Biomedical subjects
Publications and source records attributed to L Seganti.
The effect of phospholipases on rhabdovirus attachment to CER cells and the competitive binding of phospholipids and viruses to cells were studied. Results obtained indicate that, although to a different extent, some phospholipids represent a binding site for both Vesicular Stomatitis Virus (VSV) and rabies virus.
Research has been carried out on the role of different chemical groups present on human group A erythrocyte membranes and involved in the interaction with mannose-resistant (MR) adhesins of a uropathogenic E. coli strain. For this purpose several enzymes specifically acting on protein, lipid and carbohydrate components have been used to modify the erythrocyte surface structures and the effect produced by these treatments on the agglutinability of red blood cells by E. coli has been studied. Moreover different biological compounds have been tested as possible competitive inhibitors for erythrocyte receptors involved in MR agglutination by E. coli.
The inhibiting activity of various human serum lipoprotein classes and their lipid components on the infectivity of rhabdoviruses has been studied. The research has been carried out according to different experimental procedures on both the vesicular stomatitis virus (Indiana strain), and the fixed rabies virus (CVS strain). The results obtained have shown an inhibition of the infectivity of VSV and CVS, mainly linked to the very low and low density lipoprotein classes. It has also been demonstrated that the inhibitors act directly on viruses causing a decrease in their attachment to host cells.
A study has been made to clarify the importance of some carbohydrate components of goose red blood cell and BHK 21 cell membrane receptors for vesicular stomatitis virus (VSV). Experiments have been carried out by inducing enzymatic modifications on the surface of intact cells and following the interaction between VSV and treated cells. Results obtained indicate that the removal of mannose, galactose and fucose from cell membranes reduces the attachment of the virus to cell receptors.
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The chemical nature of BK virus receptors on human erythrocytes was investigated. Glycosidases, KIO4, proteases, phospholipases and other substances acting specifically on different structures of plasma membranes were used to ascertain the role of surface cell components in the interaction with BK virus. The results obtained indicate an analogy between BK virus receptors on red cells and non-antibody serum inhibitors active against haemagglutination by the same virus.
The chemical structure of human serum low density lipoproteins (LDL) involved in the inhibition of the haemagglutination by Sindbis virus was studied. Separation of lipoproteins into their protein and lipid components demonstrated that the inhibiting activity is almost completely due to the lipid moiety. The treatment of LDL and extracted lipoprotein lipids by phospholipase A2, C and D produced different effects and in particular a marked increase in the HI titre by the action of phospholipase A2. Moreover treatment with glycosidases significantly reduced the HI titre of LDL, thus suggesting the importance of carbohydrate moiety in the inhibiting lipoprotein molecule.
A total of 150 strains of staphylococci, clinically isolated, were tested for sensitivity to ovotransferrin (conalbumin). Among these, all the 50 coagulase-positive, mannitol-positive, and deoxyribonuclease-positive staphylococci appeared to be resistant to conalbumin, i.e., capable of growing in the presence of this transferrin. Among the other 100 strains, which were not classified as S. aureus, some appeared to be resistant and some were sensitive. The different behavior toward conalbumin is related to varying degrees of efficiency of the bacterial iron transport systems and, to test this, a simple method can be used, based on the addition of CrCl3 to the culture medium. The precipitation of iron produced by chromium salts has an effect on the growth of staphylococci similar to that produced by conalbumin and reveals the differences in the iron transport systems which occur in the genus Staphylococcus.
The haemagglutination-inhibiting activity of human serum towards Sindbis virus is linked to very low and low density lipoprotein classes, in particular to their lipid component. To investigate the specific role played in this inhibition by carbohydrates contained in the molecule, inhibitor separation was carried out by Concanavalin A-Sepharose affinity chromatography. A different behaviour among the inhibiting molecules in relation to the carbohydrate content was observed. The importance of mannose for the biological activity of the inhibitor is discussed.
Research was carried out in order to verify if some components of human serum, which are capable of inhibiting the hemagglutination by Sendai virus, are active even towards the hemolysis by the same virus. It was ascertained that both orosomucoid and low-density lipoproteins obtained by floatation had no action on the hemolysis by Sendai virus while lipoproteins precipitated with dextrane sulphate showed a certain inhibiting effect. This action however is not due to lipoproteins but is probably related to some substances used in the method of precipitation.
Non-antibody hemagglutination-inhibiting activity of human serum is due, at least partially, to a glycoprotein inhibitor. This inhibitor was obtained from the whole serum or the fraction VI (Cohn) by means of methods of purification generally used for the preparation of the orosomucoid and was identified more precisely with an acid alpha 1-glycoprotein.
An investigation has been carried out in order to ascertain the effect of the presence of complement on the HI antibodies of the IgM class obtained in rabbit against Sendai virus. Contrary to the results obtained by some AA. with other viruses, in this case the presence of complement in the form of fresh guinea-pig serum has not modified the HI titre. It has however been demonstrated that in the guinea-pig serum an inhibitor is present, which is active towards Sendai virus and can be identified as a 19S alpha-globulin.
The effect of 6,4'-dichloroflavan and of isoflavan and isoflavene derivatives on hepatitis A virus (HAV) infection in a monkey cell line (Frp/3 cells) was studied. These compounds were not virucidal and had no measurable effect on the adsorption of virus to the cells at 0 degrees C, whereas they exerted an inhibitory effect on viral antigen synthesis when incubated with the infected cells during HAV multiplication. Among the substances tested, 6,4'-dichloroflavan and 6,4'-dichloroisoflavan showed the highest activity. These compounds are postulated to interact with an early stage (penetration and/or uncoating) of HAV infection.
The aim of the present study was to evaluate the role of temperature in the virulence of Listeria monocytogenes, a Gram-positive facultative intracellular food-borne pathogen. The capacity of bacteria grown at 37, 25 and 4 degrees C to develop haemolytic activity, to enter the Caco-2 enterocyte-like cell line and to multiply intracellularly was investigated. We demonstrated that L. monocytogenes penetration was not significantly influenced by the growth temperature of cultures and that bacteria grown at low temperature were capable of synthesizing internalin and, during the infection process, of restoring the haemolytic phenotype which is normally lacking in the extracellular environment at 4 and 25 degrees C. It can be concluded that L. monocytogenes, frequently present in numerous environmental sources and also in refrigerated food products, produces at low temperature, the virulence factors necessary to invade intestinal cells.
A series of eleven lectins were investigated for their inhibiting activity towards herpes simplex type 1, rabies and rubella viruses. Herpes simplex virus adsorption was inhibited by Limulus polyphemus (LPA), Canavalia ensiformis (ConA) and wheat germ (WGA) agglutinins, whereas Bauhinia purpurea (BPA) and soybean agglutinins were more effective if present during viral replication; rabies virus attachment to susceptible cells was prevented by LPA and Narcissus pseudonarcissus (NPA) agglutinin whereas WGA and BPA were inhibitory at a later step; rubella virus multiplication was affected only after the attachment step by NPA, ConA and WGA.
Different natural and semisynthetic polymeric carbohydrates inhibited rabies virus infection in chicken-embryo-related cells by interfering with the virus adsorption process; a dose-dependent relationship was exhibited. Among polysaccharides tested, the neutral polymer Scleroglucan and the negatively charged Keltrol, glyloid sulphate 4324, glyloid sulphate 4327 and alginic acid were the most effective and remained active at concentrations far below the cytotoxicity threshold. Data obtained indicated that the inhibition mechanism of polymers may be related to the ability of these compounds to bind to viral envelopes, although their interaction with cell surfaces cannot be excluded. The charge density and the polymeric backbone of the molecules seem to play a role in influencing the antiviral properties, whereas other features such as the sugar moieties do not appear to be relevant.
The effect of different natural and semi-synthetic polysaccharides on Chlamydia trachomatis multiplication in Hela 229 cells was evaluated. Some neutral, negatively and positively charged carbohydrates were able, in a dose-dependent fashion, to inhibit chlamydial infection by interfering mainly with the adsorption process. The inhibiting compounds, whose effect was shown within the concentration range of 8-200 micrograms/ml, were in order of action: dextran sulphate > glyloid sulphate 4327 > glycogen sulphate 4427 > arabic gum = glyloid > chitosan > glycogen. Data obtained suggested that antichlamydial activity was not only related to the electric charge of these molecules but could also be attributed to other features of their polymeric backbone. Since carbohydrate polymers have also been shown to inhibit the early stages of infection by viral agents causing sexually transmitted diseases, the employment of these molecules for prevention or treatment of mixed viral-C. trachomatis infections can be hypothesized.
Listeria monocytogenes is an intracellular foodborne pathogen of humans and animals for which there are indications of virulence differences among strains. Various virulence properties related to different phases of infection process were investigated in L. monocytogenes strains isolated from patients affected by haematological malignancies. In these isolates, besides to the clinical history, we analysed the haemolysin production, the survival to acidic pH, the ability to enter and proliferate in human intestinal-like and human macrophagic-like cells, as well as the allelic polymorphism of the actA gene involved intracellular movement. A general heterogeneity in the virulence properties was detected which did not appear correlated with the clinical outcome of listeriosis but more probably was influenced by the status of the immune defence of the host.