The katE gene, which encodes the catalase HPII of Mycobacterium avium

Disseminated Mycobacterium avium-Mycobacterium intracellulare disease is a prevalent opportunistic infection in patients with acquired immune deficiency syndrome (AIDS). These pathogens are generally resistant to isoniazid (INH), a powerful antituberculosis drug. It is now generally accepted that the INH susceptibility of Mycobacterium tuberculosis results from the transformation of the drug into a toxic derivative, as a result of the action of the enzyme catalase-peroxidase (HPI), encoded by the katG gene. It has been speculated that the presence of a second catalase (HPII) in some mycobacterial species, but lacking in M. tuberculosis, may impair the action of INH. In this report, the nucleotide sequence of the M. avium katE gene, encoding catalase HPII, is described. This enzyme shows strong similarity to Escherichia coli catalase HPII and eukaryotic catalases. All amino acids previously postulated as participating directly in catalysis by liver catalase and most of the amino acids binding the prosthetic group are conserved in M. avium catalase HPII. The enzyme is expressed in E. coli and is inhibited by 3-amino-1,2,4-triazole (AT). Furthermore, Southern blot hybridizations and polymerase chain reaction experiments demonstrate the distribution of katE gene in several mycobacterial species. To evaluate the potentially antagonistic effect of HPII catalase on INH susceptibility, the katE gene was transformed into M. tuberculosis H37Rv and the minimum inhibitory concentration (MIC) for INH was determined. Despite strong expression of the katE gene, no change in MIC was observed, thus ruling out a possible contribution of this enzyme to the natural resistance of M. avium to the drug. The availability of the gene probe, encoding the second mycobacterial catalase HPII, should open the way for the development of new drugs and diagnostic tests to combat drug-resistant pathogen strains.