stool specimens from 185 patients were tested. Fifty-one patients were positive for C difficile or its markers, cta was most sensitive (80%), whereas cbc-eia was most specific (98%). Differences in the sensitivities of cta and Meridian-eia were minor (80% versus 73.3%) and they were equally specific (95.5%).

CONCLUSIONS

The sensitivity and specificity of eia for toxin A is similar to other tests. However, due to rapidity and ease of performance, it may be a more practical test for the diagnosis of C difficile-associated diarrhea, especially if the cytotoxin assay is not available.

Community-associated Clostridium difficile infections, Monroe County, New York, USA

Judicious use of antimicrobial drugs will reduce infections.

Evaluation of novel assays to assess the influence of different iron sources on the growth of Clostridium difficile

The ability of four Clostridium difficile strains to utilize various exogenous organic and inorganic iron sources for growth under iron-depleted (250 μM DPP) and iron-limited (75 μM DPP) conditions was analyzed in liquid broth cultures grown in tubes and in microtiter plates, and data compared with results from a bioassay developed on solid media. The growth profile of C. difficile varied depending on the iron source and availability. Addition of FeSO(4), FeCl(3), Fe citrate and ferritin allowed growth in an iron-depleted environment whereas glycoproteins (iron-saturated and low-iron lactoferrin, apo- and holo-transferrin) and heme proteins (hemoglobin, hematin and hemin) did not. All iron sources, except lactoferrin, were able to restore bacterial growth under iron-limited conditions to varying extents. The results demonstrated that the broth microtiter assay developed here was reproducible, reliable and convenient for high-throughput analysis of the growth of C. difficile compared to alternative traditional methods.

Biology of Clostridium difficile: implications for epidemiology and diagnosis

Clostridium difficile is an anaerobic, spore-forming, gram-positive rod that causes a spectrum of antibiotic-associated colitis through the elaboration of two large clostridial toxins and other virulence factors. Since its discovery in 1978 as the agent responsible for pseudomembranous colitis, the organism has continued to evolve into an adaptable, aggressive, hypervirulent strain. Advances in molecular methods and improved animal models have facilitated an understanding of how this organism survives in the environment, adapts to the gastrointestinal tract of animals and humans, and accomplishes its unique pathogenesis. The advances in microbiology have been accompanied by some important clinical observations including increased rates of C. difficile infection, increased virulence, and multiple outbreaks. The major new risk is fluoroquinolone use; there is also an association with proton pump inhibitors and increased recognition of cases in outpatients, pediatric patients, and patients without recent antibiotic use. The combination of more aggressive strains with mobile genomes in a setting of an expanded pool of individuals at risk has refocused attention on and challenged assumptions regarding diagnostic gold standards. Future research is likely to build upon the advancements in phylogenetics to create novel strategies for diagnosis, treatment, and prevention.

Changing incidence and clinical manifestations of Clostridium difficile-associated diarrhea detected by combination of glutamate dehydrogenase and toxin assay in Northern Taiwan

BACKGROUND/PURPOSE

The incidence of Clostridium difficile-associated diarrhea (CDAD) is increasing worldwide. Spread of an epidemic hypervirulent strain in southern Taiwan was associated with poor outcome. This prospective study evaluates the incidence and clinical manifestation of CDAD following a hospital-wide hand hygiene promotion program in a 2,200-bed teaching hospital in northern Taiwan.

PATIENTS AND METHODS

From June 1, 2010 to October 31, 2010, a predefined protocol was used to actively survey CDAD at 11 high-risk units. Stool samples of patients with antibiotic-associated diarrhea (AAD) were submitted for stool culture and toxin A/B assay using a combined enzyme immunoassay. CDAD was diagnosed by a positive toxin assay.

RESULTS

The incidence of CDAD was 0.45/1000 patient-days and was highest in medical intensive care units (7.9/1000 patient-days), followed by hemato-oncology wards, and infectious disease wards. Occurrence of CDAD was associated with ≥3 stool pus cells per high power field (p = 0.018), prior use of metronidazole (p = 0.029), high usage of beta-lactamase stable penicillins (p = 0.046), and anaerobe-active antibiotics (p = 0.029). No attributable mortality was found. The incidence of CDAD was lower than that previously observed (1.0/1000 patient-days in 2003, p < 0.001).

CONCLUSION

This study showed a lower incidence of CDAD and absence of attributable mortality. The impact of hand hygiene promotion and other infection control measures on decreasing incidence of CDAD warrants further elucidation.

Novel one-step method for detection and isolation of active-toxin-producing Clostridium difficile strains directly from stool samples

The alarming emergence of hypervirulent strains of Clostridium difficile with increased toxin production, severity of disease, morbidity, and mortality emphasizes the need for a culture method that permits simultaneous isolation and detection of virulent strains. The C. difficile toxins A and B are critical virulence factors, and strains can either be toxin-producing (virulent) or non-toxin-producing (nonvirulent). Strains that are isolated from human infections generally produce either toxin A or toxin B or both. The methods currently available for culturing C. difficile do not differentiate strains that produce active toxins from strains that do not produce toxins or produce inactive toxins. As a result, the identification and isolation of toxin-producing strains from stool is currently a two-step process. First, the stool is plated on a selective medium, and then suspected colonies are analyzed for toxin production or the presence of the toxin genes. We describe here a novel selective and differential culture method, the Cdifftox plate assay, which combines in a single step the specific isolation of C. difficile strains and the detection of active toxin. This assay was developed based on our recent finding that the A and B toxins of C. difficile cleave chromogenic substrates that have stereochemical characteristics similar to their natural substrate, UDP-glucose. The Cdifftox plate assay is shown here to be extremely accurate (99.8% effective) in detecting toxin-producing strains through the analysis of 528 C. difficile isolates selected from 50 tissue culture cytotoxicity assay-positive clinical stool samples. The Cdifftox plate assay advances and improves the culture approach such that only C. difficile strains will grow on this agar, and virulent strains producing active toxins can be differentiated from nonvirulent strains, which do not produce active toxins. This new method reduces the time and effort required to isolate and confirm toxin-producing C. difficile strains.

Effective utilization of evolving methods for the laboratory diagnosis of Clostridium difficile infection

Physicians should understand the performance characteristics of evolving laboratory tests used to diagnose Clostridium difficile infection if they are to correctly integrate test results with clinical information and formulate an appropriate therapeutic intervention for patients with antibiotic-associated diarrhea.

Laboratory diagnosis of Clostridium difficile infection can molecular amplification methods move us out of uncertainty?

The laboratory diagnosis of Clostridium difficile infection (CDI) continues to be challenging. Recent guidelines from professional societies in the United States note that enzyme immunoassays for toxins A and B do not have adequate sensitivity to be used alone for detecting CDI, yet the optimal method for diagnosing this infection remains unclear. Nucleic acid amplification tests (NAATs) that target chromosomal toxin genes (usually the toxin B gene, tcdB) show high sensitivity and specificity, provide rapid results, and are amenable to both batch and on-demand testing, but these tests were not universally recommended for routine use in the recent guidelines. Rather, two-step algorithms that use glutamate dehydrogenase (GDH) assays to screen for C. difficile in stool specimens, followed by either direct cytotoxin testing or culture to identify toxin-producing C. difficile isolates, were recommended in one guideline and either GDH algorithms or NAATs were recommended in another guideline. Unfortunately, neither culture nor direct cytotoxin testing is widely available. In addition, this two-step approach requires 48 to 92 hours to complete, which may delay the initiation of therapy and critical infection control measures. Recent studies also show the sensitivity of several GDH assays to be <90%. This review considers the role of NAATs for diagnosing CDI and explores their potential advantages over two-step algorithms, including shorter time to results, while providing comparable, if not superior, accuracy.

Clostridium difficile infection: a comprehensive review

Clostridium difficile is one of the most important causes of healthcare acquired diarrhea. The disease spectrum caused by C. difficile infection ranges from mild, self-limited, illness to a severe, life-threatening colitis. The incidence of C. difficile associated disease has risen dramatically over the last decade, leading to increased research interest aiming at the discovery of new virulence factors and the development of new treatment and prevention regimens. This review summarizes the pathogenesis and changing epidemiology of C. difficile associated disease, the clinical spectrum and laboratory methods to diagnose C. difficile infection, and current treatment strategies.

The Attachment, Internalization, and Time-Dependent, Intracellular Distribution of Clostridium difficile Toxin A in Porcine Intestinal Explants

Toxin A (TcdA), secreted by toxigenic strains of Clostridium difficile, produces lesions typical of C. difficile–associated disease (CDAD) in susceptible mammal species. Porcine colon explants maintained for 2 hours with TcdA developed severe lesions characterized by cell swelling, swelling of mitochondria and other organelles, distension of cytoplasmic vesicles, expansion of paracellular spaces, apoptosis, and necrosis. Severity of lesions was proportional to the dosage of toxin. No lesions were present in uninoculated control tissues after 2 hours. Receptor-mediated endocytosis is the keystone event in the pathogenesis of the toxin, and susceptibility of a given species is thought to depend on the presence of receptors in intestinal epithelial cells. The fate of TcdA applied to viable colon explants was determined by transmission electron microscopy in an anti-toxin-labeled gold assay. At 5 minutes postinoculation, the presence of TcdA was indicated at the membrane of microvilli or in the cytoplasm of epithelial cells. TcdA was also indirectly observed within endosomes or attached at their margin. A 30-minute inoculation period was associated with many more gold particles labeling structures inside the cell, although some were still attached to microvilli. Within the cell, most TcdA was associated with mitochondria of epithelial cells, but some gold particles decorated the nuclei. Endothelial cells of the lamina propria had evidence of TcdA at both their lumenal and basal aspects, as well as in the cytoplasm and, occasionally, nuclei. Gold particles also labeled the lumen of such vessels as well as leucocytes in blood vessels and the lamina propria.

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.

Two-step glutamate dehydrogenase antigen real-time polymerase chain reaction assay for detection of toxigenic Clostridium difficile

Current diagnosis of Clostridium difficile infection (CDI) relies upon detection of toxins A/B in stool by enzyme immunoassay [EIA(A/B)]. This strategy is unsatisfactory because it has a low sensitivity resulting in significant false negatives. We investigated the performance of a two-step algorithm for diagnosis of CDI using detection of glutamate dehydrogenase (GDH). GDH-positive samples were tested for C. difficile toxin B gene (tcdB) by polymerase chain reaction (PCR). The performance of the two-step protocol was compared with toxin detection by the Meridian Premier EIA kit in 500 consecutive stool samples from patients with suspected CDI. The reference standard among samples that were positive by either EIA(A/B) or GDH testing was culture cytotoxin neutralisation (culture/CTN). Thirty-six (7%) of 500 samples were identified as true positives by culture/CTN. EIA(A/B) identified 14 of the positive specimens with 22 false negatives and two false positives. The two-step protocol identified 34 of the positive samples with two false positives and two false negatives. EIA(A/B) had a sensitivity of 39%, specificity of 99%, positive predictive value of 88% and negative predictive value of 95%. The two-step algorithm performed better, with corresponding values of 94%, 99%, 94% and 99% respectively. Screening for GDH before confirmation of positives by PCR is cheaper than screening all specimens by PCR and is an effective method for routine use. Current EIA(A/B) tests for CDI are of inadequate sensitivity and should be replaced; however, this may result in apparent changes in CDI rates that would need to be explained in national surveillance statistics.

[Comparison of three Clostridium difficile culture media: interest of enhancing spore germination media?]

AIM

Clostridium difficile is the most common agent of postantibiotic and nosocomial bacterial diarrhoea. Since the emergence of the highly virulent and epidemic strain NAP1/027 in Europe, it appears necessary to isolate C. difficile strains to realize an epidemiologic follow-up by molecular typing. The aim of this work was to compare three selective culture conditions for the isolation of C. difficile.

METHODS

One hundred and thirty stools collected from patients hospitalized at Jean Verdier were swabbed on the commercial medium CLO (BioMérieux) and on a medium prepared at the laboratory (CCTa: Columbia, cefoxitine 8 mg/l, cycloserine 250 mg/l, horse blood 5 %, sodium taurocholate 0.1 %) with and without preliminary alcoholic shock (EtOH). C. difficile was isolated from 38 stools and colonies were counted on each medium.

RESULTS

The fluorescence intensity of C. difficile colonies is comparable on CLO and CCTa-EtOH media, however their aspect is more characteristic on CLO. This medium appears very selective contrary to the CCTa medium on which an associated flora obstructs the fluorescence reading and requires a new isolation of the suspect strains. On average 30 times more colonies of C. difficile are counted on CCTa+/-EtOH than on CLO, suggesting the presence of great proportions of spores in the stools.

CONCLUSIONS

The medium CLO is successful for the isolation of C. difficile despite of its selectivity. Nevertheless, it appears interesting to associate a medium enhancing spore germination as the CCTa medium inoculated after alcoholic shock to increase the sensitivity of detection while being freed from conservation and transport conditions.

Clostridium difficile 30 years on: what has, or has not, changed and why?

The report of clindamycin-associated colitis in 1974 by Tedesco et al. [Ann Intern Med 81: 429-33] stimulated an intense search for the cause of this severe complication of antibiotic use. The search culminated in early 1978 in the publication of a series of papers within 3 months that identified the causative agent as Clostridium difficile and its accompanying toxins. Thirty years later we are in the midst of a resurgence of C. difficile infection (CDI) in North America and Europe that is greater than ever previously reported and for which morbidity and mortality appear to be higher than ever seen in the past. The purpose of this review is to highlight the discoveries of the past 30 years that, in my view, have brought us to our current level of understanding of the pathogenesis, prevention and treatment of CDI, and to suggest why a disease thought to be managed so well 30 years ago could now be causing more morbidity and mortality than ever before. In the 21st century the focus should be on better understanding the relationship between the C. difficile organism and the host at the mucosal level, so that biotherapeutic and vaccine strategies for the prevention of CDI can be developed.