To the Editors:
The case study described hereafter emphasises the potentially vital importance of Mycobacterium bovis identification for appropriate tuberculosis patient management.
M. bovis, the classical causative agent of bovine tuberculosis, can be responsible for human TB, which makes this bacterium an important zoonotic species. In developed countries, the introduction of pasteurisation, preventing contamination from milk of infected cows, and eradication programmes for infected herds have considerably reduced the prevalence of human disease due to the bovine TB bacillus, but have not completely eradicated it 1–3. Nevertheless, in many developed countries, the possibility of TB due to M. bovis infection, instead of Mycobacterium tuberculosis, is considered unlikely or even disregarded by microbiologists and clinicians.
Distinction of M. bovis from M. tuberculosis has significant relevance to patient management. In contrast to the other members of the M. tuberculosis complex, M. bovis is intrinsically resistant to pyrazinamide 4. Beyond its use for specific M. bovis identification, this natural resistance is particularly important to consider. Pyrazinamide is usually given in the classical first-line TB treatment, as it is an effective sterilising drug that helps to shorten TB therapy due to its synergistic effect with rifampicin 5. Thus, in case of M. bovis infection, pyrazinamide would be ineffective if implemented in a patient's anti-TB regimen. Unfortunately, results of in vitro susceptibility assays to pyrazinamide by conventional methods are not systematically correlated to in vivo activity. Susceptibility is, therefore, not often routinely assayed in laboratories. In addition, TB due to M. bovis is clinically, radiologically and microscopically indistinguishable from disease caused by M. tuberculosis. After culture on solid media, M. bovis displays specific characteristics like dysgonic colonies, and negative biochemical test results for nitrate …