Sources of low-molecular-weight host factors that phenotypically increase the resistance of Haemophilus influenzae type b to bacteriolysis: non-identity with a factor active in gonococci

Abstract

Both gonococci and Haemophilus influenzae type b (Hib) in response to incubation with low-molecular-weight components of blood are converted to a relative resistance to killing by antibody and complement in vitro. Recently, cytidine 5′-mono-phospho-N-acetylneuraminic acid (a sialyl donor present in mammalian tissues) was found to convert gonococci. Here we report that this compound was inactive in Hib. In further contrast, the Hib-converting activity of serum was not retained by 500-M r filters, not sensitive to pH 2, and not active in the presence of growth media. Thus the phenotypic resistances in Hib and gonococci appear to have a different metabolic basis. The low-M r serum factors active in Hib remain to be identified. Filtrates of human nasopharyngeal washes were also active, further suggesting that the converted form resembles the phenotype of Hib in vivo.