National Institute of Animal Health (NIAH)

Topics in Animal Health Research 2014

12. Isolation and characterization of new genetically atypical strains of Actinobacillus pleuropneumoniae serovar 6

Japanese

Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia, which causes serious economic losses in the pig-rearing industry. To date, 15 serovars have been recognized mainly based on the antigenic diversity of capsular polysaccharides (CPS) in the organisms. Serotyping is widely performed in veterinary diagnostic laboratories since virulence differs between serovars and vaccines for A. pleuropneumoniae are serotype specific. However, cross-reactions are often observed among different serovars in a number of conventional immunological tests between serotypes 3, 6 and 8, which prevent accurate and rapid typing of field strains. To overcome such problems, a serovar-specific multiplex PCR that can discriminate among the problematic cross-reactive serovar 3, 6 and 8 strains has been developed. However, we describe here the first isolation and characterization of genetically atypical strains of A. pleuropneumoniae serovar 6. These strains are indistinguishable by the multiplex PCR that can discriminate between serovars 3, 6, and 8 since two PCR products (serovar 3- and 6-specific PCR amplicons) were amplified from the atypical strains. Nucleotide sequence analysis revealed that the atypical isolates have CPS export and synthesis gene sequences that are distinct from those of the serovar 6 reference strain. The atypical strains contain a sequence that is identical with both serovar 3- and 6-specific primers, which causes cross-reactions in multiplex PCR.
(Bacterial and Parasitic Disease Research Division)

References:

Ito H, et al (2014) J. Vet. Med. Sci. 76:601-604

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