Cell surface properties of Clostridium difficile: haemagglutination, relative hydrophobicity and charge.

Five well characterised strains of Clostridium difficile of differing virulence and two Escherichia coli strains, a verotoxigenic O157:H7 isolate and a urinary isolate, were examined for cell surface hydrophobicity and charge, and haemagglutinating ability. Phase partition in hexadecane or octan-1-ol was similar for C. difficile and E. coli, as was retention by hydrophobic interaction chromatography (HIC), indicating moderate hydrophobicity. The salt agglutination test showed E. coli to be hydrophobic and C. difficile to be hydrophilic. Relative hydrophobicity determined by HIC when charge effects were not nullified, i.e., to reflect more closely conditions in vivo, showed C. difficile to bind less well. Growth of C. difficile in caecal emulsions to simulate conditions in vivo did not alter the cell surface hydrophobicity. The phase partition method for charge determination indicated that E. coli and C. difficile had a net negative charge, although this was weaker for C difficile than E. coli. However, although E. coli exhibited a net negative charge as determined by immuno-gold electronmicroscopy (IGEM), in keeping with the results of the phase partition method, C. difficile was shown to be predominantly positively charged by IGEM, and by movement in a charged field as determined by paper electrophoresis and a novel method based on light microscope observation. A cell-wall deficient mutant of C. difficile was weakly positively charged, showing that most of the charge resides in the cell wall.