Botulism detection

The various methods used to detect botulism toxin are listed in Table 2. Some of the assays for toxin can be modified for detection and measurement of antitoxin. Although detection of toxin is often the primary purpose of the test, sometimes it is secondary to identification of toxigenic organisms. In the investigation of botulism, detection of substantial amounts of toxin in the suspected food is confirmatory of the diagnosis. This is also true for detection of any demonstrable amount in the patient s blood or feces. 

Measuring muscle-evoked responses to repetitive motor nerve electrical stimulation permits detection of presyn-aptic neuromuscular junction dysfunction. In botulism and the Lambert-Eaton syndrome, repetitive stimulation elicits a smaller than normal skeletal muscle response at the beginning of the stimulus train, due to impaired initial release of acetylcholine-containing vesicles from presyn-aptic terminals of motor neurons followed by a normal or accentuated incremental muscle response during repeated stimulation. This incremental response to repetitive stimulation in presynaptic neuromuscular disorders can be distinguished from the decremental response that characterizes autoimmune myasthenia gravis, which affects the postsynaptic component of neuromuscular junctions. 

The most prevalent BoNTs isolated in human botulism are serotypes A, B, and E. The abihty of serotypes C and D, in addition to F, to paralyze human skeletal muscle should also be noted (Hilmas, impublished). Complicating matters is the fact that all BoNTs remain stable in common beverages and retain significant potency for prolonged periods of time (>90 days) at room temperature and in biological fluids (human whole blood and serum) at physiological temperatures (Hilmas et ah, 2006b Williams et ah, 2007). In addition, BoNTs possess a remarkable ability to remain within the nerve terminal for extended periods. Keller et ah (1999) showed BoNT protein detectable by western blot for 90 days in rat spinal cord cultures. 

The administration of heterologous antitoxin was one of the first therapeutic approaches developed for botuhsm patients and remains the most effective when initiated in the early stages of intoxication. The primary limitation of antitoxin treatment was established in some of the earhest published reports on experimental botuhsm. One of these reports evaluated the pathogenesis of oral intoxication and the efficacy of antitoxin therapy in monkeys (Back and Wood, 1928). Antitoxin treatment was not effective when administered after symptoms of botulism were already apparent, despite the fact that circulating toxin could still be detected in many of the animals. 

The mouse bioassay is the standard diagnostic laboratory test for botulism (36). The procedure detects whether a type-specific antitoxin protects the mice against any bomlinum toxin that may be present in the clinical specimen. The bioassay, which takes 1-2 days to complete (range 6-96 h), can detect 0.03 ng of botulinum toxin. In addition to the bioassay, anaerobic cultures of clinical specimens can isolate the organism in 7-10 days (range 5-21) days, but a mouse bioassay is necessary to confirm that the culture isolates produced the toxin (36). 

Although the number of outbreaks has been relatively constant, the case to fatality ratio has improved markedly. From 1899 to 1950, foodborne botulism was associated with 60% mortahty from 1950 to 1996, the average annual mortahty fell to 15.5% (Shapiro et al., 1998), and decreased to 4% during the last decade (Sobel et al., 2004). These advances in survival have come primarily from improvements in critical care (Tacket et al., 1984 Sobel et al., 2004). Further reductions in morbidity and mortahty from botuhnum intoxication wiU require better methods for detection and diagnosis of BoNT outbreaks and availability of speciftc pharmacological treatments (Franz et al., 1997 Dickerson and Janda, 2006). 

Food-borne botulism (due to C botulinum) may lead to a symmetric descending paralysis that results in respiratory failure. Patients are initially alert but may suffer from dysarthria and dysphagia. Ptosis and ophthalmoplegia are also characteristic symptoms. The answer is (D). Digoxin is lethal at levels much too low to be detected by the osmolar gap method. This method is useful only for poisonings with low-potency substances of low molecular weight, eg, methanol and ethylene glycol. The answer is (A). 

Another potential explanation for the imique epidemiology of human botulism was provided in a study of botulinum toxin binding and transcytosis across polarized monolayers of two hiunan colon carcinoma cell lines (T-84 and Caco-2). Substantial binding of iodinated BoNT/A and BoNT/B to hiunan colon carcinoma cells was observed, while minimal binding of type Cl neuro-toxin was detected (Maksymowych and Simpson, 1998). Both type A and B neurotoxins were also efficiently taken up, transcytosed, and released, by the polarized human carcinoma cells, whereas minimal transcytosis of type Cl neurotoxin was observed. The patterns of neurotoxin transcytosis (A and B, but not Cl) observed in these human gut epithelial cell lines correlate with human susceptibility to foodbome botulism (Maksymowych and... 

Detection and identification of the botulism neurotoxin have been essential for diagnosis of the illness and for identifying the causative food. When van Ermengem showed the lethality for animals of the ham that caused the Ellezelles botulism outbreak in 1895 (73), the bioassay naturally became the standard test for botulism neurotoxin. The mouse is very sensitive, and the mouse LD50 determined by i.p. injection became the quantitative unit. 

Tests for detection and quantitation of botulism neurotoxins are used for the following purposes ... 

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