Evaluation of slide agglutination and ring precipitation tests for capsular serotyping of Haemophilus pleuropneumoniae

Rapid slide agglutination (RSA), quantitative plate agglutination, slow tube agglutination (STA), and ring precipitation (RP) tests were performed on 200 isolates of Haemophilus pleuropneumoniae by using the type sera produced in rabbits against five known serotype strains and one strain 202. RSA and RP tests both yielded the same results as those by STA. None of the agglutination procedures could be used for serotyping isolates that autoagglutinated in saline. The RP test was successfully used for serotyping such strains. The specificity of the RSA and RP tests confirmed by cross-absorption studies. All of the isolates except two had strong serotype-specific activities. The most common serotype isolated in Quebec was serotype 1, followed by serotype 5 and 2. None of the isolates belonged to serotype 3 and 4. Only two isolates were found to be untypable; they could possibly belong to serotype(s) not yet defined. The RSA and RP tests may be at least as reliable as the STA test, but easier to perform, less expensive, and much more rapid than any of the other methods reported. Of all the procedures studied by us, the RP test proved to be the method of choice for serotyping H. pleuropneumoniae; hence, it should replace the STA test for serotyping H. pleuropneumoniae.