microbiology, Vol 140, 263-270, Copyright © 1994 by Society for General Microbiology
Modulation of Pasteurella multocida capsular polysaccharide during growth under iron-restricted conditions and in vivo
M Jacques, M Belanger, MS Diarra, M Dargis and F Malouin
Departement de Pathologie et Microbiologie, Faculte de Medecine Veterinaire, Universite de Montreal, St-Hyacinthe, Quebec, Canada.
Addition of the iron chelators 2,2'-dipyridyl, deferoxamine mesylate or
apo-transferrin to culture media affected the composition and the
morphology of Pasteurella multocida cells. Cells grown under iron-
restricted conditions expressed iron-regulated proteins and, in addition,
iron deprivation markedly reduced the amount of capsular material covering
the cells of P. multocida. The addition of iron neutralized the effect of
these chelators on capsule production. Cells of P. multocida grown under
iron-restricted conditions were more labelled by gold particles coated with
polymyxin which is known to interact with the lipid A-core region of
lipopolysaccharides, and showed increased affinity for porcine respiratory
tract mucus than cells grown under iron-sufficient conditions. Bacterial
cells grown in vivo in peritoneal chambers in rats were also only covered
by a thin layer (15-20 nm) of capsular material. Although the capsule is
believed to be an important virulence factor, our data indicate that under
iron- restricted conditions, such as those encountered in vivo, P.
multocida may not be heavily encapsulated.
