Clostridioides difficile (including epidemiology)Microbiological features, epidemiology, and clinical presentation of Clostridioides difficile strains from MLST Clade 2: A narrative review
Introduction
Clostridioides difficile is a Gram-positive, strictly anaerobic, spore-forming bacterium, and a leading cause of antibiotic-associated diarrhea worldwide [1,2]. C. difficile infection (CDI) is defined by the presence of diarrhea, which varies from mild to severe, and either by detection of C. difficile toxins in stool samples or pseudomembranous colitis in a colonoscopy or histopathologic studies [3]. Other potential complications of CDI include toxic megacolon or even death [4].
CDI typically develops among hospital patients with risk factors beyond receiving antibiotic therapy, such as older age, exposure to health care centers, and comorbidities such as inflammatory bowel disease and immunodeficiency, among others [5]. However, the epidemiology of CDI is changing, and a growing number of community-acquired (CA) cases have been seen among individuals considered to be at low-risk, including young adults and children [6]. Furthermore, many CDI cases now show more severe symptoms and require more prolonged hospitalizations; hence the burden of this disease on health systems continues to increase [5,7].
The major virulence factors of C. difficile are toxins TcdA and TcdB, which belong to the large clostridial glycosylating toxin family. Both toxins play a role in symptom development [8,9]. Nonetheless, as demonstrated by assays in animal models, only TcdB seems to be essential for virulence [10]. Other proteins, such as the surface layer protein (SlpA), cell wall protein 84 (Cwp84), flagellar components, and the binary toxin CDT, have also been shown to play roles in CDI pathogenesis [11,12].
Comparative analyses of global collections of C. difficile whole genome sequences have demonstrated that TcdB is much more diverse than TcdA (12 vs. 7 protein sequence subtypes), possibly as a result of a higher mutation rate or distinct recombination and lateral gene transfer events in the former protein [13,14]. Both genes appear to be under purifying selection, although tcdB shows more positively selected sites [13,14].
TcdB variants differ in their biological features, immunoactivities, and potential pathogenicity, and this heterogeneity correlates with the severity of clinical outcomes during CDI progression. Depending on the sequence of its glycosyltransferase domain (GTD), which influences toxins’ functionalities and target affinities, TcdB can induce two types of cytopathic effects (CPE): a classical, arborizing, CPE in which cells develop neurite-like protrusions and remain attached to cell culture plates [15], or a TcsL-like effect that is characterized by cell rounding and clumping and surface detachment [15,16].
Together with polymorphisms in toxin alleles, strain differences in virulence have been traced to antimicrobial resistance patterns [17], spore production and germination capabilities [18], and recently to phase-variable signal transduction systems [19], c-di-GMP levels [20], and the production of alarmones [21], among other factors.
The high diversity that distinguishes this species has encouraged the implementation of various typing techniques, some of which have proven useful in epidemiological investigations and the identification of strains with unique biological properties [22,23].
The first C. difficile typing techniques were based on phenotypic traits. However, they suffered from low discriminatory power and reproducibility and were replaced by genotypic approaches.
Genotypic typing methods can be classified according to the nature of their targets and as to whether they are band- or sequence-based (Table 1). Whereas pulsed-field gel electrophoresis (PFGE) is frequently used in North America, PCR ribotyping is the most frequently used C. difficile genotyping method in Europe. Multilocus sequence typing (MLST) is more suitable for evolutionary studies, outbreak detection, and transmission or population structure studies [24].
MLST allows isolate discrimination through sequencing of 405–500 bp DNA fragments of seven or eight housekeeping genes (for C. difficile, seven gene fragments, total length 3501 bp). The obtained sequences are compared with reference sequences uploaded to internet-accessible MLST databases (https://pubmlst.org/organisms/clostridioides-difficile/) and used to generate allelic profiles composed of allele numbers assigned to sequence variants of a given locus. Each unique allele profile is assigned a sequence type number that is stored in the database to facilitate interlaboratory comparison [23,24].
As indicated by MLST, the known population of C. difficile can be distributed in eight clades (Clades 1 to 5, plus Clades C-I, C-II, and C-III) [23,25]. Whereas isolates from Clades 1-5 are more often associated with humans [26,27], the so-called cryptic Clades C-I to C-III mainly include non-toxigenic isolates from the environment [25] and, to a lesser extent, toxigenic strains implicated in CDI [30]. New STs with different host affinities, ecological adaptations, and virulence potentials are continually being identified.
According to a globally-optimized eBURST cluster analysis [28] showed herein, the C. difficile MLST Clade 2 comprises 84 STs distributed in 15 clonal complexes (Fig. 1, Fig. 2). It includes the highly recognized NAP1/027/ST01 strain, and for this reason, it has been repeatedly referred to as the “hypervirulent clade” [29,30] although the virulence and pathogenicity potential of most non-NAP1/027/ST01 strains are poorly understood or unknown. To corroborate whether increased virulence is indeed a widespread trait among members of this clade, we compared in this review microbiological, epidemiological and, clinical features of various C. difficile Clade 2 sequence types (STs).
We collected scientific articles published between 1999 and 2020 in English from the Google Scholar, JSTOR, Scopus, and PubMed databases using keywords such as “C. difficile MLST”, “C. difficile Clade 2”, “C.difficile ST01”, “C.difficile ST67”, “C.difficile ST41”, “C. difficile typing techniques”, “C. difficile transmission”, “C.difficile antibiotic-resistance”, “C. difficile toxins”, “C.difficile emergent sequence types”. A total of 31 publications were selected to elaborate elementary aspects of C. difficile, including its main virulence factors, CDI pathogenesis, epidemiology, typing techniques and, phylogenetic classification. The number of publications obtained for each ST differed, with a marked predominance of studies on the ST01 strain (n = 40). This figure was followed by papers on ST67 and ST41 (ca. 20 publications for each one). Information for STs 188/231/365 was even more scarce (less than 10 publications). A few STs, such as ST62, ST95, ST97, ST114, ST123, ST154, ST192, ST223, ST229, ST264, and ST461-464, have only been analyzed with regards to their virulence factors and origins. No information was found for 55 Clade 2 STs.
Section snippets
Microbiological features
ST01 is by far the best-described Clade 2 member. ST01 strains have been reported to overproduce toxins TcdA and TcdB subtype 2 (TcdB2) in vitro [13,31,32], arguably as a result of an 18bp deletion and a single-base-pair deletion at position 117 in the gene for the transcriptional regulator TcdC [32,33]. Strains from this ST have been linked to 3- to 23-fold higher titers than those of the main hospital strains, according to results derived from Swedish [34] and Canadian studies [35]. However,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors thank Ricardo Gutiérrez, Enzo Guerrero, Jonathan Huffman, and William Huffman for their comments and suggestions to early versions of the manuscript. This work was supported by the Vicerectory of Research of the University of Costa Rica, grant B7606.
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Clostridioides difficile in Latin America: A comprehensive review of literature (1984–2021)
2022, AnaerobeCitation Excerpt :More recently, Trindade et al. [37] emphasized that the epidemic NAP1/B1/RT027 strain had not circulated in Brazil between 2003 and 2018 and highlighted a marked fluctuation in CDI incidence in some Brazilian states during the same period. Besides, multiple groups in LA have published reviews on more specific topics, including clinical, epidemiologic, and laboratory aspects of CDI [38,39], changes in C. difficile disease and its treatment [40], antimicrobial stewardship to reduce CDI [41], C. difficile spores [42], CDI in the pediatric population [43], prevention, diagnosis and treatment of CDI in Chile [44], government guidelines in Uruguay and Chile and lack thereof in Mexico and Central America [45], the role of C. difficile toxins in CDI [46], recommendations for CDI diagnostic, treatment, and prevention [47,48], and microbiological, epidemiologic, and clinical characteristic of MLST Clade 2 C. difficile strains [49]. Letters to editors urging re-evaluation of current diagnostic and therapeutic guidelines have also been published by professional societies in Chile [50].
TFPI is a colonic crypt receptor for TcdB from hypervirulent clade 2 C. difficile
2022, CellCitation Excerpt :Together, these results suggest a possible therapeutic avenue of simultaneous inhibiting both TFPI- and CSPG4-binding abilities, which provides optimal protection from the clade 2 C. difficile TcdB. Clinical strains belonging to C. difficile clade 2 are frequently isolated in North America, Europe, and Australia, accounting for over 20% of global CDI (Badilla-Lobo and Rodríguez, 2021; He et al., 2013; Knight et al., 2021). The clade 2 lineages have been generally concerned not only because they are epidemically associated with severe symptoms but also because they exclusively produce variant forms of TcdB that exhibit varied biological activities including receptor recognition (Lanis et al., 2010; Quesada-Gómez et al., 2016; Stabler et al., 2008).
Clostridioides difficile Toxin B Induced Senescence: A New Pathologic Player for Colorectal Cancer?
2023, International Journal of Molecular SciencesCytotoxic synergism of Clostridioides difficile toxin B with proinflammatory cytokines in subjects with inflammatory bowel diseases
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