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Title: Toxin production by Clostridium botulinum.
Author: Sharma, Davinder Kumar.
ISNI:       0000 0001 3397 6710
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 1999
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The endopeptidase activity assay developed for measurement of purified botulinum neurotoxin type A (BoNT/A) in clinical therapeutic preparations has been adopted to provide a specific measure of BoNT/A activity in culture supernatants of proteolytic C. botulinum type A. Electrophoretic studies and inhibition of BoNT/A activity by anti-A antibody confirmed the specificity of the assay. The minimum detection limit was 0.2 MLD50/ml indicating the assay as more sensitive than the standard mouse bioassay or any other in vitro assay available to date. Whilst the assay did not exhibit any cross reactions with non-proteolytic (saccharolytic) clostridia, proteolytic C. botulinum types B and F and C. sporogenes showed some cross reactions. The endopeptidase assay was used to investigate physiological aspects of BoNT/A production by proteolytic C. botulinum type A strain NCTC 7272. Growth studies at 15°C, 25°C and 37°C with strain NCTC 7272 demonstrated that the first appearance of BoNT/A (0.1-1.0 MLD50 ml) occurred during mid-late exponential or early stationary phase of growth. Extracellular BoNT/A formation was not proportional to viable count. Slightly more BoNT/A was detected at 25°C than 37° or 15°C. The results of BoNT/A formation by one of the growth curves at 25°C measured by the endopeptidase assay and mouse bioassays were very similar confirming the specificity of the assay. A simple method was developed to lyre the cells so that BoNT/A formation could be subsequently measured in the endopeptidase assay. The data obtained following lysis of cells and measurement of intracellular BoNT/A showed that both intracellular BoNT/A and total BoNT/A formation is not constitutive but are more closely proportional to viable count than extracellular BoNT/A. Release of BoNT/A from cells was not associated with autolysis. The conversion of BoNT/A from the single-chain to dichain form during growth has been measured. The use of the endopeptidase assay has been also exploited to study BoNT/A formation by this strain within the population of cells. There was only a four-fold difference in BoNT/A production by cells of strain NCTC 7272, and further work in this area is warranted. Attempts were made to use MAPs for the production of monoclonal antibodies to SNAP-25 following cleavage by BoNT/E. Whilst the outcome was unsuccessful, the soundness of the principle was demonstrated
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Food safety; Botulism; Neurotoxin