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Subspecies distribution, and antibiotic susceptibility of Mycobacteroides abscessus complex isolates

F Kontos(1) G Mavromanolakis(2) S Pournaras(1)

1:Laboratory of Clinical Microbiology, Attikon University Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece; 2:Department of Internal Medicine. General Hospital of Agios Nikolaos, Crete, Greece, PC 72100 ,

Objectives. Mycobacteroides abscessus complex (MABC) is a rapidly growing mycobacterium that usually causes infections in both immunosuppressed and immunocompetent persons and encompasses three subspecies: M. abscessus subsp. abscessus (MAB), M. abscessus subsp. bolletii (MBO) and M. abscessus subsp. massiliense (MMA). This study aimed to investigate the antimicrobial susceptibility of MABC isolates recovered in two University Hospitals. 

Methods. We studied totally 47 MAB isolates (29 MAB, 12 MBO and 6 MMA) recovered from different patients during a 17-year period (2007 to 2023).     Identification to the subspecies level was conducted by sequencing of hsp65 gene.  The MICs (μg/ml) of clarithromycin, moxifloxacin, trimethoprim-sulfamethoxazole, linezolid, amikacin, ciprofloxacin, imipenem, doxycycline, and cefoxitin, were determined with the standard broth microdilution method using the commercial assay Sensititreᵀᴹ RAPMYCOI assay according to the CLSI recommendations and interpreted based on CLSI breakpoints. To investigate possible inducible clarithromycin resistance, the incubation period was extended up to 14 days.

Results. Forty-one of MABC isolates were recovered from respiratory specimens and six from blood specimens of patients with disseminated disease. Οf the isolates, 91.5 and 83% were susceptible to amikacin and linezolid, respectively. All MMA isolates and 5 MAB isolates were susceptible to clarithromycin, 4 were resistant, while  the other 32 isolates had inducible clarithromycin resistance. All strains were resistant to the other drugs tested. 

Conclusion. All strains were resistant to the majority of drugs tested. The 70% of isolates had inducible clarithromycin resistance and the prolonged incubation period up to 14 days in routine susceptibility testing is efficient for detecting this phenotype.   

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