It has been reported that the bactericidal action of bis-quaternary ammonium compounds (bis-QACs) is little influenced by the molecular hydrophobicity. of the drug or environmental conditions such as temperature or pH. In order to clarify the mode of bactericidal action of bis-QACs against Escherichia coli, the bacterioclastic action of 4, 4'-(1, 6-hexamethylenedithio) bis (1-octylpyridinium bromide) (4DTBP-6, 8) was investigated. It was suggested that 4DTBP-6, 8, which invaded the bacterial cell, induced the leakage of ATP and the inhibition of the respiratory enzymes, and resulted in cell death. Subsequently, over 2μg/ml of4DTBP-6, 8 caused an increase in the turbidity of the cell suspension, and the bactericidal activity of 4DTBP-6, 8 was extremely increased with the increase of its concentration (over 2μg/ml). It indicated that 4DTBP-6, 8 has an ability to induce a rapid and abundant secretion of the turbid materials from the cells and that such bacterioclastic ability is connected to its potent bactericidal activity. In addition, it was suggested that the first stage of bacterioclastic action of 4DTBP-6, 8 was the leakage of magnesium ion (Mg²⁺), and the leakage of the outer membrane pore protein E and lipopolysaccharides followed it. The formation of blebs and holes on the bacterial cell surface was revealed by scanning electron microscopic investigation. Transmission electron micrographs of the cells treated with 4DTBP-6, 8 showed the destruction of peptidoglycan and large missing portions of intercellular materials. Judging from these results, as the mechanism of the bacterioclastic action of bis-QACs, it is suggested that the cationic parts of bis-QACs electrically interact with the cationic parts of Mg²⁺ on the bacterial surface, then bis-QACs invade the cell membrane by displacement reaction with Mg²⁺, and rapidly destroy the bacterial cell surface structure.

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A low-molecular-weight, extracellular substance with one-electron-oxidizing activity was isolated from wood-degrading cultures of the brown-rot basidiomycetous fungus Fomitopsis palustris. The substance was partially purified by acetone precipitation, gel-filtration chromatography on Sephadex G-50 and G-25, and DEAE-Sepharose ion-exchange chromatography. The partially-purified material was a glycopeptide composed of (54%, w/w) protein and (42%, w/w) neutral carbohydrate, containing (0.06%, w/w) Fe (II) by weight. The molecular weight as estimated by Tricine-SDS-PAGE was 7, 200-10, 000; whereas the molecular weight as determined by size-exclusion or gel-filtration chromatography was 1, 000-5, 000. The glycopeptide reduced O₂to H₂O₂ and Fe (III) to Fe (II), and thus could generate hydroxyl radical via a Fenton reaction. One mg of the partially-purified glycopeptide reduced 1.7μ mol of Fe (III) to Fe (II) and contained at least 0.6μ mol of α-hydroxyketone or endiol groups. Most of the α-hydroxyketone groups were 1-amino-2-ketoses produced by the condensation of side-chain amino groups and carbohydrate aldehydes. The function of the glycopeptide in brown-rot decay is discussed.

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The colonial growth of Escherichia coli and Staphylococcus aureus on agar solidified medium (a food model system) was estimated by using a microbial calorimeter. Changes in the metabolic heat of the colonial growth over time (the growth thermogram) were obtained with good reproducibility. The actual heat evolution curves [f (t) curves] obtained from the thermograms of growing colonies gave good agreement with the changes in viable cell numbers in colonies under the same conditions. The f (t) curve was also compared with the process of colony formation. During the early period of the f (t) curve (the period of 0 - 10h after inoculation), colonies could not be observed, but at 15h after inoculation, some small colonies were visible. During the period between 15h and 25h, the numbers and size of colonies increased. During the later period of the f (t) curve (the period of 25-34h), although the size of colonies still increased, the colonial profiles on LBA medium were almost similar in spite of the continued evolution of growth heat, indicating that the direction of colony growth shifted from being predominantly radial to predominantly.vertical with regard to the agar surface. From the logarithmic f (t) curve, the exponential growth phase was estimated to be the period between 8.5 h and 13.5 h after inoculation. The growth rate constants (μ') for colonial growth obtained from the f (t) curves were 0.643±0.037 h^-1 for E. coli and 0.597±0.05811^-1 for S. aureus. The suppressive activities of salts and kumazasa (Sasa albo-marginata Makino et Shibata) extracts on colonial growth were evaluated in terms of μ_i' μ_m' derived from the f (t) curves. The MIC (minimum ihhibitory concentration) values for NaCI were estimated to be 9.7±1.5%, equivalent to a water activity (Aw) of around 0.906, against E. coli colonial growth and 12.8±1.4%, equivalent to an Aw of around 0.882, against S. aureus. The MIC value for kumazasa extracts was estimated to be 4.6±0.6% (1.79 mg of non-volatile components per 1 ml) against S. aureus colonial growth. These values were in good agreement with those obtained by the agar plate dilution method. The study of bacterial growth on solid medium, as opposed to traditional liquid culture, should provide a model system more representative of the food environment. Microbial calorimetry is a method suitable for non-destructive growth measurements of microbial colonies on solid medium.

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We studied the effects on the sporicidal activity against Bacillus subtilis spores by replacing Fe³⁺ with various kinds of metal ions in the formulation of FeCl₃·6H₂O, EDTA-2Na and ethanol, herein called the ethanol reagent and one which has already shown potent sporicidal activity (Kida et al., 2003). Metal ions used for comparison in the sporicidal activity of the ethanol reagent were Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Al³⁺, and each sporicidal activity was examined at various pHs and temperatures. Among them, the ethanol-Cu²⁺ reagent showed potent sporicidal activity at 20°C and 37°C at pH 0.3 and the ethanol-Ni²⁺ reagent also showed a potent one at both temperatures at pH 0.6 comparable to the ethanol reagent. These results show that the ethanol reagents with metal ions even other than Fe³⁺ show sporicidal activity which may be available for practical use.

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We developed a method to predict the fungal response (FR) of the sensor, Eurotium herbariorum in a fungal detector from the climatic history. Values of FR in dynamic climate conditions were predicted by integrating the rate of FR during the observation periods. FRs predicted under experimental climates were greater than FRs measured, but there was a high linear correlation between them (r=0.989). With an adjustment factor introduced into the method, the increase in the FR value during experimental climates was well predicted. These results suggested that this method might have a potential to accurately predict the FR from the climatic history.

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The addition of Diaion HP-20 resin to a medium can enhance the growth of the Legionella species. We recently reported that elemental sulfur was isolated as a growth-inhibiting substance produced endogenously by Legionella pneumophila from the methanol extracts of the resins used to culture the bacteria. In this study, we attempted to isolate other growthinhibiting substances involved in the extracts, and identified indole-3-aldehyde as one of the inhibitors. The compound was involved in the medium as a constituent and it weakly inhibited the growth of L. pneumophila, indicating that the compound partly contributes to inhibit the bacterial growth when cultured without HP-20 resins.

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