Toxins A and B are the primary virulence factors of Clostridium difficile.
Since 2002, an epidemic of C difficile-associated disease with increased morbidity and mortality has been present in Quebec province, Canada.
Dr Michel Warny and colleagues characterized the dominant strain of this epidemic.
The researchers determined whether the dominant strain produces higher amounts of toxins A and B than those produced by non-epidemic strains.
The research team obtained isolates from 124 patients from Centre Hospitalier Universitaire de Sherbrooke in Quebec.
Additional isolates from the USA, Canada, and the United Kingdom were included to increase the genetic diversity of the toxinotypes tested.
|The epidemic strain was isolated from 72 with C difficile-associated disease|
Isolate characterization included toxinotyping, pulsed-field gel electrophoresis, and polymerase chain reaction ribotyping.
The isolate characterization also included the detection of a binary toxin gene, and detection of deletions in a putative negative regulator for toxins A and B.
By use of an enzyme-linked immunoassay, the team measured the in-vitro production of toxins A and B by epidemic strain and non-dominant strain isolates.
The team found that the epidemic strain was characterized as toxinotype III, and North American pulsed-field gel electrophoresis type 1.
The polymerase chain reaction-ribotype 027 was also characterized by the epidemic strain.
The researchers noted that this strain carried the binary toxin gene cdtB and an 18-bp deletion in a putative negative regulator for toxins A and B.
The research team isolated this strain from 72 patients with C difficile-associated disease.
Peak median toxin A concentrations produced in vitro by polymerase chain reaction-ribotype 027 were 16 times higher than those measured in isolates.
The team observed that peak median toxin B concentrations produced in vitro by polymerase chain reaction-ribotype 027 were 23 times higher than those measured in isolates.
The isolates represented 12 different pulsed-field gel electrophoresis types, known as toxinotype 0.
Dr Warny's team concludes, “The severity of C difficile-associated disease caused by polymerase chain reaction-ribotype 027 could result from hyperproduction of toxins A and B.”
“Dissemination of this strain in North America and Europe could lead to important changes in the epidemiology of C difficile-associated disease.”