Characterization of Mycobacterium africanum subtype I among cows in a dairy farm in Bangladesh using spoligotyping.

Acid-fast bacilli (AFB) were detected in the autopsy lung tissue homogenate samples of four cows (variety Frisian cross) in a dairy farm in Bangladesh. Histopathological examination of the lung tissue demonstrated prominent granulomas, caseating necrosis and calcification indicative of tuberculosis (TB) infection. Mycobacteria could not be cultured from the tissue homogenate samples by Lowenstein-Jensen based conventional culture method though AFB were evident by Ziehl-Neelsen (ZN) staining of the smears of tissue homogenate and in paraffin embedded tissue slices. Spoligotyping performed on DNA extracts of paraffin embedded lung tissue samples confirmed the AFB as a member of the M. tuberculosis complex (MTBC) with a pattern assigned to M. africanum subtype I. This characterization by spoligotyping was confirmed by subjecting M. africanum subtype I isolates from other parts of the world to an alternative identification method based on DNA polymorphism in the gyrB gene (Hain Life Science, GmbH, Nehren, Germany). Since M. africanum is believed to be a human pathogen, general infection in cattle may be a public health threat. The presence of these bacteria in the animal reservoir most likely originated from a caretaker.