Environmental Mycobacterium Flora in Dairy Farms and the Effect on Intradermal Tuberculin Test Results
Date Issued
2011
Date
2011
Author(s)
Kung, Chien-Chia
Abstract
Among the more than 100 known species of the genus Mycobacterium, majority of them are described as “environmental mycobacteria” (EM), present as saprophytes in water or soil worldwide. Several species of EM are known as opportunistic pathogens and may lead to false positive diagnosis of bovine tuberculosis by intradermal tuberculin test (ITT). In Taiwan, ITT is a standard diagnostic tool for tuberculosis eradication program in dairy herds and cattle showing positive reaction are culled immediately. However, from April of 2009 to August of 2010, approximately 32％ (37/115) of the cattle culled did not exhibit typical tubercle lesions grossly or histopathologically, nor M. bovis or M. tuberculosis was detected by polymerase chain reaction (PCR).
In the present study, we used PCR to detect the heat shock protein 65 (hsp65) gene fragments of EM present in various environmental samples to evaluate the distribution of EM flora in dairy farms displaying ITT-positive result, as well as in farms with ITT-negative result as the control group. A total of 16 dairy farms were included and divided into three groups. Group A included farms which had ITT-positive history and M. bovis could be isolated from the retropharyngeal lymph node; within the 105 environmental samples of group A, the positive rate of hsp65 PCR was 50.58%. Group B were farms which had ITT-positive history but no M. bovis could be isolated from the retropharyngeal lymph nodes, indicating that these farms might be ITT false-positive; within the 194 environmental samples of group B, the positive rate of hsp65 PCR was 78.35%. Group C were farms in which dairy cattle displayed ITT-negative history; within the 88 environmental samples of group C, the positive rate of HSP65 PCR was 60.23%. The results showed that the positive rate of hsp65 PCR from Group B was clearly higher than those of group A and C (p<0.05), the cattle in these farms might have a higher chance to contact EM resulting in non-specific sensitization. To further investigate where in the farms that the cattle had higher risk of exposing to EM, each farm was divided into several different regions and it was found that the sport fields in these farms had much higher positive rates of hsp65 PCR than in other regions.
The hsp65 PCR products were sequenced and subjected to phylogenetic analysis. It was found that fourteen mycobacterial flora could only be found in all of the six farms of group B, suggesting that the EM in group B was really different from group A and group C. The results of phylogenetic analysis of the sequences of the hsp65 PCR products from environmental samples and from the milk, tissue, and blood of cattle from these farms of group B strongly supported that the EM flora should contribute to the ITT-false positivity.
Such false-positive reactors have caused severe, unnecessary economic losses not only to the producers but also to the government. Therefore, knowing the EM flora present in cattle farms and whether theses EM flora may have influence on the ITT results is rather important.
Subjects
environmental mycobacteria
intradermal tuberculin test
ITT-false positivity
heat shock protein 65
phylogenetic analysis
SDGs
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-100-R98629027-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):948d82bd2378ad7c08df78b4303d9b55