BACKGROUND Mycobacterium abscessus complex (MABC) includes species with high resistance rates among mycobacterial
pathogens. In fact, MABC infections may not respond to clarithromycin treatment, which has historically been very effective
against MABC infection. Molecular markers have been proposed to detect both acquired (
rrl polymorphisms) and inducible
(
erm(41) polymorphisms) clarithromycin resistance in MABC isolates.
OBJECTIVES This study aimed to evaluate the susceptibility profile and molecular markers of clarithromycin resistance
in MABC.
METHODS The clarithromycin susceptibility profile was determined by broth microdilution with reads on days 3, 5, 7 and 14.
Mutations in the
rrl and
erm(41) genes were evaluated by polymerase chain reaction (PCR) using specific primers, followed
by sequencing.
FINDINGS A total of 14
M. abscessus subsp.
abscessus
isolates and 28
M. abscessus subsp.
massiliense
isolates were evaluated,
and clarithromycin resistance was observed in all isolates for up to three days of incubation. None of the 42 isolates exhibited a
point mutation in the
rrl gene, while all the isolates had a T28 polymorphism in the
erm(41) gene. Moreover, all 28
M. abscessus
subsp.
massiliense isolates had a deletion in the
erm(41) gene.
MAIN CONCLUSIONS While all the MABC isolates exhibited acquired clarithromycin resistance, no isolates exhibited a point
mutation in the
rrl gene in this study. The
M. abscessus subsp.
massiliense isolates demonstrated clarithromycin resistance,
which is an uncommon phenotype. The molecular data for the rrl and
erm(41) genes were not consistent with the phenotypic test
results of clarithromycin susceptibility, indicating a lack of correlation between molecular clarithromycin resistance markers for
both acquired and inducible resistance.
