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Susceptibility patterns of Mycobacterium avium complex isolates recovered in two Greek University Hospitals 

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

Objective. Mycobacterium avium complex (MAC) consists a group of mycobacterial pathogens that causes disease in susceptible hosts. In this study, we investigated the in vitro drug susceptibility patterns of individual MAC species in antimicrobial agents commonly used to treat MAC infections.  

Materials/methods: We studied 119 M. avium (MAV) and 103 M. intracellulare (MIN) non-repetitive clinical isolates. The minimum inhibitory concentrations (MICs) for clarithromycin, amikacin, moxifloxacin, linezolid, rifampicin and rifabutin were determined with broth microdilution method using the commercial assay SensititreTM SLOMYCOI    according to the CLSI recommendations and interpreted based on CLSI breakpoints for clarithromycin (S ≤ 8 mg/l) and amikacin (S ≤ 16 mg/l) and tentative breakpoints for moxifloxacin (S ≤ 1 mg/l) and linezolid (S ≤ 8 mg/l).  

Results. Overall, 208 MAC strains (93.6 %) were susceptible to clarithromycin while only 11 (9.2%) MAV and 3 (2.9%) MIN strains were resistant (MIC > 64 mg/l). For amikacin, moxifloxacin and linezolid the CLSI breakpoints split the wild-type populations for both species. Only 67.6% of MAC isolates were categorized as susceptible to amikacin and 5.4% of isolates were categorized as susceptible to moxifloxacin and linezolid. The rifampicin WT distribution for both species was truncated at the upper end (>8 mg/L) while for rifabutin, was instead truncated at the lower end (≤0.25 mg/L).  

Conclusions. The in vitro drug susceptibility patterns of the different MAC species studied are comparable to each other. Except for clarithromycin, current breakpoints for MAC categorization should be reevaluated.

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