Fourteen-genome comparison identifies DNA markers for severe-disease-associated strains of Clostridium difficile

Comparative Genomics of Clostridioides difficile

Clostridioides difficile, a Gram-positive spore-forming anaerobic bacterium, has rapidly emerged as the leading cause of nosocomial diarrhoea in hospitals. The availability of large numbers of genome sequences, mainly due to the use of next-generation sequencing methods, has undoubtedly shown their immense advantages in the determination of C. difficile population structure. The implementation of fine-scale comparative genomic approaches has paved the way for global transmission and recurrence studies, as well as more targeted studies, such as the PaLoc or CRISPR/Cas systems. In this chapter, we provide an overview of recent and significant findings on C. difficile using comparative genomic studies with implications for epidemiology, infection control and understanding of the evolution of C. difficile.

A local-scale One Health genomic surveillance of Clostridioides difficile demonstrates highly related strains from humans, canines, and the environment

Although infections caused by Clostridioides difficile have historically been attributed to hospital acquisition, growing evidence supports the role of community acquisition in C. difficile infection (CDI). Symptoms of CDI can range from mild, self-resolving diarrhoea to toxic megacolon, pseudomembranous colitis, and death. In this study, we sampled C. difficile from clinical, environmental, and canine reservoirs in Flagstaff, Arizona, USA, to understand the distribution and transmission of the pathogen in a One Health framework; Flagstaff is a medium-sized, geographically isolated city with a single hospital system, making it an ideal site to characterize genomic overlap between sequenced C. difficile isolates across reservoirs. An analysis of 562 genomes from Flagstaff isolates identified 65 sequence types (STs), with eight STs being found across all three reservoirs and another nine found across two reservoirs. A screen of toxin genes in the pathogenicity locus identified nine STs where all isolates lost the toxin genes needed for CDI manifestation (tcdB, tcdA), demonstrating the widespread distribution of non-toxigenic C. difficile (NTCD) isolates in all three reservoirs; 15 NTCD genomes were sequenced from symptomatic, clinical samples, including two from mixed infections that contained both tcdB+ and tcdB- isolates. A comparative single nucleotide polymorphism (SNP) analysis of clinically derived isolates identified 78 genomes falling within clusters separated by ≤2 SNPs, indicating that ~19 % of clinical isolates are associated with potential healthcare-associated transmission clusters; only symptomatic cases were sampled in this study, and we did not sample asymptomatic transmission. Using this same SNP threshold, we identified genomic overlap between canine and soil isolates, as well as putative transmission between environmental and human reservoirs. The core genome of isolates sequenced in this study plus a representative set of public C. difficile genomes (n=136), was 2690 coding region sequences, which constitutes ~70 % of an individual C. difficile genome; this number is significantly higher than has been published in some other studies, suggesting that genome data quality is important in understanding the minimal number of genes needed by C. difficile. This study demonstrates the close genomic overlap among isolates sampled across reservoirs, which was facilitated by maximizing the genomic search space used for comprehensive identification of potential transmission events. Understanding the distribution of toxigenic and non-toxigenic C. difficile across reservoirs has implications for surveillance sampling strategies, characterizing routes of infections, and implementing mitigation measures to limit human infection.

Large-Scale Sequencing of Borreliaceae for the Construction of Pan-Genomic-Based Diagnostics

The acceleration of climate change has been associated with an alarming increase in the prevalence and geographic range of tick-borne diseases (TBD), many of which have severe and long-lasting effects-particularly when treatment is delayed principally due to inadequate diagnostics and lack of physician suspicion. Moreover, there is a paucity of treatment options for many TBDs that are complicated by diagnostic limitations for correctly identifying the offending pathogens. This review will focus on the biology, disease pathology, and detection methodologies used for the Borreliaceae family which includes the Lyme disease agent Borreliella burgdorferi. Previous work revealed that Borreliaceae genomes differ from most bacteria in that they are composed of large numbers of replicons, both linear and circular, with the main chromosome being the linear with telomeric-like termini. While these findings are novel, additional gene-specific analyses of each class of these multiple replicons are needed to better understand their respective roles in metabolism and pathogenesis of these enigmatic spirochetes. Historically, such studies were challenging due to a dearth of both analytic tools and a sufficient number of high-fidelity genomes among the various taxa within this family as a whole to provide for discriminative and functional genomic studies. Recent advances in long-read whole-genome sequencing, comparative genomics, and machine-learning have provided the tools to better understand the fundamental biology and phylogeny of these genomically-complex pathogens while also providing the data for the development of improved diagnostics and therapeutics.

A Review of Next Generation Sequencing Methods and its Applications in Laboratory Diagnosis

Next-generation sequencing (NGS) is a new technology used to detect the sequence of DNA and RNA and to detect mutations or variations of significance. NGS generates large quantities of sequence data within a short time duration. The various types of sequencing includes Sanger Sequencing, Pyrosequencing, Sequencing by Synthesis (Illumina), Ligation (SoLID), Single molecule Fluorescent Sequencing (Helicos), Single molecule Real time Sequencing (Pacbio), Semiconductor sequencing (Ion torrent technology), Nanopore sequencing and fourth generation sequencing. These methods of sequencing have been modified and improved over the years such that it has become cost effective and accessible to diagnostic laboratories. Management of Outbreaks, rapid identification of bacteria, molecular case finding, taxonomy, detection of the zoonotic agents and guiding prevention strategies in HIV outbreaks are just a few of the many applications of Next Generation sequencing in clinical microbiology.

Clostridioides difficile Whole-genome Sequencing Differentiates Relapse With the Same Strain From Reinfection With a New Strain

BACKGROUND

Current approaches in tracking Clostridioides difficile infection (CDI) and individualizing patient management are incompletely defined.

METHODS

We recruited 468 subjects with CDI at Mayo Clinic Rochester between May and December 2016 and performed whole-genome sequencing (WGS) on C. difficile isolates from 397. WGS was also performed on isolates from a subset of the subjects at the time of a recurrence of infection. The sequence data were analyzed by determining core genome multilocus sequence type (cgMLST), with isolates grouped by allelic differences and the predicted ribotype.

RESULTS

There were no correlations between C. difficile isolates based either on cgMLST or ribotype groupings and CDI outcome. An epidemiologic assessment of hospitalized subjects harboring C. difficile isolates with ≤2 allelic differences, based on standard infection prevention and control assessment, revealed no evidence of person-to-person transmission. Interestingly, community-acquired CDI subjects in 40% of groups with ≤2 allelic differences resided within the same zip code. Among 18 subjects clinically classified as having recurrent CDI, WGS revealed 14 with initial and subsequent isolates differing by ≤2 allelic differences, suggesting a relapse of infection with the same initial strain, and 4 with isolates differing by >50 allelic differences, suggesting reinfection. Among the 5 subjects classified as having a reinfection based on the timing of recurrence, 3 had isolates with ≤2 allelic differences between them, suggesting a relapse, and 2 had isolates differing by >50 allelic differences, suggesting reinfection.

CONCLUSIONS

Our findings point to potential transmission of C. difficile in the community. WGS better differentiates relapse from reinfection than do definitions based on the timing of recurrence.

Complete genome sequence of the Clostridium difficile LCL126

Clostridium difficile (C. difficile) is a kind of obligate anaerobic gram-positive Bacillus related with intestinal diseases and antibiotic treatment. In present study, the C. difficile genome was studied employing met genomic technology. Genome sequencing identified C. difficile LCL126 has total size of 4,301,949 bp with a 27.97% of GC content. Specifically, 4119 predicted coding genes, 188 repeat sequences, 13 prophages and 8 gene islands were detected. Additionally, gene function analysis aspect of the function annotation, effector, and virulence were concluded that total of 3367 cluster of orthologous groups of proteins genes and classified into 24 categories, while the most outstanding class was metabolic process (1533) and catalytic activity (1498). The carbohydrate-active enzymes have been detected 127 genes, pathogenicity analysis revealed that 133 reduced and 22 increased virulence (hypervirulence) genes, while 54 unaffected and 10 loss of pathogenicity genes were found. Furthermore, perform the visualization and methylation expression were revealed that the dominant types comprised m4C, m5C, and m6C with the number of 6989, 36,666, and 3534, respectively. Overall, whole genome sequence information of C. difficile LCL126 was obtained and functional prediction was revealed its possible toxicological potential genes existence.

Higher genome variability within metabolism genes associates with recurrent Clostridium difficile infection

BACKGROUND

Clostridium difficile (C. difficile) is a major source of healthcare-associated infection with a high risk of recurrence, attributable to many factors such as usage of antibiotics, older age and immunocompromised status of the patients. C. difficile has also a highly diverse genome, which may contribute to its high virulence. Herein we examined whether the genome conservation, measured as non-synonymous to synonymous mutations ratio (dN/dS) in core genes, presence of single genes, plasmids and prophages increased the risk of reinfection in a subset of 134 C. difficile isolates from our previous study in a singly hemato-oncology ward.

METHODS

C. difficile isolates were subjected to whole-genome sequencing (WGS) on Ion Torrent PGM sequencer. Genomes were assembled with MIRA5 and annotated with prokka and VRprofile. Logistic regression was used to asses the relationship between single gene presence and the odds of infection recurrence. DN/dS ratios were computed with codeml. Functional annotation was conducted with eggNOG-Mapper.

RESULTS

We have found that the presence of certain genes, associated with carbon metabolism and oxidative phosphorylation, increased the odds of infection recurrence. More core genes were under positive selective pressure in recurrent disease isolates - they were mostly associated with the metabolism of aminoacids. Finally, prophage elements were more prevalent in single infection isolates and plasmids did not influence the odds of recurrence.

CONCLUSIONS

Our findings suggest higher genetic plasticity in isolates causing recurrent infection, associated mainly with metabolism. On the other hand, the presence of prophages seems to reduce the isolates' virulence.

Genomic Delineation of Zoonotic Origins of Clostridium difficile

Clostridium difficile is toxin-producing antimicrobial resistant (AMR) enteropathogen historically associated with diarrhea and pseudomembranous colitis in hospitalized patients. In recent years, there have been dramatic increases in the incidence and severity of C. difficile infection (CDI), and associated morbidity and mortality, in both healthcare and community settings. C. difficile is an ancient and diverse species that displays a sympatric lifestyle, establishing itself in a range of ecological niches external to the healthcare system. These sources/reservoirs include food, water, soil, and over a dozen animal species, in particular, livestock such as pigs and cattle. In a manner analogous to human infection, excessive antimicrobial exposure, particularly to cephalosporins, is driving the expansion of C. difficile in livestock populations worldwide. Subsequent spore contamination of meat, vegetables grown in soil containing animal feces, agricultural by-products such as compost and manure, and the environment in general (households, lawns, and public spaces) is contributing to a persistent community source/reservoir of C. difficile and the insidious rise of CDI in the community. The whole-genome sequencing era continues to redefine our view of this complex pathogen. The application of high-resolution microbial genomics in a One Health framework (encompassing clinical, veterinary, and environment derived datasets) is the optimal paradigm for advancing our understanding of CDI in humans and animals. This approach has begun to yield critical insights into the genetic diversity, evolution, AMR, and zoonotic potential of C. difficile. In Europe, North America, and Australia, microevolutionary analysis of the C. difficile core genome shows strains common to humans and animals (livestock or companion animals) do not form distinct populations but share a recent evolutionary history. Moreover, for C. difficile sequence type 11 and PCR ribotypes 078 and 014, major lineages of One Health importance, this approach has substantiated inter-species clonal transmission between animals and humans. These findings indicate either a zoonosis or anthroponosis. Moreover, they challenge the existing paradigm and the long-held misconception that CDI is primarily a healthcare-associated infection. In this article, evolutionary, and zoonotic aspects of CDI are discussed, including the anthropomorphic factors that contribute to the spread of C. difficile from the farm to the community.

Genomics of the Pathogenic Clostridia

Whole-genome sequences are now available for all the clinically important clostridia and many of the lesser or opportunistically pathogenic clostridia. The complex clade structures of C. difficile, C. perfringens, and the species that produce botulinum toxins have been delineated by whole-genome sequence analysis. The true clostridia of cluster I show relatively low levels of gross genomic rearrangements within species, in contrast to the species of cluster XI, notably C. difficile, which have been found to have very plastic genomes with significant levels of chromosomal rearrangement. Throughout the clostridial phylotypes, a large proportion of the strain diversity is driven by the acquisition and loss of mobile elements, including phages, plasmids, insertion sequences, and transposons. Genomic analysis has been used to investigate the diversity and spread of C. difficile within hospital settings, the zoonotic transfer of isolates, and the emergence, origins, and geographic spread of epidemic ribotypes. In C. perfringens the clades defined by chromosomal sequence analysis show no indications of clustering based on host species or geographical location. Whole-genome sequence analysis helps to define the different survival and pathogenesis strategies that the clostridia use. Some, such as C. botulinum, produce toxins which rapidly act to kill the host, whereas others, such as C. perfringens and C. difficile, produce less lethal toxins which can damage tissue but do not rapidly kill the host. The genomes provide a resource that can be mined to identify potential vaccine antigens and targets for other forms of therapeutic intervention.

Comparative Genomics of Clostridium difficile

Clostridium difficile, a gram-positive spore-forming anaerobic bacterium, has rapidly emerged as the leading cause of nosocomial diarrhoea in hospitals. The availability of genome sequences in large numbers, mainly due to the use of next-generation sequencing methods, have undoubtedly shown their immense advantages in the determination of the C. difficile population structure. The implementation of fine-scale comparative genomic approaches have paved the way to global transmission and recurrence studies, but also more targeted studies such as the PaLoc or the CRISPR/Cas systems. In this chapter, we provide an overview of the recent and significant findings on C. difficile using comparative genomics studies with implication for the epidemiology, infection control and understanding of the evolution of C. difficile.

Inactivation of the dnaK gene in Clostridium difficile 630 Δerm yields a temperature-sensitive phenotype and increases biofilm-forming ability

Clostridium difficile infection is a growing problem in healthcare settings worldwide and results in a considerable socioeconomic impact. New hypervirulent strains and acquisition of antibiotic resistance exacerbates pathogenesis; however, the survival strategy of C. difficile in the challenging gut environment still remains incompletely understood. We previously reported that clinically relevant heat-stress (37-41 °C) resulted in a classical heat-stress response with up-regulation of cellular chaperones. We used ClosTron to construct an insertional mutation in the dnaK gene of C. difficile 630 Δerm. The dnaK mutant exhibited temperature sensitivity, grew more slowly than C. difficile 630 Δerm and was less thermotolerant. Furthermore, the mutant was non-motile, had 4-fold lower expression of the fliC gene and lacked flagella on the cell surface. Mutant cells were some 50% longer than parental strain cells, and at optimal growth temperatures, they exhibited a 4-fold increase in the expression of class I chaperone genes including GroEL and GroES. Increased chaperone expression, in addition to the non-flagellated phenotype of the mutant, may account for the increased biofilm formation observed. Overall, the phenotype resulting from dnaK disruption is more akin to that observed in Escherichia coli dnaK mutants, rather than those in the Gram-positive model organism Bacillus subtilis.

Molecular analysis of three Clostridium difficile strain genomes isolated from pig farm-related samples

Clostridium difficile is an anaerobic spore-forming bacillus that usually causes gastrointestinal disorders in man and other animal species. Most of the strains isolated from animals are toxigenic being the virulent ribotype (RT) 078 predominant in several animal species. Although C. difficile is pathogenic to both humans and animals, there is no direct evidence of zoonosis. Deep genome sequencing provides sufficient resolution to analyse which strains found in animals might be related to human pathogens. So far, there are only a few fully sequenced genomes of C. difficile strains isolated from domestic and wild animals. Using Illumina technology, we have sequenced the genome of three isolates; a strain isolated from the vagina of a sow (5754), one from rat (Rattus spp) intestinal content (RC10) and a third one isolated from environmental rat faeces (RF17). Both, rat and rat faeces were sampled in fattening pig farms. Our study reveals a close genetic relationship of two of these isolates with the virulent strain M120 (RT078) isolated from a human patient. The analysis of the sequences has revealed the presence of antibiotic resistance genes, mobile elements, including the transposon linked with virulence Tn6164, and the similarity of virulence factors between these isolates and human strains. This is the first study focused on the sequencing of C. difficile genomes obtained from wild animals like rats, which can be considered as potential reservoirs for humans and other animal species. This study can help to understand the genome composition and epidemiology of this bacterium species.

Genome Analysis of Clostridium difficile PCR Ribotype 014 Lineage in Australian Pigs and Humans Reveals a Diverse Genetic Repertoire and Signatures of Long-Range Interspecies Transmission

Clostridium difficile PCR ribotype (RT) 014 is well-established in both human and porcine populations in Australia, raising the possibility that C. difficile infection (CDI) may have a zoonotic or foodborne etiology. Here, whole genome sequencing and high-resolution core genome phylogenetics were performed on a contemporaneous collection of 40 Australian RT014 isolates of human and porcine origin. Phylogenies based on MLST (7 loci, STs 2, 13, and 49) and core orthologous genes (1260 loci) showed clustering of human and porcine strains indicative of very recent shared ancestry. Core genome single nucleotide variant (SNV) analysis found 42% of human strains showed a clonal relationship (separated by ≤2 SNVs in their core genome) with one or more porcine strains, consistent with recent inter-host transmission. Clones were spread over a vast geographic area with 50% of the human cases occurring without recent healthcare exposure. These findings suggest a persistent community reservoir with long-range dissemination, potentially due to agricultural recycling of piggery effluent. We also provide the first pan-genome analysis for this lineage, characterizing its resistome, prophage content, and in silico virulence potential. The RT014 is defined by a large "open" pan-genome (7587 genes) comprising a core genome of 2296 genes (30.3% of the total gene repertoire) and an accessory genome of 5291 genes. Antimicrobial resistance genotypes and phenotypes varied across host populations and ST lineages and were characterized by resistance to tetracycline [tetM, tetA(P), tetB(P) and tetW], clindamycin/erythromycin (ermB), and aminoglycosides (aph3-III-Sat4A-ant6-Ia). Resistance was mediated by clinically important mobile genetic elements, most notably Tn6194 (harboring ermB) and a novel variant of Tn5397 (harboring tetM). Numerous clinically important prophages (Siphoviridae and Myoviridae) were identified as well as an uncommon accessory gene regulator locus (agr3). Conservation in the pathogenicity locus and S-layer correlated with ST affiliation, further extending the concept of clonal C. difficile lineages. This study provides novel insights on the genetic variability and strain relatedness of C. difficile RT014, a lineage of emerging One Health importance. Ongoing molecular and genomic surveillance of strains in humans, animals, food, and the environment is imperative to identify opportunities to reduce the overall CDI burden.

Genome Sequence and Analysis of Peptoclostridium difficile Strain ZJCDC-S82

Peptoclostridium difficile (Clostridium difficile) is the major pathogen associated with infectious diarrhea in humans. Concomitant with the increased incidence of C. difficile infection worldwide, there is an increasing concern regarding this infection type. This study reports a draft assembly and detailed sequence analysis of C. difficile strain ZJCDC-S82. The de novo assembled genome was 4.19 Mb in size, which includes 4,013 protein-coding genes, 41 rRNA genes, and 84 tRNA genes. Along with the nuclear genome, we also assembled sequencing information for a single plasmid consisting of 11,930 nucleotides. Comparative genomic analysis of C. difficile ZJCDC-S82 and two other previously published strains, such as M120 and CD630, showed extensive similarity. Phylogenetic analysis revealed that genetic diversity among C. difficile strains was not influenced by geographic location. Evolutionary analysis suggested that four genes encoding surface proteins exhibited positive selection in C. difficile ZJCDC-S82. Codon usage analysis indicated that C. difficile ZJCDC-S82 had high codon usage bias toward A/U-ended codons. Furthermore, codon usage patterns in C. difficile ZJCDC-S82 were predominantly affected by mutation pressure. Our results provide detailed information pertaining to the C. difficile genome associated with a strain from mainland China. This analysis will facilitate the understanding of genomic diversity and evolution of C. difficile strains in this region.

Diversity and Evolution in the Genome of Clostridium difficile

Clostridium difficile infection (CDI) is the leading cause of antimicrobial and health care-associated diarrhea in humans, presenting a significant burden to global health care systems. In the last 2 decades, PCR- and sequence-based techniques, particularly whole-genome sequencing (WGS), have significantly furthered our knowledge of the genetic diversity, evolution, epidemiology, and pathogenicity of this once enigmatic pathogen. C. difficile is taxonomically distinct from many other well-known clostridia, with a diverse population structure comprising hundreds of strain types spread across at least 6 phylogenetic clades. The C. difficile species is defined by a large diverse pangenome with extreme levels of evolutionary plasticity that has been shaped over long time periods by gene flux and recombination, often between divergent lineages. These evolutionary events are in response to environmental and anthropogenic activities and have led to the rapid emergence and worldwide dissemination of virulent clonal lineages. Moreover, genome analysis of large clinically relevant data sets has improved our understanding of CDI outbreaks, transmission, and recurrence. The epidemiology of CDI has changed dramatically over the last 15 years, and CDI may have a foodborne or zoonotic etiology. The WGS era promises to continue to redefine our view of this significant pathogen.

Targeting surface-layer proteins with single-domain antibodies: a potential therapeutic approach against Clostridium difficile-associated disease

Clostridium difficile is a leading cause of death from gastrointestinal infections in North America. Antibiotic therapy is effective, but the high incidence of relapse and the rise in hypervirulent strains warrant the search for novel treatments. Surface layer proteins (SLPs) cover the entire C. difficile bacterial surface, are composed of high-molecular-weight (HMW) and low-molecular-weight (LMW) subunits, and mediate adherence to host cells. Passive and active immunization against SLPs has enhanced hamster survival, suggesting that antibody-mediated neutralization may be an effective therapeutic strategy. Here, we isolated a panel of SLP-specific single-domain antibodies (V_HHs) using an immune llama phage display library and SLPs isolated from C. difficile hypervirulent strain QCD-32g58 (027 ribotype) as a target antigen. Binding studies revealed a number of V_HHs that bound QCD-32g58 SLPs with high affinity (K_D = 3–6 nM) and targeted epitopes located on the LMW subunit of the SLP. The V_HHs demonstrated melting temperatures as high as 75 °C, and a few were resistant to the gastrointestinal protease pepsin at physiologically relevant concentrations. In addition, we demonstrated the binding specificity of the V_HHs to the major C. difficile ribotypes by whole cell ELISA, where all V_HHs were found to bind 001 and 027 ribotypes, and a subset of antibodies were found to be broadly cross-reactive in binding cells representative of 012, 017, 023, and 078 ribotypes. Finally, we showed that several of the V_HHs inhibited C. difficile QCD-32g58 motility in vitro. Targeting SLPs with V_HHs may be a viable therapeutic approach against C. difficile-associated disease.

Identification and characterization of glycoproteins on the spore surface of Clostridium difficile

In this study, we identify a major spore surface protein, BclA, and provide evidence that this protein is glycosylated. Following extraction of the spore surface, solubilized proteins were separated by one-dimensional PAGE and stained with glycostain to reveal a reactive high-molecular-mass region of approximately 600 kDa. Tandem mass spectrometry analysis of in-gel digests showed this band to contain peptides corresponding to a putative exosporangial glycoprotein (BclA3) and identified a number of glycopeptides modified with multiple N-acetyl hexosamine moieties and, in some cases, capped with novel glycans. In addition, we demonstrate that the glycosyltransferase gene sgtA (gene CD3350 in strain 630 and CDR3194 in strain R20291), which is located immediately upstream of the bclA3 homolog, is involved in the glycosylation of the spore surface, and is cotranscribed with bclA3. The presence of anti-β-O-GlcNAc-reactive material was demonstrated on the surface of spores by immunofluorescence and in surface extracts by Western blotting, although each strain produced a distinct pattern of reactivity. Reactivity of the spore surface with the anti-β-O-GlcNAc antibody was abolished in the 630 and R20291 glycosyltransferase mutant strains, while complementation with a wild-type copy of the gene restored the β-O-GlcNAc reactivity. Phenotypic testing of R20291 glycosyltransferase mutant spores revealed no significant change in sensitivity to ethanol or lysozyme. However, a change in the resistance to heat of R20291 glycosyltransferase mutant spores compared to R20291 spores was observed, as was the ability to adhere to and be internalized by macrophages.

Semiquantitative analysis of clinical heat stress in Clostridium difficile strain 630 using a GeLC/MS workflow with emPAI quantitation

Clostridium difficile is considered to be the most frequent cause of infectious bacterial diarrhoea in hospitals worldwide yet its adaptive ability remains relatively uncharacterised. Here, we used GeLC/MS and the exponentially modified protein abundance index (emPAI) calculation to determine proteomic changes in response to a clinically relevant heat stress. Reproducibility between both biological and technical replicates was good, and a 37°C proteome of 224 proteins was complemented by a 41°C proteome of 202 proteins at a 1% false discovery rate. Overall, 236 C. difficile proteins were identified and functionally categorised, of which 178 were available for comparative purposes. A total of 65 proteins (37%) were modulated by 1.5-fold or more at 41°C compared to 37°C and we noted changes in the majority of proteins associated with amino acid metabolism, including upregulation of the reductive branch of the leucine fermentation pathway. Motility was reduced at 41°C as evidenced by a 2.7 fold decrease in the flagellar filament protein, FliC, and a global increase in proteins associated with detoxification and adaptation to atypical conditions was observed, concomitant with decreases in proteins mediating transcriptional elongation and the initiation of protein synthesis. Trigger factor was down regulated by almost 5-fold. We propose that under heat stress, titration of the GroESL and dnaJK/grpE chaperones by misfolded proteins will, in the absence of trigger factor, prevent nascent chains from emerging efficiently from the ribosome causing translational stalling and also an increase in secretion. The current work has thus allowed development of a heat stress model for the key cellular processes of protein folding and export.

Structure of Clostridium difficile PilJ exhibits unprecedented divergence from known type IV pilins

Type IV pili are produced by many pathogenic Gram-negative bacteria and are important for processes as diverse as twitching motility, cellular adhesion, and colonization. Recently, there has been an increased appreciation of the ability of Gram-positive species, including Clostridium difficile, to produce Type IV pili. Here we report the first three-dimensional structure of a Gram-positive Type IV pilin, PilJ, demonstrate its incorporation into Type IV pili, and offer insights into how the Type IV pili of C. difficile may assemble and function. PilJ has several unique structural features, including a dual-pilin fold and the incorporation of a structural zinc ion. We show that PilJ is incorporated into Type IV pili in C. difficile and present a model in which the incorporation of PilJ into pili exposes the C-terminal domain of PilJ to create a novel interaction surface.

Sequence similarity of Clostridium difficile strains by analysis of conserved genes and genome content is reflected by their ribotype affiliation

PCR-ribotyping is a broadly used method for the classification of isolates of Clostridium difficile, an emerging intestinal pathogen, causing infections with increased disease severity and incidence in several European and North American countries. We have now carried out clustering analysis with selected genes of numerous C. difficile strains as well as gene content comparisons of their genomes in order to broaden our view of the relatedness of strains assigned to different ribotypes. We analyzed the genomic content of 48 C. difficile strains representing 21 different ribotypes. The calculation of distance matrix-based dendrograms using the neighbor joining method for 14 conserved genes (standard phylogenetic marker genes) from the genomes of the C. difficile strains demonstrated that the genes from strains with the same ribotype generally clustered together. Further, certain ribotypes always clustered together and formed ribotype groups, i.e. ribotypes 078, 033 and 126, as well as ribotypes 002 and 017, indicating their relatedness. Comparisons of the gene contents of the genomes of ribotypes that clustered according to the conserved gene analysis revealed that the number of common genes of the ribotypes belonging to each of these three ribotype groups were very similar for the 078/033/126 group (at most 69 specific genes between the different strains with the same ribotype) but less similar for the 002/017 group (86 genes difference). It appears that the ribotype is indicative not only of a specific pattern of the amplified 16S–23S rRNA intergenic spacer but also reflects specific differences in the nucleotide sequences of the conserved genes studied here. It can be anticipated that the sequence deviations of more genes of C. difficile strains are correlated with their PCR-ribotype. In conclusion, the results of this study corroborate and extend the concept of clonal C. difficile lineages, which correlate with ribotypes affiliation.

Differential stress transcriptome landscape of historic and recently emerged hypervirulent strains of Clostridium difficile strains determined using RNA-seq

C. difficile is the most common cause of nosocomial diarrhea in North America and Europe. Genomes of individual strains of C. difficile are highly divergent. To determine how divergent strains respond to environmental changes, the transcriptomes of two historic and two recently isolated hypervirulent strains were analyzed following nutrient shift and osmotic shock. Illumina based RNA-seq was used to sequence these transcriptomes. Our results reveal that although C. difficile strains contain a large number of shared and strain specific genes, the majority of the differentially expressed genes were core genes. We also detected a number of transcriptionally active regions that were not part of the primary genome annotation. Some of these are likely to be small regulatory RNAs.

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.

Diversity of cwp loci in clinical isolates of Clostridium difficile

An increased incidence of Clostridium difficile infection (CDI) is associated with the emergence of epidemic strains characterized by high genetic diversity. Among the factors that may have a role in CDI is a family of 29 paralogues, the cell-wall proteins (CWPs), which compose the outer layer of the bacterial cell and are likely to be involved in colonization. Previous studies have shown that 12 of the 29 cwp genes are clustered in the same region, named after slpA (cwp1), the slpA locus, whereas the remaining 17 paralogues are distributed throughout the genome. The variability of 14 of these 17 cwp paralogues was determined in 40 C. difficile clinical isolates belonging to six of the currently prevailing PCR ribotypes. Based on sequence conservation, these cwp genes were divided into two groups, one comprising nine cwp loci having highly conserved sequences in all isolates, and the other five loci showing low genetic conservation among isolates of the same PCR ribotype, as well as between different PCR ribotypes. Three conserved CWPs, Cwp16, Cwp18 and Cwp25, and two variable ones, Cwp26 and Cwp27, were characterized further by Western blot analysis of total cell extracts or surface-layer preparations of the C. difficile clinical isolates. Expression of genetically invariable CWPs was well conserved in all isolates, whilst genetically variable CWPs were not always expressed at comparable levels, even in strains containing identical sequences but belonging to different PCR ribotypes. This is the first report on the distribution and variability of a number of genes encoding CWPs in C. difficile.

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.

Proteomic comparison of historic and recently emerged hypervirulent Clostridium difficile strains

Clostridium difficile in recent years has undergone rapid evolution and has emerged as a serious human pathogen. Proteomic approaches can improve the understanding of the diversity of this important pathogen, especially in comparing the adaptive ability of different C. difficile strains. In this study, TMT labeling and nanoLC-MS/MS driven proteomics were used to investigate the responses of four C. difficile strains to nutrient shift and osmotic shock. We detected 126 and 67 differentially expressed proteins in at least one strain under nutrition shift and osmotic shock, respectively. During nutrient shift, several components of the phosphotransferase system (PTS) were found to be differentially expressed, which indicated that the carbon catabolite repression (CCR) was relieved to allow the expression of enzymes and transporters responsible for the utilization of alternate carbon sources. Some classical osmotic shock associated proteins, such as GroEL, RecA, CspG, and CspF, and other stress proteins such as PurG and SerA were detected during osmotic shock. Furthermore, the recently emerged strains were found to contain a more robust gene network in response to both stress conditions. This work represents the first comparative proteomic analysis of historic and recently emerged hypervirulent C. difficile strains, complementing the previously published proteomics studies utilizing only one reference strain.

Characterization of a stable, metronidazole-resistant Clostridium difficile clinical isolate

Background

Clostridium difficile are Gram-positive, spore forming anaerobic bacteria that are the leading cause of healthcare-associated diarrhea, usually associated with antibiotic usage. Metronidazole is currently the first-line treatment for mild to moderate C. difficile diarrhea however recurrence occurs at rates of 15–35%. There are few reports of C. difficile metronidazole resistance in the literature, and when observed, the phenotype has been transient and lost after storage or exposure of the bacteria to freeze/thaw cycles. Owing to the unstable nature of the resistance phenotype in the laboratory, clinical significance and understanding of the resistance mechanisms is lacking.

Methodology/Principal Findings

Genotypic and phenotypic characterization was performed on a metronidazole resistant clinical isolate of C. difficile. Whole-genome sequencing was used to identify potential genetic contributions to the phenotypic variation observed with molecular and bacteriological techniques. Phenotypic observations of the metronidazole resistant strain revealed aberrant growth in broth and elongated cell morphology relative to a metronidazole-susceptible, wild type NAP1 strain. Comparative genomic analysis revealed single nucleotide polymorphism (SNP) level variation within genes affecting core metabolic pathways such as electron transport, iron utilization and energy production.

Conclusions/Significance

This is the first characterization of stable, metronidazole resistance in a C. difficile isolate. The study provides an in-depth genomic and phenotypic analysis of this strain and provides a foundation for future studies to elucidate mechanisms conferring metronidazole resistance in C. difficile that have not been previously described.

Clostridium difficile in foods and animals: history and measures to reduce exposure

Many articles have summarized the changing epidemiology of Clostridium difficile infections (CDI) in humans, but the emerging presence of C. difficile in foods and animals and possible measures to reduce human exposure to this important pathogen have been infrequently addressed. CDIs have traditionally been assumed to be restricted to health-care settings. However, recent molecular studies indicate that this is no longer the case; animals and foods might be involved in the changing epidemiology of CDIs in humans; and genome sequencing is disproving person-to-person transmission in hospitals. Although zoonotic and foodborne transmission have not been confirmed, it is evident that susceptible people can be inadvertently exposed to C. difficile from foods, animals, or their environment. Strains of epidemic clones present in humans are common in companion and food animals, raw meats, poultry products, vegetables, and ready-to-eat foods, including salads. In order to develop science-based prevention strategies, it is critical to understand how C. difficile reaches foods and humans. This review contextualizes the current understanding of CDIs in humans, animals, and foods. Based on available information, we propose a list of educational measures that could reduce the exposure of susceptible people to C. difficile. Enhanced educational efforts and behavior change targeting medical and non-medical personnel are needed.

Implementation of standardised surveillance for Clostridium difficile infections in Australia: initial report from the Victorian Healthcare Associated Infection Surveillance System

Detection of a hypervirulent strain of Clostridium difficile in Victoria led to commencement of targeted surveillance for C. difficile infection in 2010. Cases were reported through the Victorian Healthcare Associated Infection Surveillance System. Between 1 October 2010 and 31 March 2011, 477 cases of C. difficile infection were identified; 11 (2.3%) secondary to a hypervirulent strain. Three hundred and seventy (1.7 per 10,000 occupied bed days) were healthcare associated. Data reflect successful implementation of continuous surveillance for C. difficile infection. With hypervirulent C. difficile infection now reported in other Australian states, development of a national data repository for C. difficile infection is necessary.

Phosphorylation of the synthetic hexasaccharide repeating unit is essential for the induction of antibodies to Clostridium difficile PSII cell wall polysaccharide

Clostridium difficile is emerging worldwide as a major cause of nosocomial infections. The negatively charged PSII polysaccharide has been found in different strains of C. difficile and, thereby, represents an important target molecule for a possible carbohydrate-based vaccine. In order to identify a synthetic fragment that after conjugation to a protein carrier could be able to induce anti-PSII antibodies, we exploited a combination of chemical synthesis with immunochemistry, confocal immunofluorescence microscopy, and solid state NMR. We demonstrate that the phosphate group is crucial in synthetic glycans to mimic the native PSII polysaccharide; both native PSII and a phosphorylated synthetic hexasaccharide repeating unit conjugated to CRM(197) elicit comparable immunogenic responses in mice. This finding can aid design and selection of carbohydrate antigens to be explored as vaccine candidates.

Comparative transcriptional analysis of clinically relevant heat stress response in Clostridium difficile strain 630

Clostridium difficile is considered to be one of the most important causes of health care-associated infections worldwide. In order to understand more fully the adaptive response of the organism to stressful conditions, we examined transcriptional changes resulting from a clinically relevant heat stress (41 °C versus 37 °C) in C. difficile strain 630 and identified 341 differentially expressed genes encompassing multiple cellular functional categories. While the transcriptome was relatively resilient to the applied heat stress, we noted upregulation of classical heat shock genes including the groEL and dnaK operons in addition to other stress-responsive genes. Interestingly, the flagellin gene (fliC) was downregulated, yet genes encoding the cell-wall associated flagellar components were upregulated suggesting that while motility may be reduced, adherence--to mucus or epithelial cells--could be enhanced during infection. We also observed that a number of phage associated genes were downregulated, as were genes associated with the conjugative transposon Tn5397 including a group II intron, thus highlighting a potential decrease in retromobility during heat stress. These data suggest that maintenance of lysogeny and genome wide stabilisation of mobile elements could be a global response to heat stress in this pathogen.

Analysis of a Clostridium difficile PCR ribotype 078 100 kilobase island reveals the presence of a novel transposon, Tn6164

Background

Clostridium difficile is the main cause of antibiotic associated diarrhea. In the past decade, the number of C. difficile patients has increased dramatically, coinciding with the emergence of two PCR ribotypes 027 and 078. PCR ribotype 078 is also frequently found during C. difficile outbreaks in pigfarms. Previously, the genome of the PCR ribotype 078 strain M120, a human isolate, was described to contain a unique insert of 100 kilobases.

Results

Analysis of this insert revealed over 90 open reading frames, encoding proteins originating from transposons, phages and plasmids. The insert was shown to be a transposon (Tn6164), as evidenced by the presence of an excised and circularised molecule, containing the ligated 5’and 3’ends of the insert. Transfer of the element could not be shown through filter-mating experiments. Whole genome sequencing of PCR ribotype 078 strain 31618, isolated from a diarrheic piglet, showed that Tn6164 was not present in this strain. To test the prevalence of Tn6164, a collection of 231 Clostridium difficile PCR ribotype 078 isolates from human (n = 173) and porcine (n = 58) origin was tested for the presence of this element by PCR. The transposon was present in 9 human, tetracycline resistant isolates, originating from various countries in Europe, and none of the pig strains. Nine other strains, also tetracycline resistant human isolates, contained half of the transposon, suggesting multiple insertion steps yielding the full Tn6164. Other PCR ribotypes (n = 66) were all negative for the presence of the transposon. Multi locus variable tandem repeat analysis revealed genetic relatedness among transposon containing isolates. Although the element contained several potential antibiotic resistance genes, it did not yield a readily distinguishable phenotype.

Conclusions

Tn6164 is a newly described transposon, occurring sporadically in C. difficile PCR ribotype 078 strains. Although no transfer of the element could be shown, we hypothesize that the element could serve as a reservoir of antibiotic resistance genes for other bacteria. Further research is needed to investigate the transfer capabilities of the element and to substantiate the possible role of Tn6164 as a source of antibiotic resistance genes for other gut pathogens.

Systems biology approach for new target and biomarker identification

The pharmaceutical industry is spending increasingly large amounts of money on the discovery and development of novel medicines, but this investment is not adequately paying off in an increased rate of newly approved drugs by the FDA. The post-genomic era has provided a wealth of novel approaches for generating large, high-dimensional genetic and transcriptomic data sets from large cohorts of preclinical species as well as normal and diseased individuals. This systems biology approach to understanding disease-related biology is revolutionizing our understanding of the cellular pathways and gene networks underlying the onset of disease, and the mechanisms of pharmacological treatments that ameliorate disease phenotypes. In this article, we review a number of approaches being used by pharmaceutical and biotechnology companies, e.g., high-throughput DNA genotyping, sequencing, and genome-wide gene expression profiling, to enable drug discovery and development through the identification of new drug targets and biomarkers of disease progression, drug pharmacodynamics, and predictive markers for selecting the patients most likely to respond to therapy.

Cefoperazone-treated mice as an experimental platform to assess differential virulence of Clostridium difficile strains

The toxin-producing bacterium C. difficile is the leading cause of antibiotic-associated colitis, with an estimated 500,000 cases C. difficile infection (CDI) each year in the US with a cost approaching 3 billion dollars. Despite the significance of CDI, the pathogenesis of this infection is still being defined. The recent development of tractable murine models of CDI will help define the determinants of C. difficile pathogenesis in vivo. To determine if cefoperazone-treated mice could be utilized to reveal differential pathogenicity of C. difficile strains, 5-8 week old C57BL/6 mice were pretreated with a 10 d course of cefoperazone administered in the drinking water. Following a 2-d recovery period without antibiotics, the animals were orally challenged with C. difficile strains chosen to represent the potential range of virulence of this organism from rapidly fatal to nonpathogenic. Animals were monitored for loss of weight and clinical signs of colitis. At the time of harvest, C. difficile strains were isolated from cecal contents and the severity of colitis was determined by histopathologic examination of the cecum and colon. Cefoperazone treated mice challenged with C. difficile strains VPI 10463 and BI1 exhibited signs of severe colitis while infection with 630 and F200 was subclinical. This increased clinical severity was correlated with more severe histopathology with significantly more edema, inflammation and epithelial damage encountered in the colons of animals infected with VPI 10463 and BI1. Disease severity also correlated with levels of C. difficile cytotoxic activity in intestinal tissues and elevated blood neutrophil counts. Cefoperazone treated mice represent a useful model of C. difficile infection that will help us better understand the pathogenesis and virulence of this re-emerging pathogen.