Phylogenetic relationship of equine Actinobacillus species and distribution of RTX toxin genes among clusters

Kuhnert, Peter; Berthoud, Hélène; Christensen, Henrik; Bisgaard, Magne; Frey, Joachim (2003). Phylogenetic relationship of equine Actinobacillus species and distribution of RTX toxin genes among clusters. Veterinary research, 34(3), pp. 353-359. Paris: Editions scientifiques Elsevier 10.1051/vetres:2003010

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Equine Actinobacillus species were analysed phylogenetically by 16S rRNA gene (rrs) sequencing focusing on the species Actinobacillus equuli, which has recently been subdivided into the non-haemolytic A. equuli subsp. equuli and the haemolytic A. equuli subsp. haemolyticus. In parallel we determined the profile for RTX toxin genes of the sample of strains by PCR testing for the presence of the A. equuli haemolysin gene aqx, and the toxin genes apxI, apxII, apxIII and apxIV, which are known in porcine pathogens such as Actinobacillus pleuropneumoniae and Actinobacillus suis. The rrs-based phylogenetic analysis revealed two distinct subclusters containing both A. equuli subsp. equuli and A. equuli subsp. haemolyticus distributed through both subclusters with no correlation to taxonomic classification. Within one of the rrs-based subclusters containing the A. equuli subsp. equuli type strain, clustered as well the porcine Actinobacillus suis strains. This latter is known to be also phenotypically closely related to A. equuli. The toxin gene analysis revealed that all A. equuli subsp. haemolyticus strains from both rrs subclusters specifically contained the aqx gene while the A. suis strains harboured the genes apxI and apxII. The aqx gene was found to be specific for A. equuli subsp. haemolyticus, since A. equuli subsp. equuli contained no aqx nor any of the other RTX genes tested. The specificity of aqx for the haemolytic equine A. equuli and ApxI and ApxII for the porcine A. suis indicates a role of these RTX toxins in host species predilection of the two closely related species of bacterial pathogens and allows PCR based diagnostic differentiation of the two.

Item Type:

Journal Article (Original Article)


05 Veterinary Medicine > Department of Infectious Diseases and Pathobiology (DIP) > Institute of Veterinary Bacteriology

UniBE Contributor:

Kuhnert, Peter and Frey, Joachim


500 Science
500 Science > 570 Life sciences; biology
600 Technology > 630 Agriculture




Editions scientifiques Elsevier




Peter Kuhnert-Ryser

Date Deposited:

21 Jan 2014 09:34

Last Modified:

26 Dec 2014 11:15

Publisher DOI:


PubMed ID:


Uncontrolled Keywords:

Actinobacillus, horse, RTX toxin, phylogeny, diagnostic




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