Temperature-dependent regulation of Mycobacterium abscessus glycopeptidolipid expression affects colony morphotype, biofilm formation and virulence: implications for future research

Abstract

Biofilm formation allows bacterial pathogens to colonize the environment and host mucosal surfaces, setting the stage for development of invasive disease. Glycopeptidolipid (GPL) allows Mycobacterium abscessus (Mabs) to form biofilms, and GPL expression is associated with the smooth colony morphotype. The purpose of this study is to further characterize temperature-dependent regulation of our well-characterized isolate 390R. Mabs isolates cultured on agar plates at different temperatures were assessed for GPL expression using thin layer chromatography. The ability of isolates to replicate in macrophages was assessed using human monocyte-derived macrophage tissue culture, and the ability to form biofilms was assessed using the Calgary Biofilm Device. Two-way ANOVA with Bonferroni post-hoc test was used to assess statistical significance. The 390R isolate exhibited a temperature-dependent gradient of GPL expression with none expressed when grown at 37° C, and a gradual increase in GPL expression over a range of temperatures until the full complement of GPL species present in derivative strain 390S was expressed at 23° C. Mabs 390R—37° C stock was able to replicate in monocyte-derived macrophage monolayers whereas Mabs 390R – 23° C stock demonstrated significantly reduced growth. Conversely, Mabs 390R – 23° C formed biofilm comparable to that seen with 390S which constitutively expresses the full complement of GPLs at both temperatures. There was no temperature-dependent GPL expression in a series of rough patient lung isolates nor in a series of smooth isolates obtained during healthcare facility outbreaks. The loss of Mabs GPL expression at human body temperature suggests a mechanism whereby smooth environmental strains of Mabs might transition from environmental saprophytes to invasive human pathogens and/or return to the environment from a human host as a smooth morphotype capable of colonizing or infecting additional humans. Although we did not identify temperature-dependent GPL regulation in isolates from patients or medical settings, the loss of temperature- dependent GPL expression may occur as Mabs strains evolve within the lungs of the infected human host. Further studies are needed to identify the mechanism underlying this phenomenon, its clinical and epidemiologic significance, and whether it is relevant to other NTM that exist as free-living saprophytes capable of colonizing or infecting humans.