Further characterization of Pasteurella haemolytica-like bacteria isolated from swine enteritis

Partial characterization of the leukotoxin of Pasteurella haemolytica-like bacteria isolated from swine enteritis

Pasteurella haemolytica-like (PHL) strains isolated from diarrheic pigs are known to produce a leukotoxin that is lethal to ruminant leukocytes. In the present study, 12 PHL strains were screened for leukotoxin production using a tetrazolium dye-reduction assay. Sterile culture supernatant from strain 6213A, the maximum leukotoxin producer, was used as the crude leukotoxin for characterization studies. The leukotoxin was inactivated by heat at 60 degrees C and by trypsin, protease, and amylase. Toxicity was retained over a pH range of 3.0-11.0. The leukotoxin was lethal to polymorphoneutrophils (PMNs) of cattle, sheep, goat, and swine. Chromosomal DNA of all 12 PHL strains hybridized with a 3.9 kb Pasteurella haemolytica A1 leukotoxin probe, indicating similarities between the leukotoxin genes of P. haemolytica and PHL strains.

Sequence analysis of leukotoxin secretion determinants from a Pasteurella haemolytica-like organism

The pHLBD genes encoding the secretion functions for the 105 kDa RTX leukotoxin of Pasteurella haemolytica-like (PHL) organism has been cloned and sequenced. Like analogous genes from other RTX determinants, the pHLBD genes lie immediately downstream from the leukotoxin structural gene, pHLA. Although isolated from a diverse group of gram-negative organisms, the pHLBD genes and the characterized RTX BD genes from other organisms exhibit a high degree of homology at both the DNA and predicted amino acid sequence levels. We have previously reported the cloning of the leukotoxin gene (pHLCA) (Chang et al., Infect. Immun. 61:2089-2095), which encodes a 105-kda polypeptide with cytotoxic activity. DNA sequence analysis of the pHLBD genes shows 83.93% and 86.05% homologous to that of P. haemolytica IktBD genes, respectively.