Detection of strain-specific antigenic epitopes on the lipo-oligosaccharide of Haemophilus parasuis by use of monoclonal and polyclonal antibodies.

OBJECTIVE: To investigate the antigenic diversity of lipo-oligosaccharides of Haemophilus parasuis. PROCEDURES: Immunoblot assays were done with monoclonal and polyclonal antibodies on whole-cell lysates. Individual colonies of H parasuis strains H 54, H 53, and H 128 were tested for reactivity with lipo-oligosaccharide-specific monoclonal antibodies after a single passage on chocolate agar, and colonies of strain H 54 were analyzed after 10 passages. Colony blot tests were used to screen H parasuis strains for spontaneously occurring antigenic variation in their lipo-oligosaccharides. RESULTS: Eight H parasuis strains were separated into 4 lipo-oligosaccharide serovars on the basis of immunoblot reactions with 3 polyclonal rabbit antisera. Nine monoclonal antibodies against lipo-oligosaccharides of a lipo-oligosaccharide-serovar I strain reacted with all tested serovar I strains but failed to react with other H parasuis strains. CONCLUSIONS: Variations in the antigenic reactivity after 1 or 10 passages on chocolate agar were not observed. The serovar I lipo-oligosaccharide strains included virulent as well as avirulent H parasuis strains, indicating that these epitopes do not correlate directly with virulence properties of H parasuis.

Invasion and replication of Brucella abortus in three different trophoblastic cell lines.

This study was performed to compare the replication of the pathogenic strain Brucella abortus 2308 in three trophoblastic cell lines derived bovine placentas at different gestational stages. The trophoblastic cell lines were obtained from a 13-15 day embryo, from 5-month placentomal tissue and from an 8-month extra-placentomal portion of the placenta. The infection rate was similar in all cell lines at 4 h. Colony-forming Units were counted at 4, 8, 12, 24 and 30 h post-inoculation. At 12, 16, 24 and 30 h B. abortus rapidly replicated within the 5-month and 8-month trophoblastic cell lines, but grew slowly within trophoblastic cells derived from embryonic tissue. Electron microscopic studies consistently showed clusters of B. abortus in trophoblastic cells derived from 5- and 8-month placentas, while few cells of the embryonic line were infected and these contained only 1-2 bacteria per cell. It was concluded that B. abortus can infect trophoblastic cells throughout the gestational period but bacterial multiplication does not occur in these cells before middle or late gestation.