Comparison of the indirect haemagglutination and gel diffusion test for serotyping Haemophilus parasuis

The aim of this study was to compare the use of indirect haemagglutination (IHA) and gel diffusion (GD) tests for serotyping Haemophilus parasuis by the Kielstein-Rapp-Gabrielson scheme. All 15 serovar reference strains, 72 Australian field isolates, nine Chinese field isolates, and seven isolates from seven experimentally infected pigs were evaluated with both tests. With the IHA test, 14 of the 15 reference strains were correctly serotyped – with serovar 10 failing to give a titre with serovar 10 antiserum. In the GD test, 13 reference strains were correctly serotyped – with antigen from serovars 7 and 8 failing to react with any antiserum. The IHA methodology serotyped a total of 45 of 81 field isolates while the GD methodology serotyped a total of 48 isolates. For 29 isolates, the GD and IHA methods gave discordant results. It was concluded that the IHA is a good additional test for the serotyping of H. parasuis by the KRG scheme if the GD methodology fails to provide a result or shows unusual cross-reactions.

Isolation of Pseudomonas pseudomallei from clay layers at defined depths

Twelve strains of Pseudomonas pseudomallei were isolated from the soil and water of a sheep paddock over a two-year period. The organism was recovered from the clay layer of the soil profile as well as from water that seeps into this layer during the "wet" season. Five isolates were obtained before the commencement of the "wet" season; environmental factors appear to play an important role in the survival of Ps. pseudomallei during the "dry" season. Lower isolation rates were recorded than those indicated by workers in southeast Asia and Iran.