Microbiologica最新文献

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).

This study provides evidence that pyelonephritogenic strains of Escherichia coli, which do not produce soluble hemolysin and possess mannose-resistant hemagglutinating activity, are able to adhere and penetrate to HEp-2 cells. Invasion and intracellular survival were analyzed by transmission electron microscopy and by viable counts after killing of extracellular bacteria by gentamicin. Cytochalasin D, which blocks polymerization of G-actin, markedly reduced the entry of E. coli into the cells and inhibited intracellular mobility of the bacteria. By using indirect fluorescent staining with anti-actin rabbit serum, direct evidence was obtained that interaction with the cytoskeleton of HEp-2 cells is necessary for invasion.

A total of 376 serum samples from dogs, humans and livestock were examined for complement-fixing (CF) antibodies against rabies virus. High CF antibody titres (up to 1:1024) were detected among unvaccinated dogs aged 3 months and above as in vaccinated ones, thus establishing endemicity of the virus in the area. An antibody titre of 1:128 was detected in the serum of a puppy aged below 3 months and is unlikely to be due to residual maternal antibodies. It rather provides evidence for seroconversion at that age and further establishes endemicity of the virus. Moderate to high CF antibody titres (greater than or equal to 1:64) were detected in 44.9% of the unvaccinated dogs, 6.3% of the cattle and 2.8% of the humans. These antibody titres indicate either exposure to rabies virus or inapparent infection by rabies-related viruses.

This paper describes the antigenic characteristics of a strain of Borrelia burgdorferi isolated from a patient seronegative for Lyme borreliosis, in the early stage of the illness. The strain was not recognized by a late serum sample from the patient; the isolate reacted in immunoblotting with some of the monoclonal antibodies directed against the immunodominant antigens of Borrelia burgdorferi. In addition to the OspA antigen this strain carries also the epitopes of OspB proteins, unlike the majority of European Borrelia burgdorferi strains.

In view of developing an enzyme-linked immunosorbent assay (ELISA) for the determination of IgG antibody to human cytomegalovirus, a rapid microneutralization (Nt) assay was used to test five positive standard sera containing increasing amounts of specific antibody and a negative standard serum. The standard serum containing the minimal amount of detectable Nt antibody was selected as a cut-off standard for the ELISA test. Following preliminary testing on previously characterized sera which gave expected results, the ELISA assay was tested in the field on 992 sera from blood donors. In parallel, sera were tested by Nt and complement fixation (CF). ELISA detected 82 negative and 910 positive sera. Nt gave concordant result except for two ELISA-negative sera, which showed Nt antibody titers of 1:10. The absorbance value of these two sera was just below that of the cut-off. Thus, for ELISA, the sensitivity was 99.8% (910/912) and specificity 100% (80/80). CF gave results concordant with ELISA and Nt, except for 23 sera (2 ELISA- and Nt-negative, and 21 ELISA- and Nt-positive) showing anticomplementary activity. Quantitation of specific ELISA antibody was achieved by interpolation from a calibation curve. Nt appears to be the reference test to establish the ELISA cut-off.

In previous works, we noted that porins, surface components of Gram negative bacteria, are toxic for human spermatozoa. In this work we see that porins of E. coli labeled with I125 (0.1-1.0 microgram/ml) bind to spermatozoa, showing the presence of saturable molecular configurations of 0.5-0.6 micrograms/ml. In the presence of non labeled porins, the binding of labeled porins to the spermatozoa is greatly reduced. At saturating concentrations of 0.6 micrograms/ml labeled porins, the binding reaches a saturation plateau at about 15 min.

Sera from a sample of healthy Italian people were tested in an indirect immunofluorescence assay (IFA) for reactivity to a Human Herpesvirus-6 (HHV-6) strain called CV, isolated from a baby with exanthem subitum (Portolani et al., 1990). Seropositivity values of 83.78%, 92.68% and 63.64% were found in subjects aged 3 months-6 years, 6-18 years and over 18 years respectively. Sera from cordal blood, sera from subjects with evidence of active infection by Cytomegalovirus (CMV) or by Epstein-Barr virus (EBV), sera from seropositive adults to Human Immunodeficiency Virus type 1 (HIV) were also investigated for antibodies to the same HHV-6 strain. Values of antibody incidence and antibody content to HHV-6 in these groups of sera were generally higher than in the other groups. HHV-6 reinfections of both endogenous and exogenous origin and antibody cross-reactivity were considered among the reasons of this increase. HHV-6 seropositivity values in healthy Italian people and in people from different countries were also discussed in the light of the antigenic characteristics of the HHV-6 strains used and of the different test conditions.

Six samples of fermented milk preparations were examined for the presence of bifidobacteria. Identification was based on fermentation tests, genetic relatedness studies and electrophoretic analysis. Contrary to label information, Bifidobacterium animalis was the only species present.

Uptake of Leishmania major and Leishmania infantum promastigotes by U937 cells was determined by microscopic observation and by using radiolabelled parasites. With both species we observed an increase in uptake after parasite pretreatments with fibronectin, and a decrease in uptake after cell pretreatment with interferon-gamma (IFN gamma). When both pretreatments were performed, the uptake was significantly decreased only in L. infantum experiments. These findings may be of some importance in the evaluation of IFN gamma as a leishmanicidal agent.

The effect of pigmentation and coagulase on the virulence of a capsule-lacking Staphylococcus aureus were studied using iron-compromised mice. The presence of either coagulase or pigmentation maintained the viability of this bacterium in the peritoneal cavity. Both coagulase and pigmentation, however, lead not only to maintained viability, but also to its proliferation in the peritoneal macrophages. The iron was found to enhance the virulence of this bacterium, but iron enhancement was contingent on the presence of either pigmentation or coagulase or preferably both.