Characterization of nontypeable Actinobacillus pleuropneumoniae isolates

Two Actinobacillus pleuropneumoniae isolates from clinical cases of porcine pleuropneumonia in Japan were positive in the capsular serovar 15–specific PCR assay, but nontypeable (NT) in the agar gel precipitation (AGP) test. Nucleotide sequence analysis of gene clusters involved in the biosynthesis of capsular polysaccharide (CPS) and lipopolysaccharide O-polysaccharide (O-PS) revealed that both clusters contained transposable element ISApl1 of A. pleuropneumoniae belonging to the IS30 family. Immunoblot analysis revealed that these 2 isolates could not produce O-PS. We conclude that the ISApl1 of A. pleuropneumoniae can interfere in the biosynthesis of both CPS and O-PS.