| Actinobacillus pleuropneumoniae is the causative agent of porcine hemorrhagic pleuropneumonia, a severe and contagious respiratory disease. While many virulence factors in A. pleuropneumoniae have been identified, there are still many unanswered questions and unknown proteins which represent potential antibiotic targets or effective vaccines. An in vivo technology system (IVET) developed in A. pleuropneumoniae was refined so that novel virulence factors could be identified and characterized.; Using this system, twenty five unique in vivo induced (ivi) clones were identified. These clones contained promoters that were induced during infection of the pig (in vivo) but had minimal expression on rich laboratory media (in vitro). These genes that were upregulated during infection could be divided into four categories: proteins previously identified as virulence factors, those required for metabolism during rapid growth and colonization, proteins of known function that had not been previously characterized as required for virulence, and unknown proteins.; One of these ivi genes encodes Ohr, an organic hydroperoxide reductase. Ohr was shown to be regulated in response to organic peroxides. Ohr functions during the oxidative stress that occurs subsequent host immune cell influx and degranulation to release oxygen radicals. Ohr and its regulator are serotype-specific, found only in three of the twelve serotypes. The characterization of ohr shows the new information that can be gained from the use of IVET screens to identify virulence genes.; In order to further characterize the identified ivi genes, as well as to construct potential vaccines, genetically defined attenuated mutants are required. Mutant construction was attempted for both ohr and for ilvI, a gene involved in isoleucine-leucine-valine biosynthesis.; The characterization of ohr and initial analysis of ilvI have shown not only the potential information that can be gained through the use of IVET, but in addition, the many questions that arise. IVET has contributed to the understanding of A. pleuropneumoniae pathogenesis through the identification of virulence factors and by providing an initial platform from which more questions can be asked. |
