Response of Bacillus thuringiensis Al Hakam Endospores to Gas Dynamic Heating in a Shock Tube

Experiments were conducted in a gas-driven shock tube to investigate shock wave-induced damage to Bacillus thuringiensis Al Hakam endospores over a wide range of post-shock temperatures in non-oxidative gas environments. The results were compared with previous studies on B. atrophaeus and B. subtilis and demonstrate that B. thuringiensis Al Hakam exhibited a qualitatively similar response to rapid shock heating, even though this strain has a significantly different endospore structure. B. thuringiensis Al Hakam endospores were nebulized into an aqueous aerosol, which was loaded into the Stanford aerosol shock tube, and subjected to shock waves of controlled strength. Endospores experienced uniform test temperatures between 500 and 1000 K and pressures ranging from 2 atm to 7 atm for approximately 2.5 ms. During this process the bio-aerosol was monitored using in situ time-resolved laser absorption and scattering diagnostics. Additionally, shock-treated bio-aerosol samples were extracted for ex situ analysis including viability plating, flow cytometry and scanning electron microscopy (SEM) imaging. B. thuringiensis Al Hakam endospores lost the ability to form colonies at post-shock temperatures above 500 K while significant breakdown in morphology was observed only for post-shock temperatures above 700 K. While viability loss and endospore morphological deterioration adhere to a similar framework across all endospore species studied, phenomena unique to B. thuringiensis Al Hakam were noted in the SEM images and optical extinction data. This initial characterization of the response of B. thuringiensis Al Hakam spores treated with shock/blast waves shows that these methods have potential for spore inactivation and detection.