Use of a polymerase chain reaction method to detect the leukotoxin gene lktA in biogroup and biovariant isolates of Pasteurella haemolytica and P trehalosi.

To determine whether Pasteurella haemolytica and P trehalosi isolates possess the structural gene for Pasteurella leukotoxin lktA and whether beta-hemolytic activity of these isolates correlated with detection of the lktA gene. 147 P haemolytica isolates from 21 biovariant groups and 101 P trehalosi isolates from 7 biovariant groups. In addition, P multocida and organisms from 7 other genera were tested to establish specificity of the procedure. Isolates were observed for beta-hemolysis. A polymerase chain reaction (PCR) procedure was used to amplify the RTX domain of the Pasteurella lktA gene. The lktA gene was detected in 108 (44%) isolates, including 15 associated with respiratory tract disease. All but 2 (98%) of the isolates that had the lktA gene were beta-hemolytic when grown on sheep blood agar. The remaining 140 isolates were negative for the lktA gene and hemolytic activity. Hemolytic activity of P haemolytica and P trehalosi isolates correlated with detection of the lktA gene for all but 2 isolates. However, 56% of isolates tested were negative for the lktA gene and beta-hemolytic activity. Leukotoxin production and secretion is a major virulence factor when other conditions are favorable for disease development. Therefore, identification of strains that possess the lktA gene may aid in the evaluation of the pathogenic potential of Pasteurella strains carried by wild and domestic animals.