Development of typing methods of Actinobacillus pleuropneumoniae based on the antigenic and genetic diversity of the protective outer membrane lipoprotein

Actinobacillus pleuropneumoniae is a causative agent of porcine pleuropneumonia that is one of the important bacterial diseases of the respiratory tract of pigs. The disease occurs worldwide and results in serious economic losses to the pig-rearing industry. In this review, new typing methods based on the antigenic and genetic diversity of a protective outer membrane lipoprotein (OmlA), that have been developed for control and epidemiological study of the disease, are described. First, the gene for the OmlA of an A. pleuropneumoniae field isolate (serotype 5a) has been cloned and characterized. The lipoprotein has been shown to be a protective antigen of the organism. Southern blot and the nucleotide sequence analysis of the gene for the lipoprotein have revealed the presence and diversity of the gene in A. pleuropneumoniae. Secondly, based on the antigenic diversity of OmlA, Western blot analysis with specific antisera against three antigenically distinct OmlAs has been developed. The antisera can differentiate A. pleuropneumoniae into three groups. Finally, based on the genetic diversity of OmlA, a PCR-restriction fragment length polymorphism (RFLP) typing method has been developed. This method can divide A. pleuropneumoniae into five groups. The grouping results by the Western blot analysis were correlated with that by the PCR-RFLP typing method. In addition, the PCR-RFLP typing method can be performed in almost all veterinary diagnostic laboratories since the method does not require specific antisera and expensive reagents and apparatus. Therefore, the PCR-RFLP typing method can be substituted for other OmlA typing and seems to be the most convenient and practical OmlA typing method at present. The new typing methods developed in this study should be used as tools which are effective and practical for control of porcine pleuropneumonia caused by A. pleuropneumoniae.