Characterization of apxIVA, a new RTX determinant of Actinobacillus pleuropneumoniae.
A fourth type of RTX determinant was identified in Actinobacillus pleuropneumoniae and was designated apxIVA. When expressed in Escherichia coli, recombinant ApxIVA showed a weak haemolytic activity and co-haemolytic synergy with the sphingomyelinase (beta-toxin) of Staphylococcus aureus. These activities required the presence of an additional gene, ORF1, that is located immediately upstream of apxIVA. The apxIVA gene product could not be detected in A. pleuropneumoniae cultures grown under various conditions in vitro; however, pigs experimentally infected with A. pleuropneumoniae serotypes 1, 5 and 7 started to produce antibodies that reacted with recombinant ApxIVA 14 d post-infection, indicating that apxIVA is expressed in vivo. In addition, sera from pigs naturally and experimentally infected with any of the serotypes all reacted with recombinant ApxIVA. The apxIVA gene from the serotype 1 A. pleuropneumoniae type strain Shope 4074T encodes a protein with a predicted molecular mass of 202 kDa which has typical features of RTX proteins including hydrophobic domains in the N-terminal half and 24 glycine-rich nonapeptides in the C-terminal half that bind Ca2+. The glycine-rich nonapeptides are arranged in a modular structure and there is some variability in the number of modules in the ApxIVA proteins of different serotypes of A. pleuropneumoniae. The deduced amino acid sequences of the ApxIVA proteins have significant similarity with the Neisseria meningitidis iron-regulated RTX proteins FrpA and FrpC, and to a much lesser extent with other RTX proteins. The apxIVA gene could be detected in all A. pleuropneumoniae serotypes and seems to be species-specific. Although the precise role of this new RTX determinant in pathogenesis of porcine pleuropneumonia needs to be determined, apxIVA is the first in vivo induced toxin gene that has been described in A. pleuropneumoniae.
Schaller
Alain
A
Institute for Veterinary Bacteriology, University of Berne, Länggassstrasse 122, CH-3012 Berne, Switzerland.
Kuhn
Rolf
R
Institute for Veterinary Bacteriology, University of Berne, Länggassstrasse 122, CH-3012 Berne, Switzerland.
Kuhnert
Peter
P
Institute for Veterinary Bacteriology, University of Berne, Länggassstrasse 122, CH-3012 Berne, Switzerland.
Nicolet
Jacques
J
Institute for Veterinary Bacteriology, University of Berne, Länggassstrasse 122, CH-3012 Berne, Switzerland.
Anderson
Timothy J
TJ
Department of Pathobiology, University of Guelph, Guelph, Ontario, Canada N1G2W1.
Maclnnes
Janet I
JI
Department of Pathobiology, University of Guelph, Guelph, Ontario, Canada N1G2W1.
Segers
Ruud P A M
RPAM
Intervet International BV, AKZO-NOBEL, NL-5830 AA Boxmer, The Netherlands.
Frey
Joachim
J
Institute for Veterinary Bacteriology, University of Berne, Länggassstrasse 122, CH-3012 Berne, Switzerland.
D000189:Actinobacillus Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary; D016977:Actinobacillus pleuropneumoniae / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D015139:Blotting, Southern; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D000939:Epitopes; D015870:Gene Expression; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013552:Swine; D013553:Swine Diseases / Q000276:immunology / Q000382:microbiology
D000907:Antibodies, Bacterial; C122177:ApxIVA protein, Actinobacillus pleuropneumoniae; D001426:Bacterial Proteins; D000939:Epitopes; D011993:Recombinant Fusion Proteins; D002118:Calcium