Irradiation of medical-use polymers causes chemical and physical changes in plastic polymer materials. The effects of ionizingradiation on these materials have been studied; the re- spective literature is reviewed to provide the basis for a safety evaluation of plastics exposed to irradiation sterilization treatment. Permeability of plastic films is generally not affected; deterioration of mechanical properties, that may occur with certain polymers, can usually be controlled with adequate stabilizers; and changes in infrared and UV/VIS spectra are observed with different irradiation doses. Gaseous radiolysis products include hydrogen, methane, CO2, CO, hydrocarbons, and, for chlorine-containing polymers, hydrogen chloride. A range of volatile products, mainly hydrocarbons, alcohol, aldehyde, ketone, and carboxyllc acids, has been characterized for low density polyethylene and polypropylene, but other important materials, e.g., polystyrene and poly (vinyl chloride), are less well-investigated. Radiation-induced changes are shown to depend on the chemical structure of the polymer, on the composition (additives) and processing history of the plastic, and on the irradiation conditions.
The effect of the surface charge of stainless steel particles on the adsorption behavior of pectin was studied over the pH range of 2.5 to 5.0. Stainless steel particles having different surface charge properties were prepared by chemical passivation in nitric acid, ozone oxidation, and heat treatment. The degree of the ionization of pectin increased with increasing pH, inducing a more extended structure. The saturation amount of pectin adsorbed (Γ s) on all the surface-treated stainless steel particles increased with decreasing pH, showing the largest values at pH 2.5. The Γ s also depended on the apparent density of the positive surface charge of stainless steel particles. It was found that the relative binding strength of unionized pectin on positively charged stainless steel surfaces was lower than that of ionized molecules and it also depended on the apparent density of the positive surface charge of stainless steel particles. These results showed that the surface charge of stainless steel, as well as the degree of the ionization of pectin, was an important factor determining the adsorption behavior of pectin at stainless steel-water interfaces.
To examine whether ATP in microbial cells could survive a thermal treatment, changes in microbial ATP content during the heat treatment were studied with a bioluminescent assay. The ATP content inEscherichia coilcell lysate did not decrease when heated at 90°C for up to 10 min. When cell suspensions ofE. coli, Klebsiellasp., Staphylococcus aureus, andSaccharomyces cerevisiaewere heated at 58°C, the content of the whole cell suspension ATP, ATPw, slightly decreased to a certain level. The viable cells of the suspensions measured by a plate count method were rapidly inactivated. Changes in the contents of ATPW, ATPc (cell fraction), and ATPf (cell filtrate fraction) of microbial cell suspensions during the heating process at 58°C were then studied. The contents of ATPw and ATPc gradually decreased for all organisms. The increase in the contents of ATPf forE. coliandKlebsiellasp. showed that the intracellular ATP would leak out. WhenE. coilcells were heated at various temperatures of 66-54°C, the content of ATPw decreased to a similar level at these temperatures. The contents of ATPc and ATPf approached to certain levels, which were temperature dependent.
Experiments were conducted to develop a microbial soil amendment for controlling plantparasitic nematodes using Streptomyces isolates NA-128, -150, -303, -359, -369 and -494. The acetone extracts of the cultured broth of these isolates suppressed the motility of secondstage juveniles of Meloidogyne incognita. These nematode-controlling Streptomyces isolates (NS isolates) are expected to control root-knot nematodes in the field. We examined how NS isolates could be maintained on various agricultural materials (carrier), and found that paperpulp compost and vermiculite could maintain them at a high density for a long time. In a pot experiment in a greenhouse, treatments with NS isolates fixed on paper-pulp compost increased the shoot length and fresh shoot weight of cucumber plants, and suppressed gall formation as compared to the NS untreated control. These effects became more remarkable by using paperpulp compost as a carrier for fixation of NS. There was a significant interaction effect involving NS treatments and the carrier type on cucumber growth. In addition, NA-494 treatment with paper-pulp compost had the most remarkable effects on cucumber growth.
he antimycotic activities of thymoquinone against some species of Saprolegnia pathogenic to fish as well as its toxic effect on selected farm fishes were investigated. Two Saprolegnia species pathogenic to fish, S. parasitica NJM 8604 and S. salmonis NJM 9851, were used. The minimum inhibitory concentrations (MICs) of thymoquinone against Saprolegnia parasitica and S. salmonis were 150 and 125 μg/ml, respectively, while the fungicidal effects on both strains were seen at 160 μg/ml. Tested zoospores of both Saprolegnia strains could not germinate after being exposed to 4 μg/ml of thymoquinone for 30 min. Thymoquinone was toxic to salmonids but less toxic to cyprinids.
Vibrio parahaemolyticus is an important etiological agent of gastroenteritis associated with seafood consumption in Japan and many parts of the world. Thermostable direct hemolysin (TDH) and TDH-related hemolysin(TRH), encoded by the tdh and trh genes respectively, are the most recognized pathogenic factors of this bacterium. During this study a high percentage of V. parahaemolyticus isolated from an area was found to be positive for the tdh and/or trh genes by PCR, although almost all of the isolates lacked the ability to produce active hemolysin. Such tdh and/or trh positive strains were isolated from a specific coastal area, but not isolated from four other areas of the Seto-Inland Sea. This particular area, Kojima Bay, receives freshwater from several adjacent rivers, and such influx of water may have special effects on the growth V. parahaemolyticus, as evidenced by the high density of this bacterium in water samples (2300 to 4600 per 100 ml). V. parahaemolyticus of various sero-groups were isolated from each area; however, Kojima Bay samples were dominated by O1, O3, and O4 sero-groups.
The correlation between bacterial concentration and the change in electrical conductivity was investigated for the indirect conductimetric assay which measures the conductivity change of an alkaline solution (NaOH) that absorbs the CO2 produced by bacterial growth and metabolism. The conductivity of the NaOH solution for a sample containing a higher bacterial concentration changed faster than that for a sample containing a lower concentration, and the logarithmic initial bacterial concentration (CB0) was related to the time (tD), at which the conductivity of the absorbent changed, in a linear fashion. We derived theoretically the validity of the linear relationship and estimated the generation time (tg) from the relationship. The tg values obtained by the indirect conductimetric assay were almost identical to those obtained by the direct conductimetric assay and the Standard Plate Count method.
The effect of the metabolites of actinomycetes on the motility of the root-knot nematode, Meloidogyne incognita, was investigated. A thousand strains of actinomycetes were obtained from about 500 soil samples, and the suppressive effect of the acetone extract of each culture on the motility of the second-stage juveniles of M. incognita was examined. We found that the motility was suppressed by the extracts of six isolates, NA-128, -150, -303, -359, -369 and NA-494. From the taxonomic characteristics, all six isolates were Streptomyces. In this report, we describe a method to screen for actinomycetes which suppress the motility of root-knot nematode and the taxonomy of six actinomycetes isolates (Streptomyces species) screened.