A simple dynamic model of competition between two types of microorganisms, one of which produces an inhibitory substance in an ideal chemostat, was developed to study the survival mechanism of an exogenous microbial strain introduced into an ecosystem possessing antagonistic activity against it. Numerical simulations of the model were carried out in 12 cases depending on the disposition of the growth rate curves of the two types of microorganisms and on the sensitivity of the microorganisms against the inhibitory substance. From the results, it was demonstrated that production of an inhibitory substance gives its producer a chance to exclude the competitor under conditions in which the producer would be otherwise excluded by the competitor. It was also found that production of a substance which is inhibitory not only against the competitor but also against the producer itself (autoinhibitory) allows the two microbial strains to coexist under conditions in which the competitor would otherwise be excluded. It was suggested that production of some inhibitory substances and tolerance to such substances are desirable characteristics for exogenous microorganisms to survive in microbial ecosystems, and a large inoculum density of exogenous microorganisms has a positive effect on their survival rate in some cases.

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Calorimetric studies were conducted on the antimicrobial action of p-hydroxybenzoate alkyl esters (parabens), which are commomly used as preservatives in cosmetic products, and the parameters to quantitatively predict their actions on the microbial strains were determined. The result obtained was that their action on both Saccharomyces cerevisiae and Klebsiella pneumoniae became stronger as the number of carbon atoms in the alkyl chain increased. When comparing the affinity of the drugs to both microorganisms based on the drug concentration required to inhibit growth activity by 50%, a linear relationship was observed to exist between the number of carbon atoms in an alkyl chain and the affinity. In addition, the same drug exhibited a higher effect on S. cerevisiae than on K. pneumoniae, which may be due to the difference in the membrane structures of the microorganisms.

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Novel bis-quaternary ammonium compounds (bis-QACs), 5, 5'- [2, 2'-(tetramethylenedicarbonyldioxy) diethyl] bis (3-alkyl-4-methylthiazolium iodide) s (5DEBT-4, n: alkyl chain length, n=8, 10, 12, 14, 16 or 18) were synthesized and characterized. The chemical structure of 5DEBT-4, n is a symmetrical dimer which is composed of two N-alkyl-5-(2-hydroxyethyl)-4- methylthiazolium iodides (T-n) connected by a tetramethylene chain. Both the bacteriostatic activity and the bactericidal activity of 5DEBT-4, n were higher than those of T-n and were scarcely affected by the length of the alkyl chain unlike general mono-QACs. 5DEBT-4, n exhibited a wide-ranging and effective antimicrobial activity against both bacteria and fungi, compared with a bactericide, benzyldimethyldodecylammonium chloride (BAC), and a fungicide, 2-(4-thiazolyl) benzimidazole (TBZ), both of which are widely used. The bacteriostatic activity of 5DEBT-4, n was reduced with the increase in molecular hydrophobicity, while the bactericidal activity was not influenced by that. This result suggests that the hydrophobic materials in the medium interacts with 5DEBT-4, n, especially when possessing longer alkyl chains, and covers the active moiety of the agents. Furthermore, it was implied that properties other than the molecular hydrophobicity contribute to the bactericidal action. 5DEBT-4, n showed a higher bactericidal activity in the ranges of pH 5 to 8.5 and 10 to 40°C than T-n and was little influenced by pH and temperature.

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The synthetic drugs developed against dermatophytic infections caused by Trichophyton rubrum are not altogether free of side effects. The therapeutic measures sometimes become toxic to humans. With that in view, extracts from five plants, plentifully available in India, were tested under in vitro conditions upon the variants of T. rubrum causing cutaneous and superficial skin infections at Rourkela, Orissa, India. It was observed that oils of Azadirachta indica, Pongamia glabra and extracts from the rhizomes of Curcuma longa were highly effective in inhibiting the growth of the fungal variants in this part of the world. In this paper, the in vitro minimal inhibiting concentration of these plant extracts were determined against 4 variants of T. rubrum.

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The colony hybridization (CH) method as a rapid method for detecting Legionellaspp. was compared with the conventional culture method. In the comparison of colony count in which a suspension ofL. pneumophila was examined, a positive correlation was shown between the results by both methods. The regression line was Y=0.85+1.34Xand the correlation coefficient was 0.95. The maximum number of detectable colonies on the plate was 144 colony forming units, although there was a tendency for the CH data to give slightly lower counts than those of the culture method. The detection time in the CH method was half of that in the culture method, and the final result was obtained within 4 or 5 d. In addition the results by the CH method were rarely influenced by other contaminating microorganisms, since the transfer of colonies was performed at the initial stage of culture.

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To determine a favorable medium for detecting fungal extracellular protease, a plate method was examined. In this study, 12 fungal strains were tested with 4 different types of Czapek Dox agar medium containing skim milk, and the clear zones around the colonies were compared on the different types of medium. Among them, 9 strains produced extracellular proteases. Triton X-100 was required to detect an extracellular protease fromAlternaria alternata, while in case of Peniciliium frequentans, saccharose was required. It was found that the media supplemented with both Triton X-100 and saccharose gave acceptable results in terms of extracellular protease detection.

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This paper describes the isolation and identification of an antimicrobial compound againstStreptococcus mutansfrom the leaves ofDiospyros kaki. After repeated chromatography of the weakly acidic fraction of acetone extracts, an antimicrobial compound againstS.mutanswas isolated. The chemical structure of the active compound was elucidated by spectroscopic methods, and identified as kaempferol. Kaempferol is an aglycone of astragalin (kaempferol 3-O-β-D-glucopyranoside) which has been isolated from the leaves ofD.kaki. The minimum inhibitory concentrations of kaempferol againstStreptococcus mutans, Escherichia coli, Bacillus subtilis, andStaphylococcus aureuswere estimated.

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Fifteen 3-substituted thioxopyrrolidines were synthesized and assayed for their antimicrobial activities against Eurotium chevalieri, Schizosaccharomyces pombeand Staphylococcus epidermidis.3- [(α-Alkoxy)-α-methoxy] methyl-(1-7) and 3- [(α-alkoxy)-α-methylthio] met hyl-2-thioxopyrrolidines (8-11) showed antimicrobial activity againstE. chevalieriandS. epidermidis, and their activity increased by lengthening the alkoxyl chain. 3-Alkoxymethylene- 2-thioxopyrrolidines (12-15) were less active against the fungi and the bacteria. For the thioxopyrrolidines, a positive correlation was observed between the hydrophobicity of the compounds and their activities against E. chevalieri. On the other hand, against the yeast, compounds 8-15 behaved differently from 1-7, and the highest activity was associated with the ethoxy (9) and the propoxy (14) derivatives of compounds 8-11 and 12-15, respectively.

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Bacillus sp. HR6 and Bacillus subtilis ATCC6051 were compared in terms of their growth, activity of α -amylase, and pattern of heat evolution. Bacillus sp. HR6 grew faster than B. subtilis ATCC6051 at temperatures higher than 45 °C. The maximum activities of α -amylase were 304 and 280 U/ml for Bacillus sp. HR6 and B. subtilis ATCC6051, respectively. The highest activity of α-amylase from Bacillus sp. HR6 was observed at 70 °C, and more than 60% of that was still seen at 75 °C. In case of B. subtilis ATCC6051, the maximum activity was observed at 65 °C, and 30% of that was seen at 75 °C. A rapid heat evolution was found for Bacillus sp. HR6 in comparison with that for B. subtilis ATCC6051 when cultivation was initiated in bean curd refuse at 50 °C. However, there was no obvious difference in the heat evolution patterns between two strains at the starting temperature of 27 °C. These results suggest that Bacillus sp. HR6 has a higher activity in decomposing bean curd refuse than B. subtilis ATCC6051 at higher temperatures.

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The dark brown pigments contained in molasses wastewater (MW) are hardly decomposed by usual microorganisms. In light of this, Aspergillus usamiiandCoriolus versicolorwere selected for mutation induction by C⁵⁺ion-beams or γ-irradiation to increase their ability to decolorize these brown pigments. In this study, the decolorization yield from crude MW was 40 to 42% after 2-3 d incubation at 8-fold dilutions by mutant strains of A.usamiiwhich were obtained by ion-beam irradiation while it was 30% by the parent strain. In the case of C. versicolor, the decolorization yield was increased to ca. 70% by the mutant strains after 5 to 6 d incubation at 8-hold dilutions whereas the yield was 51% by the parent strain.

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