It is well documented that aflatoxin contamination in foods presents significant economic and public health burdens worldwide. Aflatoxins, particularly aflatoxin B1 (AFB1), have been implicated in the etiology of disease and death in many parts of the world, necessitating research initiatives for intervention strategies designed to diminish biological exposure. Calcium montmorillonite clays (e.g. NovaSil Plus, NSP) have been found to tightly bind and inactivate aflatoxins in the gastrointestinal tract of multiple animal species. In the future, the hypothesis is that this strategy may also be appropriate for humans. Thus, the overall research goal was to investigate NSP suitability for human use through in vitro characterization followed by in vivo evaluation of NSP-AFB1 sorption and most importantly, safety of the clay. The first objective was to characterize the in vitro and in vivo sorption efficiency of NSP-AFB1 sorption and determine potential interactions with vitamin A (VA). Isothermal analysis suggested that NSP binds AFB1 with high capacity, affinity, and specificity in aqueous solution and further indicated that NSP does not appear to interact with VA. Subsequent short-term studies in Sprague-Dawley (S-D) rats and broiler chicks indicated that dietary inclusion of NSP (0.25%) significantly reduced AFB1 bioavailability without exerting overt toxicity. The second objective was to evaluate potential adverse effects of chronic ingestion of dietary NSP using male and female S-D rats in the absence of aflatoxins. Although statistically significant changes to a few parameters were noted, the differences did not appear to be NSP- or dose-dependent, suggesting that NSP at dietary inclusion levels as great as 2.0% (w/w) does not produce overt toxicity. Thus, this information increases the feasibility for using NSP in human trials in populations at high risk for aflatoxicosis. The third objective was to establish representative baseline data on human exposure to aflatoxins by collecting and quantifying urinary AFM1 in volunteers living in four separate communities in Ejura district of Ghana. Results revealed that urinary AFM1 in the study population was substantially high (mean = 1,850.86 ± 274.59 pg/mg creatinine), indicating that this particular population was highly exposed to aflatoxins and could be used for future intervention trials.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 24, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Georgia Davis. Vita. Includes bibliographical references.

Thesis (Ph. D.)(Microbiology)--University of Pretoria, 2003. / Includes bibliographical references.

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The inoculation of Aspergillus flavus spores into a culture of Streptococcus lactis in LTB medium resulted in none or little aflatoxin production even though growth of the fungus was not hindered. The drop in pH and reduced nutrients in the medium as the result of S. lactis growth were not the cause of the observed inhibition. The inhibition was not eliminated by the addition of carbohydrate equal to the amount utilized by the bacterium prior to the inoculation with the fungus. Aflatoxin production was also inhibited when S. lactis was inoculated after A. flavus had grown. In addition to inhibiting the synthesis of aflatoxin, S. lactis also degraded pre-formed toxin. Aflatoxin, on the other hand, not only reduced the growth of S. lactis but also affected the morphology of the bacterial cell--the cells became elongated and formed long chains. / S. lactis produced and excreted the inhibitor into the medium during the early stage of growth (4 h). The inhibitor was a heat stable low molecular weight compound (MW (LESSTHEQ) 500). Neither volatile (acetic) nor non-volatile (succinic and lactic) acids which were detected in extracts containing the inhibitor were responsible for this inhibition. Lactic acid was found in larger quantities in mixed cultures and its addition to mono fungus culture was found to stimulate aflatoxin production. Chloroform: methanol extraction of the S. lactis culture filtrate removed all the activity to the organic phase. Further, the active compound was insoluble in hexane, not extracted by sodium bicarbonate and was soluble in acetone, indicating a polar lipid. Autoradiographic studies showed that the inhibitor was a product of glucose metabolism. Further characterization indicated that the inhibitor was a phosphoglycolipid containing an aromatic ring structure. / Filtrate extracts of A. flavus grown in presence of S. lactis were toxic to Bacillus megaterium but did not exhibit mutagenic or carcinogenic activity in the Salmonella/Mammalian microsome mutagenicity test.

The age of Aspergillus parasiticus (1-11-105Wh1) mycelium was found to have an influence on the level of enzymes, responsible for the conversion of sterigmatocystin to aflatoxin B[1] and O-methylsterigmatocystin, present. These enzymes were active over a wide range of temperature and pH. Production of a cell free system by lyophiliization yielded the highest aflatoxin B[1] synthesising activity. Three other methods of preparing the cell free system capable of synthesising aflatoxin B[1] were also studied, ie,: french press, protoplast, and grinding, but with limited success. The lyophilized preparation had narrower temperature and pH optima for the conversion than whole mycelia. Initial purification of the aflatoxin B[1] synthesising enzyme was achieved by separating the crude cell free extract by gel filtration. The enzyme activity was located in a membrane fraction. The involvement of endoplasmic reticulum was indirectly concluded by the use of marker enzyme and chelating agents. This membrane fraction was ultracentrifuged and the released extrinsic proteins were separated by gel filtration. A fraction containing two proteins which were capable of converting sterigmatocystin to aflatoxin B[1] was isolated and characterised by isoelectric focusing and gel electrophoresis. The temperature and pH optima together with the cofactor requirements were studied. The Michaelis-Menten constant (Km) and the stoichiometry for the conversion of sterigmatocystin to aflatoxin B[1] was determined. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.

Graduation date: 1970

Thesis (Ph. D.)--Virginia Commonwealth University, 2007. / Prepared for: Dept. of Chemistry. Bibliography: leaves 120-134. Available online via the Internet.