Use of two selective media and a broth motility test can aid in identification or exclusion of Bacillus anthracis.

During the anthrax attack of 2001, the Florida Department of Health (FDOH) Bureau of Laboratories in Tampa received hundreds of isolates suspected of being Bacillus anthracis. None were confirmed to be B. anthracis since most isolates were motile and not even in the Bacillus cereus group. Although the sentinel laboratories now send fewer isolates to FDOH laboratories, should another attack occur the number of isolates submitted would likely increase dramatically, and this upsurge would seriously challenge personnel who are expected to be busy examining an increased number of environmental samples. We examined two selective and differential growth media and alternative motility methods that could be used to streamline the processing of suspicious isolates. Of 60 isolates previously sent to the FDOH laboratory, 56 were endospore-forming gram-positive rods and only 7 grew on mannitol-egg yolk-polymyxin B agar and/or the Anthracis chromogenic agar. Microscopic observation of early-log-phase growth (2 to 3 h) in a shaking broth was the best method to detect motility in 40 isolates that appeared nonmotile in the motility media investigated. One of these growth media and microscopic examination of shaken broth cultures can be used to show that an isolate is not B. anthracis before expensive molecular and antibody-based tests are performed. By doing so, costs could be reduced and analysis time shortened.