Role of DNA and bacteriophage in Campylobacter auto-agglutination

Auto-agglutinated and non-agglutinated cells of Campylobacter jejuni and C. coli were examined by transmission electronmicroscopy in phosphotungstate negative stain. Agglutination was induced by three factors (1) extracellular DNA, (2) an aggregated protein, probably a bacteriophage precursor, and (3) free phage-tail sheaths. Auto-agglutinated cells were often "leaky," with a mantle of adhering DNA. About 80% of the auto-agglutinated cells could be resuspended after treatment with DNAase. Flagella were loosely embedded in protein aggregates, especially in phage-infected cultures. They were clumped in a side-by-side arrangement by free phage-tail sheaths. These findings suggest that auto-agglutination could be minimised in suspensions of organisms intended for use in agglutination tests by harvesting early logarithmic-phase cells containing no more than a low phage population. The most common C. jejuni phage had a contractile tail, a head diameter of 60-70 nm, and an overall length of 180-210 nm. A phage isolated from C. jejuni strain 1590 was morphologically identical with C. coli phage.