A study of the relationship betylieen the resistance of mycobacterium tumerculoms to iiso icotbwc acid hydrazide (isoniazid) and to thiophen-2-carboxylic acid hydrazide

Abstract Thiophen-2-carboxylic acid hydrazide (TCH) is used to distinguish TCH-sensitive bovine, ‘Asian human’ and ‘African’ strains from TCH-resistant ‘classical’ human strains of Mycobacterium tuberculosis . It has been claimed that this test cannot be applied to isoniazid-resistant strains as these also become resistant to TCH. Although such cross-resistant mutants were readily isolated in vitro , a study of the incidence of TCH resistance in a large series of INH-sensitive and -resistant strains isolated from patients indicated that the emergence of this type of mutant is the exception rather than the rule in vivo . Thus, the use of TCH for subdividing the species M. tuberculosis remains valid for epidemiological purposes, irrespective of the occurrence of isoniazid resistance.