Detection of drug resistance in mycobacterial isolates in cattle and buffaloes
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Date
2021
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Abstract
Bovine tuberculosis is a chronic disease of animals caused by M. bovis. Culture is
considered as gold standard for identification of a case of tuberculosis. Transmission of
infection to humans is by consumption of unpasteurized milk. The emergence of drug
resistant strains is a public health issue. A total of 200 animals (cattle and buffaloes)
from organized dairy farm were screened by CITT. A total of 15 blood samples from the
reactors tested positive by CITT, 57 tissue samples from PM Hall, GADVASU and from
dead animals in the field, 6 trans-tracheal washes from animals with respiratory distress
were collected. The samples were subjected to isolation by inoculating on Middlebrook
7H11 media and L-J media after proper decontamination. All the tissue specimens and
transtracheal washes were subjected to ZN staining. The isolates obtained were
subjected to acid fast staining and identified by biochemical testing. Extracted DNA
from specimens and isolates were subjected to PCR for detection of MTC. The isolates
were subjected to PCR for detection of drug resistance to rifampicin, isoniazid and
streptomycin. Out of 57 tissue samples, 15 blood samples and six transtracheal washes,
24 tissue samples, two blood samples and one transtracheal wash, respectively were
found to be positive for MTC. Out of all the samples subjected to isolation only 17
isolates were obtained (16 from tissue and one from transtracheal wash), six isolates
were found to be positive for MTC by polymerase chain reaction, five from tissue
samples and only one isolate from transtracheal wash. No isolate was obtained from
blood samples. All the isolates showed clumps of acid-fast bacilli by ZN staining. Based
on the biochemical tests six isolates were identified as Mycobacterium bovis. Out of six,
four isolates which were positive for MTC and remaining five isolates other than MTC
showed resistance to rifampicin. None of the isolates were resistant to streptomycin and
isoniazid. This study emphasizes that antitubercular drug susceptibility testing of
mycobacterial isolates from animals should be performed in order to estimate the
magnitude of the risk of drug-resistant tuberculosis transmission to humans.