**4. Genotypic Chracterization of** *Pasteurella multocida*

Since the initial development of the PCR in 1985, the basic principle of *in vitro* nucleic acid amplification through repetitive cycling has had extensive application in all aspects of fundamental and applied clinical sciences [16]. The application of PCR technology for *Pasteurella multocida* identification was first reported in 1994 when primers constructed from the sequence of the toxA gene (encoding the dermonecrotic toxin implicated in progressive atrophic rhinitis) were used to detect toxigenic *Pasteurella multocida* strains. PCR techniques play a critical role in the clinical laboratory diagnosis as rapid and specific detection of microorganism. It has provided remarkable advances in the diagnosis of infectious agents, particularly in cases where the presence of organism is having significance. Lichtensteiger *et al.* [17] investigated the feasibility of PCR for accurate, rapid detection of toxigenic *Pasteurella multocida* from swabs. They developed a PCR protocol which resulted into amplification of an 846-nucleotide segment of the toxA gene. They developed a concordance of PCR results with (i) detection of toxA gene with colony blot hybridization, (ii) detection of toxA protein with colony immunoblot analysis, and (iii) lethal toxicity of sonicate in mice in a test set of 40 swine diagnostic isolates. Results of an enzyme-linked immunosorbent assay for toxA agreed with the other

assays except for a negative reaction in one of the 19 isolates that the other assays identified as toxigenic. They suggested that PCR detection of toxigenic *Pasteurella multocida* directly from clinical swab specimens should be feasible.
