Objective: To evaluate the reliability of thiophen-2-carboxylic acid hydrazine (TCH) test for identification of Mycobacterium bovis (M. bovis).
Methods: A total of 4069 clinically isolated strains were identified by P-Nitrobenzoic acid medium (500 mg/L) and TCH medium (5 mg/L). Mycobacterium tuberculosis (M. tuberculosis) complex strains susceptible to 5 mg/L TCH were further tested for susceptibility to 2 mg/L TCH. Spacer oligonucleotide typing (spoligotyping) and multi-loci PCR were also performed to identify TCH susceptible strains.
Results: Among the 4069 isolated strains there were 3929 strains belonging to M. tuberculosis complex (MTBC) of which 245 were susceptible to 5 mg/L TCH. Of these 245 strains, 20 were also susceptible to 2 mg/L TCH, while only 1 strain was identified to be M. bovis by both spoligotyping and multi-loci PCR.
Conclusion: TCH susceptibility test (either 5 mg/L or 2 mg/L) is not a reliable method for identification of M. bovis.