A method for identifying Bacillus anthracis, the causative agent of anthrax, has been cleared for diagnostic use by the U.S. Food and Drug Administration (FDA).
The test, known as the Gamma Phage Assay, was modified by scientists at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) to improve its performance and reliability when used with clinical specimens. The original form of the Gamma Phage Assay was first developed by the Centers for Disease Control and Prevention (CDC) in the mid-1950s.
The modified gamma phage method is the first diagnostic test to gain FDA approval for human use within the Laboratory Response Network (LRN). This network, established by the CDC, is charged with maintaining an integrated system of state and local public health, federal, military, and international laboratories that can respond to bioterrorism, chemical terrorism and other public health emergencies.
According to USAMRIID senior scientist John W. Ezzell, the Gamma Phage Assay is a classical bacteriological method that has been used at USAMRIID and other laboratories for years as part of an extensive array of methods used to identify B. anthracis. The gamma phage is a virus capable of entering bacterial cells and causing cell destruction, or lysis--and it is specific to B. anthracis.
"Because of that specificity, the gamma phage gives a highly readable result," Ezzell explained. "Wherever the virus is added to the surface of a culture plate that has been inoculated with suspicious anthrax colony growth, you can see clear zones where the B. anthracis cells have been destroyed--whereas other bacterial cells grow unaffected."
Well before the anthrax attacks of 2001, scientists at USAMRIID and the CDC recognized the need for an FDA accepted method for identifying B. anthracis in clinical specimens. In 2002, FDA's Division of Clinical Laboratory Devices agreed to recognize tests for B. anthracis as eligible for classification with a 510(k) premarket notification process--the designation given to devices and other non-biologics.
USAMRIID, with support from CDC, prepared and submitted a 510(k) Premarket Notification using both USAMRIID and CDC data on use of the gamma phage method. With FDA recognition of the assay as substantially equivalent to the classical assay used prior to 1976, it will be available for use for testing in designated civilian and military clinical laboratories.