Abstract

Objective: This study aimed to identify subspecies of Mycobacterium abscessus complex (MABC) isolates from clinical samples by a molecular technique and to determine mutations responsible for macrolide and aminoglycoside resistance. We also aimed to investigate the correlation of phenotypic and molecular test results by examining the resistance to antimicrobial agents according to CLSI standard using the liquid microdilution test.

Methods: 27 MABC isolates from clinical samples were examined. Molecular subspecies identification and mutations responsible for aminoglycoside (rrs mutation) and macrolide resistance (rrl mutation) were determined using the GenoType NTM-DR test. The resistance phenotypes of the strains to various antimicrobial agents were investigated by the Sensititre™ RAPMYCOI AST microdilution test.

Results: Of the 27 isolates tested, 21 were M. abscessus subsp. abscessus, three were M. abscessus subsp. bolletii, and three were M. abscessus subsp. massiliense; rrs and rrl mutations were not observed in any strains. Except for one isolate, all M. abscessus subsp. abscessus strains showed the erm(41) T28 genotype, which indicates inducible macrolide resistance. The correlation between the GenoType NTM-DR and phenotypic susceptibility test results was 81% (k=0.5, p=0.02) for inducible macrolide resistance and 89% for acquired macrolide resistance. The most effective antimicrobial agents were amikacin, cefoxitin, imipenem, linezolid, and tigecycline.

Conclusion: Although the GenoType NTM-DR test is reliable in identifying and detecting molecular macrolide and aminoglycoside resistance, there were discrepancies in the results. We recommend confirming the results with the phenotypic susceptibility method after growth on culture. Although the M. abscessus complex is resistant to many antimicrobial agents, it has shown high sensitivity to amikacin, cefoxitin, imipenem, linezolid, and tigecycline. High levels of inducible macrolide resistance in isolates indicate the importance of subtyping and sensitivity testing of isolates in patients where culture conversion has not been achieved.