Abstract
Mycobacteria are a large family of over 100 species, most of which do not cause diseases in humans. The majority of the mycobacterial species are referred to as nontuberculous mycobacteria (NTM), meaning they are not the causative agent of tuberculous (TB) or leprosy, i.e., Mycobacterium tuberculous complex and Mycobacterium leprae, respectively. The latter group is undoubtedly the most infamous, with TB infecting an estimated 10 million people and causing over 1.2 million deaths in 2017 alone TB and leprosy also differ from NTM in that they are only transmitted from person to person and have no environmental reservoir, whereas NTM infections are commonly acquired from the environment. It took until the 1950′s for NTM to be recognised as a potential lung pathogen in people with underlying pulmonary disease and another three decades for NTM to be widely regarded by the medical community when Mycobacterium avium complex was identified as the most common group of opportunistic pathogens in AIDS patients. This review focuses on an emerging NTM called Mycobacterium abscessus (M. abs). M. abs is a rapidly growing NTM that is responsible for opportunistic pulmonary infections in patients with structural lung disorders such as cystic fibrosis and bronchiectasis, as well as a wide range of skin and soft tissue infections in humans. In this review, we discuss how we came to understand the pathogen, how it is currently treated and examine drug resistance mechanisms and novel treatments currently in development. We highlight the urgent need for new and effective treatments for M. abs infection as well as improved in vivo methods of efficacy testing.
Highlights
Mycobacterium abs was first isolated in 1952 by Moore and Frerichs from a 63-year-old woman’s knee abscess [1] and since our understanding of the pathogen has rapidly and somewhat turbulently expanded. When it was first isolated, it was suggested by the authors that M. abs was an entirely new species of nontuberculous mycobacteria (NTM) and was given its name due to its ability to produce subcutaneous abscesses. At this point, M. abs was considered to be a pathogen of low virulence due to the perception that it was primarily a pathogen causing cutaneous infections that appeared transient and self-limiting [1]. 40 years after its discovery, M. abs was first implicated in pulmonary infections after an analysis of 154 patients with rapidly growing mycobacteria (RGM) pulmonary infections revealed that 82% of the isolates were M. abs; the disease was considered to be slowly progressive but virulent [2]
This was preceded by an observation of four patients with pulmonary disease caused by the related organism Mycobacterium chelonae; the cause of these infections cannot be confirmed as M. abs [3]
M. abs is increasingly being recognised as an important pathogen responsible for a wide range of infections and implicated in severe, and often untreatable pulmonary infections in people with cystic fibrosis (CF) and other structural lung disorders
Summary
Mycobacterium abs was first isolated in 1952 by Moore and Frerichs from a 63-year-old woman’s knee abscess [1] and since our understanding of the pathogen has rapidly and somewhat turbulently expanded. When it was first isolated, it was suggested by the authors that M. abs was an entirely new species of nontuberculous mycobacteria (NTM) and was given its name due to its ability to produce subcutaneous abscesses At this point, M. abs was considered to be a pathogen of low virulence due to the perception that it was primarily a pathogen causing cutaneous infections that appeared transient and self-limiting [1]. Using this new rpoB gene sequencing technique aided with the more traditional biochemical assays and 16S rRNA gene sequencing, the authors were able to produce an accurate phylogenetic tree of various NTM They concluded that this novel isolate was a new species closely related to and likely recently derived from M. abs. M. abs pulmonary infections in non-CF patients have been previously reviewed [38]
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