Mycobacterium abscessus Genetic Determinants Associated with the Intrinsic Resistance to Antibiotics.

Mylene Gorzynski,Tiana Jaramillo,Elizaveta Dzalamidze,Tiana Week,Lia Danelishvili

doi:10.3390/microorganisms9122527

Mylene Gorzynski, Tiana Jaramillo + Show 3 more

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https://doi.org/10.3390/microorganisms9122527

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Journal: Microorganisms	Publication Date: Dec 7, 2021
Citations: 7	License type: CC BY 4.0

Affiliation: Oregon State University

Abstract

Mycobacterium abscessus subsp. abscessus (MAB) is a fast-growing nontuberculous mycobacterium causing pulmonary infections in immunocompromised and immunocompetent individuals. The treatment of MAB infections in clinics is extremely challenging, as this organism is naturally resistant to most available antibiotics. There is limited knowledge on the mechanisms of MAB intrinsic resistance and on the genes that are involved in the tolerance to antimicrobials. To identify the MAB genetic factors, including the components of the cell surface transport systems related to the efflux pumps, major known elements contributing to antibiotic resistance, we screened the MAB transposon library of 2000 gene knockout mutants. The library was exposed at either minimal inhibitory (MIC) or bactericidal concentrations (BC) of amikacin, clarithromycin, or cefoxitin, and MAB susceptibility was determined through the optical density. The 98 susceptible and 36 resistant mutants that exhibited sensitivity below the MIC and resistance to BC, respectively, to all three drugs were sequenced, and 16 mutants were found to belong to surface transport systems, such as the efflux pumps, porins, and carrier membrane enzymes associated with different types of molecule transport. To establish the relevance of the identified transport systems to antibiotic tolerance, the gene expression levels of the export related genes were evaluated in nine MAB clinical isolates in the presence or absence of antibiotics. The selected mutants were also evaluated for their ability to form biofilms and for their intracellular survival in human macrophages. In this study, we identified numerous MAB genes that play an important role in the intrinsic mechanisms to antimicrobials and further demonstrated that, by targeting components of the drug efflux system, we can significantly increase the efficacy of the current antibiotics.

Highlights

Mycobacterium abscessus subsp. abscessus (MAB) is a fast-growing non-tuberculous mycobacterium (NTM) responsible for severe respiratory and mucosal infections in patients with preexisting lung conditions such as chronic obstructive pulmonary disease, cystic fibrosis, and emphysema [1,2]
In attempts to identify MAB genes that play a role in an antibiotic intrinsic resistance, the transposon library of gene knockout mutants was evaluated in comparison to the parental MAB 19977 for increased or decreased susceptibility to the aminoglycoside, macrolide, and cephalosporin groups of beta-lactam antibiotics AMK, CLA, and FOX, respectively
Mycobacterium abscessus subsp. abscessus has been long-recognized as one of the most antibiotic-resistant NTMs; the basis of intrinsic resistance is still poorly understood, making its treatment extremely challenging in clinics [5,7]

Summary

Introduction

Mycobacterium abscessus subsp. abscessus (MAB) is a fast-growing non-tuberculous mycobacterium (NTM) responsible for severe respiratory and mucosal infections in patients with preexisting lung conditions such as chronic obstructive pulmonary disease, cystic fibrosis, and emphysema [1,2]. Abscessus (MAB) is a fast-growing non-tuberculous mycobacterium (NTM) responsible for severe respiratory and mucosal infections in patients with preexisting lung conditions such as chronic obstructive pulmonary disease, cystic fibrosis, and emphysema [1,2]. In the United States, pulmonary M. abscessus complex infections range 2.6–13.0% [3,4], with successful treatment rates in only 45.6% of patients, highlighting a need for more satisfactory therapy strategies [5]. The current recommended treatment regiments for MAB consist of intravenous and multidrug therapy with macrolide and aminoglycoside or beta-lactams [8]. Recent studies have identified MAB strains with genetic polymorphisms of target genes that confer resistance to specific antibiotics [10,11], further complicating the treatment outcome. About 20% of MAB isolates in US have specific point mutations in the erm(41) gene, conferring resistance to CLA [12]. While the resistance to aminoglycosides is mainly associated with mutations in the rrs gene (encoding the 16S rRNA) or aminoglycoside-modifying enzymes, mutations in the rrl gene that encode the 23S rRNA have been shown to cause macrolide resistance [9,14]

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