Abstract Rationale It is projected pathogenic bacteria will thrive in exacerbated environments caused by anthropogenic climate change, although how environmental nontuberculous mycobacteria (NTM) will respond has yet to be determined. We hypothesized that smooth environmental NTM would transition to a more virulent rough morphology under exacerbating temperature and humidity conditions resulting in more severe macrophage infection outcomes. Methods Smooth and rough morphotypes of Mycobacterium abscessus were isolated from a soil sample collected from a geographic NTM hotspot. Both smooth and rough isolates were cultured on Middlebrook 7H10 plates under these conditions: 1) 30 °C (86 °F) +ambient humidity (control), 2) 30 °C+100% humidity, and 3) 40 °C (104 °F) +ambient humidity and CFU enumerated at 24- to 168hrs post-incubation. Colonies were imaged on the Keyence VHX-7000 and measured to determine how colony diameter (i. e. , size) and how close smooth or rough colony shape is to a perfect circle (i. e. , circularity) change. Results Generally, smooth and rough isolates grew equally across all time-points, and conditions tested. Colony diameter of smooth MABS exposed to both 40 °C and 100% humidity significantly widened compared to smooth controls (p 0. 0001), whereas, exposure to 40 °C significantly increased colony size of rough MABS compared to rough controls (p 0. 0001), a trend not observed under 100% humidity. When compared to control conditions, colony circularity significantly decreased for smooth MABS with exposure to 100% humidity and for rough MABS at 40 °C (p ≤ 0. 0001) ; that is, colonies were becoming rougher. Thus, the exacerbating climate conditions tested herein resulted in appreciable changes to MABS size and morphology. Next, “climate change adapted” MABS were collected after 24-, 48-, 168hrs and subjected to RNAseq. lrgD₂ (gramicidin synthesis subunit) and rocD (ornithine aminotransferase) were the top genes most differentially expressed between smooth and rough MABS isolates compared to their controls at all time-points. Finally, to investigate whether “climate change adapted” MABS isolates showed enhanced capacity for macrophage infection, the 48- and 168hr climate change adapted isolates were used to infect THP1 macrophages at 1: 1 MOI and cell-associated CFU recorded. Regardless of the climate condition the soil MABS were exposed prior to infection, smooth showed significantly higher CFU at 168hrs compared to rough. Yet, protracted exposure at elevated temperature induced significantly more macrophage cell death by rough isolates than smooth from the same exposure as indicated by LDH assays. Conclusions Overall, extended exposure to extreme temperature conditions promoted reduced circularity for both smooth and rough MABS isolates, but enhanced macrophage virulence by adapted rough MABS isolates. This abstract is funded by: National Science Foundation #1743587
Honda et al. (2026) studied this question.