Phylogenomic and Molecular Demarcation of the Core Members of the Polyphyletic Pasteurellaceae Genera Actinobacillus, Haemophilus, and Pasteurella

The genera Actinobacillus, Haemophilus, and Pasteurella exhibit extensive polyphyletic branching in phylogenetic trees and do not represent coherent clusters of species. In this study, we have utilized molecular signatures identified through comparative genomic analyses in conjunction with genome based and multilocus sequence based phylogenetic analyses to clarify the phylogenetic and taxonomic boundary of these genera. We have identified large clusters of Actinobacillus, Haemophilus, and Pasteurella species which represent the “sensu stricto” members of these genera. We have identified 3, 7, and 6 conserved signature indels (CSIs), which are specifically shared by sensu stricto members of Actinobacillus, Haemophilus, and Pasteurella, respectively. We have also identified two different sets of CSIs that are unique characteristics of the pathogen containing genera Aggregatibacter and Mannheimia, respectively. It is now possible to demarcate the genera Actinobacillus sensu stricto, Haemophilus sensu stricto, and Pasteurella sensu stricto on the basis of discrete molecular signatures. The other members of the genera Actinobacillus, Haemophilus, and Pasteurella that do not fall within the “sensu stricto” clades and do not contain these molecular signatures should be reclassified as other genera. The CSIs identified here also provide useful diagnostic targets for the identification of current and novel members of the indicated genera

Pathological study of Clarias gariepinus (Burchell, 1822) sub-adult artificially infected with Pseudomonas aeruginosa

Hematology and histopathological variations in Clarias gariepinus sub-adults subjected to oral challenge with Pseudomonas aeruginosa ATCC27853 were studied for a period of 21 days, with a view to assess the pathogenesis of the bacteria and compared with a control. The results were compared statistically using One-way ANOVA. The symptoms of the infected fish included tail and fin rot, internal hemorrhages and skin patches of superficial ulcers. Tissue sections revealed marked loss and sloughing off of the gill lamellar epithelium, liver showed that hepatocytes appear finely reticulated and foamy; however there were a few foci of large cytoplasmic vacuolations of the hepatocytes and the sinusoids were moderately congested while the intestine showed shortened rugae; the submucosa glands were reduced in numbers; however the surface epithelial cells appeared to be proliferating rapidly and immature (hyperplastic). There was a significant reduction in the mean values of packed cell volume from 34.67±5.2% to 22.33±0.3%, hemoglobin from 9.77±0.2g/dL to 6.97±0.2g/dL, red blood cell from 2.23±0.3x1012/L to 1.27±0.1 x1012/L and lymphocyte count from 69.00±2.3% to 52.33±0.9% of C. gariepinus after three weeks of exposure to P. aeruginosa. However, the reverse was the case in the mean values obtained for white blood cell and neutrophil for infected fish which were reasonably higher when compared to that of uninfected fish (17.13±0.5 to10.80±0.3x109/L) and (47.33±1.2% to 30.33±2.9%) respectively. It could therefore be concluded that changes in organs and blood parameters of fish occur proportionately to pathogen invasion