Stepwise pathogenic evolution of Mycobacterium abscessus

Jump starting pathogen evolution Mycobacteria are mostly environmental saprotrophs, but during human history, some have become our pathogens. In the past 50 years or so, intractable and virulent infections of Mycobacterium abscessus have emerged in people with cystic fibrosis. Bryant et al. investigated how these mycobacteria have evolved into human pathogens so quickly (see the Perspective by Brugha and Spencer). Chronic infections in the lung offer plenty of evolutionary scope for the emergence of virulent clones after horizontal gene transfer and hypermutation. Pathogens are acquired by environmental contamination, which leaves open a window for clinical control because the most virulent clones survive poorly outside the body. Therefore, immediate treatment and enhanced infection-control measures for M. abscessus cases could reduce opportunities for the evolution of direct person-to-person transmission. Science , this issue p. eabb8699 ; see also p. 465