Mycobacterium abscessus Phospholipase C Expression Is Induced during Coculture within Amoebae and Enhances M. abscessus Virulence in Mice

Abstract

Mycobacterium abscessusis a pathogenic, rapidly growing mycobacterium involved in pulmonary and cutaneo-mucous infections worldwide, to which cystic fibrosis patients are exquisitely susceptible. The analysis of the genome sequence ofM. abscessusshowed that this bacterium is endowed with the metabolic pathways typically found in environmental microorganisms that come into contact with soil, plants, and aquatic environments, where free-living amoebae are frequently present.M. abscessusalso contains several genes that are characteristically found only in pathogenic bacteria. One of them isMAB_0555, encoding a putative phospholipase C (PLC) that is absent from most other rapidly growing mycobacteria, includingMycobacterium chelonaeandMycobacterium smegmatis. Here, we report that purified recombinantM. abscessusPLC is highly cytotoxic to mouse macrophages, presumably due to hydrolysis of membrane phospholipids. We further showed by constructing and using anM. abscessusPLC knockout mutant that loss of PLC activity is deleterious toM. abscessusintracellular survival in amoebae. The importance of PLC is further supported by the fact thatM. abscessusPLC was found to be expressed only in amoebae. Aerosol challenge of mice withM. abscessusstrains that were precultured in amoebae enhancedM. abscessuslung infectivity relative toM. abscessusgrown in broth culture. Our study underlines the importance of PLC for the virulence ofM. abscessus. Despite the difficulties of isolatingM. abscessusfrom environmental sources, our findings suggest thatM. abscessushas evolved in close contact with environmental protozoa, which supports the argument that amoebae may contribute to the virulence of opportunistic mycobacteria.