Evaluation of heat-sensitive, neutrophil-toxic, and hemolytic activity of Haemophilus (Actinobacillus) pleuropneumoniae.
Cytotoxic and hemolytic activity of Haemophilus (Actinobacillus) pleuropneumoniae serotype 1 strain CM5 was investigated because of the potential role as a virulence determinant. Viable bacteria were toxic for porcine and bovine neutrophils, whereas bacteria killed by heat treatment at 60 C for 1 hour were not. Similarly, bacteria-free culture supernatant was cytotoxic and hemolytic in assays that used porcine neutrophils and erythrocytes, whereas supernatant treated at 60 C for 1 hour had no activity. Erythrocytes from various species were susceptible to the hemolytic activity of bacteria-free culture supernatant, with ovine and bovine erythrocytes being most sensitive. The neutrophil-toxic and hemolytic activity of bacteria-free culture supernatant was inhibited by cholesterol and oxygen and abolished after trypsin digestion. The neutrophil-toxic and hemolytic activity was preserved during storage at or less than 4 C, but was lost rapidly at 56 C or 80 C. Neutralizing antibodies were demonstrated in serum of pigs and rabbits immunized with 10-fold concentrated culture supernatant of strain CM5 and in field pigs that had recovered from natural infection with H pleuropneumoniae serotype 1. Bacteria-free culture supernatants of 18 strains, including H pleuropneumoniae serotypes 1 through 10, Actinobacillus suis, and Haemophilus taxon minor group, were tested for heat-sensitive, neutrophil-toxic, and hemolytic activity. Fifteen strains were neutrophil toxic, but only 10 of these were hemolytic. Haemophilus pleuropneumoniae, serotype 1, strain VLS557; serotype 5, strain K17; and Haemophilus taxon minor group strain 33PN were neither cytotoxic nor hemolytic.
Rosendal
S
S
Department of Veterinary Microbiology and Immunology, Ontario Veterinary College, University of Guelph, Ontario, Canada.
Devenish
J
J
MacInnes
J I
JI
Lumsden
J H
JH
Watson
S
S
Xun
H
H
D000818:Animals; D000907:Antibodies, Bacterial / Q000032:analysis; D001427:Bacterial Toxins / Q000276:immunology / Q000633:toxicity*; D002417:Cattle; D002470:Cell Survival; D004912:Erythrocytes / Q000032:analysis; D006190:Haemophilus / Q000302:isolation & purification / Q000472:pathogenicity*; D006192:Haemophilus Infections / Q000276:immunology / Q000662:veterinary; D006207:Half-Life; D006461:Hemolysis; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D009504:Neutrophils / Q000166:cytology* / Q000201:enzymology; D013552:Swine; D013553:Swine Diseases / Q000276:immunology
D000907:Antibodies, Bacterial; D001427:Bacterial Toxins; D007770:L-Lactate Dehydrogenase