Amebas de vida livre no intestino humano: evidências de parasitismo

Moura, Hércules; Salazar, Homero Coutinho; Fernandes, Octávio; Lisboa, Denise Costa; Carvalho, Francisca Gonçalves de

doi:10.1590/s0036-46651985000300007

Cited by 14 publications

(7 citation statements)

References 8 publications

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“…The selected FLA are, W. magna belonging to the Vahlkampfiidae family and Vermamoeba vermiformis , belonging to Vermamoebidae family and one of the most common free-living protists in human environments (de Moura et al . 1985 ; Bradbury 2014 ; Delafont et al . 2018 ).…”

Section: Introductionmentioning

confidence: 99%

Role of amoebae for survival and recovery of ‘non-culturable’ Helicobacter pylori cells in aquatic environments

Dey

Rieger

Banting

et al. 2020

FEMS Microbiology Ecology

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Helicobacter pylori is a fastidious Gram-negative bacterium that infects over half of the world's population, causing chronic gastritis and is a risk factor for stomach cancer. In developing and rural regions where prevalence rate exceeds 60%, persistence and waterborne transmission are often linked to poor sanitation conditions. Here we demonstrate that H. pylori not only survives but also replicates within acidified free-living amoebal phagosomes. Bacterial counts of the clinical isolate H. pylori G27 increased over 50-fold after three days in co-culture with amoebae. In contrast, a H. pylori mutant deficient in a cagPAI gene (cagE) showed little growth within amoebae, demonstrating the likely importance of a type IV secretion system in H. pylori for amoebal infection. We also demonstrate that H. pylori can be packaged by amoebae and released in extracellular vesicles. Furthermore, and for the first time, we successfully demonstrate the ability of two free-living amoebae to revert and recover viable but non-cultivable coccoid (VBNC)-H. pylori to a culturable state. Our studies provide evidence to support the hypothesis that amoebae and perhaps other free-living protozoa contribute to the replication and persistence of human-pathogenic H. pylori by providing a protected intracellular microenvironment for this pathogen to persist in natural aquatic environments and engineered water systems, thereby H. pylori potentially uses amoeba as a carrier and a vector of transmission.

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Section: Introductionmentioning

confidence: 99%

Role of amoebae for survival and recovery of ‘non-culturable’ Helicobacter pylori cells in aquatic environments

Dey

Rieger

Banting

et al. 2020

FEMS Microbiology Ecology

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“…Subclinical infections caused by these protozoa are probably common among healthy individuals, in whom protozoa harbored in the nose and throat can, in weaker periods, behave as facultative parasites [5,6]). In Brazil, cases of human diseases caused by these amoebae have been described [7][8][9][10] derived from water [11][12][13][14] and dust from external environments [15,16]. The few reports of FLA occurring in internal environments all involve hospitals [1,18].…”

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confidence: 99%

Prevalence of potentially pathogenic free-living amoebae from Acanthamoeba and Naegleria genera in non-hospital, public, internal environments from the city of Santos, Brazil

et al. 2009

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Acanthamoeba and Naegleria species are free-living amoebae (FLA) found in a large variety of natural habitats. The prevalence of such amoebae was determined from dust samples taken from public non-hospital internal environments with good standards of cleanliness from two campuses of the same University in the city of Santos (SP), Brazil, and where young and apparently healthy people circulate. The frequency of free-living amoebae in both campuses was 39% and 17% respectively, with predominance of the genus Acanthamoeba. On the campus with a much larger number of circulating individuals, the observed frequency of free-living amoebae was 2.29 times larger (P< 0.00005). Two trophozoite forms of Naegleria fowleri, are the only species of this genus known to cause primary amoebian meningoencephalitis, a rare and non-opportunistic infection. We assume that the high frequency of these organisms in different internal locations represents some kind of public health risk.

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“…Before Salmonella can invade their host, they must pass through the harsh environments of stomach acid and bile salts and colonize the intestinal epithelium in competition with more abundant bacterial species. In addition, they must evade generalist predators such as protozoa, which also inhabit intestinal environments (40)(41)(42). Bacterial populations are constrained by the action of protozoan predation, including Yersinia in river water (43), Rhizobium in groundwater and soil (44,45), Xanthomonas in soil (46), Archaea in the rumen (47), and numerous bacterial species resident in the water column (46,48,49) or in soil (50).…”

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confidence: 99%

“…Bacterial populations are constrained by the action of protozoan predation, including Yersinia in river water (43), Rhizobium in groundwater and soil (44,45), Xanthomonas in soil (46), Archaea in the rumen (47), and numerous bacterial species resident in the water column (46,48,49) or in soil (50). Because amoebae are abundant predators in vertebrate intestinal tracts (40)(41)(42), they likely act in similar manners to control populations of enteric species.…”

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confidence: 99%

Protozoan predation, diversifying selection, and the evolution of antigenic diversity in Salmonella

Wildschutte

Wolfe

Tamewitz

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

145

139

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Extensive population-level genetic variability at the Salmonella rfb locus, which encodes enzymes responsible for synthesis of the O-antigen polysaccharide, is thought to have arisen through frequency-dependent selection (FDS) by means of exposure of this pathogen to host immune systems. The FDS hypothesis works well for pathogens such as Haemophilus influenzae and Neisseria meningitis, which alter the composition of their O-antigens during the course of bloodborne infections. In contrast, Salmonella remains resident in epithelial cells or macrophages during infection and does not have phase variability in its O-antigen. More importantly, Salmonella shows host-serovar specificity, whereby strains bearing certain O-antigens cause disease primarily in specific hosts; this behavior is inconsistent with FDS providing selection for the origin or maintenance of extensive polymorphism at the rfb locus. Alternatively, selective pressure may originate from the host intestinal environment itself, wherein diversifying selection mediated by protozoan predation allows for the continued existence of Salmonella able to avoid consumption by host-specific protozoa. This selective pressure would result in high population-level diversity at the Salmonella rfb locus without phase variation. We show here that intestinal protozoa recognize antigenically diverse Salmonella with different efficiencies and demonstrate that differences solely in the O-antigen are sufficient to allow for prey discrimination. Combined with observations of the differential distributions of both serotypes of bacterial species and their protozoan predators among environments, our data provides a framework for the evolution of high genetic diversity at the rfb locus and host-specific pathogenicity in Salmonella.T he enteric pathogen Salmonella enterica presents at least 70 different O-antigens [the outermost structure of the Gramnegative lipopolysaccharide (LPS)] to mammalian immune systems (1); this polysaccharide decorates the outer surface of the cell. Historically, extensive genetic diversity at the rfb locus, which encodes enzymes directing O-antigen synthesis (2-6), has been attributed to frequency-dependent selection (FDS) (7,8) imposed by the host immune system (5, 9, 10). Novel rfb loci would have an advantage because their cognate O-antigens would be unrecognized by immune systems (Fig. 1A); strains carrying rare loci would have higher fitness and would avoid rapid stochastic loss, rising to higher frequency. Yet selective advantages decrease with abundance; as a result, strains with common rfb loci cannot dominate the population or elicit a selective sweep (7) because their fitnesses become lower as they become more abundant. In concert, FDS prevents the loss of rare alleles or the dominance of common alleles, thus maintaining diversity (8).According to the FDS model, expression of different LPS molecules through gene regulation allows invading bacteria to escape host immunity, survive, and proceed throughout its life cycle; this hypothesis explains...

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Amebas de vida livre no intestino humano: evidências de parasitismo

Cited by 14 publications

References 8 publications

Role of amoebae for survival and recovery of ‘non-culturable’ Helicobacter pylori cells in aquatic environments

Role of amoebae for survival and recovery of ‘non-culturable’ Helicobacter pylori cells in aquatic environments

Prevalence of potentially pathogenic free-living amoebae from Acanthamoeba and Naegleria genera in non-hospital, public, internal environments from the city of Santos, Brazil

Protozoan predation, diversifying selection, and the evolution of antigenic diversity in Salmonella

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