Complement-dependent bactericidal activity for E. coli K12 in serum of preterm newborn infants.

Complement-dependent serum bactericidal activity for E. coli K12 was assessed in 12 term infants and in 16 preterm infants. In both groups of newborns, at birth, bactericidal reaction by the classical pathway of complement activation was impaired with respect to normal controls at less than 0.001 level of significance (as estimated by Student's t-test). The serum bactericidal reaction by the alternative pathway of complement activation was significantly impaired only in preterm newborns, being normal in term infants. At a time corresponding to 40 weeks' gestational age also in preterm newborns alternative pathway mediated bactericidal activity for E. coli K12 was found normal. Classical pathway mediated bactericidal activity became normal only at an age corresponding to 52 weeks' gestational age.