Toxigenic status of Clostridium difficile in a large Spanish teaching hospital

Prevalence and molecular types of Clostridium difficile isolates from faecal specimens of patients in a tertiary care centre

Clostridium difficile infection (CDI) leads to considerable morbidity and mortality among hospitalized patients. Faecal specimens from 1110 hospitalized patients suspected for CDI were cultured for isolation of C. difficile and characterization of virulence genes. PCR was carried out for toxigenic genes tcdA, tcdB, cdtA and cdtB and PCR-RFLP for fliC and slpA genes. Of 174 (15.7%) C. difficile isolates, 121 (69.5%) were toxigenic, amongst which 68 (56.2%) also had both tcdA and tcdB genes. The remaining 53 (43.8%) of the isolates also had at least one of the toxin genes. Binary toxin genes (cdtA and cdtB) with only one of the two components were present in 16 (9.2%) of the 174 isolates. The other virulence genes - fliC and slpA - were present in 100% of the isolates. The most frequent PCR-RFLP type of fliC gene was type I (n = 101), followed by type VII (n = 49) and type III (n = 24). The slpA gene presented with three combinations of patterns. Characterization of virulence genes in C. difficile isolates is of extreme importance for epidemiological surveillance and control of outbreaks owing to the capacity of this bacterium to adapt to new environmental circumstances, leading to the emergence of new epidemic strains.

Epidemiology and clinical features of toxigenic culture-confirmed hospital-onset Clostridium difficile infection: a multicentre prospective study in tertiary hospitals of South Korea

Hypervirulent Clostridium difficile strains, most notably BI/NAP1/027, have been increasingly emerging in Western countries as local epidemics. We performed a prospective multicentre observational study from December 2011 to May 2012 to identify recent incidences of toxigenic culture-confirmed hospital-onset C. difficile infections (CDI) and their associated clinical characteristics in South Korea. Patients suspected of having been suffering from CDI more than 48 h after admission and aged ≥20 years were prospectively enrolled and provided loose stool specimens. Toxigenic C. difficile culture (anaerobic culture+toxin A/B/binary gene PCR) and PCR ribotyping were performed in one central laboratory. We enrolled 98 toxigenic culture-confirmed CDI-infected patients and 250 toxigenic culture-negative participants from three hospitals. The incidence of toxigenic culture-confirmed hospital-onset CDI cases was 2.7 per 10,000 patient-days. The percentage of severe CDI cases was relatively low at only 3.1%. UK ribotype 018 was the predominant type (48.1%). There were no hypervirulent BI/NAP1/027 isolates identified. The independent risk factors for toxigenic culture-confirmed hospital-onset CDI were invasive procedure (odds ratio (OR) 7.3, P=0.003) and past CDI history within 3 months (OR 28.5, P=0.003). In conclusion, the incidence and severity of CDI in our study were not higher than reported in Western countries.

Clostridium difficile binary toxin CDT: mechanism, epidemiology, and potential clinical importance

Binary toxin (CDT) is frequently observed in Clostridium difficile strains associated with increased severity of C. difficile infection (CDI). CDT belongs to the family of binary ADP-ribosylating toxins consisting of two separate toxin components: CDTa, the enzymatic ADP-ribosyltransferase which modifies actin, and CDTb which binds to host cells and translocates CDTa into the cytosol. CDTb is activated by serine proteases and binds to lipolysis stimulated lipoprotein receptor. ADP-ribosylation induces depolymerization of the actin cytoskeleton. Toxin-induced actin depolymerization also produces microtubule-based membrane protrusions which form a network on epithelial cells and increase bacterial adherence. Multiple clinical studies indicate an association between binary toxin genes in C. difficile and increased 30-d CDI mortality independent of PCR ribotype. Further studies including measures of binary toxin in stool, analyses of CDI mortality caused by CDT-producing strains, and examination of the relationship of CDT expression to TcdA and TcdB toxin variants and PCR ribotypes are needed.

Comparative genome and phenotypic analysis of Clostridium difficile 027 strains provides insight into the evolution of a hypervirulent bacterium

A genome comparison of non-epidemic and epidemic strains of Clostridium difficile reveals gene gains that could explain how a hypervirulent strain has emerged

Background

The continued rise of Clostridium difficile infections worldwide has been accompanied by the rapid emergence of a highly virulent clone designated PCR-ribotype 027. To understand more about the evolution of this virulent clone, we made a three-way genomic and phenotypic comparison of an 'historic' non-epidemic 027 C. difficile (CD196), a recent epidemic and hypervirulent 027 (R20291) and a previously sequenced PCR-ribotype 012 strain (630).

Results

Although the genomes are highly conserved, the 027 genomes have 234 additional genes compared to 630, which may contribute to the distinct phenotypic differences we observe between these strains relating to motility, antibiotic resistance and toxicity. The epidemic 027 strain has five unique genetic regions, absent from both the non-epidemic 027 and strain 630, which include a novel phage island, a two component regulatory system and transcriptional regulators.

Conclusions

A comparison of a series of 027 isolates showed that some of these genes appeared to have been gained by 027 strains over the past two decades. This study provides genetic markers for the identification of 027 strains and offers a unique opportunity to explain the recent emergence of a hypervirulent bacterium.

Heterogeneity of large clostridial toxins: importance of Clostridium difficile toxinotypes

Clostridium difficile toxinotypes are groups of strains defined by changes in the PaLoc region encoding two main virulence factors: toxins TcdA and TcdB. Currently, 24 variant toxinotypes (I-XXIV) are known, in addition to toxinotype 0 strains, which contain a PaLoc identical to the reference strain VPI 10463. Variant toxinotypes can also differ from toxinotype 0 strains in their toxin production pattern. The most-studied variant strains are TcdA-, TcdB+ (A-B+) strains and binary toxin CDT-producing strains. Variations in toxin genes are also conserved on the protein level and variant toxins can differ in size, antibody reactivity, pattern of intracellular targets (small GTPases) and consequently in their effects on the cell. Toxinotypes do not correlate with particular forms of disease or patient populations, but some toxinotypes (IIIb and VIII) are currently associated with disease of increased severity and outbreaks worldwide. Variant toxinotypes are very common in animal hosts and can represent from 40% to 100% of all isolates. Among human isolates, variant toxinotypes usually represent up to 10% of strains but their prevalence is increasing.

Molecular characterization and antimicrobial susceptibility patterns of Clostridium difficile strains isolated from hospitals in south-east Scotland

Clostridium difficile isolates (n=149) collected in south-east Scotland between August and October 2005 were typed by four different methods and their susceptibility to seven different antibiotics was determined. The aims were to define the types of strain occurring in this region and to determine whether there were any clonal relationships among them with respect to genotype and antibiotic resistance pattern. Ribotyping revealed that 001 was the most common type (n=113, 75.8 %), followed by ribotype 106 (12 isolates, 8.1 %). The majority of the isolates (96.6 %, n=144) were of toxinotype 0, with two toxinotype V isolates and single isolates of toxinotypes I, IV and XIII. PCR and restriction analysis of the fliC gene from 147 isolates gave two restriction patterns: 145 of pattern VII and two of pattern I. Binary toxin genes were detected in only three isolates: two isolates of ribotype 126, toxinotype V, and one isolate of ribotype 023, toxinotype IV. S-types showed more variation, with 64.5 % (n=40) of the common S-type (4939) and 21 % (n=13) of S-type 4741, with six other S-types (one to three isolates each). All ribotype 001 isolates were of the same S-type (4939), with three isolates of other ribotypes being this S-type. No resistance was found to metronidazole or vancomycin, with resistance to tetracycline only found in 4.3 % of the isolates. A high proportion of isolates were resistant to clindamycin (62.9 %), moxifloxacin, ceftriaxone (both 87.1 %) and erythromycin (94.8 %). Resistance to three antibiotics (erythromycin, clindamycin and ceftriaxone) was seen in 66 isolates, with erythromycin, ceftriaxone and moxifloxacin resistance seen in 96 isolates. Resistance to all four of these antibiotics was found in 62 isolates and resistance to five (the above plus tetracycline) in one isolate: a ribotype 001, toxinotype 0 strain. Whilst ribotype 001 was the most commonly encountered type, there was no evidence of clonal relationships when all other typing and antibiotic resistance patterns were taken into account.

Implications of the changing face of Clostridium difficile disease for health care practitioners

Recent reported outbreaks of Clostridium difficile-associated disease in Canada have changed the profile of C difficile infections. Historically, C difficile disease was thought of mainly as a nosocomial disease associated with broad-spectrum antibiotics, and the disease was usually not life threatening. The emergence of an epidemic strain, BI/NAP1/027, which produces a binary toxin in addition to the 2 classic C difficile toxins A and B and is resistant to some fluoroquinolones, was associated with large numbers of cases with high rates of mortality. Recently, C difficile has been reported more frequently in nonhospital-based settings, such as community-acquired cases. The C difficile disease is also being reported in populations once considered of low risk (children and young healthy women). In addition, poor response to metronidazole treatment is increasing. Faced with an increasing incidence of C difficile infections and the changing profile of patients who become infected, this paper will reexamine the current concepts on the epidemiology and treatment of C difficile-associated disease, present new hypotheses for risk factors, examine the role of spores in the transmission of C difficile, and provide recommendations that may enhance infection control practices.

Variant forms of the binary toxin CDT locus and tcdC gene in Clostridium difficile strains

Variability in the genes for toxin A, toxin B and other pathogenicity locus regions is well known and is the basis for the distribution of Clostridium difficile strains into variant toxinotypes. Previous data have indicated that some C. difficile strains have a non-functional truncated form of the binary toxin (CDT) locus. This study analysed variability in the CDT locus and the presence of deleted tcdC genes in C. difficile strains. A total of 146 strains were screened, including known variant toxinotypes and non-variant A+B+ (toxinotype 0) and A-B- C. difficile strains. In all of the strains studied, only two forms of the CDT locus were found: a full-length 4.3 kb fragment encoding the functional binary toxin or a truncated 2.3 kb fragment. Whilst the full-length CDT locus was found almost exclusively in variant toxinotypes, the truncated form was detected in 79% of toxinotype 0 strains. Non-toxinogenic A-B- strains with a truncated version were not found and only rarely possessed the full-length CDT locus (A-B-CDT+ strains). Four different forms of the tcdC gene were found; three represented deleted versions and typically were found in toxinotypes III-VII, XI, XIV-XVI and XXIV.

Antimicrobial therapy of Clostridium difficile-associated diarrhea

Clostridium difficile-associated diarrhea (CDAD) is the most common etiologically-defined cause of hospital-acquired diarrhea. Caused by the toxins of certain strains of C difficile, CDAD represents a growing concern, with epidemic outbreaks in some hospitals where very aggressive and difficult-to-treat strains have recently been found. Incidence of CDAD varies ordinarily between 1 to 10 in every 1,000 admissions. Evidence shows that CDAD increases morbidity, length of stay, and costs. This article described the clinical manifestations of CDAD, related risk factors, considerations for confirming CDAD, antimicrobial and non-antimicrobial treatment of CDAD, and issues related to relapses. The article concludes with a discussion of recent epidemic outbreaks involving CDAD.