Characterization of Aqx and its operon: the hemolytic RTX determinant of Actinobacillus equuli

Berthoud, H; Frey, Joachim; Kuhnert, Peter (2002). Characterization of Aqx and its operon: the hemolytic RTX determinant of Actinobacillus equuli. Veterinary microbiology, 87(2), pp. 159-174. Amsterdam: Elsevier 10.1016/S0378-1135(02)00048-2

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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.

Item Type:

Journal Article (Original Article)


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

UniBE Contributor:

Frey, Joachim and Kuhnert, Peter


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








Peter Kuhnert-Ryser

Date Deposited:

24 Jan 2014 08:51

Last Modified:

30 Dec 2014 02:30

Publisher DOI:


PubMed ID:


Uncontrolled Keywords:

Actinobacillus equuli, RTX, Virulence factor, Horse




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