Combinations of
antibiotics, each individually effective against Mycobacterium abscessus, are routinely coadministered based on the concept that this minimizes the spread of antibiotic resistance. However, our in vitro data contradict this assumption and instead document antagonistic interactions between two
antibiotics (
clarithromycin and
amikacin) used to treat M. abscessus
infections. Clinically relevant concentrations of
clarithromycin induced increased resistance to both
amikacin and itself. The induction of resistance was dependent on whiB7, a transcriptional activator of intrinsic antibiotic resistance that is induced by exposure to many different
antibiotics. In M. abscessus, the deletion of whiB7 (MAB_3508c) resulted in increased sensitivity to a broad range of
antibiotics. WhiB7 was required for transcriptional activation of genes that confer resistance to three commonly used anti-M. abscessus drugs:
clarithromycin,
amikacin, and
tigecycline. The whiB7-dependent gene that conferred
macrolide resistance was identified as erm(41) (MAB_2297), which encodes a ribosomal
methyltransferase. The whiB7-dependent gene contributing to
amikacin resistance was eis2 (MAB_4532c), which encodes a Gcn5-related N-
acetyltransferase (GNAT). Transcription of whiB7 and the resistance genes in its regulon was inducible by subinhibitory concentrations of
clarithromycin but not by
amikacin. Thus, exposure to
clarithromycin, or likely any whiB7-inducing
antibiotic, may antagonize the activities of
amikacin and other drugs. This has important implications for the management of M. abscessus
infections, both in
cystic fibrosis (CF) and non-CF patients.