Bacillus endospore resistance to gas dynamic heating

Abstract

Aim: To develop a novel laboratory procedure for the study of shock wave‐induced damage to Bacillus endospores. Methods and Results: Bacillus atrophaeus endospores are nebulized into an aerosol, loaded into the stanford aerosol shock tube and subjected to shock waves of controlled strength. Endospores experience uniform test temperatures between 500 and 1000 K and pressures ranging from 2 to 7 atm, for a relatively short time (2–3 ms). During this process, the bioaerosol is observed using in situ laser absorption and scattering diagnostics. Additionally, shock‐treated samples are extracted for ex situ analysis including viability plating, flow cytometry and SEM imaging. Measurements indicate that endospores lose the ability to form colonies when heated to test temperatures above 500 K while significant breakdown in morphology is observed at test temperatures above 750 K. Conclusion: These results demonstrate the disruption of essential biochemical pathways or biomolecules prior to the onset of significant endospore morphological deterioration. Significance and Impact of the Study: This novel laboratory approach to study the interaction of endospores with shock waves provides an experimental means to investigate the mechanisms of endospore resistance to rapid heating. In addition, this methodology allows for the direct simulation of a blast wave–bioaerosol interaction in an atmospheric environment.

Inactivation of bacterial spores subjected to sub-second thermal stress

“…We also assessed the accuracy of our temperature measurements and the distribution of heat along the length of the wire by using blackbody calibration, which showed that the wire temperature measurement fit to theoretical values precisely, especially below 1000°C. Unlike the reported temperature measurements using thermocouples in the gas-phase spore inactivation studies that show a certain spatial temperature distribution [17][18][19][20][21][22][23][24][25], our results show a narrow temperature distribution along the entire length of the wire (see the evenly distributed temporal light intensity on wire in Fig. S4).…”

“…3B). Together, our results indicate that surface attached spores heated in our fast heating scheme ($10 4°C /s) behave similar to dry spores heated in other aerosol heating schemes [17][18][19][20][21][22][23][24][25].…”

“…Thus, stand-off neutralization methods which can sustain higher temperatures (>200°C) for short periods of time (sub-seconds) are being considered, and these new temperaturetime-kill histories of spore inactivation require evaluation. Aerosol methods have recently been employed to evaluate thermal and chemical kills of spores at extreme heating conditions [17][18][19][20][21][22][23][24][25]. These approaches have the advantage of isotropic and rapid heat transfer to individual spores, as well as controllable shorter heating times (milliseconds to seconds) and higher heating temperatures (>200°C) [17][18][19][20][21][22][23][24][25].…”

A second-generation constrained reaction volume shock tube

“…To summarize the above review, two separate techniques have generally been employed to confine a gas mixture to part of a shock tube: a ball valve [11][12][13] and a gate valve [14][15][16][17] (note that the use of thin diaphragms for gas separation in shock tube driven sections 18 is uncommon because the diaphragm fragments created as the incident shock wave shatters the diaphragm interfere with diagnostics located in the test section). Of the two techniques, we consider the gate valve to be superior for our application because it is thinner and occupies less volume than a ball valve (particularly for our relatively large 11.53-cm diameter tube).…”

“…In that work, the buffer gas was chosen to be the same as that of the test gas but with no fuel aerosol droplets, and the gate valve was located approximately 1.2 m from the shock tube 17 who employed it to confine a post-reflected-shock gas/endospore aerosol mixture after expansion wave-induced cooling in order to collect samples of biological aerosols. The technique used by Gates et al is similar to that used in single pulse shock tubes, 11-13 except a sliding gate valve was used instead of a ball valve.…”