Pathology, isolation and characterisation of virulent and diverse Mannheimia haemolytica and Pasteurella multocida associated with fatal pneumonia in sheep, Rajasthan, India

Abstract

Pneumonia, a major sheep disease, causes high mortality among affected animals predominantly the lambs. It is caused by a number of microbes including Mannheimia haemolytica/Pasteurella multocida. It was aimed to explore the pathology in the lungs due to pneumonia, and to isolate and characterise the virulent M. haemolytica/P. multocida strains. The lung tissues and heart blood specimens were collected by necropsy of sheep (n = 96). These samples were used for isolation and characterisation of M. haemolytica/P. multocida. Moreover, the fresh and square-shaped lung pieces were also taken to perform the histopathological analysis. Grossly, the petechial and ecchymotic haemorrhages, congestion and consolidation in lung lobes were observed at necropsy. Pneumonia was diagnosed as acute fibrinous-bronchopneumonia (36), suppurative chronic bronchopneumonia (10), acute interstitial pneumonia (32) and acute pulmonary congestion (18) based on histological lesions. Bacterial isolation recovered M. haemolytica alone or along with P. multocida and/or Bibersteinia trehalosi identified by phenotypic characters and sequencing of 16S rRNA. Haemolytic colonies were documented to carry the PHSSA, plpE and Rpt2 genes. P. multocida identification at species level was carried out by KMT1 gene detection. These isolates were noted to carry the capsule types A (hyaD-hyaC gene) and D (dcbF gene) and outer membrane protein genes ompH and omp87. Sequencing revealed nucleotide variability in Rpt2, ompH and omp87 genes.We highlighted the occurrence of fatal ovine pneumonic pasteurellosis/mannheimiosis caused and/or complicated by virulent M. haemolytica/P. multocida strains.