A CHEMICALLY DEFINED MEDIUM INDUCES RESISTANCE TO LIPOPOLYSACCHARIDE ANTIBODY IN HAEMOPHILUS-INFLUENZAE TYPE-B

Haemophilus influenzae type b was more resistant to killing by lipopolysaccharide (LPS) antibody and complement after growth in defined medium than in conventional broths. Resistance correlated with decreased binding of LPS antibody, as determined by a whole-cell enzyme-linked immunosorbent assay. An inhibition radioimmunoassay was used to determine that bacteria grown in defined medium contained about 2.5 times more capsule than bacteria grown in conventional broth. No major differences were noted in the electrophoretic patterns of outer membrane proteins or LPS. The defined medium did not increase the resistance of a capsule-deficient mutant. Resistance and increased encapsulation could be reproduced after growth in conventional broth supplemented with magnesium, glutamic acid, and aspartic acid. Thus, the growth medium may influence the content of capsule on H. influenzae type b, and may in turn, influence the binding and bactericidal activity of LPS antibody to the cells.