This image depicted numbers of Bacillus anthracis
bacterial colonies, which had been allowed to grow on sheeps blood agar (SBA) for a 24 hour period. In this particular view youll note the appearance of what is termed a "plaque" (arrowhead), which represents an area where the bacteria had been lysed, or destroyed by the application of a localized amount of gamma phage-containing solution. Highly specific to B. anthracis
, these gamma phage viruses, i.e., bacteriophages, attacked the B. anthracis
bacteria, subsequently leaving this circular plaque devoid of bacterial organisms. The specificity of these gamma phages to B. anthracis
makes this a positive test for the presence of this bacterium.