Antibacterial activity of disodium succinoyl glycyrrhetinate,a derivative of glycyrrhetinic acid against Streptococcus mutans

Streptococcus mutans is a cariogenic bacterium that localizes in the oral cavity. Glycyrrhetinic acid (GRA) is a major component of licorice extract. GRA and several derivatives, including disodium succinoyl glycyrrhetinate (GR‐SU), are known to have anti‐inflammatory effects in humans. In this study, the antimicrobial effect of GRA and its derivatives against the S. mutans UA159 strain were investigated. Minimum inhibitory concentrations (MICs) of GRA and GR‐SU showed antibacterial activity against the S. mutans strain, whereas other tested derivatives did not. Because GR‐SU is more soluble than GRA, GR‐SU was used for further experiments. The antibacterial activity of GR‐SU against 100 S. mutans strains was evaluated and it was found that all strains are susceptible to GR‐SU, with MIC values below 256 µg/mL. A cell viability assay showed that GR‐SU has a bacteriostatic effect on S. mutans cells. As to growth kinetics, sub‐MICs of GR‐SU inhibited growth. The effect of GR‐SU on S. mutans virulence was then investigated. GR‐SU at sub‐MICs suppresses biofilm formation. Additionally, GR‐SU greatly suppresses the pH drop caused by the addition of glucose and glucose‐induced expression of the genes responsible for acid production (ldh and pykF) and tolerance (aguD and atpD). Additionally, expression of enolase, which is responsible for the carbohydrate phosphotransferase system, was not increased in the presence of GR‐SU, indicating that GR‐SU suppresses incorporation of sugars into S. mutans. In conclusion, GR‐SU has antibacterial activity against S. mutans and also decreases S. mutans virulence.     

Specific inhibition of aspartase by S-2,3-dicarboxyaziridine

Aspartase of Escherichia coli was inhibited in a competitive manner by S-2,3-dicarboxyazirdine (DCAZ), an antibacterial substance against Aeromonas salmonesida. The inhibition constant (Ki) was 55 microM, which was as low as less than one tenth that of the Km value for the substrate, L-aspartate. In view of the fact that both aspartase and fumarase (J. Greenhut et al. (1985) J. Biol. Chem. 260, 6684-6686) were inhibited by DCAZ in competitive manners, common features of the reaction mechanism of the two enzymes were discussed.     

Effects of the Addition of Humic Substances on Soil Protease Activities in Andosols in the Presence of Cadmium

Cadmium extraction, sorption, and immobilization seem to be the effective mechanisms in detoxification of Cd-contaminated soil. Humic substances present in soils may play an important role both in controlling the negative effects of pollution with Cd and in stabilizing soil enzymes. In this context, we have compared the effects of humic substances on soil protease activities in the presence and absence of Cd in forest and cultivated field soil samples. The samples were taken from surface soils of Andosols in a single upland area of the Kanto district in Japan. Humic substances extracted from the two soils showed differences in elemental composition, the degree of condensation of aromatic groups, and the proportions of major functional groups. Compared with the control soil samples, those with added humic substances showed a significant increase in protease activities, even in the presence of Cd (10 and 50 mg Cd kg^?1 soil). However, the addition of Cd decreased the protease activities, protein contents, and soil pH in both soil samples at each of the two levels of humic substance fortification (+5% and +10%). Moreover, protease activities showed significant negative correlation with exchangeable Cd, but adding humic substances did not lead to a reduction in either sample. Thus, although the addition of humic substances increased and stabilized protease activities, it did not lead to a clear reversal of enzyme inhibition by Cd. The obtained results indicate that in both soil samples the humic substances used in this study did not have sufficient affinity to adsorb Cd, and the impact on enzyme activities depends on the difference in chemical characteristics of the added organic matter, as suggested by the difference in enhancement of protease activities between forest and cultivated field soil samples.     

Morphological study on the 'seams' in the multiroot formation of rat molar teeth.

'Seams' of the root furcation with multiroots in rat molar teeth, termed by Lester and Boyde, were investigated using transmitted light and scanning electron microscopy in the formation process. The seam was formed in the junctional line of Hertwig's epithelial root sheaths. The seam formation will be classified into three types in the initial stage based on the position of the epithelial root sheaths approaching each other: (1) the close junction or the very narrow slit or gap formed between them, (2) the clear gap containing mesenchymal cells and (3) the gap containing one blood vessel. When the roots were formed, the seam was formed as follows: (1) the slight ridge composed of the cellular cementum, (2) the proliferation or the depression in the dentine formation and (3) the accessory or lateral canal of the root. These structures were variously combined with each other into one seam, although the slight ridge was very common.     

Course of infection and humoral response to Leishmania major in inbred Meriones unguiculatus

Numerous species of Meriones have been incriminated as natural reservoir hosts of Leishmania major in Mongolia, Soviet Asia, Afghanistan, the Middle East, and North Africa. However, little is known about the immunological response or course of infection in these small rodents. In this study, 40 commercially obtained inbred Meriones unguiculatus were divided into equal groups and injected in the right hind footpad with various doses of L. major promastigotes or with medium only. At regular intervals, blood was collected from the animals for subsequent evaluation of the kinetics of anti-L. major serum antibody production. Footpad lesions were measured periodically for 13 wk, beginning just before infection. The humoral response to infection and the course and severity of disease were dose related. However, metastasis lymph nodes, liver, spleen, and secondary cutaneous sites occurred at each of the doses tested.     

Consecutive monitoring of lifelong production of conidia by individual conidiophores of Blumeria graminis f. sp. hordei on barley leaves by digital microscopic techniques with electrostatic micromanipulation

Conidial formation and secession by living conidiophores of Blumeria graminis f. sp. hordei on barley leaves were consecutively monitored using a high-fidelity digital microscopic technique combined with electrostatic micromanipulation to trap the released conidia. Conidial chains formed on conidiophores through a series of septum-mediated division and growth of generative cells. Apical conidial cells on the conidiophores were abstricted after the conidial chains developed ten conidial cells. The conidia were electrically conductive, and a positive charge was induced in the cells by a negatively polarized insulator probe (ebonite). The electrostatic force between the conidia and the insulator was used to attract the abstricted conidia from the conidiophores on leaves. This conidium movement from the targeted conidiophore to the rod was directly viewed under the digital microscope, and the length of the interval between conidial septation and secession, the total number of the conidia produced by a single conidiophore, and the modes of conidiogenesis were clarified. During the stage of conidial secession, the generative cells pushed new conidial cells upwards by repeated division and growth. The successive release of two apical conidia was synchronized with the successive septation and growth of a generative cell. The release ceased after 4-5 conidia were released without division and growth of the generative cell. Thus, the life of an individual conidiophore (from the erection of the conidiophore to the release of the final conidium) was shown to be 107 h and to produce an average of 33 conidia. To our knowledge, this is the first report on the direct estimation of life-long conidial production by a powdery mildew on host leaves.