MODULATION OF PASTEURELLA-MULTOCIDA CAPSULAR POLYSACCHARIDE DURING GROWTH UNDER IRON-RESTRICTED CONDITIONS AND IN-VIVO

Addition of the iron chelators 2.2'-dipyridyl. deferoxamine mesylate o r apo-transferrin to culture media affected the composition and the mo rphology of Pasteurella multocida cells. Cells grown under iron-restri cted conditions expressed iron-regulated proteins and, in addition, ir on deprivation markedly reduced the amount of capsular material coveri ng the cells of P. multocida. The addition of iron neutralized the eff ect of these chelators on capsule production. Cells of P. multocida gr own under iron-restricted conditions were more labelled by gold partic les 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 r ats were also only covered by a thin layer (15-20 nm) of capsular mate rial. Although the capsule is believed to be an important virulence fa ctor, our data indicate that under iron-restricted conditions, such as those encountered in vivo, P. multocida may not be heavily encapsulat ed.