Comparison of Detection Methods for Bacillus anthracis in High Background Food Matrices

Introduction:  Bacillus anthracis, the etiological agent of anthrax, can cause severe zoonotic disease in humans. While strong cultural detection methods exist, a reliable screening method is imperative for ruling out samples in large volumes of food samples. This study is based upon a parallel comparison between four commercially available B. anthracis detection kits and four culture media in pre and post enriched ground in beef.

Purpose:  This study’s objective was to conduct a comparison study between commercially available kits and culture media for the detection of B. anthracis in high background food matrices.

Methods:  Matrix limit of detection studies were conducted in parallel on the Smart II, BADD, Biothreat Alert, and Tetracore kits and select cultural media from both direct and overnight enrichments.  Four fortification levels of anthrax were fortified in ground beef ranging from 1x10³ to 1x10⁶ CFU/g. The manufacturer’s instructions were carried out for each method. Each kit method and fortification level was replicated in triplicate. The ELISA method was read at the endpoint absorbance at 405 nm and cultural plates were enumerated after overnight incubation. Non-target strains were examined for exclusivity.

Results:  The kits evaluated post enrichment, the lateral flow device BADD performed with a 66.7% detection sensitivity at 1x10⁴ CFU/g. Tetracore ELISA kits demonstrated a 66.7% sensitivity at 1x10⁴ CFU/g, but a 100% sensitivity at 1x10⁵ CFU/g post enrichment. All kits demonstrated 100% specificity against exclusivity strains. SBA, MYP, ACA, and PLET demonstrated high levels of B. anthracis and non-target bacteria post enrichment.  

Significance:  The data from this study suggest food matrices contaminated with >1x10⁴ CFU/g, the BADD LFD kits and Tetracore ELISA kits may offer a suitable screening tool for the detection of B. anthracis in foods, post enrichment.