Sequence diversity, cytotoxicity and antigenic similarities of the leukotoxin of isolates of Mannheimia species from mastitis in domestic sheep

• Published in: Veterinary microbiology 2014-11, Vol.174 (1-2), p.172-179
• Main Authors: Omaleki, Lida, Browning, Glenn F., Barber, Stuart R., Allen, Joanne L., Srikumaran, Subramaniam, Markham, Philip F.
• Format: Article
• Language: English
• Subjects: Animals; Base Sequence; Blotting, Western - veterinary; Cluster Analysis; Cross Reactions - immunology; Electrophoresis, Gel, Two-Dimensional - veterinary; Exotoxins - genetics; Exotoxins - toxicity; Female; Gene Transfer, Horizontal - genetics; Genetic Variation; Leukotoxin; Mannheimia - genetics; Mannheimia glucosida; Mannheimia haemolytica; Mannheimia haemolytica - genetics; Mastitis; Mastitis - genetics; Mastitis - microbiology; Mastitis - veterinary; Molecular Sequence Data; Neutralisation; Neutralization Tests - veterinary; Pasteurellaceae Infections - genetics; Pasteurellaceae Infections - veterinary; Phylogeny; Sequence Analysis, DNA - veterinary; Sheep; Sheep Diseases - microbiology; Sheep, Domestic; Species Specificity; Virulence Factors - genetics; Virulence Factors - metabolism
• ISSN: 0378-1135; 1873-2542
• DOI: 10.1016/j.vetmic.2014.08.009

•The lktA genes of Mannheimia haemolytica causing mastitis in sheep are more diverse than those carried by M. glucosida.•The lktA genes in Mannheimia species form ovine mastitis appear to have been transferred horizontally.•The leukotoxin of Mannheimia glucosida is more potent those that of Mannheimia haemolytica.•LktA of M. glucosida induces more broadly cross-reactive antibody than LktAs of M. haemolytica. Species within the genus Mannheimia are among the most important causes of ovine mastitis. Isolates of these species can express leukotoxin A (LktA), a primary virulence factor of these bacteria. To examine the significance of variation in the LktA, the sequences of the lktA genes in a panel of isolates from cases of ovine mastitis were compared. The cross-neutralising capacities of rat antisera raised against LktA of one Mannheimia glucosida, one haemolytic Mannheimia ruminalis, and two Mannheimia haemolytica isolates were also examined to assess the effect that variation in the lktA gene can have on protective immunity against leukotoxins with differing sequences. The lktA nucleotide distance between the M. haemolytica isolates was greater than between the M. glucosida isolates, with the M. haemolytica isolates divisible into two groups based on their lktA sequences. Comparison of the topology of phylogenetic trees of 16S rDNA and lktA sequences revealed differences in the relationships between some isolates, suggesting horizontal gene transfer. Cross neutralisation data obtained with monospecific anti-LktA rat sera were used to derive antigenic similarity coefficients for LktA from the four Mannheimia species isolates. Similarity coefficients indicated that LktA of the two M. haemolytica isolates were least similar, while LktA from M. glucosida was most similar to those for one of the M. haemolytica isolates and the haemolytic M. ruminalis isolate. The results suggested that vaccination with the M. glucosida leukotoxin would generate the greatest cross-protection against ovine mastitis caused by Mannheimia species with these alleles.