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Toxins 2018, 10(5), 173;

β-Hemolysis May Not Be a Reliable Indicator of Leukotoxicity of Mannheimia haemolytica Isolates

Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-7040, USA
Author to whom correspondence should be addressed.
Received: 21 March 2018 / Revised: 20 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
(This article belongs to the Special Issue Leukotoxins)
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Mannheimia (Pasteurella) haemolytica causes bronchopneumonia in domestic and wild ruminants. Leukotoxin is the critical virulence factor of M. haemolytica. Since β-hemolysis is caused by a large number of leukotoxin-positive M. haemolytica isolates, all β-hemolytic M. haemolytica isolates are considered to be leukotoxic as well. However, conflicting reports exist in literature as to the leukotoxic and hemolytic properties of M. haemolytica. One group of researchers reported their leukotoxin-deletion mutants to be hemolytic while another reported their mutants to be non-hemolytic. The objective of this study was to determine whether β-hemolysis is a reliable indicator of leukotoxicity of M. haemolytica isolates. Ninety-five isolates of M. haemolytica were first confirmed for presence of leukotoxin gene (lktA) by a leukotoxin-specific PCR assay. Culture supernatant fluids from these isolates were then tested for presence of leukotoxin protein by an ELISA, and for leukotoxic activity by a cytotoxicity assay. All isolates were tested for β-hemolysis by culture on blood agar plates. Sixty-two isolates (65%) produced leukotoxin protein while 33 isolates (35%) did not. Surprisingly, 18 of the 33 isolates (55%), that did not produce leukotoxin protein, were hemolytic. Of the 62 isolates that produced leukotoxin, 55 (89%) were leukotoxic while 7 (11%) were not. All except one of the 55 leukotoxic isolates (98%) were also hemolytic. All seven isolates that were not leukotoxic were hemolytic. Taken together, these results suggest that β-hemolysis may not be a reliable indicator of leukotoxicity of M. haemolytica isolates. Furthermore, all M. haemolytica isolates that possess lktA gene may not secrete active leukotoxin. View Full-Text
Keywords: Mannheimia haemolytica; leukotoxin; leukotoxicity; hemolysis; indicator Mannheimia haemolytica; leukotoxin; leukotoxicity; hemolysis; indicator

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Bavananthasivam, J.; Shanthalingam, S.; Kugadas, A.; Raghavan, B.; Batra, S.; Srikumaran, S. β-Hemolysis May Not Be a Reliable Indicator of Leukotoxicity of Mannheimia haemolytica Isolates. Toxins 2018, 10, 173.

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