Berthoud H, Frey J, Kuhnert P
Institute of Veterinary Bacteriology, University of Bern, Laenggass-Str. 122, CH-3012, Switzerland.
Vet Microbiol. 2002 Jun 20;87(2):159-74. doi: 10.1016/s0378-1135(02)00048-2.
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.
马驹放线杆菌是巴斯德菌科的成员，是新生马驹常见致命败血症以及关节炎、胸膜炎、肺炎或腹膜炎等其他更慢性疾病的病原体。它也可能从健康马匹的口腔中分离出来。已知马驹放线杆菌有溶血分离株，但迄今为止尚未描述该细菌物种的毒力决定因素。通过用特异性基因探针筛选溶血马驹放线杆菌菌株，鉴定出一种溶血素，命名为Aqx（马驹放线杆菌RTX（结构毒素中的重复序列））。通过对aqxCABD操纵子的表征，证明这种溶血素是一种RTX型毒素。所有溶血马驹放线杆菌分离株都含有功能性aqxCABD操纵子，并通过遗传和表型分析表明表达了Aqx溶血素。重组aqx构建体在大肠杆菌中的表达表明，结构毒素AqxA是马驹放线杆菌的溶血素。其溶血活性可被针对AqxA产生的特异性抗体抑制。对分类学上分散的马驹放线杆菌组和相关菌株的16S rRNA基因（rrs）进行序列分析，确定了两个系统发育上不同的组。Aqx操纵子的存在与这种系统发育分组无关。该操纵子在两组马驹放线杆菌菌株中均有发现，在那里它决定溶血活性，据推测是一种决定性毒力因子。在巴斯德菌科的密切相关成员中未发现aqx操纵子。Aqx溶血素的描述将为研究马驹放线杆菌的发病机制开辟新途径。
