Immune defence mechanism against blood-borne Pasteurella multocida in turkeys

Pasteurella multocida: diseases and pathogenesis

Pasteurella multocida is an enigmatic pathogen. It is remarkable both for the number and range of specific disease syndromes with which it is associated, and the wide range of host species affected. The pathogenic mechanisms involved in causing the different syndromes are, for the most part, poorly understood or completely unknown. The biochemical and serological properties of some organisms responsible for quite different syndromes appear to be similar. Thus, the molecular basis for host predilection remains unknown. The recent development of genetic manipulation systems together with the availability of multiple genome sequences should help to explain the association of particular pathological conditions with particular hosts as well as helping to elucidate pathogenic mechanisms.

Protective immunity conferred by attenuated aroA derivatives of Pasteurella multocida B:2 strains in a mouse model of hemorrhagic septicemia

Hemorrhagic septicemia (HS) is a fatal systemic disease of cattle and buffaloes. In South Asia HS is caused by infection with Pasteurella multocida serotype B:2. Some control is achieved with alum-precipitated or oil-adjuvanted killed whole-cell vaccines injected subcutaneously, but these vaccines provide only short-term immunity and require annual administration for effective use. Live attenuated vaccines have the advantage of a natural route of entry into the host, but for live strains to be used as vaccines, the mode of attenuation should be well defined. We constructed aroA attenuated derivatives of two P. multocida serotype B:2 strains by allelic exchange of the native aroA sequence with aroA sequences disrupted with a kanamycin resistance cassette or with marker-free aroA sequences containing an internal deletion. These strains were confirmed to be aroA mutants by PCR and Southern blot analysis, enzyme assay, and lack of growth on minimal medium. The aroA derivatives were highly attenuated for virulence in a mouse model of HS. Mouse challenge experiments showed that intraperitoneal or intranasal vaccination of an aroA strain completely protected mice against challenge with a high dose (>1,000 50% lethal doses) of either the parent strain or the other wild-type B:2 strain. The spread of the parent and the aroA derivatives to different organs was compared when the organisms were inoculated by different routes.

Pasteurella multocida enters polarized epithelial cells by interacting with host F-actin

We investigated the interaction of an avian strain of Pasteurella multocida with the cytoskeleton of MDCK cells, which formed a polarized epithelium when grown on type I collagen coated filters. Bacteria were incubated with MDCK cells for 30 min. 2, 4 and 6 hours and their location and association with the cell cytoskeleton determined by double-label immunofluorescence confocal microscopy. Cells were stained with a polyclonal antiserum to the outer-membrane proteins of P. multocida and with rhodamine phalloidin which specifically binds filamentous (F) actin. Confocal microscopy revealed that bacteria entered the cells by 30 min, and that by 6 hours there was a marked alteration in the actin cytoskeleton in which long filaments were reorganized to discrete foci of short actin filaments, within which were one or more bacteria. Electron microscopy demonstrated that by 2 hours, each bacterium was associated with many short 5-6 nm filaments. Treatment of MDCK cells with cytochalasin D for either 30 minutes or 24 hours prior to infection disrupted the actin cytoskeleton and inhibited entry of P. multocida.