Y-006. Comparison of Physical Properties of Anthrax Spore Surrogates

A. L. Boyko1, J. C. Brown1, R. Floyd1, Y. J. Choi2, T. J. M. Luo2, K. T. Madhusudhan1;
1Clean Earth Technologies, LLC, Winston Salem, NC, 2North Carolina State Univ., Raleigh, NC.

Background: Anthrax spore surrogates have been used for modeling of the aerial plume dispersions in the environment to simulate the behavior of Bacillus anthracis with high fidelity. Although B. anthracis (BA) is categorized in B. cereus (BC) group, B. atrophaeus (BG) is the most widely used spore surrogate. The purpose of the study is to question the assumption whether BG is a valid surrogate for BA by comparing the physical properties of BG and BC spores in “dry” and “wet” states. Study results will lead to the selection of a high fidelity surrogate for reliably modeling the properties of BA spores. Methods: Length and width measurements of “dry” and “wet” spores of BG and BC were determined by scanning electron microscopy (SEM) and environmental scanning electron microscope (ESEM), respectively. Computed physical parameters such as aspect ratio, surface area, perimeter, volume, and packing efficiency were compared between BG and BC spores. Additionally, surface hydrophobicity was determined by Microbial Adhesion to Hexadecane (MATH) and hydrophobic chromatography to compare surrogate spores. Results: Comparison of physical characteristics between BG and BC spores computed from either SEM or ESEM data (N=58) showed significant differences (p<0.0001) although packing efficiency was the same among both species. A parallel comparison of SEM and ESEM data for a given spore revealed significant physical differences (p<0.0001) for BG spores between the two methods. Additionally, surface hydrophobicity studies revealed BC spores are 64% more hydrophobic than BG spores. Conclusion: The study reveals differences in physicochemical properties between the less commonly used BC spore surrogate and BG spores in “dry” and “wet” states. These findings will lead to the selection of a more appropriate simulant that better resembles the properties of BA spores. Funding for this work is provided by the Technical Support Working Group (TSWG), Project 5, Task 3.10.