Comparison of bacterial cultivation, PCR, in situ hybridization and immunohistochemistry as tools for diagnosis of Haemophilus somnus pneumonia in cattle

The aim of the present study was to compare the potential of bacterial cult ivation (BC), PCR, in situ hybridisation (ISH), and immunohistochemistry (M C) in the diagnosis of Haemophilus somnus, when applied to pneumonic bovine tissue. Lungs from 65 field cases submitted for bacteriological examinatio n were included in the study. The PCR-detection was performed on three diff erent samples: plate-PCR (detection on plate washes after incubation of lun g tissue on agar plates); swab-PCR (direct detection on a swab from the cut surface); and, whenever possible, a bronchus-PCR (direct detection on a sw ab from the main bronchus of the right cranial lung lobe). In order to exam ine the pathological significance of the findings, a histopathological exam ination of the cases was performed. H. somnus was detected by one or more t echniques in 33 cases in total. By BC the bacterium was isolated from 10 ca ses, MC and ISH were positive in 17 and 19 cases, and plate- and swab-PCR w ere positive in 21 and 29 cases, respectively. The bronchus-PCR was positiv e in 30 out of 61 cases examined. The PCR-technique was the most sensitive method, and as this technique is fast and relatively inexpensive, it should be considered as a supplementary tool in the diagnosis of H. somnus induce d calf pneumonia. (C) 2000 Elsevier Science B.V. All rights reserved.