Growth of Haemophilus influenzae type b in the presence of bovine aortal endothelial cells.

In serum-free medium in the presence of bovine aortal endothelial cells (BAOEC), Haemophilus influenzae type b was capable of extensive proliferation compared to that in serum-free medium alone. An unidentified low-molecular-mass (less than 2000 kDa) compound(s) was, in part, responsible for this phenomenon. There were changes in the outer-membrane protein profiles between broth-grown (the original inoculum) and BAOEC-grown organisms, particularly in the 45-70 kDa range. Both broth- and BAOEC-grown bacteria were serum sensitive in vitro but could be converted to a serum-resistant phenotype, resembling that found in vivo, by incubation in a serum filtrate.