Hydrophobic properties and extraction of Bacillus anthracis spores from liquid foods

The objectives of this study were to characterize the hydrophobic properties of three strains of Bacillus anthracis using the microbial adherence to hydrocarbons (MATH) assay and determine the recovery of spores by hexadecane extraction from water, milk and orange juice using a modified version of this assay. In water mixtures, the hydrophobicity of B. anthracis spores ranged from 5 to 80% as the concentration of hexadecane and the mixing time increased. Two of the three strains showed significantly different hydrophobicity values. Increased pre-incubation temperature of the spore suspension had inconsistent effects on hydrophobicity across the three strains. The hydrophobicity of spores did not change significantly during storage at 4 °C. However, recovery of spores in the hexadecane fraction from aqueous mixtures was always less than 5% even at conditions in which the hydrophobicity values were greater than 40%. The recovery of spores in the hexadecane fraction increased to almost 20% when the hexadecane was mixed with milk or orange juice, although the majority of spores remained in the aqueous phase. The B. anthracis spores were relatively hydrophobic according to the MATH assay, but this test was not a good predictor of the partitioning of B. anthracis spores to hexadecane. The separation of B. anthracis from food matrices using hexadecane extraction was ineffective. Although the modified MATH assay was not able to efficiently extract B. anthracis from various food media, development of methods for rapid concentration and separation of this and other select agents from food remains vital to food defense.