Comparison of a modified broth microdilution Sensititre™ SLOMYCOI assay with the CLSI-recommended agar disk elution method for antimicrobial susceptibility testing of Mycobacterium haemophilum.

OBJECTIVES

Mycobacterium haemophilum is a fastidious nontuberculous mycobacterium that causes severe infections in immunocompromised patients. Due to its complex growth requirements, its detection and antimicrobial susceptibility testing (AST) remain challenging. This study aimed to compare the performance of a modified commercial broth microdilution method (Sensititre™ Myco susceptibility plates with added haemin) with the standard Clinical and Laboratory Standards Institute (CLSI) agar disk elution method for AST of M. haemophilum.

METHODS

We conducted 20 comparative AST tests on M. haemophilum ATCC 29548 and 10 clinical isolates, using the CLSI agar disk elution method as the reference. MICs were determined using both methods, and categorical concordance was assessed for multiple antibiotics.

RESULTS

The overall concordance between methods was 81.4%. High agreement was observed for clarithromycin, linezolid, trimethoprim-sulfamethoxazole and rifampicin (90%-100%), while lower concordance was noted for amikacin (40%), ciprofloxacin (75%) and doxycycline (65%). Sensititre™ microdilution plates demonstrated superior standardization, ease of use and reduced contamination risks compared to the agar disk method.

CONCLUSIONS

The modified Sensititre™ microdilution method is a reliable alternative to the agar disk elution method for AST of M. haemophilum. It provides precise MIC values and is better suited for routine clinical use due to improved reproducibility and efficiency.