Biomedical subjects

L Seganti

Publications and source records attributed to L Seganti.

At least 37 records · Page 2Linked to original sources

PubMed1996

Antiviral effect of a polysaccharide from Sclerotium glucanicum towards herpes simplex virus type 1 infection.

Among different neutral polysaccharides from natural sources, scleroglucan from Sclerotium glucanicum significantly inhibits the replication of herpes simplex virus type 1 on Vero cells. Scleroglucan belongs to a class of exopolymers, expressed by members of genus Sclerotium and consists of a linear beta-1,3-linked glucopyranose with side chains of single glucopyranose residues linked through beta-1,6 glycosidic bonds. The effective antiviral concentration of this polysaccharide is far from the cytotoxicity threshold and consequently this natural product possesses a good selectivity index. Results obtained in experiments carried out in order to clarify the mechanism of action of this carbohydrate indicate that the block of infection occurs during the very early phases of the viral mutliplication cycle since the highest inhibitory effect took place when it was added during the attachment step. The antiviral effect of scleroglucan seems to be related to its binding with membrane glycoproteins of HSV-1 particles which impedes the complex interactions of the virus with the cell plasma membrane.

Animals↗

PubMed1996

The effects of inhibitors of vacuolar acidification on the release of Listeria monocytogenes from phagosomes of Caco-2 cells.

To evaluate the role of the acidic pH of phagosomes on the invasive ability and fate of Listeria monocytogenes within host cells, entry and replication of this gram-positive bacterium in a human enterocyte-like cell line (Caco-2) were investigated by a combination of biochemical and ultrastructural approaches. The effects of inhibitors of vacuolar acidification--the lipophilic weak base ammonium chloride, the carboxylic ionophore monensin and the vacuolar proton ATPase inhibitor bafilomycin A1--on the bacterial invasion pathway were analysed. These agents, which raise the intracellular vesicle acidic pH of living cells by different mechanisms, affected L. monocytogenes replication in Caco-2 cells. Bacteria internalised by bafilomycin-treated cells were unable to escape from phagosomes, as demonstrated by electronmicroscopy. The results provide evidence that low pH is required for efficient intracellular growth of L. monocytogenes.

Ammonium Chloride↗

PubMed1996

Iron availability affects entry of Listeria monocytogenes into the enterocytelike cell line Caco-2.

The influence of iron on the entry of Listeria monocytogenes into Caco-2 cells was studied. Iron availability was found to modify the surface hydrophobicity and protein profile of L. monocytogenes, with the result that cell invasion strongly increased upon bacterial growth in iron-rich medium. The enhanced invasive capability of iron-overloaded L. monocytogenes cells correlates to the higher-level expression of the inlAB virulence genes, which were positively iron regulated at the transcriptional level.

Bacterial Adhesion↗

PubMed1996

In vitro study of a double infection by herpes simplex virus type 2 and Chlamydia trachomatis.

Sexually transmitted diseases (STDs) may recognize multiple etiological agents. Among them, Chlamydia trachomatis (Ct) and herpes simplex virus type 2 (HSV-2) cause symptomatic, subclinical and asymptomatic infections of the urogenital tract which can lead to serious sequelae. In the present study the coinfection and superinfection by Ct and HSV-2 in epithelial cultured cells from human cervix (HeLa 229) are described. A double infection, followed by the intracellular synthesis of chlamydial and viral antigens, was established. Both synergistic and interfering phenomena were recorded: viral antigen synthesis resulted increased whereas Ct inclusion bodies were produced to a lower extent.

Antigens, Bacterial↗

PubMed1995

Enhancement of rotavirus infectivity by saturated fatty acids.

The effect of different saturated fatty acids from 10 to 16 carbon atom chains and some derivatives on the infectivity of SA-11 rotavirus was examined. Both fatty acids and derivatives induced an increase of rotavirus infected LLC-MK2 cells when present during viral absorption to host cells. Capric acid and palmitic acid were the most effective with a dose-dependent relationship. These last lipids, in the same experimental conditions, failed to restore the susceptibility to infection of LLC-MK2 cells made resistant by neuraminidase treatment or to allow cell infection by non-infectious single-shelled viral particles. Results obtained suggest that the enhancing effect on viral infectivity by saturated fatty acids requires previous binding of rotaviral outer capsid proteins to sialic acid containing cell receptors.

Animals↗

PubMed1995

Invasion of cultured human cells by Streptococcus pyogenes.

The invasive capacity of streptococcal strains belonging to groups A and B was evaluated by infecting human epithelial and endothelial cells and monitoring the number of viable intracellular bacteria at different times postinfection. All strains tested entered eukaryotic cells (HeLa, HEp2 and HUVE), with Streptococcus pyogenes exhibiting a higher invasion efficiency than group B streptococci (GBS). No intracellular multiplication was observed, and GBS remained viable 24 h postinfection, whereas S. pyogenes were gradually killed. We found that cytochalasin D almost completely inhibited internalization of all bacterial strains, whereas colchicine had no effect, indicating that host microfilaments play a major role in bacterial internalization. Moreover, the use of the lysosomotropic agent ammonium chloride enabled us to demonstrate that a pH increase in the intracellular vesicles did not affect streptococcal entry. These results were documented by electron microscopic observations which revealed the different steps in the invasion pathway, including a fusion event between phagosomes containing S. pyogenes and lysosomes.

Ammonium Chloride↗

PubMed1995

Inhibition of herpes simplex virus infection by negatively charged and neutral carbohydrate polymers.

Different natural and semisynthetic polysaccharides were evaluated for their inhibitory effect on in vitro replication of herpes simplex virus (HSV) types 1 and 2. Some neutral and negatively charged carbohydrates were able to inhibit viral infection by interfering mainly with the adsorption process showing a dose-dependent relationship. Their effect was shown within the concentration range of 200-0.8 micrograms/ml, and the inhibiting compounds were in order of action: dextran sulfate = scleroglucan = lambda carrageenan > glyloid sulfate 4324 > locust beam gum towards HSV-1 and dextran sulfate = glyloid sulfate 4324 = lambda carrageenan > scleroglucan > glycogen sulfate 4435 towards HSV-2. The data obtained indicate that the antiviral activity of polysaccharides was not only related to their electric charge. Other characteristics of the molecules such as the polymeric backbone, the carbohydrate moieties and the degree of polymerization could play a role in influencing their antiviral properties.

Animals↗

PubMed1994

Effect of lactoferricin B, a pepsin-generated peptide of bovine lactoferrin, on Escherichia coli HB101 (pRI203) entry into HeLa cells.

Bovine lactoferrin and a pepsin-generated peptide of bovine lactoferrin, known as lactoferricin B, were tested for an ability to influence the cell-invasive properties of an Escherichia coli HB101 strain carrying the plasmid pRI203, which encodes the Yersinia pseudotuberculosis inv gene. At non-cytotoxic and non-bactericidal concentration (0.5 mg/ml) lactoferricin B lowered by about tenfold the cell invasion capability of E. coli HB101 (pRI203), whereas no effect was observed when bovine lactoferrin was added during the infection of HeLa cell monolayers. The step of the invasion process affected by lactoferrin B was the internalization since the adhesion of bacteria to HeLa cells was unaltered in the presence of the peptide. Latex beads coated with lactoferrin B bound to HeLa cell monolayers and induced the agglutination of bacterial cells, indicating that this highly cationic peptide interacts directly with both eukaryotic and bacterial surfaces. Moreover, we demonstrated that the anti-invasive effect induced by lactoferrin B was reversed when the medium was supplemented with Ca2+, Mg2+ and Fe2+ ions which diminished its affinity binding. Our findings suggest that lactoferrin B effectiveness towards E. coli HB101 (pRI203) invasion is correlated to its binding capability on the eukaryotic and bacterial cell surfaces.

Animals↗

PubMed1994

The effect of iron on the invasiveness of Escherichia coli carrying the inv gene of Yersinia pseudotuberculosis.

The effect of growth in iron-excess or iron-limitation conditions on the invasiveness for HeLa cells of Escherichia coli HB101 carrying plasmid pRI203 which bears the invasion gene of Yersinia pseudotuberculosis was examined. Iron-limitation reduced adhesion and the number of organisms internalised by HeLa cells by about 100-fold. The reduced adhesion of iron-starved bacteria correlated with reduced hydrophobicity and the reduced invasiveness appeared to depend on the plasmid copy number, which was 3.5-fold less than in bacteria grown in iron excess.

Bacterial Adhesion↗

PubMed1994

Rotavirus and poliovirus co-infection in HT-29 cells.

The effect of a mixed poliovirus-rotavirus infection in HT-29 cells, a gut tumour derived cell line highly susceptible to both viruses, has been analyzed. The obtained results showed an increase of poliovirus multiplication in cells super-infected or co-infected with rotavirus, whereas the pre-infection with poliovirus had an interfering effect on rotavirus replication.

Antigens, Viral↗

PubMed1994

Invasiveness of Shigella flexneri in poliovirus infected HT-29 cells.

In this paper we report the effect in HT-29 cells of mixed infections with poliovirus type 1 and Shigella flexneri serotype 5 strain M90T and derivative strains differing in adhesive as well as invasive properties. HT-29 epithelial intestinal cells derived from a human colon adenocarcinoma are a good model for coinfection studies because they are susceptible both to poliovirus replication and to S. flexneri invasion. The results show that 48 h after infection by poliovirus the invasiveness of wild-type S. flexneri M90T and of its adherent and invasive derivative M90T (pIL22) is increased. However, the alterations produced in HT-29 cells at the later stage of poliovirus infection are not sufficient to promote the internalization of simply non invasive, or non invasive but adherent, isogenic derivative bacterial strains.

Bacterial Adhesion↗

PubMed1993

Influence of lactoferrin on the entry process of Escherichia coli HB101 (pRI203) in HeLa cells.

Lactoferrin (Lf) is an iron-binding protein which plays an important role in the host defense systems of different mucosal surfaces including the intestinal mucosa. In the present research the role of apo-Lf and iron-saturated Lf in the invasion process of enteroinvasive bacteria, grown in iron stress or excess, was investigated. As enteroinvasive bacterium, Escherichia coli HB101 strain harboring a plasmid which contains the chromosomal inv gene from Yersinia pseudotuberculosis was utilized. The product of this gene (invasin) enables this microorganism to invade human epithelial cultured cells (HeLa). The results obtained showed that apo-Lf and iron-saturated Lf added at physiological concentration during the infection exerted a significant inhibition of adhesion (3.2 x 10(5) instead 3.4 x 10(6) adherent bacteria grown in iron excess; 1.6 x 10(3) instead of 2.3 x 10(4) adherent bacteria grown in iron-limited medium) and internalization (4.0 x 10(5) instead of 3.7 x 10(6) internalized bacteria grown in iron excess; 2.1 x 10(3) instead 2.8 x 10(4) internalized bacteria grown in iron-limited medium). It has also been demonstrated that in these experimental conditions Lf binds to HeLa cell membrane as well as to bacterial outer membrane. It is likely that this binding interfere with the early events of interaction between bacteria and eukaryotic cells. This inhibiting effect of Lf on the invasion efficiency of E. coli HB101 (pRI203) could be related to the cationic nature of the molecule, although other mechanisms cannot be ruled out.

Adhesins, Bacterial↗

PubMed1992

SA-11 rotavirus binding to human serum lipoproteins.

An investigation of SA-11 rotavirus binding to human serum lipoproteins was carried out. Various subclasses of lipoproteins, purified by ultracentrifugal flotation, and apoproteins were tested for their activity in inhibiting viral infectivity and hemagglutination. All tested lipoprotein subclasses (very low, low and high density, lipoproteins; VLDL, LDL, HDL, HDL1) were shown to interact with SA-11 rotavirus: VLDL and LDL were the most active in preventing rotavirus replication, whereas HDL and HDL1 inhibited viral hemagglutination to a greater extent. Moreover, A1 and A2 apoproteins were effective towards both viral infectivity and hemagglutination. Results obtained are in agreement with a preferential interaction of VP7 or VP4 proteolytic products with low density lipoproteins and of VP8* with high density lipoproteins. Binding of SA-11 to lipoproteins or apoproteins was also quantified by an enzyme-linked immunosorbent assay procedure and lipoproteins-virus interaction was visualized by electron microscopy.

Animals↗

PubMed1992

Effect of inhibitors of HeLa cell structures and functions on Escherichia coli HB101 (PRI203) entry process.

We investigated the effect of some eucaryotic cytoplasmic structure and function inhibitors on the entry into HeLa cells of the Escherichia coli HB101 K12 strain, harbouring the recombinant plasmid pRI203, in which is cloned a 3.2 Kb chromosomal fragment of Yersinia pseudotuberculosis. Substances impairing microfilament structures and functions (cytochalasin B and trifluoroperazine) significantly reduced invasion ability whereas microtubule organization inhibitors (colchicine and vinblastine) were ineffective. Data obtained with a lipophilic weak base (methylamine), which raises the pH of intracellular vesicles, demonstrated that, in entry pathway of E. coli HB101 (pRI203), endosome acidification is not required. Host cell energy has been shown to contribute to bacterial internalization since the presence of oxidative phosphorylation and glycolysis inhibitors (sodium azide, 2-dinitrophenol and 2-deoxy-D-glucose) during the invasion process, affected bacterial entry.

Colchicine↗

PubMed1992

Effect of enterovirus infection on susceptibility of HeLa cells to Shigella flexneri invasivity.

Invasiveness of Shigella flexneri M90T in HeLa cells was significantly increased when cells were preinfected with poliovirus 1, coxsackievirus B3 and echovirus 6. This effect was dependent on the dose of virus used, evident at early stages of viral infection and lasted hours before the appearance of a cytopathic effect. An increase of bacterial invasion ability was also noticed when HeLa cells were incubated with UV-inactivated enteroviruses. This enhancing effect obtained with both viable and UV-inactivated enteroviruses was not observed when in coinfection experiments HN555, a mutant of S. flexneri M90T which lacked invasive properties, was used. The data presented here suggest that the early steps of enterovirus infection induce some alterations of HeLa cells which are responsible for the enhancing of the invasiveness of S. flexneri M90T, but not sufficient to promote internalization of a non-invasive strain.

Animals↗

PubMed1992

Involvement of membrane carbohydrates of HeLa cells in the E. coli HB101 (pRI203) invasive pathway.

The recombinant plasmid pRI203 carries a Yersinia pseudotuberculosis chromosomal gene that makes E. coli K-12 HB101 strain able to synthetize an outer membrane protein, invasin, which interacts with integrin receptors of eukaryotic cells, enabling this microorganism to penetrate human cultured animal cells. In this study we evaluated the involvement of HeLa cell membrane structural components in the early phases of the invasive pathway of E. coli HB101 (pRI203). When HeLa cell monolayers were treated with several enzymes we showed that trypsin-, proteinase K- and neuraminidase-sensitive components are required for bacterial invasion. Comparison of the ability of simple and complex carbohydrates to inhibit bacterial invasion indicated that N-acetyl neuraminic acid, N-acetyl glucosamine and mucin were the most effective competitive inhibitors. Among glycolipids, gangliosides enhanced bacterial entry in HeLa cells. The results obtained suggest that N-acetyl neuraminic acid and N-acetyl glucosamine-containing glycoproteins and/or glycolipids participate as putative HeLa cell binding sites for the penetration process of E. coli HB101 (pRI203).

Acetylglucosamine↗

PubMed1991

Rabies virus infection in Aedes pseudoscutellaris cells: a study on receptorial structures.

Rabies virus is able to infect in vitro a wide range of homeothermic and poikilothermic cells but little is known about its multiplication in arthropod cells. In this research the infection of rabies virus in Aedes pseudoscutellaris cells, a mosquito cell line susceptible to mosquito-borne viruses, was studied. After 60 days of incubation at 26 degrees C up to 70% of infected cells showed the synthesis of both viral nucleocapsid and envelope antigens, although viral yield and cell damage could not be detected. Research performed in order to investigate the role of membrane carbohydrate moieties in rabies virus-mosquito cell interaction suggested the participation of galactose and N-acetylglucosamine whereas sialic acid, known to be a rabies binding site in many homeothermic cell lines, was not involved.

Aedes↗

PubMed1991

Influence of polyions on the early steps of enterovirus infection.

The influence of electric charged molecules on the early phases of enterovirus infection was studied in order to select antiviral compounds able to prevent viral attachment. The effect of different polyelectrolytes on the multiplication of coxsackie virus B3, echovirus 6 and hepatitis A virus was investigated in susceptible cells by adding the drug before, during or after the viral adsorption period. Among polyanions, the polysaccharides heparin and dextran sulfate inhibited viral infectivity, dextran sulfate being the most effective mainly towards hepatitis A virus infection. DEAE-dextran and protamine sulfate, generally recognized as enhancers of infectivity of naked and enveloped viruses, exhibited an inhibitory effect towards the three picornaviruses tested. Only in the case of hepatitis A did DEAE-dextran slightly improve viral antigen synthesis. The inhibitory effect shown by compounds belonging to positive and negative polyions suggests that the electric charge is not sufficient by itself to explain the antiviral activity of these drugs.

Animals↗