Comparison of Selected Actinobacillus Species with A Hemolytic Variety of Actinobacillus from Irradiated Swine

Pure cultures of hemolytic bacteria were isolated from blood or synovial fluid of 5 swine that had been stressed by irradiation. In their morphological, cultural, and biochemical characteristics, the isolates were similar to known strains of Actinobacillus lignieresii and Actinobacillus equuli. Comparative bacteriological and serological studies were conducted with the 5 isolates, a hemolytic strain isolated previously from the fetal membrane of a foal, and 8, 5 and 3 known strains of A. lignieresii, A. equuli, and Actinobacillus mallei, respectively. No remarkable differences among swine and foal isolates and strains of A. lignieresii and A. equuli were revealed. Minor and variable differences were seen in utilization of melibiose, mannitol, and salicin and in production of hemolysin. The isolates were serologically related to strains of A. equuli and A. lignieresii. Consistent with other findings, it was found that strains of A. equuli and A. lignieresii comprise a serologically heterogeneous group with intergrading antigenic characteristics. The primary basis for the separate speciation of A. equuli and A. lignieresii in Bergey's Manual of Determinative Bacteriology, 7th edition-the ability to produce nitrites from nitrates by the former but not by the latter species-was not affirmed. Strains of both species reduced nitrates to nitrites. In view of these findings, it is proposed that the specific taxon equuli be discontinued and that strains heretofore classified as such be reclassified in the species A. lignieresii. Bacteriologically and serologically, all 3 strains of A. mallei were remarkably different from other Actinobacillus strains. Because of the known biological affinities of A. mallei with Pseudomonas pseudomallei, it is proposed that the species A. mallei be transferred to the genus Pseudomonas, viz., Pseudomonas mallei.