Comparison of serogrouping and polyacrylamide gel electrophoresis for typing Clostridium difficile

A Mouse Model of Mild Clostridioides difficile Infection for the Characterization of Natural Immune Responses

(1) Background: We describe a model of primary mild-Clostridioides difficile infection (CDI) in a naïve host, including gut microbiota analysis, weight loss, mortality, length of colonization. This model was used in order to describe the kinetics of humoral (IgG, IgM) and mucosal (IgA) immune responses against toxins (TcdA/TcdB) and surface proteins (SlpA/FliC). (2) Methods: A total of 105 CFU vegetative forms of C. difficile 630Δerm were used for challenge by oral administration after dysbiosis, induced by a cocktail of antibiotics. Gut microbiota dysbiosis was confirmed and described by 16S rDNA sequencing. We sacrificed C57Bl/6 mice after different stages of infection (day 6, 2, 7, 14, 21, 28, and 56) to evaluate IgM, IgG against TcdA, TcdB, SlpA, FliC in blood samples, and IgA in the cecal contents collected. (3) Results: In our model, we observed a reproducible gut microbiota dysbiosis, allowing for C. difficile digestive colonization. CDI was objectivized by a mean weight loss of 13.1% and associated with a low mortality rate of 15.7% of mice. We observed an increase in IgM anti-toxins as early as D7 after challenge. IgG increased since D21, and IgA anti-toxins were secreted in cecal contents. Unexpectedly, neither anti-SlpA nor anti-FliC IgG or IgA were observed in our model. (4) Conclusions: In our model, we induced a gut microbiota dysbiosis, allowing a mild CDI to spontaneously resolve, with a digestive clearance observed since D14. After this primary CDI, we can study the development of specific immune responses in blood and cecal contents.

Management of an Outbreak ofClostridium difficile–Associated Disease Among Geriatric Patients

Objective.

To describe a nosocomial outbreak ofClostridium difficile–associated disease (CDAD).

Design.

A traditional outbreak investigation.

Setting.

Geriatric department of a tertiary care teaching hospital from March through April 2003.

Methods.

The outbreak was detected by theC. difficilesurveillance program of the infection control unit. CDAD was diagnosed by stool culture and fecal toxin A detection with a qualitative rapid immunoassay. Isolates ofC difficilewere serotyped and genotyped using pulsed-field gel electrophoresis.

Results.

The incidence of CDAD increased from 27 cases per 100,000 patient-days in the 6-month period before the outbreak to 99 cases per 100,000 patient-days during the outbreak. This outbreak involved 21 of 92 patients in 4 geriatric wards, which were located at 2 geographically distinct sites and staffed by the same medical team. The mean age of patients was 83 years (range, 71-100 years). Five (24%) of the 21 patients had community-acquired diarrhea, and secondary hospital transmission resulted in 3 clusters involving 16 patients. Serotyping and genotyping were performed on isolates in stool specimens from 19 different patients; 16 of these isolates were serotype A1, whereas 3 displayed profiles different from the outbreak strain. Management of this outbreak consisted in reinforcement of contact isolation precautions for patients with diarrhea, cohorting of infected patients in the same ward, and promotion of hand hygiene. Relapses occurred in 6 (29%) of 21 patients.

Conclusion.

Control of this rapidly developing outbreak of CDAD was obtained with early implementation of cohorting and ward closure and reinforcement of environmental disinfection, hand hygiene, and enteric isolation precautions.

Reprint of New opportunities for improved ribotyping of C. difficile clinical isolates by exploring their genomes

Clostridium difficile causes outbreaks of infectious diarrhoea, most commonly occurring in healthcare institutions. Recently, concern has been raised with reports of C. difficile disease in those traditionally thought to be at low risk i.e. community acquired rather than healthcare acquired. This has increased awareness for the need to track outbreaks and PCR-ribotyping has found widespread use to elucidate epidemiologically linked isolates. PCR-ribotyping uses conserved regions of the 16S rRNA gene and 23S rRNA gene as primer binding sites to produce varying PCR products due to the intergenic spacer (ITS1) regions of the multiple operons. With the explosion of whole genome sequence data it became possible to analyse the start of the 23S rRNA gene for a more accurate selection of regions closer to the end of the ITS1. However the following questions must still be asked: (i) Does the chromosomal organisation of the rrn operon vary between C. difficile strains? and (ii) just how conserved are the primer binding regions? Eight published C. difficile genomes have been aligned to produce a detailed database of indels of the ITS1's from the rrn operon sets. An iPad Filemaker Go App has been constructed and named RiboTyping (RT). It contains detail such as sequences, ribotypes, strain numbers, GenBank numbers and genome position numbers. Access to various levels of the database is provided so that details can be printed. There are three main regions of the rrn operon that have been analysed by the database and related to each other by strain, ribotype and operon: (1) 16S gene (2) ITS1 indels (3) 23S gene. This has enabled direct intra- and inter-genomic comparisons at the strain, ribotype and operon (allele) levels in each of the three genomic regions. This is the first time that such an analysis has been done. By using the RT App with search criteria it will be possible to select probe combinations for specific strains/ribotypes/rrn operons for experiments to do with diagnostics, typing and recombination of operons. Many more incomplete C. difficile whole genome sequencing projects are recorded in GenBank as underway and the rrn operon information from these can also be added to the RT App when available. The RT App will help simplify probe selection because of the complexity of the ITS1 in C. difficile even in a single genome and because other allele-specific regions (16S and 23S genes) of variability can be relationally compared to design extra probes to increase sensitivity.

New opportunities for improved ribotyping of C. difficile clinical isolates by exploring their genomes

Clostridium difficile causes outbreaks of infectious diarrhoea, most commonly occurring in healthcare institutions. Recently, concern has been raised with reports of C. difficile disease in those traditionally thought to be at low risk i.e. community acquired rather than healthcare acquired. This has increased awareness for the need to track outbreaks and PCR-ribotyping has found widespread use to elucidate epidemiologically linked isolates. PCR-ribotyping uses conserved regions of the 16S rRNA gene and 23S rRNA gene as primer binding sites to produce varying PCR products due to the intergenic spacer (ITS1) regions of the multiple operons. With the explosion of whole genome sequence data it became possible to analyse the start of the 23S rRNA gene for a more accurate selection of regions closer to the end of the ITS1. However the following questions must still be asked: (i) Does the chromosomal organisation of the rrn operon vary between C. difficile strains? and (ii) just how conserved are the primer binding regions? Eight published C. difficile genomes have been aligned to produce a detailed database of indels of the ITS1's from the rrn operon sets. An iPad Filemaker Go App has been constructed and named RiboTyping (RT). It contains detail such as sequences, ribotypes, strain numbers, GenBank numbers and genome position numbers. Access to various levels of the database is provided so that details can be printed. There are three main regions of the rrn operon that have been analysed by the database and related to each other by strain, ribotype and operon: (1) 16S gene (2) ITS1 indels (3) 23S gene. This has enabled direct intra- and inter-genomic comparisons at the strain, ribotype and operon (allele) levels in each of the three genomic regions. This is the first time that such an analysis has been done. By using the RT App with search criteria it will be possible to select probe combinations for specific strains/ribotypes/rrn operons for experiments to do with diagnostics, typing and recombination of operons. Many more incomplete C. difficile whole genome sequencing projects are recorded in GenBank as underway and the rrn operon information from these can also be added to the RT App when available. The RT App will help simplify probe selection because of the complexity of the ITS1 in C. difficile even in a single genome and because other allele-specific regions (16S and 23S genes) of variability can be relationally compared to design extra probes to increase sensitivity.

Typing of Clostridium difficile isolates endemic in Japan by sequencing of slpA and its application to direct typing

A typing system for Clostridium difficile using sequencing of the surface-layer protein A encoding gene (slpA) was evaluated and used to analyse clinical isolates in Japan. A total of 160 stool specimens from symptomatic patients in Japan was examined and 87 C. difficile isolates were recovered. slpA sequence typing was found to have reliable typability and discriminatory power in comparison with PCR ribotyping, and the typing results were highly reproducible and comparable. slpA sequence typing was used to type C. difficile in DNA extracted directly from stool specimens. Among the 90 stool specimens in which direct typing results were obtained, 77 specimens were positive for C. difficile culture, and typing results from isolated strains agreed with those from direct typing in all 77 specimens. The slpA sequence type smz was dominant at all four hospitals examined, and this endemic type was detected by culture and/or direct typing in 61 (62 %) of 99 stool specimens positive for toxic culture and/or direct slpA sequence typing. Comparison of epidemic strains reported throughout the world revealed one isolate identified as slpA sequence type gc8, which was found to correspond to PCR ribotype 027 (BI/NAP1/027), whereas no isolates were found with the slpA gene identical to that of PCR ribotype 078 strain. slpA sequence typing is valuable for comparison of C. difficile strains epidemic in diverse areas because the typing results are reproducible and can easily be shared. In addition, slpA sequence typing could be applied to direct typing without culture.

Genetic relatedness of Clostridium difficile isolates from various origins determined by triple-locus sequence analysis based on toxin regulatory genes tcdC, tcdR, and cdtR

A triple-locus nucleotide sequence analysis based on toxin regulatory genes tcdC, tcdR and cdtR was initiated to assess the sequence variability of these genes among Clostridium difficile isolates and to study the genetic relatedness between isolates. A preliminary investigation of the variability of the tcdC gene was done with 57 clinical and veterinary isolates. Twenty-three isolates representing nine main clusters were selected for tcdC, tcdR, and cdtR analysis. The numbers of alleles found for tcdC, tcdR and cdtR were nine, six, and five, respectively. All strains possessed the cdtR gene except toxin A-negative toxin B-positive variants. All but one binary toxin CDT-positive isolate harbored a deletion (>1 bp) in the tcdC gene. The combined analyses of the three genes allowed us to distinguish five lineages correlated with the different types of deletion in tcdC, i.e., 18 bp (associated or not with a deletion at position 117), 36 bp, 39 bp, and 54 bp, and with the wild-type tcdC (no deletion). The tcdR and tcdC genes, though located within the same pathogenicity locus, were found to have evolved separately. Coevolution of the three genes was noted only with strains harboring a 39-bp or a 54-bp deletion in tcdC that formed two homogeneous, separate divergent clusters. Our study supported the existence of the known clones (PCR ribotype 027 isolates and toxin A-negative toxin B-positive C. difficile variants) and evidence for clonality of isolates with a 39-bp deletion (toxinotype V, PCR ribotype 078) that are frequently isolated worldwide from human infections and from food animals.

Molecular analysis of Clostridium difficile at a university teaching hospital in Japan: a shift in the predominant type over a five-year period

Clostridium difficile isolates recovered from patients admitted to a teaching hospital in Japan over a 5-year period were analyzed. Two molecular typing systems, PCR ribotyping and pulsed-field gel electrophoresis (PFGE) analysis, were used. Twenty-six PCR ribotypes were found among the 148 isolates. The predominant type at our hospital appeared to shift during the study period, from PCR ribotype a in 2000 (15/33, 45%) to PCR ribotype f in 2004 (18/28, 64%). By using PFGE with thiourea added to both the gel and running buffer, all 148 Clostridium difficile isolates were successfully classified into 37 types and 61 subtypes. The PCR ribotype f isolates were further classified into four types and 11 subtypes by PFGE. The PFGE patterns of the 11 subtypes differed from each other by only 1 to 4 bands, suggesting that these differences might reflect genetic changes during patient-to-patient transmission over the 5-year period analyzed, and that PCR ribotype f isolates might be outbreak-related. In addition, the PCR ribotype f was identical to the PCR ribotype designated smz, which is reported to have caused multiple outbreaks in Japan. These results confirmed that PCR ribotype f (type smz) has specific virulence or survival factors that make it more likely to cause nosocomial outbreaks at Japanese hospitals. PCR ribotype 027, which has been reported to have caused recent outbreaks in North America and Europe, was recovered from one patient in this study; however, this strain was community-acquired. Our findings emphasize the importance of monitoring specific strains to control and prevent nosocomial infection.

New PCR ribotypes of Clostridium difficile detected in children in Brazil

A total of 35 Brazilian isolates of Clostridium difficile from faecal stools and four isolates from hospital environments were analyzed by PCR ribotyping. A whole cell protein profile (as an alternative for serogrouping), in vitro toxin production and susceptibility to vancomycin, metronidazole and clindamycin were also investigated. All strains were typeable by both phenotypic and genotypic methods, and a total of 13 different PCR ribotypes were identified, of which seven (132, 133, 134, 135, 136, 142 and 143) were considered new types and accounted for 78.5% of all samples evaluated (including hospital environments). A non-toxigenic C. difficile PCR ribotype 133 was detected in all children groups examined (inpatients, outpatients and healthy children), whilst toxigenic PCR ribotypes 015, 131, 134 and 135 were associated mostly with symptomatic children. Serogroups G and D were disseminated both in patients from the community and from the pediatric hospital, with group G prevalent among outpatient children. All strains were susceptible to vancomycin and metronidazole but high levels of resistance to clindamycin were found, especially among serogroups G and D. Co-existence of different ribotypes and serogroups in the same individual was observed. The new seven ribotypes found in this investigation may represent strains characteristic of this region of Brazil.

Sequence and phylogenetic analysis of the gene for surface layer protein, slpA, from 14 PCR ribotypes of Clostridium difficile

Clostridium difficile is the commonest cause of antibiotic-associated diarrhoea, with the hospitalized elderly being at particular risk. The organism makes a crystalline surface protein layer (S-layer), encoded by the slpA gene, the product of which is cleaved to give two mature peptides which associate to form the layer. The larger peptide (high molecular weight; HMW), derived from the C-terminal portion of the precursor, is relatively conserved, whereas the smaller peptide (low molecular weight; LMW), derived from the N-terminal portion of the precursor, is a dominant antigen which substantially forms the basis for serotyping of isolates. PCR ribotyping is a more discriminatory typing method, based on the intergenic rRNA. We obtained the sequence for slpA and some flanking DNA from a collection of C. difficile strains of 14 ribotypes isolated from elderly patients. Sequences from different ribotypes were compared with one another and with published sequences. Sequences from C. difficile ribotypes 046 and 092 were identical. Sequences from ribotype pairs 005 and 054, 012 and 046/092, 014 and 066 and 031 and 094 differed by 1-3 nt in the slpA gene. There were ultimately nine ribotypes or groups of ribotypes with very different slpA sequences, particularly in the region encoding the LMW peptide. The sequence from ribotype 002 was very different from previously published sequences. The DNA segment sequenced included the 5' 315 bp of a secA homologue, encoding a putative transport protein required for peptide secretion across the plasma membrane. The amino acid sequences of the predicted HMW peptides were aligned and a neighbour-joining tree was produced using 10,000 bootstrap replicates. The predicted SecA N-terminal region was similarly analysed. For both SlpA and SecA, a strong association was found between ribotypes 012, 046/092, 017, 031 and 094. Ribotypes 001 and 078 formed part of this clade for SlpA but not SecA, indicating independent evolution for slpA and secA, presumably because they come under different selection pressures.

Prevalence and characterization of a binary toxin (actin-specific ADP-ribosyltransferase) from Clostridium difficile

In addition to the two large clostridial cytotoxins (TcdA and TcdB), some strains of Clostridium difficile also produce an actin-specific ADP-ribosyltransferase, called binary toxin CDT. We used a PCR method and Southern blotting for the detection of genes encoding the enzymatic (CDTa) and binding (CDTb) components of the binary toxin in 369 strains isolated from patients with suspected C. difficile-associated diarrhea or colitis. Twenty-two strains (a prevalence of 6%) harbored both genes. When binary toxin production was assessed by Western blotting, 19 of the 22 strains reacted with antisera against the iota toxin of C. perfringens (anti-Ia and anti-Ib). Additionally, binary toxin activity, detected by the ADP-ribosyltransferase assay, was present in only 17 of the 22 strains. Subsequently, all 22 binary toxin-positive strains were tested for the production of toxins TcdA and TcdB, toxinotyped, and characterized by serogrouping, PCR ribotyping, arbitrarily primed PCR, and pulsed-field gel electrophoresis. All binary toxin-positive strains also produced TcdB and/or TcdA. However, they had significant changes in the tcdA and tcdB genes and belonged to variant toxinotypes III, IV, V, VII, IX, and XIII. We could differentiate 16 profiles by using typing methods, indicating that most of the binary toxin-positive strains were unrelated.

International typing study of toxin A-negative, toxin B-positive Clostridium difficile variants

Clinically important strains of Clostridium difficile that do not produce toxin A but produce toxin B and are cytotoxic (A(-)/B(+)) have been reported from multiple countries. In order to compare the relatedness of these strains, we typed 23 A(-)/B(+) C. difficile isolates from the United Kingdom (6 isolates), Belgium (11 isolates), and the United States (6 isolates) by three well-described typing methods. Restriction endonuclease analysis (REA), PCR ribotyping, and serogrouping differentiated 11, 4, and 3 different strain types, respectively. Twenty-one of the 23 A(-)/B(+) variants had a 1.8-kb truncation of the toxin A gene characteristic of toxinotype VIII strains; 20 of the 21 toxinotype VIII-like strains were PCR type 17. PCR type 17 isolates could be differentiated into two separate strain groups by serogrouping and by REA. REA further discriminated these isolates into eight subgroups (REA types). PCR type 17-serogroup F-REA group CF isolates were recovered from all three countries, and one specific REA type, CF4, was recovered from patients with C. difficile disease in the United Kingdom and the United States. C. difficile A(-)/B(+) variants of apparent clonal origin are widely distributed in Europe and North America.

Clostridium difficile genotyping based on slpA variable region in S-layer gene sequence: an alternative to serotyping

Recent investigations of Clostridium difficile cell wall components have revealed the presence of an S-layer encoded by the slpA gene. The aim of this study was to determine whether slpA genotyping can be used as an alternative to serotyping. The variable regions of slpA were amplified by PCR from serogroup reference strains and various clinical isolates chosen randomly. Amplified products were analyzed after restriction enzyme digestion and DNA sequencing. The sequences of the variable region of the SlpA protein were found to be strictly identical within a given serogroup but divergent between serogroups. These preliminary results suggest that PCR-restriction fragment length polymorphism, in conjunction with DNA sequencing of the slpA variable region, could constitute an alternative typing method for determining C. difficile serotypes.

Molecular characterization of the surface layer proteins from Clostridium difficile

Many bacteria express a surface-exposed proteinaceous layer, termed the S-layer, which forms a regular two-dimensional array visible by electron microscopy. Clostridium difficile is unusual in expressing two S-layer proteins (SLPs), which are of varying size in a number of strains. In an approach combining molecular biology with mass spectrometric sequencing strategies, we have identified the structural gene (slpA) for the S-layer from three strains of C. difficile. Both proteins are derived from a common precursor, and processing involves the removal of a signal peptide and a second cleavage to release the two mature SLPs. To our knowledge, this is the first example in which two SLPs have been shown to derive from a single gene product through post-translational processing, rather than from the expression of separate genes. The higher molecular weight (MW) SLP is highly conserved among the three strains, whereas the lower MW SLP shows considerable sequence diversity, reflecting the results from Western blotting. The high-MW SLP shows weak homology to N-acetyl muramoyl-L-alanine amidase from Bacillus subtilis, and both the native SLP from C. difficile and a recombinant protein expressed in Escherichia coli were found to display amidase activity by zymography. The high-MW SLPs showed evidence of glycosylation, whereas the lower MW proteins did not. A family of genes with sequence homology to the amidase domain of the high-MW SLP was identified in the C. difficile strain 630 genome, some of which are located in the same region of the genome as slpA and were shown by reverse transcription-polymerase chain reaction (RT-PCR) analysis to be transcribed.

Analysis of Clostridium difficile isolates from nosocomial outbreaks at three hospitals in diverse areas of Japan

Clostridium difficile isolates recovered from patients with C. difficile-associated diarrhea (CDAD) at three hospitals located in diverse areas of Japan were analyzed by three typing systems, PCR ribotyping, pulsed-field gel electrophoresis (PFGE), and Western immunoblotting. At the three hospitals examined, a single PCR ribotype strain (type smz) was predominant and accounted for 22 (65%) of 34, 18 (64%) of 28, and 11 (44%) of 25 isolates, respectively. All of the 51 isolates that represented PCR ribotype smz were nontypeable by PFGE because of DNA degradation. Since the type smz strain did not react with any of the antisera against 10 different serogroups (A, B, C, D, F, G, H, I, K, and X), we prepared a new antiserum against a type smz isolate. All 51 type smz isolates presented identical banding patterns, reacting with the newly prepared antiserum (designated subserogroup JP-0 of serogroup JP). These results were compared with those of a strain from a hospital outbreak that occurred in New York, which has been identified as type J9 by restriction enzyme analysis and type 01/A by arbitrarily primed PCR but was nontypeable by PFGE because of DNA degradation. This strain was reported to be epidemic at multiple hospitals in the United States. The J9 strain represented a PCR ribotype pattern different from that of a type smz strain and was typed as subserogroup G-1 of serogroup G by immunoblot analysis. A single outbreak type causing nosocomial CDAD in Japan was found to be different from the strain causing multiple outbreaks in the United States, even though the outbreak strains from the two countries were nontypeable by PFGE because of DNA degradation.

Molecular characterization of fliD gene encoding flagellar cap and its expression among Clostridium difficile isolates from different serogroups

The fliD gene encoding the flagellar cap protein (FliD) of Clostridium difficile was studied in 46 isolates belonging to serogroups A, B, C, D, F, G, H, I, K, X, and S3, including 30 flagellated strains and 16 nonflagellated strains. In all but three isolates, amplification by PCR and reverse transcription-PCR demonstrated that the fliD gene is present and transcribed in both flagellated and nonflagellated strains. PCR-restriction fragment length polymorphism (RFLP) analysis of amplified fliD gene products revealed interstrain homogeneity, with one of two major patterns (a and b) found in all but one of the strains, which had pattern c. A polyclonal monospecific antiserum raised to the recombinant FliD protein reacted in immunoblots with crude flagellar preparations from 28 of 30 flagellated strains but did not recognize FliD from nonflagellated strains. The fliD genes from five strains representative of the three different RFLP groups were sequenced, and sequencing revealed 100% identity between the strains with the same pattern and 88% identity among strains with different patterns. Our results show that even though FliD is a structure exposed to the outer environment, the flagellar cap protein is very well conserved, and this high degree of conservation suggests that it has a very specific function in attachment to cell or mucus receptors.

Comparison of toxinotyping and PCR ribotyping of Clostridium difficile strains and description of novel toxinotypes

Toxinotyping and PCR ribotyping are two methods that have been used to type Clostridium difficile isolates. Toxinotyping is based on PCR-RFLP analysis of a 19 kb region encompassing the C. difficile pathogenicity locus. PCR ribotyping is based on comparison of patterns of PCR products of the 16S-23S rRNA intergenic spacer region. Representative strains (101) from a C. difficile PCR ribotype library and 22 strains from previously described toxinotypes were analysed to compare ribotyping with toxinotyping. Within this panel of strains all 11 toxinotypes (0-X) described previously and an additional 5 novel toxinotypes (XI-XV) were observed. PCR ribotyping and toxinotyping correlated well and usually all strains within a given ribotype had similar changes in toxin genes. The new toxinotype XI comprises strains that did not express toxins TcdA or TcdB at detectable levels, but contained part of the tcdA gene. Strains of toxinotype XII exhibit changes only in the 5' end of the tcdB gene. Toxinotype XIV is composed of strains that have a large insertion at the beginning of the tcdA gene. A total of 25 of the 89 tested PCR ribotypes of C. difficile contained variant strains. It was estimated that they represent 7.7% of the total number of strains in the Anaerobe Reference Unit collection.

Phenotypic and genotypic diversity of the flagellin gene (fliC) among Clostridium difficile isolates from different serogroups

Phenotypic and genotypic diversity of the flagellin gene (fliC) of Clostridium difficile was studied in 47 isolates from various origins belonging to the serogroups A, B, C, D, F, G, H, I, K, X, and S3. Electron microscopy revealed 17 nonflagellated strains and 30 flagellated strains. PCR and reverse transcription-PCR demonstrated that the flagellin gene was present in all strains and that the fliC gene was expressed in both flagellated and nonflagellated strains. Southern blotting showed the presence of only one copy of the gene and three different hybridization patterns. DNA sequence analysis of fliC from the strains belonging to serogroups C, D, and X, representative of each profile, disclosed great variability in the central domain, whereas the N- and C-terminal domains were conserved. The variability of the flagellin gene fliC was further studied in the isolates by PCR-restriction fragment length polymorphism (RFLP) analysis. Nine different RFLP groups were identified (I to IX), among which three (I, VII, and VIII) corresponded to numerous serogroups whereas the six others (II, III, IV, V, VI, and IX) belonged to a single serogroup. Flagellin gene RFLP analysis could constitute an additional typing method employable in conjunction with other typing methods currently available.

Development of a new PCR-ribotyping method for Clostridium difficile based on ribosomal RNA gene sequencing

PCR-ribotying, a typing method based on polymorphism in the 16S-23S intergenic spacer region, has been recently used to investigate outbreaks due to Clostridium difficile. However, this method generates bands of high and close molecular masses which are difficult to separate on agarose gel electrophoresis. To improve reading of banding patterns of PCR-ribotyping applied to C. difficile, a partial sequencing of the rRNA genes (16S and 23S) and intergenic spacer region has been performed, then a new set of primers located closer to the intergenic spacer region has been defined. The new PCR gave reproducible patterns of bands easy to separate on agarose gel electrophoresis. Each of the 10 serogroups and 11 subgroups of serogroup A produced a different pattern. This typing method has evidenced major qualities such as easiness, rapidity and reproducibility. However, its discriminatory power has to be evaluated to validate its importance as a typing tool for C. difficile.

A novel toxinotyping scheme and correlation of toxinotypes with serogroups of Clostridium difficile isolates

Two hundred nineteen Clostridium difficile isolates from 22 serogroups were screened for changes in the genes coding for toxin B (tcdB) and toxin A (tcdA). Parts of the toxin genes were amplified, and the PCR fragments were checked for length polymorphisms and cut with several restriction enzymes to monitor restriction fragment length polymorphisms (RFLPs). For 47 strains (21%), differences in the toxin genes were found compared to the toxin genes of reference strain VPI 10,463. Polymorphisms were usually observed in both toxin genes. RFLPs were more commonly found in the tcdB gene, in which a single restriction enzyme could give up to five different patterns. Restriction sites seemed to be less heterogeneous in the tcdA gene, in which for most enzymes only two different RFLPs were recognized. However, deletions were observed in tcdA, and four new types of shortened tcdA genes are described. According to the changes in their toxin genes, variant strains could be divided into 10 groups (toxinotypes I to X). A toxinotype was characterized by similar patterns of changes in the toxin genes and in other regions of the pathogenicity locus and also similar pulsed-field gel electrophoresis patterns. Variant toxinotypes were found in 9 of the 22 serogroups studied, and some toxinotypes were clearly associated with specific serogroups. Toxinotype VIII is characteristic for all strains of serogroup F. Other serogroups in which variant toxinotypes were commonly found are A1, A15, E, and X. Testing of variability in C. difficile toxin genes not only might be useful as a molecular typing system but also could have implications in diagnostics and pathogenesis.

Identification of toxin A-negative, toxin B-positive Clostridium difficile by PCR

Toxigenic strains of Clostridium difficile have been reported to produce both toxins A and B nearly always, and nontoxigenic strains have been reported to produce neither of these toxins. Recent studies indicate that it is not always true. We established a PCR assay to differentiate toxin A-negative, toxin B-positive (toxin A-, toxin B+) strains from both toxin-positive (toxin A+, toxin B+) strains and both toxin-negative (toxin A-, toxin B-) strains as an alternative to cell culture assay and enzyme-linked immunosorbent assay (ELISA). By using the PCR primer set NK11 and NK9 derived from the repeating sequences of the toxin A gene, a shorter segment (ca. 700 bp) was amplified from toxin A-, toxin B+ strains compared to the size of the segment amplified from toxin A+, toxin B+ strains (ca. 1,200 bp), and no product was amplified from toxin A-, toxin B-strains. We examined a total of 421 C. difficile isolates by PCR. Of these, 48 strains showed a shorter segment by the PCR, were negative by ELISAs for the detection of toxin A, and were positive by cell culture assay. Although the cytotoxin produced by the toxin A-, toxin B+ strains was neutralized by anti-toxin B serum, the appearance of the cytotoxic effects on Vero cell monolayers was distinguishable from that of toxin A+, toxin B+ strains. By immunoblotting, the 44 toxin A-, toxin B+ strains were typed to serogroup F and the remaining four strains were serogroup X. Pulsed-field gel electrophoresis separated the 48 strains into 19 types. The PCR assay for the detection of the repeating sequences combined with PCR amplification of the nonrepeating sequences of either the toxin A or the toxin B gene is indicated to be useful for differentiating toxin A-, toxin B+ strains from toxin A+, toxin B+ and toxin A-, toxin B- strains and will contribute to elucidation of the precise role of toxin A-, toxin B+ strains in intestinal diseases.

Genotyping of outbreak-related and sporadic isolates of Clostridium difficile belonging to serogroup C

Serogroup C of Clostridium difficile is the serogroup most frequently related to outbreaks. Fifty-six toxigenic serogroup C isolates of C. difficile were genotyped by ribotyping PCR (ribo-PCR), random amplified polymorphic DNA (RAPD) assay, and pulsed-field gel electrophoresis (PFGE). Thirty-five of the 56 isolates were recovered from four unrelated outbreaks (Belgium, 1987, 1992, and 1995; France, 1992 to 1993) 7 derived from a spatiotemporal cluster in Cotonou, Benin (1992), and 14 were sporadic isolates. The serogroup C reference strain, also isolated during an outbreak (Belgium, 1983), was genotyped too. Ribo-PCR, the RAPD assay, and PFGE generated 2, 5, and 11 major genotypes, respectively. Combination of the three methods finally yielded 13 general types, although ribo-PCR did not play any role in enhancing resolution. Three general types were recovered from all the isolates from the five outbreaks and the cluster, with two types being predominant. The 14 sporadic serogroup C isolates were divided into 11 overall genotypes. These results indicate that genotyping methods, and more particularly the combination of the RAPD assay and PFGE, can resolve genetic diversity within toxigenic, serogroup C C. difficile strains. Also, this study suggests that outbreak-related serogroup C strains are limited to a few genetically stable and apparently very widely (internationally and intercontinentally) distributed genotypes.

Relapses or reinfections: analysis of a case of Clostridium difficile-associated colitis by two typing systems

Immunoblotting and pulsed-field gel electrophoresis of Clostridium difficile isolates were employed to differentiate reinfection by a newly acquired strain from relapse by an original strain in a 10-year-old patient with four episodes of C. difficile-associated colitis. Immunoblot typing demonstrated subserogroup K-1 of serogroup K for the first and second organisms, subserogroup A-1 of serogroup A for the third organism, and subserogroup G-4 of serogroup G for the fourth organism. PFGE analysis revealed consistent results with immunoblot analysis except that the strains from the fourth episode, whose DNA constantly degraded, were nontypable by this method. Five separate isolates of C. difficile from a specimen of each episode showed identical PFGE patterns, indicating that infections of multiple strains probably did not occur in this patient. These typing results suggested that the second episode after a 17-day course of vancomycin therapy represented a relapse by the strain causing the first episode, and that the third and fourth episodes after tapering vancomycin therapy were reinfections by other strains. Both immunoblot and PFGE typing systems are promising tools for analyzing recurrence of C. difficile infection.

Enzyme electrophoresis combined with serogrouping for improved differentiation of Clostridium difficile strains

We used enzyme electrophoresis to study a set of epidemiologically related and unrelated isolates of Clostridium difficile. The 53 strains belonged to the most frequent serogroups (A1, C, G, H and K). Nine electrophoretic profiles were defined on the basis of five enzymes, and two were characteristic of a single strain. Each serogroup was resolved into two or three different enzyme patterns. By combining the two methods we were able to resolve the strains into 12 types. There was an excellent correlation between enzyme electrophoresis and serogrouping data. This method may be of use in investigating nosocomial transmission.

Comparison of arbitrarily primed PCR with restriction endonuclease and immunoblot analyses for typing Clostridium difficile isolates

Arbitrarily primed PCR (AP-PCR) was used to genotype 26 clinical isolates of Clostridium difficile previously analyzed by immunoblotting (IB) and 20 isolates typed by restriction endonuclease analysis (REA) with HindIII. Two levels of differentiation were achieved with the AP-PCR approach by use of two different arbitrary primers. With the 19-mer arbitrary primer T-7 (first level of differentiation), a good correlation was found between IB and AP-PCR typing. Twenty isolates grouped into six IB types were separated into seven major AP-PCR types. These seven AP-PCR groups were further discriminated into 12 subtypes after genotyping with the arbitrary primer PG-05 (second level of differentiation). The remaining six isolates, all of different IB types, showed a unique and distinct DNA banding pattern with both of the arbitrary primers, T-7 and PG-05. Twenty isolates representing 20 REA types from 15 REA groups were resolved into 13 AP-PCR DNA profiles with the arbitrary primer T-7. A good correlation was found at this level of differentiation between the major REA groups, Y and M, and AP-PCR typing. While AP-PCR with this primer failed to differentiate isolates in REA groups J, G, R, and B, AP-PCR with PG-05 resolved these four isolates into four distinct AP-PCR types. In addition, one of three M strains and one of four Y strains displayed a slightly different DNA banding pattern by AP-PCR (with PG-05) from that of the other strains in the group. We conclude that AP-PCR is a rapid and sensitive method which not only complements other typing schemes but also may be a substitute and prove to be especially suited for immediate epidemiological tracking of nosocomial infections due to C. difficile.

Biochemical properties and whole-cell protein profiles of group G streptococci isolated from dogs

Whole-cell protein profiles obtained by SDS-PAGE were used in conjunction with physiological tests to differentiate strains of Streptococcus canis isolated from dogs. Fermentation of trehalose and lactose, aesculin hydrolysis together with production of beta-D-glucuronidase and alpha-D-galactosidase allowed the demonstration of nine different biotypes. However, visual analysis of the protein patterns and comparison by the coefficient of Dice showed minor differences in band patterns among strains. Only two different profiles were observed. Although a correlation between biotyping and protein profile has been found, this kind of analysis did not provide the basis for a typing method.

Application of typing by pulsed-field gel electrophoresis to the study of Clostridium difficile in a neonatal intensive care unit

Pulsed-field gel electrophoresis (PFGE) analysis of restriction pattern polymorphism was applied to type Clostridium difficile isolated from neonates hospitalized in a neonatal intensive care unit, and the results were compared with those of immunoblot analysis. C. difficile was isolated from fecal specimens of 41 (61%) of 67 neonates during a 5-month investigation. All of these neonates were asymptomatic. Fifty-five C. difficile isolates from 32 patients were analyzed by PFGE after digestion with SmaI and SacII endonucleases and by immunoblotting with 10 different antisera. Fifty-three of 55 isolates from 30 patients were identical by PFGE analysis after SmaI and SacII digestion and immunoblot analysis. Two isolates were different from each other and from the epidemic group by both PFGE and immunoblot analysis. All 53 epidemic isolates were nontoxigenic, while the two remaining isolates were toxigenic. These results suggest that nosocomial spread of nontoxigenic C. difficile infection in the neonatal intensive care unit and suggest that both PFGE and immunoblot are powerful typing tools for the epidemiological study of C. difficile.

Identification of outbreak-associated and other strains of Clostridium difficile by numerical analysis of SDS-PAGE protein patterns

Seventy-three cultures of Clostridium difficile isolated both during, and in the period immediately following, an outbreak of infection in a group of three hospitals, were characterized by one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins. Each protein pattern was characterized by the presence of one or two dense bands which were highly reproducible. The protein patterns were used as the basis for a numerical analysis which divided the strains into five phenons (electrophoretic or EP types). The majority, 60 of the 73 cultures, belonged to a single phenon which included strains from both patients and the environment. We conclude that high-resolution SDS-PAGE of proteins provides an effective method for typing C. difficile and therefore for tracing the possible spread of epidemic strains in hospitals and other institutions, thereby allowing a better understanding of the epidemiology of the organism.

Comparison of restriction endonuclease analysis, ribotyping, and pulsed-field gel electrophoresis for molecular differentiation of Clostridium difficile strains

A combined clinical and molecular epidemiologic analysis of 46 strains of Clostridium difficile, including 16 nosocomial isolates from one ward (outbreak ward) plus 17 other nosocomial isolates and 13 community-acquired isolates, was performed. HindIII digests of total cellular DNA were analyzed by restriction enzyme analysis (REA) and ribotyping; SmaI digests were analyzed by pulsed-field gel electrophoresis (PFGE). Isolates were assigned to typing groups on the basis of the profiles detected; isolates with closely related profiles were assigned to subgroups. The 16 isolates from the outbreak ward were resolved by both REA and PFGE into five distinct groups; 13 isolates represented two REA groups and three PFGE groups and two isolates were resolved as distinct groups by both techniques. DNA obtained from one isolate was persistently partially degraded, precluding analysis by PFGE. Seventeen sporadic nosocomial isolates were resolved by REA and PFGE into comparable numbers of groups (i.e., nine groups) and subgroups (i.e., 15 and 14 subgroups, respectively), with two isolates not evaluable by PFGE. The 13 epidemiologically unrelated community-acquired isolates were assigned to 11 groups by REA and to 12 groups by PFGE. Overall, ribotyping identified only nine groups among the 46 isolates. We conclude that REA and PFGE have comparable discriminatory powers for epidemiologic typing of C. difficile isolates and that ribotyping is appreciably less discriminatory. For a few isolates, partial DNA degradation prevented analysis by PFGE but not by REA or ribotyping; the cause of the degradation is unknown.

Rapid detection of toxigenic Clostridium difficile in fecal samples by magnetic immuno PCR assay

Rapid detection of toxigenic Clostridium difficile in fecal samples was accomplished with the magnetic immuno PCR assay (MIPA). Elaborate DNA extraction techniques were unnecessary. First, we generated a mouse monoclonal antibody (MAb) reactive with only C. difficile, Clostridium sordellii, and Clostridium bifermentans. Then, magnetic beads were coated with the MAb, incubated with fecal samples to allow binding with C. difficile, extracted from the stool with a magnet, and processed in the PCR with primers specific for the toxin B gene. After optimizing MIPA by raising the number of PCR cycles from 35 to 40 and adding Chelex 100 to the PCR mixture, we found a sensitivity of 96.7%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 94.1% when compared with the culture of cytotoxic C. difficile from fecal samples. MIPA is a rapid, easy, and sensitive PCR method for demonstrating the presence of toxigenic C. difficile in stool samples and avoids the disadvantage of elaborate extraction of DNA from fecal samples.

Investigation of an outbreak of Clostridium difficile infection in a general hospital by numerical analysis of protein patterns by sodium dodecyl sulfate-polyacrylamide gel electrophoresis

One hundred forty-five cultures of Clostridium difficile, including strains from an apparent nosocomial outbreak of infection, were characterized by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins. Each protein pattern was characterized by the presence of one to three dense bands which were highly reproducible. The first 100 strains (in chronological order) were used as the basis for a numerical analysis which divided the strains into 17 phenons (EP types 1 to 17). The protein patterns of the remaining 45 strains were identified to type by comparing their individual patterns against a data base made up of the protein patterns of the first 100 strains. EP type 1 was the most common, with 70 of 139 (50%) patient isolates having this pattern type, and it accounted for 26 of 35 strains (74%) from patients in a medical teaching ward from which the outbreak was believed to have originated. This type was also found as a high proportion of isolations in a number of other medical and oncology wards, but the majority of these isolates occurred subsequent to the isolations on the initial outbreak ward. This technique can therefore provide a method for tracing the possible spread of epidemic strains in hospitals and other institutions and may contribute to a better understanding of the epidemiology of C. difficile.

Human antibody response to Clostridium difficile toxin A in relation to clinical course of infection

This study investigated whether differences in fecal and serum antitoxin A antibody levels may account for the duration of Clostridium difficile-associated diarrhea (CDAD) and the occurrence of relapses. By an enzyme linked-immunosorbent assay, we tested 40 patients with CDAD including 25 patients without immunodeficiency and 15 patients receiving antineoplastic drugs. Two hundred eighty serum samples and 80 normal stool samples were investigated as controls. In nonimmunocompromised patients, serum immunoglobulin (IgG) and fecal IgA antitoxin A antibody titers were significantly higher in patients who suffered a single episode (n = 21) than in those with relapsing CDAD (n = 4) whose titers were at control levels. Of these 25 patients, eight suffered from diarrhea which lasted for more than 2 weeks. These patients had significantly lower serum- and feces-specific antibody levels than the others who presented symptoms of shorter duration. In cytostatic-treated patients, antitoxin A antibody levels were similar to controls, but relapses occurred in a single case. These data suggest an association between a defective humoral response to toxin A and a more severe form of C. difficile infection. They also indicate that other host-related factors control the severity of CDAD and remain to be elucidated.

Genomic fingerprinting of Clostridium difficile isolates by using a random amplified polymorphic DNA (RAPD) assay

This study describes the use of a new and easy method called random amplified polymorphic DNA (RAPD) assay to distinguish strains of C. difficile. We used two single short primers (AP4 and AP5) with arbitrary nucleotide sequences in a polymerase chain reaction to amplify genomic DNA. The profiles observed after electrophoretic separation were able to distinguish 20 reference C. difficile strains previously serotyped by Delmée's method. The fingerprints of 11 epidemiologically unrelated C. difficile strains clearly yielded a DNA polymorphism between all the strains. Latterly, RAPD profiles of 11 C. difficile strains isolated from 2 independent suspected outbreaks showed, in each case, a predominant banding pattern corresponding to an epidemic strain. These results suggest that RAPD assay could be a valuable tool for epidemiological studies.

Use of an enzyme-linked immunoassay for Clostridium difficile serogrouping

An enzyme-linked immunoassay (ELISA) with 11 Clostridium difficile serogroup-specific antisera was applied for serogrouping of C. difficile colonies from 314 consecutive positive fecal samples. Two hundred forty-nine strains (79%) were correctly serogrouped, 57 (18%) belonged to serogroups other than the 11 which were evaluated and gave a negative reaction with all antisera, and 8 isolates (2.5%) did not react with their corresponding antisera. ELISA is a rapid and reliable method for serogrouping C. difficile and should allow for the automation of this procedure.

Comparison of typing methods for Clostridium difficile isolates

A simple discriminative typing method for Clostridium difficile has been developed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins and restriction enzyme analysis are relatively simple techniques but are difficult to evaluate, especially the restriction enzyme analysis. Immunoblotting and restriction fragment length polymorphism typing facilitate simple discrimination of patterns.

Improvement of Clostridium difficile isolation by heat-shock and typing of the isolated strains by SDS-PAGE

Clostridium difficile plays an essential role in causing pseudomembranous colitis. We looked for the presence of these bacteria in the stools of 169 hospitalized patients and 38 nurses from wards with cases of diarrhea (207 subjects). The study was divided into three parts. In the first part, we compared three methods for isolating Clostridium difficile from stool samples: pre-selection with heat-shock, direct plating on Cycloserine-Cefotaxime-Fructose Agar (CCFA) and culturing in a selective broth medium. Final identification of Clostridium difficile was achieved by gas-chromatography and ApiZym. From the 207 consecutively obtained stool specimens, Clostridium difficile was isolated in 108 (52%) when pre-treated by heat-shock compared to only 26 (13%) when plated on modified CCFA and 23 (11%) when cultured in selective broth medium. Pre-selection significantly increases the isolation rate for Clostridium difficile and should be used in further epidemiological research. In the second part of our study, a retrospective review of subjects' records showed that the heat-shock method detected Clostridium difficile in all age groups at a higher rate than the other methods. In the third part of our study, we typed the 157 isolates of Clostridium difficile strains by protein patterns using SDS-PAGE, and 16 distinct groups were identified. In 19 cases different Clostridium difficile strains were found in the same subject by SDS-PAGE. Finally, the isolated strains were compared with strains from Brussels and Freiburg. Matching patterns were noted in only three cases.

Typing of Clostridium difficile by western immunoblotting with 10 different antisera

Western blotting (immunoblotting) with antisera against each of 10 reference serogroups was evaluated as a means of typing Clostridium difficile. A total of 164 clinical isolates of C. difficile were tested. Variations in band profiles in each serogroup were used to type isolates into subserogroups. This technique was useful for an epidemiological investigation.

Epidemiological aspects of infections caused by Bacteroides fragilis and Clostridium difficile

Bacteroides fragilis and Clostridium difficile are two of the most common anaerobes associated with human disease. Studies on the epidemiology of Bacteroides fragilis are limited and are based predominantly on serogrouping, which suggests intraspecies differences. Further studies using newer techniques for typing are required to elucidate the epidemiological characteristics of this important pathogen. By contrast, numerous phenotypic, immunological and molecular methods have been developed for typing and fingerprinting of Clostridium difficile and applied in epidemiological studies to show conclusively that Clostridium difficile is nosocomially acquired and that there is transmission and cross-infection between hospital patients.

Purification and characterization of an immunodominant 36 kDa antigen present on the cell surface of Clostridium difficile

The 36 kDa antigen represents the major EDTA-extracted protein of Clostridium difficile strains belonging to electrophoretic group 2. Antibodies to this antigen are found in sera of patients with C. difficile-associated diarrhoea. The 36 kDa antigen was extracted from C. difficile C253 by EDTA and purified by gel filtration (Sephacryl S300) and ion exchange chromatography (DEAE-Trisacryl M). The molecular weight of the purified protein was 36 kDa as determined by SDS-PAGE, also in non-reducing conditions. By gel filtration, the molecular size appeared to be 72 kDa and was not modified by the presence of EDTA or SDS in the column buffer. Since IEF showed a single isoelectric form of pI 4.6, the protein could be a homodimeric molecule. Immunofluorescence demonstrated that the 36 kDa antigen was located on the surface of the C. difficile cell. Monospecific antiserum raised in rabbits reacted positively with the 36 kDa protein of most group 2 C. difficile strains isolated from antibiotic-associated diarrhoea (AAD) outbreaks in Italy and other European countries.

The use of molecular techniques for epidemiologic typing of Candida species

The availability of an epidemiologic typing system for Candida species that is sensitive, rapid, inexpensive, and easy to perform would clearly be an advantage to the mycologist, microbiologist, and epidemiologist in the ongoing struggle to understand the epidemiology and pathogenesis of candidiasis. This is particularly true given the increasing prominence of organisms such as C. albicans and C. tropicalis which are ubiquitous members of the normal flora yet are also important causes of nosocomial bloodstream infection. Unfortunately, the ideal epidemiologic typing system does not yet exist. Current data suggest that the molecular typing methods of restriction endonuclease digestion of genomic DNA with ethidium bromide staining (DEtBr typing) and electrophoretic karyotyping using pulsed-field electrophoresis offer rapid, simple, and sensitive means of discriminating strains of Candida species. These methods appear at present to be the most practical typing methods for both large- and small-scale epidemiologic studies. Other typing methods using specific DNA probes provide a powerful means of identifying strains and will undoubtedly be applied more broadly in the future. Thus far, studies employing molecular typing methods have documented that (1) most patients are colonized by one strain of Candida species, (2) isolates of Candida species recovered from blood or deep tissue sites are generally identical to those obtained from colonization sites before infection developed, and (3) nosocomial transmission of a single strain of C. albicans may occur, particularly in an intensive care unit setting. Given the limitations of the available typing methods and the complex nature of the patients at risk for candidiasis, both the epidemiologist and laboratory scientist must use these methods with clear epidemiologic objectives in mind. Whenever possible, all organisms to be typed should be typed by the same person on the same day, and typing should always include unrelated as well as epidemiologically related isolates. Additional studies, based upon sound epidemiologic principles, will be necessary to clarify the role of the various molecular typing methods as epidemiologic markers of Candida species and to further our understanding of the epidemiology and pathogenesis of candidiasis.

Nontoxigenic strains of Clostridium difficile lack the genes for both toxin A and toxin B

A total of 39 toxigenic and 20 nontoxigenic strains of Clostridium difficile were tested for the presence of either toxin A or toxin B by the polymerase chain reaction (PCR). All toxigenic strains produced cytotoxin as assayed by using highly sensitive fetal lung fibroblasts and were positive for toxin A as well as toxin B in the PCR assay. All nontoxigenic strains failed to produce toxin and were negative in the PCR assay. This study shows that nontoxigenic strains of Clostridium difficile lack the toxin A as well as the toxin B gene.

Clostridium difficile infection in a geriatric ward

In a prospective, longitudinal study we searched for the presence of Clostridium difficile in the stools of 100 consecutively hospitalized elderly patients (mean age: 82; SD: 9.5 years). C. difficile was found on admission in 6 patients, 3 of whom were asymptomatic carriers. Ten patients acquired C. difficile during hospitalization. Four different types of C. difficile were isolated. The various types were clustered in time, indicating that the infection was acquired from the environment.

Control of nosocomial transmission of Clostridium difficile based on sporadic case surveillance

The recognition of a cluster of antibiotic-associated nosocomial Clostridium difficile disease (NCDD) caused by serotype C in a surgical ward led to a hospital-wide NCDD surveillance and control program. The initial step included: (a) gas-liquid chromatography screening of inpatients' diarrheal stools; (b) enteric isolation precautions, cohorting and terminal room disinfection in wards with a cluster of two or more NCDD cases per month. During a 12-month period, the quarterly incidence of NCDD remained unchanged and six new clusters of serotype C, K, and H infections occurred, giving a global incidence of 1.5/1,000 admissions. C. difficile spores were recovered from 36.7% surfaces of case patient rooms versus 6.7% in control rooms. More intensive control measures were evaluated: (a) culture screening of inpatients' diarrheal stools; (b) early therapy, enteric isolation precautions, and daily meticulous room disinfection for each sporadic NCDD case. Surface disinfection reduced the contamination level four-fold (p = 0.04). In the following 12 months, no cluster occurred and the incidence of NCDD fell to 0.3/1,000 admission (protective efficacy 73%, 95% confidence interval: 46-87%). These observations suggest that early therapy, isolation precautions, and surface disinfection, focused on patients with sporadic NCDD detected by active surveillance, can prevent nosocomial transmission of C. difficile.

Characterization of flagella of Clostridium difficile and their role in serogrouping reactions

Slide agglutination with rabbit antisera allows the differentiation of 10 serogroups of Clostridium difficile, namely, A, B, C, D, F, G, H, I, K, and X. Each serogroup displays a specific protein profile in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, except for A, which displays 12 different protein profiles (A1 to A12). In the present work, electron microscopy revealed the presence of uniformly distributed flagella in the reference strains of serogroups G and K and in all strains representative of the 12 subgroups within serogroup purified by differential centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of these preparations revealed one distinct band with an apparent molecular mass of approximately 39 kilodaltons. Antiserum was prepared by immunizing a rabbit with the serogroup A flagellin, which had been eluted from the gel. In immunoblotting, this antiserum cross-reacted with the flagellin of the other strains. When the cells were deflagellated by a short sonication, the cross-reactions observed by slide agglutination with A, G, and K antisera were suppressed. Similarly, shearing of flagella allowed specific slide agglutination of the 12 subgroups of serogroup A.

Primary infection of ascitic fluid with Clostridium difficile

A case of a primary infection of ascitic fluid with a toxigenic strain of Clostridium difficile is described. The strain belonged to the serogroup H which is often implicated in pseudomembranous colitis. Nevertheless, our patient did not have any sign of colitis or diarrhoea before the ascitic infection. She was successfully treated by the intravenous administration of metronidazole but relapsed a few weeks later. A similar strain of serogroup H was again isolated.

Detection of specific antigens for ten serogroups of Clostridium difficile

We previously described a serogrouping technique for Clostridium difficile based on slide agglutination with rabbit antisera raised against formol-treated cells. It allows the differentiation of ten serogroups, namely A, B, C, D, F, G, H, I, K and X. Each serogroup displays a specific profile with several distinctive bands by polyacrylamide gel electrophoresis (PAGE). In this study we investigated the common and specific antigenic determinants of the ten serogroups by immunoblotting. In a first experiment, whole cell proteins of the ten reference strains were separated by SDS-PAGE, transferred onto nitrocellulose membrane and immunoblotted against their homologous and heterologous antisera. Each serogroup was characterized by several common bands and one or two specific antigens which were proven to correspond to the lowest molecular weight distinctive band observed on PAGE profiles. New rabbit antisera were subsequently raised against the purified specific antigen obtained by electro-elution from polyacrylamide gels. Immunoblots were repeated with these new antisera: all reactions were serogroup specific except one minor cross reaction between C and F. The antisera still agglutinated the homologous strain without any cross agglutination, suggesting that the serogroup specific determinant is a surface antigen responsible for agglutination.