Identification and serotyping of Haemophilus pleuropneumoniae by coagglutination test

A coagglutination test for the identification and serotyping of Haemophilus pleuropneumoniae is described. A total of 360 H. pleuropneumoniae strains were isolated from pulmonary tissues of feeder pigs which died of acute pleuropneumonia. All of the isolates were serotyped by coagglutination, and the results were confirmed by the ring precipitation test. The most common serotype isolated in Quebec was serotype 1, followed by serotypes 5, 2, and 7. None of the isolates belonged to serotypes 3, 4, or 6. Mixed infections due to H. pleuropneumoniae of more than one serotype in the same animal were encountered. Serotype 1 was the only common isolate among the mixed-serotype infections. The coagglutination test was more sensitive than was the ring precipitation test. Serotyping by the coagglutination test is inexpensive, rapid, reliable, and easy to perform.