Gamma processing of Arabic bread for immune system-compromised cancer patients.

Arabic bread prepared from local Saudi flour contained a total of up to 10(4) organisms per g. Most of these were bacterial spores that survived the baking process (1.3 X 10(2) to 3.5 X 10(3] and a small number of yeasts and molds (10 to 40 cells per g). The organisms in Arabic bread appear to be harmless to healthy individuals. However, for immune system-compromised cancer patients and bone marrow transplant recipients, it is prudent to irradiate the bread to reduce microbial contamination. The decimal reduction doses (10% survival) for the most radiation-resistant organisms (spore formers) in bread were 0.11 to 0.15 Mrad. Accordingly, 0.6 Mrad was sufficient to reduce the number of spores in Arabic bread by a factor of 10,000, i.e., to less than 1/g. This treatment constitutes radiation pasteurization (radicidation), and to this extent, provides a margin of microbiological safety. Sensory evaluation by the nine-point hedonic scale showed no detectable loss of organoleptic quality of bread up to 0.6 Mrad, while irradiation to 2.5 Mrad induced unacceptable organoleptic changes.

Genetic control of heat resistance and thermotolerance by recA and uvrA in E. coli K12.

Several recA and uvrA derivatives of E. coli K12 AB1157 develop a transient increase in heat resistance, i.e. induced thermotolerance after a brief exposure to 43.5 degrees C (less than 1 h). Thermotolerance was identified from the appearance of an inflection in the survival curve or from the loss of heat resistance in the presence of chloramphenicol (CAM) or rifampicin. Heat resistance and induced thermotolerance were enhanced by recA and uvrA gene functions and their contribution was roughly as follows: AB1157 (recA+ uvrA+) greater than AB2463 (recA- uvrA+) greater than AB1886 (recA+ uvrA-) greater than AB2480 (recA- uvrA-). In heat resistance, uvrA and recA contributed approximately equally and their effects were additive. Induced thermotolerance developed sooner and was maintained at a higher level in the presence of uvrA as compared with recA. Since uvrA-dependent excision repair is scheduled prior to recA-dependent (postreplication) repair, induction of thermotolerance may be linked to DNA repair. Although recA and uvrA play a distinct role, they are not essential, and thermotolerance can develop in the absence of either one or both of these gene functions. Furthermore, since thermotolerance can be induced in recA mutants (AB2463 and AB2480), its biochemical pathway must be different from that of the recA-dependent SOS system.

Role of chelation and water binding of calcium in dormancy and heat resistance of bacterial endospores.

The possible relationship between the water binding by bacterial endospores and their dormancy and heat resistances has been examined in terms of the coordination characteristics of the spore-bound calcium. Stabilities of the calcium complexes of typical cytoplasmic and structural spore components were determined by potentiometric equilibrium pH measurements in model systems consisting of DPA, glycine, alanine, glutamic acid, alanyl-glutamic acid, triglycine, and tetraglycine. The Ca++-form and H+-form spores of Clostridium botulinum 33A were investigated in vivo with respect to their water sorption and heat-resistance characteristics. The results suggest that the complexing of calcium and Ca(II)-DPA may be biologically significant for spore resistance and dormancy at the following three levels: (1) complexing with spore cytoplasmic pool constituents consistent with the idea of a metal-chelate cross-linked cytoplasm or spore cement stabilizing the essential biological macromolecules, (2) complexing with structural components of the spore as indicated by the interaction with model peptides, and (3) coordination with water to produce an apparently dehydrated environment in the spore as evident from the much greater water-sorption capacity of the Ca++-form spores vs the much smaller water sorption of the H+-form spores. Interestingly enough, DPA itself, in the absence of metal ion, showed some interaction with di-, tri-, and tetrapeptides and a weak but detectable interaction with amino acids. Although the exact mode of the DPA-peptide interaction is not clear, it is attractive to speculate about its possible involvement in the control of spore dormancy and resistance.