cdc.gov/botulism/botulism.htm. The Caspase activity current gold-standard assay, the mouse protection bioassay, is impractical in situations needing high-throughput analysis of multiple samples possibly at multiple geographical locations. In 2003 the National Institute of Allergy and Infectious Disease (NIAID) issued recommendations for new assays needed to detect
botulism (NIAID Expert Panel on Botulism Diagnostics, Bethesda Maryland, May 2003). These recommendations stated that any new assay should be “”universal”", should be able to detect variants of all toxin types, should be type-specific to determine proper antitoxin treatment, and should be sensitive and quantitative to determine risk assessment. Various methods that have been reported to address these requirements include immunological assays such as ELISA, ECL western blotting and Immuno-PCR, see more enzymatic PD0332991 in vitro assays such as EndoPEP assays and molecular techniques such as PCR [42–47]. The assays developed thus far offer a more rapid means of diagnosing botulism, but each also has limitations in such areas as sample throughput, cost, inability to distinguish toxin types, ease of use and false negative results [18, 48]. PCR is a valuable methodology because it is sensitive, specific,
cost-effective, portable, automatable, and high-throughput. However, PCR methods have certain limitations, such as the inability to distinguish between biologically active toxin genes and silent toxin genes in the bacterium . While this is an important limitation as it is the protein toxin rather than the DNA encoding it that poses the threat, this is a rare occurrence since complete loss of toxicity in C. botulinum strains is usually accompanied by loss of phage or plasmids that contain toxin complex genes (personal observations of the co-authors) [49–51]. However, the consistent presence of C. botulinum DNA in even highly purified toxin CYTH4 preparations can serve as a surrogate marker and indicate the presence of toxin when C. botulinum contamination is suspected (T. Smith, unpublished
data). Several different PCR methods have been reported, ranging from conventional electrophoresis-based PCR, including multiplex PCR, to real-time PCR and probe hybridization [20, 23, 27, 28, 38, 48, 52, 53]. Each PCR-based method is reportedly faster and cheaper than the standard mouse protection bioassay . However, most PCR assays detect a narrow range of toxin types, notably A, B, E and/or F, and do not consider the known genetic variation (subtypes) within each particular toxin type [32, 33, 54, 55]. Botulinum neurotoxins, and their genes, exhibit an extreme amount of variability. Currently, there have been over 26 toxin subtypes identified. These toxin subtypes vary by ~1-32% at the amino acid level and their genes vary by approximately the same percentage at the nucleotide level.