Subinhibitory Doses of Aminoglycoside Antibiotics Induce Changes in the Phenotype of Mycobacterium abscessus

Abstract

bSubinhibitory doses of antibiotics have been shown to cause changes in bacterial morphology, adherence ability, and resistance to antibiotics. In this study, the effects of subinhibitory doses of aminoglycoside antibiotics on Mycobacterium abscessus were investigated. The treatment of M. abscessus cells with subinhibitory doses of amikacin was found to change their colony from a smooth to a rough morphotype and increase their ability to adhere to a polyvinylchloride plate, aggregate in culture, and resist phagocytosis and killing by macrophages. M. abscessus cells treated with a subinhibitory dose of amikacin also became more potent in Toll-like receptor 2 (TLR-2) stimulation, leading to increased tumor necrosis factor alpha (TNF-␣) production by macrophages. The MAB_3508c gene was shown to play a role in mediating these phenotypic changes, as its expression in M. abscessus cells was increased when they were treated with a subinhibitory dose of amikacin. In addition, overexpression of MAB_3508c in M. abscessus cells caused changes similar to those induced by subinhibitory doses of amikacin, including a switch from smooth to rough colony morphology, increased ability to aggregate in liquid culture, decreased motility, and increased resistance to killing by macrophages. These findings suggest the importance of using sufficient doses of antibiotics for the treatment of M. abscessus infections.A ntibiotics have been widely used to treat infectious diseases. However, at subinhibitory concentrations, antibiotics may act as signal molecules and modulate bacterial phenotypes such as virulence, colony morphology, and biofilm formation (1, 2). Transcriptomic and proteomic analyses reveal that subinhibitory doses of antibiotics can cause significant changes in gene expression profiles in Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Pseudomonas aeruginosa (1,(3)(4)(5).Mycobacterium abscessus is a rapid-growing nontuberculosis mycobacterium. It is a common cause of infections in patients after tympanostomy tube placement and in those with surgical wounds or cystic fibrosis (6-10). Prolonged antibiotic therapy is generally required for treatment of infections caused by M. abscessus because of its intrinsic and acquired resistance to multiple antibiotics. Commonly used antibiotics for M. abscessus infections include clarithromycin, cefoxitin, tigecycline, and amikacin (AMK) (11).Amikacin is an aminoglycoside and is the most effective bactericidal antibiotic for M. abscessus. We have found that subinhibitory doses of amikacin can convert colonies of M. abscessus from a smooth to a rough morphotype. Because colony morphology is related to virulence, we investigated the effects of subinhibitory doses of amikacin on various activities of M. abscessus. MATERIALS AND METHODSBacteria and culture media. The M. abscessus cs1c-S strain used in this study is an attenuated variant derived from the clinical isolate cs1c-R (12). M. abscessus cells were grown at 37°C on Middlebrook 7H11 (Difco, USA) agar plates supplement...

Functional characterization of the Mycobacterium abscessus genome coupled with condition specific transcriptomics reveals conserved molecular strategies for host adaptation and persistence

“…In addition to whib7 up-regulation, erythromycin exposure induced a large majority (7/8) of the MAB homologs of the WhiB7 regulon indicative of an evolutionarily conserved WhiB7 driven response to macrolides. whiB7 in MAB is also induced in response to sub-inhibitory concentrations of the aminoglycoside amikacin [ 38 ] and is the second most strongly induced gene in response to kanamycin exposure. Intriguingly however, in response to kanamycin exposure only two of the 8 MAB homologs of the Whib7 regulon, whib7 and the putative macrolide transporter MAB_1846 were induced.…”

Glycopeptidolipids, a Double-Edged Sword of the Mycobacterium abscessus Complex

“…External factors, such as sub-inhibitory antibiotic concentrations, can promote a transient S-to-R change with more aggregated cultures and a higher resistance to phagocytosis ( Tsai et al, 2015 ). Strangely, these phenotypes were neither linked to a loss of GPL production nor to the differential expression of genes within the gpl cluster, but were rather mediated by MAB_3508c , homologous to whiB7 and conferring extreme resistance to antibiotics in M. abscessus ( Hurst-Hess et al, 2017 ).…”

Treatment of Mycobacterium abscessus Complex

“…In vitro data suggest that subinhibitory amikacin levels may be not just less effective but also harmful by causing physiologic changes to the organism that make it more robust and virulent. 78,79 Even more concerning, in vitro data suggest that MABc organisms with a functional erm gene may be able to induce amikacin resistance on macrolide exposure through a WhiB7-dependent network of resistance genes. 80 These data need additional confirmatory work and in vivo evaluation, but it is worrisome given the prevalence of both macrolides and amikacin in many regimens and raises the question of whether this contributes to the poor outcomes for subsp abscessus where a functional erm gene is frequently present and macrolides still often used.…”