Serological characterisation of Actinobacillus pleuropneumoniae

In the most recent study on the serological characterisation of Australian isolates of A pleuropneumoniae, a large percentage of isolates either gave cross-reactions with serovars 3 and 6 (47/256 isolates) or no reaction at all (91/256 isolates).11 This study was performed using slide agglutination and GD, techniques which had performed effectively in the past.5 The high incidence of isolates that could not be clearly serotyped was clear evidence that these methods were no longer as effective. Several recent studies have shown that, of the available serotyping methods, IHA and QGD are the most effective methods for correctly serotyping A pleuropneumoniae isolates.10,12,13 In this paper, we describe the set-up and validation of IHA and QGD for the serotyping of A pleuropneumoniae using the reference strains for the 12 serovars and rabbit hyper-immune sera raised against these 12 strains. The use of the IHA and QGD to examine isolate HS143, selected to represent the problem isolates from the earlier study11 is then reported. In addition, we describe the serological characterisation of 378 isolates of A pleuropneumoniae obtained as part of a national referral service for the identification of porcine haemophili. We also re-examine a subset of the cross-reacting and non-typable isolates reported in our previous serotyping study.11