The Journal of Medical Microbiology, Vol 41, Issue 1 45-50, Copyright © 1994 by Society for General Microbiology
The influence of growth medium on serum sensitivity of Bacteroides species
E. Allan and I. R. Poxton
Department of Medical Microbiology, University of Edinburgh Medical School.
The susceptibility of 12 different Bacteroides strains (representing nine
species) to the bactericidal effect of human serum complement was
investigated. When grown in nutrient-rich proteose peptone-yeast extract
medium, all 12 strains were, to varying degrees, sensitive to serum.
However, when grown in Van Tassell and Wilkins's minimal medium, six of the
12 strains became markedly more serum resistant. Five of these six strains
became totally resistant to serum when grown in heat-inactivated (56
degrees C, 30 min) sheep serum. By Percoll discontinuous density
centrifugation and light microscopy, the ratio of bacteria with large and
small capsules was found to vary with the growth medium used.
Lipopolysaccharide (LPS) was extracted with aqueous phenol after growth in
the three media. Polyacrylamide gel electrophoresis (PAGE) and silver
staining of the LPS showed some differences in LPS profiles in all strains
tested. Therefore, variation of growth conditions results in alterations of
both the expression of surface structures and, in some cases, sensitivity
to serum. The biochemical basis for these changes requires further
investigation.
