The bactericidal activity of a quaternary ammonium salt, didecyldimethylammonium chloride (DDAC), was depressed by the presence of soap, sodium laurate (NaLA): the minimum lethal concentration (MLC) of DDAC against Staphylococcus aureus was 63 and 250 μg/ml in the absence and presence of 0.01% NaLA, respectively. The neutralizing effect was studied in relation with the mode of action of DDAC. The apparent uptake of DDAC by the cell was not repressed by NaLA's presence when compared to that in its absence. The solution of NaLA showed alkaline pH, but the biocidal activity of DDAC was higher at pH 11 than at pH 7. Although the presence of NaLA had no significant effect on DDAC's action on increasing the turbidity of the cell suspension, the mixture of these reagents alone without cells exhibited some turbidity. From these findings it is deduced that NaLA can form a less active complex with DDAC by both ionic and hydrophobic interactions, suggesting that the positive charge as well as the hydrophobicity of the side chains in DDAC moiety plays an important role in its bactericidal activity. Key words: Bacteric

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A multiplex batch calorimeter was used to monitor the heat evolution during incubation of yeast cultures in the presence of decanoic acid at various concentrations. The changes observed in the recorded growth thermograms when the concentration of decanoic acid increased were quantitatively described using the values of the growth rate constantμ determined for each culture from the calorimetric recording. This made possible the calculation of the 50% inhibitory concentration (K _μ) and the 100% inhibitory concentration (MIC _μ) of decanoic acid in relation to the growth of four yeast strains at 30°C. By using adequate control cultures, it was possible to distinguish the separate inhibitory effect of decanoic acid and ethanol, as well as their combined effect. Other experiments with a strain of Saccharomyces cerevisiae showed that the “apparent” K_μ and MIC _μ values (calculated on the basis of the total decanoic acid added to the cultures) increased with the pH, while the corresponding K _μ and MIC _μ values calculated on the basis of the amount of undissociated decanoic acid remained relatively constant, indicating that the toxic action is due mainly to the undissociated form of the acid. The “apparent” K _μ and MIC _μ values of decanoic acid at pH 5.5 also depended on the ethanol concentration in the medium, showing a marked decrease when the initial ethanol concentration varied from 0.33% to about 1.0% (v/v), and then decreasing only slightly when the concentration of ethanol increased to 6.25% (v/v).

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It has been often observed that bacteria seemingly adapt to sucrose monoesters of fatty acids, which are supposed to be effective nontoxic antimicrobial agents. In the present experiment, effects of the esters on the germination, outgrowth and vegetative growth of Bacillus cereus were investigated with reference to the adaptation phenomenon. The esters showed inhibitory effect on the development of spores into multiplying cells by preventing outgrowth, in the order of effectiveness of lauryl ester>palmityl ester>stearyl ester. However, the cells of which growth had been once inhibited again developed in the medium. This resumption of growth occurred almost in parallel to a decrease in the concentration of the esters in the medium. Vegetative growth of cells was also prevented by the addition of esters, but the growthinhibited cells again recovered their ability to grow during further incubation in the medium. Furthermore, it was found that esterase is released from germinated spores and growing cells. Taken together, the results indicated that the loss of antimicrobial activity of the esters observed during cultivation is due to the decomposition of the esters by esterase.

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The effects of polyoxyethylene cetyl ether (PCE) on the cellular uptake and the antibacterial activity of butyl p-hydroxybenzoate (BP) by bacteria were studied using an aqueous suspension of Escherichia coli. The BP in the cell suspension was distributed in the cells and aqueous phase. PCE added to the BP solution was responsible for reducing the BP uptake into the cells and inhibiting the antibacterial activity of BP due to the formation of a complex between BP and PCE micelles. The uptake and antibacterial activity of BP were proportional to the unbound BP concentration in the aqueous bulk solution. However, the addition of PCE repressed BP uptake in the cells and enhanced BP activity compared with those values expected from unbound BP in the aqueous surfactant solution. These results suggested that direct interactions between PCE and bacterial cells increased the susceptibility of bacteria. The decrease in BP uptake into bacterial cells was thus concluded to be responsible for the reduction in the antibacterial activity of BP in an aqueous surfactant solution, and the measurement of paraben uptake by microbial cells was found to be a reliable means for assessing inactivation in an aqueous solution in the presence of surfactants.

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We propose here the bioproduction of a surface active agent (biosurfactant) from acetic acid as an innovative strategy for using waste sludge as a source of acetic acid by anaerobic digestion, and basic studies on biosurfactant production, characterization and application were performed. Pseudomonas putida BH was screened out of 23 laboratory stock culture strains as a bacterial strain capable of producing (a) kerosene-emulsifying surfactant (s) form acetic acid. It produced a biosurfactant during the logarithmic growth phase from acetic and propionic acids. The crude biosurfactant, recovered by extraction with benzene, contained sugar, protein and lipid at 16, 22, and 3% (w/w), respectively. Molecular weight of the surfactant was estimated as approximately 2 million by gel filtration. The crude biosurfactant showed emulsifying and solubilizing activities against a variety of hydrocarbons, and was especially effective against aromatics. Addition of 50 mg/l of the crude biosurfactant markedly enhanced biodegradation of kerosene by an enrichment culture, while the biosurfactant itself was readily mineralized by a non-acclimated activated sludge, suggesting its successful application to oilbioremediation. Experimental results indicate that it may be possible to apply the proposed strategy in future.

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The Candida strains isolated from human pathogenic lesions were tested with different concentrations of heavy metals to determine the in vitro minimal growth inhibitory concentration of the salts. The test, being a new one, can help to develop ancillary candidostatic measures.

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The acute toxicity levels of 5 kinds of fungicide against the free-living protozoal ciliate Colpoda aspera were tested in cocultivation with Alcaligenes faecalis IFO13111. The fungicides used were products containing the following effective components: dimethilimol (DMM), admixture of ziram, thiram and polyoxin (ZTP), flutolanil (FLN), streptomycin (SM), or 8- hydroxyquinoline copper and captan (CHC). Each fungicide was added at varying concentrations, and the effective concentration (EC₅₀) at which the specific growth rate of C. aspera was reduced to 50% after 24 h culture was defined as the acute toxicity of the fungicide tested. It was found that ZTP had the highest level of toxicity, followed by CHC, SM, DMM and FLN. When the fungicides were evaluated in terms of safety on the basis of indices obtained by dividing normally applicable concentrations (NC) by EC₅₀, the safety levels of SM, DMM and FLN were high compared to those of ZTP and CHC.

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The effects of polyoxyethylene cetyl ether on the antibacterial activity of butyl p-hydroxybenzoate (BP) were studied using five strains of bacteria. The antibacterial activity of BP in an aqueous solution was inhibited by the non-ionic surfactant due to a decrease in unbound BP in an aqueous phase resulting from the incorporation of BP into surfactant micelles, whereas it was greater than that anticipated from unbound BP. Non-ionic surfactant was thus concluded to increase the susceptibility of bacteria against BP due to direct interactions with the cells.

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The sewage treatment sludge after being composted has been suggested as a soil conditioner. In this study, the changes in components and microflora of the sludge during the composting process were examined. The organic matter and water content decreased during composting. Achromobacter sp. were abundant in the raw material, but decreased gradually, while Bacillus sp. increased. The composting did not decrease viable bacteria or coliform groups. The effects of composting on pathogenic bacteria were not clear. These findings suggested that the decrease of organic matter, water content, and the changes in microflora could be useful indexes of the composting condition.

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