SEROGROUP-F STRAINS OF CLOSTRIDIUM-DIFFICILE PRODUCE TOXIN-B BUT NOT TOXIN-A

Most toxigenic strains of Clostridium difficile produce two toxins: an enterotoxin (toxin A) and a cytotoxin (toxin B). Only one strain (str ain 8864) has been reported to produce toxin B but no toxin A. Serogro up F strains (44) of C. difficile, often isolated from asymptomatic in fants, have been examined for toxin production. These strains, which w ere from distinct geographical and clinical sources, did not produce a ny detectable toxin A in vitro when examined in three distinct immunoa ssays. Nevertheless, all the strains produced a cytotoxin. Immunologic al differences between the cytotoxin of the serogroup F strains and th at produced by C. difficile strain VPI 10463 (serogroup G) were demons trated with monoclonal antibodies specific for either the toxin B prod uced by C. difficile strain VPI 10463 or C. sordellii lethal toxin (LT ). Polymerase chain reaction amplification with primers derived from C . difficile strain VPI 10463 toxin A and B genes showed that serogroup F strains seem to possess a toxin B gene homologous with that of stra in VPI 10463 and at least fragments of the toxin A gene. When axenic m ice were inoculated with serogroup F strains, the animals survived; th ey did not develop diarrhoea and no toxin A could be detected in their faeces. However, cytotoxin was detected. Furthermore, these mice were protected against subsequent challenge with the otherwise lethally to xigenic C. difficile strain VPI 10463. The serogroup F strains appeare d to be homogeneous and distinct from other C. difficile strains with regard to toxin production.