Susceptibility of Campylobacter jejuni to strain-specific bactericidal activity in sera of infected patients.

Campylobacter jejuni is a common cause of inflammatory enteritis, which in normal hosts is usually self-limited and resolves without antibiotic therapy. C. jejuni bacteremia is very rare. We examined sera for bactericidal activity that might be important in limiting the extent of C. jejuni infection in man. We studied the ability of nonimmune sera and homologous and heterologous immune sera from infected patients to kill different fresh case isolates of C. jejuni in vitro. The reduction of the log10 concentration of viable C. jejuni (log10 killing) by fresh sera from nonimmune donors was only 0.2. Log10 killing by homologous acute sera varied from 0 to 3.8 (mean, 1.8). Convalescent sera showed remarkable log10 killing of only homologous C. jejuni, with values of 2.7 to 4.4 (mean, 3.7). The bactericidal effects of acute and convalescent sera were abrogated by heat and EDTA chelation, indicating mediation by complement. The role of classical complement pathway activation was supported by chelating sera with magnesium EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N, N, N', N'-tetraacetic acid] and by reconstitution experiments with heat-inactivated sera, C2-deficient serum, and purified C2. The requirement of specific antibody for the serum bactericidal effect was indicated by the loss of bactericidal activity when immune sera were absorbed with homologous but not heterologous whole C. jejuni isolates. The presence of specific antibodies was further documented by agglutination of only homologous C. jejuni suspensions by heat-inactivated immune sera. Studies with polymorphonuclear leukocytes suggested that ingestion and killing of two C. jejuni strains were modest and variable in the presence of heat-inactivated homologous serum. In summary, the data document a potent serum bactericidal effect that develops rapidly and specifically during C. jejuni enteritis and may be an important factor in host defense against C. jejuni.