Characterization of Aqx and its operon: the hemolytic RTX determinant of Actinobacillus equuli.
Abstract: Actinobacillus equuli, a member of the family Pasteurellaceae is the etiologic agent of a frequently lethal septicemia in neonatal foals as well as other more chronic diseases like arthritis, pleuritis, pneumonia or peritonitis. It may also be isolated from the oral cavity of healthy horses. Hemolytic isolates of A. equuli are known but so far no virulence determinants have been described for this bacterial species. By screening hemolytic A. equuli strains with specific gene probes, a hemolysin, designated Aqx (A. equuli RTX (repeats in the structural toxin)) was identified. This hemolysin was shown to be an RTX type of toxin by characterization of the aqxCABD operon. All hemolytic A. equuli isolates contained a functional aqxCABD operon and expressed the Aqx hemolysin as shown by genetic and phenotypic assays. The structural toxin AqxA is the hemolysin of A. equuli as shown by expression of recombinant aqx constructs in E. coli. Its hemolytic activity can be inhibited by specific antibodies raised against AqxA. Sequence analysis of the 16S rRNA gene (rrs) of the taxonomically diffuse group of A. equuli and related strains defined two phylogenetically distinct groups. The presence of the Aqx operon is not correlated with this phylogenetic grouping. The operon is found in both groups of A. equuli strains where it specifies the hemolytic activity and is supposedly to be a determinative virulence factor. The aqx operon was not found in closely related members of the Pasteurellaceae family. The description of the Aqx hemolysin will open new ways for studying the pathogenesis of A. equuli.
Publication Date: 2002-05-30 PubMed ID: 12034544DOI: 10.1016/s0378-1135(02)00048-2Google Scholar: Lookup
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- Journal Article
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Summary
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The research article focuses on the characterization of a hemolytic toxin, Aqx, and its operon in Actinobacillus equuli, a bacterium that causes septicemia and other diseases in foals. The study explores how this toxin and its operon contribute to the bacterium’s virulence and lays a foundation for future understanding and control of the pathogenesis of A. equuli.
About Actinobacillus equuli
- Actinobacillus equuli belongs to the Pasteurellaceae family and is typically responsible for causing often lethal septicemia in newborn foals, in addition to other long-term diseases like arthritis, pleuritis, pneumonia, or peritonitis.
- The bacterium can also be found in the oral cavity of healthy horses.
- Previously, no virulence factors for this bacterial species were known.
The Discovery of Aqx: A Hemolytic Toxin
- The researchers identified a hemolysin, Aqx (A. equuli RTX), in hemolytic A. equuli strains. Hemolysin is a toxin that lyses red blood cells.
- The gene set that codes for this, the aqxCABD operon, was also identified and characterized.
- All hemolytic A. equuli strains contained the functional aqxCABD operon and expressed the Aqx hemolysin, as confirmed by genetic and phenotypic assays.
Structural Toxins and Phylogenetic Grouping
- AqxA, a structural toxin, was revealed as the hemolysin of A. equuli, using recombinant aqx constructs in E. coli.
- Its hemolytic activity can be suppressed by specific antibodies created against AqxA.
- Sequence analysis of the 16S rRNA gene (rrs) of A. equuli and related strains established two phylogenetically distinct groups.
- The host of the Aqx operon does not correlate with this phylogenetic grouping. The operon is present in both groups of A. equuli strains.
Presence of the aqx Operon and its Significance
- The aqx operon is hypothesized to be a crucial virulence factor, as it defines the hemolytic activity of A. equuli.
- Interestingly, this operon was not found in other closely related members of the Pasteurellaceae family.
- The study of the Aqx hemolysin opens new paths to understanding the pathogenesis of A. equuli, which can be critical in developing interventions or treatments for the diseases caused by this bacterium.
Cite This Article
APA
Berthoud H, Frey J, Kuhnert P.
(2002).
Characterization of Aqx and its operon: the hemolytic RTX determinant of Actinobacillus equuli.
Vet Microbiol, 87(2), 159-174.
https://doi.org/10.1016/s0378-1135(02)00048-2 Publication
Researcher Affiliations
- Institute of Veterinary Bacteriology, University of Bern, Laenggass-Str. 122, CH-3012, Switzerland.
MeSH Terms
- Actinobacillus / chemistry
- Actinobacillus / genetics
- Actinobacillus Infections / microbiology
- Actinobacillus Infections / veterinary
- Animals
- Bacterial Toxins / chemistry
- Bacterial Toxins / genetics
- Base Sequence
- Blotting, Western / veterinary
- Cloning, Molecular
- DNA Probes / chemistry
- DNA, Bacterial / chemistry
- DNA, Bacterial / genetics
- Horse Diseases / microbiology
- Horses
- Molecular Sequence Data
- Neutralization Tests / veterinary
- Operon / genetics
- Phylogeny
- Polymerase Chain Reaction / veterinary
- Recombinant Proteins
- Sequence Alignment
- Sequence Analysis, DNA
Citations
This article has been cited 8 times.- Vereecke N, Vandekerckhove A, Theuns S, Haesebrouck F, Boyen F. Whole genome sequencing to study antimicrobial resistance and RTX virulence genes in equine Actinobacillus isolates.. Vet Res 2023 Apr 5;54(1):33.
- Kamali M, Carossino M, Del Piero F, Peak L, Mitchell MS, Willette J, Baker R, Li F, Kenéz Á, Balasuriya UBR, Go YY. Pathological Features and Genomic Characterization of an Actinobacillus equuli subsp. equuli Bearing Unique Virulence-Associated Genes from an Adult Horse with Pleuropneumonia.. Pathogens 2023 Jan 31;12(2).
- Frey J. RTX Toxins of Animal Pathogens and Their Role as Antigens in Vaccines and Diagnostics.. Toxins (Basel) 2019 Dec 10;11(12).
- Uchida-Fujii E, Niwa H, Kinoshita Y, Nukada T. Actinobacillus species isolated from Japanese Thoroughbred racehorses in the last two decades.. J Vet Med Sci 2019 Sep 3;81(9):1234-1237.
- Huang BF, Kropinski AM, Bujold AR, MacInnes JI. Complete genome sequence of Actinobacillus equuli subspecies equuli ATCC 19392(T).. Stand Genomic Sci 2015;10:32.
- Röttig A, Steinbüchel A. Acyltransferases in bacteria.. Microbiol Mol Biol Rev 2013 Jun;77(2):277-321.
- Oz HS, Ebersole JL, de Villiers WJ. The macrophage pattern recognition scavenger receptors SR-A and CD36 protect against microbial induced pregnancy loss.. Inflamm Res 2011 Jan;60(1):93-7.
- Linhartová I, Bumba L, Mašín J, Basler M, Osička R, Kamanová J, Procházková K, Adkins I, Hejnová-Holubová J, Sadílková L, Morová J, Sebo P. RTX proteins: a highly diverse family secreted by a common mechanism.. FEMS Microbiol Rev 2010 Nov;34(6):1076-112.
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