Effect of the complement system on the sensitivity of Campylobacter jejuni and Campylobacter coli to human blood serum.

We determined the sensitivity of five strains of Campylobacter jejuni and C. coli isolated from children with diarrhea and from chicken feces to normal human blood serum (undiluted and at concentrations of 10, 30, 50 and 70%), a hypogammaglobulinemic serum and a complement-deficient serum. Both species were highly sensitive to the bactericidal activity of human serum, regardless of their source. The highest bactericidal activity was observed with pooled fresh normal serum, with bacterial survival rates inversely correlated to serum dilutions. Inactivated serum had the least bactericidal activity. When complement was partially restored to inactivated serum, lower survival rates were observed. The hypogammaglobulinemic-normal complement-containing serum had strong bactericidal activity whereas the normal immunoglobulin-containing but complement-deficient serum had little bactericidal activity. These results suggest that Campylobacter may be able to directly activate complement by the alternative pathway.