Susceptibility of Haemophilus paragallinarum to bactericidal activity of normal and immune chicken sera.

Abstract

Bactericidal (BC) activity of fresh or heated, normal (NCS) and immune (ICS) chicken sera was investigated with encapsulated and nonencapsulated variants dissociated from serotype HA-1 strain 221 of Haemophilus paragallinarum. The BC titer was expressed as the highest serum-dilution reducing viable cell count by 50% after reaction time of 3 hr. Nonencapsulated organisms were shown to be sensitive to the BC activity of fresh NCS, in which no specific antibodies were demonstrable, but encapsulated organisms resisted the BC activity. Fresh ICS with the detectable hemagglutination-inhibition (HI) and agglutination antibodies were bactericidal for both encapsulated and nonencapsulated organisms, but the activity was completely lost by heating at 56°C for 30 min. The BC activity appears to be due to the antibodies against HA-L hemagglutinin and/or L agglutinogen located on outer membrane of the cell, but not to the antibodies against capsular or other somatic antigens except for the HA-L and L antigens.