Evaluation of chitosan salt properties in the production of AgNPs materials with antibacterial activity

In this study, water-soluble chitosan salts (chitosan amine sulfopropyl salts) were prepared from chitosan samples with different molecular weights and deacetylation degrees. These soluble-in-water polymer salts allowed us to produce, in an eco-friendly and facile method, silver nanoparticles (AgNPs) with better control on size and polydispersity, even at large silver concentrations than their corresponding chitosan sample. Chitosan salt-based materials (films and scaffolds) were analyzed in terms of antibacterial properties against Staphylococcus aureus ATCC23915 or Pseudomonas aeruginosa ATCC 27853. 3D scaffolds enhanced the effect of the chitosan-AgNPs combination compared to the equivalent films.

Strategies for the identification of virulence determinants in human pathogenic fungi

The incidence of fungal infections is increasing in different countries. The current available therapy of these infections does not satisfy all requirements in terms of specificity and therapeutic index, a fact that has stimulated the scientific community to identify fungal virulence determinants. Several pathogenic fungi are opportunistic and, therefore, identification of virulence genes is difficult, given their close relationship with host cells. In recent years, the development of genetic tools in several pathogenic fungi has enabled the development of genetic strategies for their identification. These include several strategies based on the phenotypic analysis of strains or environmental conditions in which the expression of the putative gene(s) is either altered or deleted; and this is accomplished through the development of in vitro or in vivo systems. In the near future, this research will produce a better picture of fungal pathogenesis and therefore define novel promising targets in antifungal therapy.

Signal transduction pathways and cell-wall construction in Candida albicans

Signal transduction pathways are the molecular mechanisms responsible for detecting and transmitting changes in the surrounding environment to the nucleus where appropriate responses are generated. The cell wall is the most external structure of the fungal cell and, in pathogenic fungi, is responsible for specifically interacting with the mammalian host cell in a highly dynamic interplay. Recent work has shown the role that some signal transduction pathways, involving members of the MAP kinase family, have in this process in the nonpathogenic model organism Saccharomyces cerevisiae. However, as yet little is known about these phenomena in pathogenic fungi. The aim of this review is to characterize the existing signal transduction pathways in Candida albicans and their relationship with the cell-wall construction.

Virulence genes in the pathogenic yeast Candida albicans

In recent years, the incidence of fungal infections has been rising all over the world. Although the amount of research in the field of pathogenic fungi has also increased, there is still a need for the identification of reliable determinants of virulence. In this review, we focus on identified Candida albicans genes whose deletant strains have been tested in experimental virulence assays. We discuss the putative relationship of these genes to virulence and also outline the use of new different systems to examine the precise effect in virulence of different genes.

Plasmid-encoded toxin of enteroaggregative Escherichia coli is internalized by epithelial cells

We have previously described a 104-kDa protein termed Pet (for plasmid-encoded toxin) secreted by some strains of enteroaggregative Escherichia coli (EAEC). Through an unknown mechanism, this toxin (i) raises transepithelial short-circuit current (Isc) and decreases the electrical resistance of rat jejunum mounted in the Ussing chamber, (ii) causes cytoskeletal alterations in HEp-2 cells and HT29/C1 cells, and (iii) is required for histopathologic effects of EAEC on human intestinal mucosa. Pet is a member of the autotransporter class of secreted proteins and together with Tsh, EspP, EspC, ShMu, and SepA proteins comprises the SPATE subfamily. Here, we show that Pet is internalized by HEp-2 cells and that internalization appears to be required for the induction of cytopathic effects. Evidence supporting Pet internalization includes the facts that (i) the effects of Pet on epithelial cells were inhibited by brefeldin A, which interferes with various steps of intracellular vesicular transport; (ii) immunoblots using anti-Pet antibodies detected Pet in the cytoplasmic fraction of intoxicated HEp-2 cells; (iii) Pet was detected inside HEp-2 cells by confocal microscopy; and (iv) a mutant in the passenger domain cleavage site, which prevents Pet release from the bacterial outer membrane, did not produce cytopathic effects on epithelial cells, whereas the release of mutant Pet from the outer membrane with trypsin yielded active toxin. We have also shown that the Pet serine protease motif is required to produce cytopathic effects but not for Pet secretion. Our results suggest an intracellular mode of action for the Pet protease and are consistent with we our recent report suggesting an intracellular mode of action for Pet.

Immunodulation of rat serum and mucosal antibody responses to Entamoeba histolytica trophozoites by beta-1,3-glucan and cholera toxin

Systemic and mucosal and immune responses can be manipulated with immunomodulators. Here we show the modulatory effects of cholera toxin (CT) and beta-1,3-glucan (GLU) on the rat antiamebic serum and fecal antibody responses to one or four intraperitoneal (IP) or intragastric (IG) doses of glutaraldehyde-fixed Entamoeba histolytica trophozoites (GFT). One IP dose of GFT maximized serum IgM and IgG antiamebic antibodies on days 4 and 9, respectively; CT coadministration increased IgM antibodies, whereas IgG titers increased with CT or GLU; coproantibodies were undetectable after GFT alone or coadministered with GLU, whereas CT coadministration maximized fecal IgA antibodies on day 6. One IG dose of GFT alone increased serum IgM and IgG antibodies 2.5 times and no further increases were detected using GLU, whereas CT doubled serum IgG antibodies; GFT did not affect the coproantibody responses, whereas GLU coadministration maximized IgG coproantibody levels on day 6 and CT increased IgG and IgA coproantibody levels on the same day. On the other hand, four IG doses of GFT alone or with GLU induced tolerance, whereas GFT alone via the IP route increased serum antibodies slightly and GLU coadministration increased serum IgG antibody titers 300-fold. CT coadministration by both routes increased IgA coproantibodies, and simultaneous CT+GLU coadministration induced lower responses than either CT or GLU. Different antiamebic immune responses might therefore be attained through the use of different immunization routes and immunomodulators to induce protective immunity against intestinal or extraintestinal amebiasis.

Pet toxin from enteroaggregative Escherichia coli produces cellular damage associated with fodrin disruption

Pet toxin is a serine protease from enteroaggregative Escherichia coli which has been described as causing enterotoxic and cytotoxic effects. In this paper we show that Pet produces spectrin and fodrin (nonerythroid spectrin) disruption. Using purified erythrocyte membranes treated with Pet toxin, we observed degradation of alpha- and beta-spectrin chains; this effect was dose and time dependent, and a 120-kDa protein fraction was observed as a breakdown product. Spectrin degradation and production of the 120-kDa subproduct were confirmed using specific antibodies against the alpha- and beta-spectrin chains. The same degradation effect was observed in alpha-fodrin from epithelial HEp-2 cells, both in purified cell membranes and in cultured cells which had been held in suspension for 36 h; these effects were confirmed using antifodrin rabbit antibodies. The spectrin and fodrin degradation caused by Pet is related to the Pet serine protease motif. Fluorescence and light microscopy of HEp-2 Pet-treated cells showed morphological alterations, which were associated with irregular distribution of fodrin in situ. Spectrin and fodrin degradation by Pet toxin were inhibited by anti-Pet antibodies and by phenylmethylsulfonyl fluoride. A site-directed Pet mutant, which had been shown to abolish the enterotoxic and cytotoxic effects of Pet, was unable to degrade spectrin in erythrocyte membranes or purified spectrin or fodrin in epithelial cell assays. This is a new system of cellular damage identified in bacterial toxins which includes the internalization of the protease, induction of some unknown intermediate signaling steps, and finally the fodrin degradation to destroy the cell.

Cytoskeletal effects induced by pet, the serine protease enterotoxin of enteroaggregative Escherichia coli

We have previously described enteroaggregative Escherichia coli (EAEC) strains that induce cytotoxic effects on T84 cells, ligated rat ileal loops, and human intestine in culture. Such strains secrete a 104-kDa protein termed Pet (for plasmid-encoded toxin). We have also shown previously that the Pet toxin induces rises in short-circuit current and decreases the electrical resistance in rat jejunum mounted in an Ussing chamber. The nucleotide sequence of the pet gene revealed that Pet is a member of the autotransporter class of secreted proteins. Here we show that a concentrated supernatant of E. coli HB101 harboring the minimal pet clone pCEFN1 induces temperature-, time- and dose-dependent cytopathic effects on HEp-2 cells and HT29 C1 cells in culture. The effects were characterized by release of the cellular focal contacts from the glass substratum, followed by complete rounding of the cells and detachment from the glass. Staining of the Pet-treated cells with Live/Dead viability stain revealed that >90% of rounded cells were viable. Pet-intoxicated HEp-2 and HT29 cells stained with fluorescein-labeled phalloidin revealed contraction of the cytoskeleton and loss of actin stress fibers. However, the effects of Pet were not inhibited by cytoskeleton-altering drugs, including colchicine, taxol, cytochalasin D, and phallicidin. The Pet protein induced proteolysis in zymogram gels, and preincubation with the serine protease inhibitor phenylmethylsulfonyl fluoride resulted in complete abrogation of Pet cytopathic effects. We introduced a mutation in a predicted catalytic serine residue and found that the mutant (Pet S260I) was deficient in protease activity and did not produce cytopathic effects, cytoskeletal damage, or enterotoxic effects in Ussing chambers. These data suggest that Pet is a cytoskeleton-altering toxin and that its protease activity is involved in each of the observed phenotypes.

Role of the mitogen-activated protein kinase Hog1p in morphogenesis and virulence of Candida albicans

The relevance of the mitogen-activated protein (MAP) kinase Hog1p in Candida albicans was addressed through the characterization of C. albicans strains without a functional HOG1 gene. Analysis of the phenotype of hog1 mutants under osmostressing conditions revealed that this mutant displays a set of morphological alterations as the result of a failure to complete the final stages of cytokinesis, with parallel defects in the budding pattern. Even under permissive conditions, hog1 mutants displayed a different susceptibility to some compounds such as nikkomycin Z or Congo red, which interfere with cell wall functionality. In addition, the hog1 mutant displayed a colony morphology different from that of the wild-type strain on some media which promote morphological transitions in C. albicans. We show that C. albicans hog1 mutants are derepressed in the serum-induced hyphal formation and, consistently with this behavior, that HOG1 overexpression in Saccharomyces cerevisiae represses the pseudodimorphic transition. Most interestingly, deletion of HOG1 resulted in a drastic increase in the mean survival time of systemically infected mice, supporting a role for this MAP kinase pathway in virulence of pathogenic fungi. This finding has potential implications in antifungal therapy.

Cloning and sequence of a 3.835 kbp DNA fragment containing the HIS4 gene and a fragment of a PEX5-like gene from Candida albicans

We have isolated the Candida albicans HIS4 (CaHIS4) gene by complementation of a his4-34 Saccharomyces cerevisiae mutant. The sequenced DNA fragment contains a putative ORF of 2514 bp, whose translation product shares a global identity of 44% and 55% to the His4 protein homologs of S. cerevisiae and Kluyveromyces lactis, respectively. Analysis of CaHIS4 sequence suggests that, similarly to S. cerevisiae HIS4, it codes for a polypeptide having three separate enzymatic activities (phosphoribosyl-AMP cyclohydrolase, phosphoribosyl-ATP pyrophosphohydrolase and histidinol dehydrogenase) which reside in different domains of the protein. A C. albicans his4 strain is complemented with this gene when using a C. albicans-S. cerevisiae-Escherichia coli shuttle vector, thus enabling the construction of a host system for C. albicans genetic manipulation. In addition, upstream of the sequenced CaHIS4 sequence, we have found the 3'-terminal half of a gene encoding a PEX5-like protein.

Pet, an autotransporter enterotoxin from enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) is an emerging cause of diarrheal illness. Clinical data suggest that diarrhea caused by EAEC is predominantly secretory in nature, but the responsible enterotoxin has not been described. Work from our laboratories has implicated a ca. 108-kDa protein as a heat-labile enterotoxin and cytotoxin, as evidenced by rises in short-circuit current and falls in tissue resistance in rat jejunal tissue mounted in an Ussing chamber. Here we report the genetic cloning, sequencing, and characterization of this high-molecular-weight heat-labile toxin. The toxin (designated the plasmid-encoded toxin [Pet]) is encoded on the 65-MDa adherence-related plasmid of EAEC strain 042. Nucleotide sequence analysis suggests that the toxin is a member of the autotransporter class of proteins, characterized by the presence of a conserved C-terminal domain which forms a beta-barrel pore in the bacterial outer membrane and through which the mature protein is transported. The Pet toxin is highly homologous to the EspP protease of enterohemorrhagic E. coli and to EspC of enteropathogenic E. coli, an as yet cryptic protein. In addition to its potential role in EAEC infection, Pet represents the first enterotoxin within the autotransporter class of secreted proteins. We hypothesize that other closely related members of this class may also produce enterotoxic effects.

In vitro effects of a high-molecular-weight heat-labile enterotoxin from enteroaggregative Escherichia coli

The pathogenic mechanisms of enteroaggregative Escherichia coli (EAggEC) infection are not fully elucidated. In this work we show that an ammonium sulfate precipitate of culture supernatant of EAggEC strain 049766 increased the potential difference (PD) and the short-circuit current (Isc) in rat jejunal preparations mounted in Ussing chambers. The precipitate contained two major proteins of 108 and 116 kDa, which were partially copurified by chromatography in DEAE-cellulose. This chromatographic fraction (peak I) increased jejunal PD and Isc in a dose-dependent manner, accompanied by a decrease in tissue electrical resistance. These effects were inhibited by incubation of peak I at 75 degreesC for 15 min or for 1 h with proteinase K at 37 degreesC. Rabbit polyclonal antibodies against peak I containing both the 108- and 116-kDa proteins inhibited the enterotoxic effect. Specific polyclonal antibodies raised against the 108-kDa but not against the 116-kDa protein inhibited the enterotoxic effect, suggesting that the 108-kDa protein is the active toxic species. Moreover, another EAggEC strain (065126) producing the 116-kDa protein but not the 108-kDa protein had no effect on rat jejunal mucosa in the Ussing chamber. The >100-kDa fraction derived from prototype EAggEC strain 042, which also expressed both 108- and 116-kDa proteins, also produced an enterotoxic effect on rat jejunal preparations in Ussing chambers; however, the same strain cured of its 65-MDa adherence plasmid did not. A subclone derived from the 65-MDa plasmid expressing the 108-kDa toxin (and not the 116-kDa protein) elicited rises in Isc. Tissue exposed to any preparation containing the 108-kDa toxin exhibited similar histopathologic changes, characterized by increased mucus release, exfoliation of cells, and development of crypt abscesses. Our data suggest that some EAggEC strains produce a ca. 108-kDa enterotoxin/cytotoxin which is encoded on the large virulence plasmid.

Candida albicans: genetics, dimorphism and pathogenicity

Candida albicans is a dimorphic fungus that causes severe opportunistic infections in humans. Recent advances in molecular biology techniques applied to this organism (transformation systems, gene disruption strategies, new reporter systems, regulatable promoters) allow a better knowledge of both the molecular basis of dimorphism and the role of specific genes in Candida morphogenesis. These same molecular approaches together with the development of appropriate experimental animal models to analyze the virulence of particular mutants, may help to understand the molecular basis of Candida virulence.

Intragastric immunization of rats with Entamoeba histolytica trophozoites induces cecal mucosal IgE, eosinophilic infiltration, and type I hypersensitivity

We have investigated the role of IgE in the local immunity of intestinal amebiasis, a parasitic infection known to induce specific antibody-forming cells (AFC) and IgA antibodies in rodents and humans. We found that intragastric immunization of rats with glutaraldehyde-fixed Entamoeba histolytica trophozoites significantly increased antiameba AFC in the Peyer's patches and spleen and that the lamina propria of the cecum from immunized animals was infiltrated by eosinophils armed with IgE antibodies. Morphometric analysis showed that IgE-containing cells and eosinophils were nearly three times more abundant in the cecum of immunized rats. Antigenic challenge with amebal lysates provoked an increase in the short-circuit current and in the transepithelial potential difference in Ussing-chambered cecum preparations from immunized rats. Although eosinophilia and the increase of IgE are common consequences of infection by parasitic worms, our results indicate that local immunity in intestinal amebiasis also involves IgE deposition, eosinophil infiltration, and type I hypersensitivity, which may explain some symptoms of amebic dysentery such as colic, abdominal tension, tenesmus, and bloody stools.

Reduced virulence of Candida albicans MKC1 mutants: a role for mitogen-activated protein kinase in pathogenesis

Deletion of the Candida albicans mitogen-activated protein kinase MKC1 gene gave rise to viable cells whose cell integrity was affected (F. Navarro-García, M. Sánchez, J. Pla, and C. Nombela, Mol. Cell. Biol. 15:2197-2206, 1995). In an experimental infection system using a murine model, the C. albicans mkc1 delta/mkc1 delta strain was found to be less pathogenic than the parental strain, as show the different time of survival, percentage of mortality, fungal load in the most representative organs, and histological analysis. This is the first study that shows the involvement of the cell integrity pathway in the pathogenicity of a dimorphic fungus.

In vivo and in vitro experimental intestinal amebiasis in Mongolian gerbils (Meriones unguiculatus)

One of the main drawbacks of experimental amebiasis is the lack of an adequate animal model for invasive intestinal lesions. Mongolian gerbils are useful because both intestinal and hepatic amebiasis can be produced experimentally with Entamoeba histolytica trophozoites. In this paper we show results obtained with in vivo and in vitro models of intestinal amebiasis in gerbils. We inoculated gerbils intracecally with monoxenic cultures of a highly virulent E. histolytica HM1:IMSS substrain. In the in vivo model an increase in mucus production was observed during the first 6 h of interaction. Microulcerative mucosal lesions appeared at 24-72 h postinoculation. Inflammatory infiltrate and edema of the lamina propria were associated with superficial foci of necrosis. At 96 h the cecal mucosa had an almost normal appearance and live amebas were no longer detected. In the in vitro model, early damage was detected in cecal strips mounted in Ussing chambers as a rapid fall in potential difference, short-circuit current, and transepithelial resistance that correlated with the extent of the microscopic lesions produced. The latter consisted of cellular edema and the appearance of small, translucent vacuoles at the base of epithelial cells. Further damage led to loss of intercellular junctions, destruction of interglandular epithelial cells, and edema of the lamina propria. The present results demonstrate that the gerbil is useful as an experimental model for the analysis of early stages of invasive intestinal amebiasis both in vivo and in vitro.

Cloning of the Candida albicans HIS1 gene by direct complementation of a C. albicans histidine auxotroph using an improved double-ARS shuttle vector

ARS2 and ARS3 are two Candida albicans (Ca) DNA fragments with autonomous replicating activity that have been shown to promote non-integrative genetic transformation of both Ca and Saccharomyces cerevisiae (Sc). We have developed several shuttle vectors based on either ARS fragment, or the combination of both, and using the CaURA3 gene as a selection marker. The combination of ARS2 and ARS3 fragments in a single vector did not increase transformation frequencies but improved the stability of transformant plasmids in Ca cells, so that the degree of intracellular recombination was reduced. A Ca genomic DNA library was constructed on the double-ARS vector, pRM1, to be used for direct cloning in Ca by complementation of the histidine auxotrophy of strain CA9. By screening this library, we cloned CaHIS1, the Ca gene that encodes ATP phosphoribosyl transferase, one of the enzymes that participates in histidine biosynthesis. The deduced protein, CaHis1p, is 60.6% identical (73% similar) to ScHis1p (EC 2.4.2.17). The cloned gene is the first auxotrophic gene marker mapped to fragment I of chromosome 5 in the standard Ca genetic map. Our results represent the first demonstration of a direct cloning system in the opportunistic fungus Ca that does not require the use of an intermediate host such as Sc for plasmid rescue. This system could be used for the isolation of any gene affected in Ca mutants displaying a selectable or identifiable phenotype.

Chromosome reorganization in Candida albicans 1001 strain

The karotype of Candida albicans 1001, a pathogenic isolate, presents two additional chromosome bands when compared with C. albicans 1006 strain. These two bands were a 2600 kb chromosome located between chromosome group 1-R and chromosome 2 (named chromosome 2*) and a 710 kb small chromosome, called snc due to its similarity in size to the supernumerary chromosome in strain WO-1. A comparison of karyotypes of strains 1001, 1006 and WO-1 has enabled us to conclude that chromosomes 2 and 7 are involved in such a reorganization giving rise to the new chromosome bands of strain 1001. We describe a tentative physical map of C. albicans 1001 based on the previously outlined map of C. albicans strain 1006.

Entamoeba histolytica: increase of enterotoxicity and of 53- and 75-kDa cysteine proteinases in a clone of higher virulence

We compared the enterotoxicity and cysteine proteinases (CP) of the low-virulence Entamoeba histolytica HM1 strain with the highly virulent 1659 clone, derived from HM1 by hamster liver passages. Enterotoxicity of 50,000 freeze-thawed trophozoites was determined on 0.28-cm2 intestinal segments mounted in Ussing chambers; CP activity of Nonidet-P40 amebal lysates was assayed by gelatin-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and carbobenzoxy-L-arginine-L-arginyl-p-nitroaniline, a CP-specific substrate. Treatment of gerbil cecum segments with amebal lysates caused an immediate fall of their electrophysiologic properties (potential difference, short-circuit current, and transmural resistance) whose decay rates were clearly faster with 1659 than with HM1 lysates. Nonimmune and immune antiamebic human sera and the CP-specific inhibitor E-64 (trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane) prevented the fall of the electrophysiologic properties. Gelatinases, less active in HM1 than in 1659 trophozoites, were better preserved in lysates containing 10 mM p-hydroxymercuribenzoate (pHMB) to prevent autoproteolysis: in lysates without pHMB nearly no gelatinase bands were observed in HM1 samples, whereas intense 30K, 35K, 44K, and 75K bands were seen in 1659 samples; in lysates with pHMB only 53K and 75K bands were found that were much more intense in 1659 samples, 75K being barely visible in HM1 samples. The overall CP activity was 17 times higher in 1659 than in HM1 lysates, was inhibited by E-64 (mean inhibitory dose, 20 microM), was stimulated by 2-mercaptoethanol (ME) 3.7 times in HM1 and 2.4 times in 1659 lysates, and was reactivated by ME in lysates containing pHMB. Most of the CP activity in HM1 lysates sedimented at 15,600g but predominated in 1659 supernatants. The increase of E. histolytica virulence thus correlates with a remarkable increase both of in vitro enterotoxicity and of two CPs (53K and 75K), suggesting that these proteinases are significant pathogenicity factors.

Functional characterization of the MKC1 gene of Candida albicans, which encodes a mitogen-activated protein kinase homolog related to cell integrity

Mitogen-activated protein (MAP) kinases represent a group of serine/threonine protein kinases playing a central role in signal transduction processes in eukaryotic cells. Using a strategy based on the complementation of the thermosensitive autolytic phenotype of slt2 null mutants, we have isolated a Candida albicans homolog of Saccharomyces cerevisiae MAP kinase gene SLT2 (MPK1), which is involved in the recently outlined PKC1-controlled signalling pathway. The isolated gene, named MKC1 (MAP kinase from C. albicans), coded for a putative protein, Mkc1p, of 58,320 Da that displayed all the characteristic domains of MAP kinases and was 55% identical to S. cerevisiae Slt2p (Mpk1p). The MKC1 gene was deleted in a diploid Candida strain, and heterozygous and homozygous strains, in both Ura+ and Ura- backgrounds, were obtained to facilitate the analysis of the function of the gene. Deletion of the two alleles of the MKC1 gene gave rise to viable cells that grew at 28 and 37 degrees C but, nevertheless, displayed a variety of phenotypic traits under more stringent conditions. These included a low growth yield and a loss of viability in cultures grown at 42 degrees C, a high sensitivity to thermal shocks at 55 degrees C, an enhanced susceptibility to caffeine that was osmotically remediable, and the formation of a weak cell wall with a very low resistance to complex lytic enzyme preparations. The analysis of the functions downstream of the MKC1 gene should contribute to understanding of the connection of growth and morphogenesis in pathogenic fungi.

Expression and in vivo determination of firefly luciferase as gene reporter in Saccharomyces cerevisiae

The LUC gene coding for Photinus pyralis firefly luciferase was cloned in different yeast episomal plasmids in order to assess its possibilities as an in vivo reporter gene. Activity of the enzyme in transformed cells in vivo was measured by following light emission and assay conditions optimized in intact cells, with regard to oxygen concentration, temperature, cell concentration in assay mixtures and external ATP concentration. Among the factors tested, light emission was drastically influenced by the external pH in the assay (which resulted in a ten-fold amplification signal) and by substrate permeability. The growth phase of the cells was also important for the level of activity detected. Cloning of firefly luciferase gene under the control of different yeast-regulated promoters (ADH1, GAL1-10) enabled us to measure their strength which correlated well with previously described data. We conclude that firefly luciferase is an adequate gene reporter for the in vivo sensitive determination of gene expression and promoter strength in yeast.

Entamoeba histolytica: electrophysiologic and morphologic effects of trophozoite lysates on rabbit colon

Although in acute intestinal amoebiasis the events occurring during the initial interaction of Entamoeba histolytica trophozoites with the mucosa of the large intestine probably determine the invasion by the parasites, an appropriate experimental model to study them does not exist. To develop such a model we used rabbit colonic segments (0.28 cm2) mounted in Ussing-type chambers. These preparations had electrophysiological properties (potential difference, short-circuit current, and electrical resistance) similar in magnitude and duration to those reported for stripped colonic mucosa. Lysates from 50,000 Entamoeba invadens PZ strain trophozoites (virulent to reptiles) added to the mucosal side of preparations had no effect, whereas lysates from the same number of E. histolytica HM1 strain trophozoites (virulent to humans) caused an immediate decay of electrophysiological properties. E. histolytica lysates induced the formation of translucent vacuoles at the bases of epithelial cells and separation between the epithelium and the lamina propria. The specificity and speed of the electrophysiologic effects of E. histolytica lysates and their correlation with the microscopic lesions suggest that this model may be useful to analyze the initial pathogenic events of intestinal amoebiasis.

Dose- and time-dependent functional and structural damage to the colon mucosa by Entamoeba histolytica trophozoite lysates

Analysis of the initial interaction between Entamoeba histolytica trophozoites and the large intestine is impossible in humans and very difficult in experimental animals. To circumvent this obstacle we treated the luminal side of full-thickness rabbit colon segments mounted in Ussing-type chambers with trophozoite lysates of the E. histolytica HM1 virulent strain. Exposure to lysates for up to 90 min produced dose- and time-dependent effects on the colon, consisting of (a) increased decay rates for potential difference, short-circuit current, and transmural resistance and (b) mucosal damage ranging from vacuolation at the bases and shortening of epithelial cells to the loss of intercellular junctions, destruction of microvilli, and necrosis of interglandular epithelial zones. This acute model of intestinal amebiasis is sensitive, fast, and reliable.

Dot-enzyme-linked immunosorbent assay (Dot-ELISA) of anti-Entamoeba histolytica antibodies in human serum and colostrum

Seroepidemiologic and clinical studies of amoebiasis require improved methods for the detection and titration of anti-Entamoeba histolytica (Eh) trophozoite antibodies. We have developed a Dot-enzyme-linked immunosorbent assay (Dot-ELISA) to titrate anti-Eh antibodies in human serum and colostrum. The anti-Eh serum IgG antibody titers from healthy individuals and from patients with amoebic liver abscess obtained, with our Dot-ELISA were similar to those obtained with a standard ELISA, but the background values were lower. Significant anti-Eh sIgA antibody titers were found in seven out of 42 colostrum samples of mothers of newborn children with diarrhea. Our Dot-ELISA is rapid, inexpensive, and might be used for the diagnosis of individuals and in seroepidemiologic studies of amoebiasis.