Identification of two adhesins of Actinobacillus seminis

Actinobacillus seminis is an autochthon of ovine reproductive organs. However, it is also considered to be a pathogen of these animals and is responsible for causing epididymitis and low fertility, among other pathological diseases. In this study, we describe the identification of two proteins functioning as adhesins in A. seminis. After obtaining surface proteins of this bacterium, two proteins of approximately 25 and 40 kDa were partially purified by ion interchange chromatography. Both proteins interacted with bovine fibronectin and fibrinogen, and they cross-reacted with a polyclonal serum from a sheep infected with A. seminis. Both proteins were identified by mass spectrometry analysis as phosphoglycerate mutase and elongation factor-Tu, respectively. A. seminis was able to adhere to cultured human bladder cells, and pre-incubation of A. seminis with the polyclonal sera against these proteins significantly inhibited their ability to adhere to cells but adherence was not affected by pre-immune serum, indicating their activity as adhesins. The identification of proteins involved in the adhesion of A. seminis to tissues and that serve as virulence factors will help furtherour understanding of the pathogenic mechanisms of this bacterium.