CHARACTERIZATION OF OUTER MEMBRANE PROTEINS OF Pasteurella multocida OF PORCINE ORIGIN
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Date
2016-07
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Assam Agricultural University, Khanapara, Guwahati
Abstract
The present study was undertaken with a view to isolate and identify Pasteurella multocida from apparently healthy, diseased and dead pigs by both conventional and molecular methods, to study the pathogenicity of the isolates in mice, to prepare partially purified outer membrane proteins (OMPs) from most local virulent porcine strains (capsular types A and D), to study the protein profile of OMPs extract by SDS-PAGE, to identify the immunogenic proteins of OMPs by western blotting, to purify these proteins by size exclusion chromatography and to study the immunogenic potential of oil-adjuvanted vaccine prepared from the purified immunodominant OMPs in mice challenged with virulent homologous and heterologous capsular types of P. multocida.
In the present investigation, a total of 357 samples including nasal swabs (187), tracheal swabs (18), lung (125) and heart blood (27) from apparently healthy, diseased and dead pigs were examined for isolation of P. multocida. Of these, 17 (4.76%) samples yielded P. multocida. More isolates were obtained from nasal swabs (9) from apparently healthy and diseased pigs than that of tracheal swabs (4) and lung tissues (4) from apparently healthy and dead pigs.
All the 17 isolates showed cultural, morphological, staining and biochemical characteristics typical of P. multocida. The isolates were further confirmed as P. multocida on the basis of detection of species-specific gene (KMT1) by P. multocida species-specific PCR (PM-PCR). Among the 17 isolates, 6 (35.29%) were identified as capsular type A and 11 (64.71%) were identified as capsular type D based on multiplex capsular PCR results targeting hyaD-hyaC and dcbF genes, respectively.
Mouse pathogenicity trial of 19 isolates of P. multocida revealed that the isolates induced 33.33 to 100.00 per cent mortality within 72 hours of inoculation. Two isolates (LS-3 and NS-4) were found to be comparatively more pathogenic causing 100.00 per cent mortality in the inoculated mice within 24-48 hours post inoculation and were selected for extraction of OMPs.
Two most pathogenic strains of P. multocida, one each of types A and D (LS-3 and NS-4) were selected for extraction of OMPs. Analysis of OMPs of P. multocida type A by SDS-PAGE revealed presence of 21 protein bands with MWs ranging from 192.1 to 20.0 kDa. Among these protein, 36.8 and 25.0 kDa proteins appeared to be the major OMPs followed by 20.0, 56.5, 83.4, 47.4, 76.1, 51.2, 35.0, 99.2, 67.5 and 105.5 kDa protein bands based on band intensity in SDS-PAGE. While, OMPs of P. multocida type D showed presence of 22 protein bands with MWs ranging from 134.0 to 15.0 kDa. Among these protein, 35.7 and 25.0 kDa proteins appeared to be the major OMPs followed by 15.0, 56.2, 99.2, 47.1, 44.4, 66.5, 50.8, 78.5, 40.8 and 73.7 kDa proteins.
The comparative evaluation of protein profiles of OMPs of serotypes A and D of P. multocida of porcine origin revealed that both the types shared three proteins with MWs 134.0, 99.2 and 25.0 kDa, of which the 25.0 kDa protein was found to be a major OMPs based on band intensity.
The western blot analysis of the partially purified OMPs of P. multocida type A showed five major immunogenic proteins of MWs 83.4, 56.5, 36.8, 25.0 and 20.0 kDa giving strong immunostaining reaction with hyperimmune serum raised in rabbits. On the other hand, the partially purified OMPs of P. multocida type D showed five major immunogenic proteins of MWs 99.2, 56.2, 35.7, 25.0 and 15.0 kDa. Both the types shared a major immunogenic protein with MW 25.0 kDa.
Size exclusion chromatography showed 10 peaks in OMPs extract of P. multocida type A and 13 peaks in OMPs extract of type D. In P. multocida type A, the five peaks of OMPs contained the protein fractions with molecular masses 83.4, 56.5, 36.8, 25.0 and 20.0 kDa, while in type D, the five peaks contained the protein fractions with MWs 99.2, 56.2, 35.7, 25.0 and 15.0 kDa.
Mice immunized with oil-adjuvanted purified OMPs vaccines of P. multocida types A and D were challenged with 1x102 cfu of live P. multocida types A and D through subcutaneous (s/c) route and were found to be fully protective (100%). The organisms could not be re-isolated from the inoculated mice sacrificed after 7 days. The control group of mice showed 100 per cent mortality and died of septicaemia within 48 to 72 hours after challenge with 1x102 cfu of live P. multocida types A and D. Re-isolation of the organisms used for challenge infection was possible from the heart blood and the internal organs of dead mice of the control group.
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