Characterization of a Toxin A-Negative, Toxin B-Positive Strain of Clostridium difficile Responsible for a Nosocomial Outbreak of Clostridium difficile -Associated Diarrhea

Abstract

Clostridium difficile-associated diarrhea (CAD) is a very common nosocomial infection that contributes significantly to patient morbidity and mortality as well as to the cost of hospitalization. Previously, strains of toxin A-negative, toxin B-positive C. difficile were not thought to be associated with clinically significant disease. This study reports the characterization of a toxin A-negative, toxin B-positive strain ofC. difficile that was responsible for a recently described nosocomial outbreak of CAD. Analysis of the seven patient isolates from the outbreak by pulsed-field gel electrophoresis indicated that this outbreak was due to transmission of a single strain of C. difficile. Our characterization of this strain (HSC98) has demonstrated that the toxin A gene lacks 1.8 kb from the carboxy repetitive oligopeptide (CROP) region but apparently has no other major deletions from other regions of the toxin A or toxin B gene. The remaining 1.3-kb fragment of the toxin A CROP region from strain HSC98 showed 98% sequence homology with strain 1470, previously reported by M. Weidmann in 1997 (GenBank accession number Y12616), suggesting that HSC98 is toxinotype VIII. The HSC98 strain infecting patients involved in this outbreak produced the full spectrum of clinical illness usually associated with C. difficile-associated disease. This pathogenic spectrum was manifest despite the inability of this strain to alter tight junctions as determined by using in vitro tissue culture testing, which suggested that no functional toxin A was produced by this strain.

Essential role of toxin A in C. difficile 027 and reference strain supernatant-mediated disruption of Caco-2 intestinal epithelial barrier function

“…Our findings using Caco-2 cells are consistent with those previously reported using the T84 epithelial cell line and purified toxins A and B [27]. The inability of supernatant samples of a toxin A-negative, toxin B-positive strain of C. difficile, as shown by us and also reported previously [16], further supports the concept of the lack of a biological effect of apically-applied toxin B in intestinal epithelial monolayers. These findings imply the presence of distinct receptors for toxins A and B, with receptors for the latter only present on the basolateral surface of epithelial cells.…”

Epidemiology of Clostridium difficile infections in a tertiary-care hospital in Korea

“…Toxin A-negative ribotype 017 strains were known to be prevalent in East Asia, whereas their prevalence in Europe and North America was as low as 0.2-8% [6,10,[20][21][22]. Studies of the outcomes and clinical manifestations of CDI caused by toxin A-negative toxin B-positive ribotype 017 strains have reported conflicting results: some found no difference from other ribotypes [10,[23][24][25], while others reported more severe disease and significantly worse outcomes [24,26]. Ribotypes 001 and 014 were reported as prevalent in Europe (16% and 10%, respectively), where they were distributed over a large area [6].…”

Laboratory diagnosis of Clostridium difficile disease

“…Finally, in one of the latest kits, the detection of toxin A is coupled with the detection of a glutamate dehydrogenase, a C. difficile-specific enzyme found in toxigenic as well as in non-toxigenic isolates. The reason why kits detecting both toxins have been developed is mainly because some isolates from clinical cases have been shown to produce only toxin B [15]. In our experience, such strains are very rarely observed.…”