INCONGRUENT RESISTANCE TO AMINOGLYCOSIDES IN MULTIDRUG-RESISTANT MYCOBACTERIUM TUBERCULOSIS STRAINS

Since the discovery of the bactericidal activity of aminoglycosides, streptomycin, kanamycin, amikacin, and capreomycin (a macrocyclic peptide) have been widely used to treat tuberculosis and multidrug-resistant (MDR) tuberculosis. In general practice, resistance to kanamycin is often used as the sole criterion for defining extensively drug-resistant tuberculosis, assuming that all other drugs in this group or related drugs are resistant to certain strains. However, the assumption of cross-resistance between drugs in the same group is not always true for Mycobacterium tuberculosis. This prompted us to conduct a study to determine the concordance resistance pattern between aminoglycosides and the macrocyclic peptide capreomycin.A total of 2383 mycobacterial strains isolated from suspected MDR cases were subjected to susceptibility testing with aminoglycosides (kanamycin and amikacin), the polypeptide capreomycin, and ofloxacin to determine the resistance pattern. Cultures and susceptibility testing were performed using an automated BACTEC MGIT 960 instrument. Positive susceptibility samples were confirmed by PCR.The results showed that, of the total 2383 strains, 844 (35.41%) were susceptible to all four drugs, and 1539 (64.58%) strains showed resistance in the form of multi- or mono-resistance. The results also showed that of the 474 kanamycin-resistant mycobacterial strains, 86.7% and 77.6% were resistant to amikacin and capreomycin, respectively. Conversely, of the 425 amikacin- resistant mycobacterial strains, 3.3% were susceptible to kanamycin. Our findings suggest that performing susceptibility testing for individual drugs within a class may not provide an accurate strain status and may not be sufficient to make clinical decisions. It is necessary to conduct susceptibility testing of all MDR-TB strains with all aminoglycoside and macrocyclic peptide drugs before subjecting patients to comprehensive drug therapy