Lysozyme as a barrier to growth of Bacillus anthracis strain Sterne in liquid egg white, milk and beef

In this study, we investigated the role of lysozyme on the viability of <i>Bacillus cereus</i>, <i>Bacillus subtilis</i>, <i>Bacillus pumilus</i> and <i>Bacillus anthracis</i> (Sterne) in egg white (EW), ground beef and milk. At 35 Celsius degree in EW, growth rates (GR) for <i>B. cereus</i>, <i>B. subtilis</i>, <i>B. pumilus</i> and <i>B. anthracis</i> were 0.005, -0.018, -0.028 and -0.029 OD₆₀₀/h, respectively. Heat-treating EW at 55 and 60 Celsius degree reduced the inactivating effect of EW by 3.1 and 10.5-fold, respectively. Addition of lysozyme (2 mg/ml) to 60 Celsius degree -treated EW increased the inactivation rate 5.76-fold, indicating involvement of lysozyme in <i>B. anthracis</i> inactivation. <i>B. anthracis</i> inactivation was influenced by pH, as shown by a progressive increase in inactivation rate from 0.25 to -4.42 logs CFU/h over a pH range of 6.0-8.5. Adding 2 mg/ml lysozyme to milk and ground beef also suppressed the growth of <i>B. anthracis</i> 3.3 and 6.5-fold, respectively. These data indicate that lysozyme, as a natural component of EW or potential additive in other foods, could reduce biothreat risks presented by bioterror agents.