On the life-history of a soil amoeba,

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A blockmodel study of managerial hierarchies, verbal networks, and organizational culture in four hospitals

This study demonstrates and applies a social network methodology for studying the dynamics of hierarchies in organizations. Social network (blockmodel) analysis of verbal networks in four hospitals contrasted hierarchical and structurally equivalent partitions of the sociomatrices of frequent ties and perceptions of organizational culture. It was found that the verbal networks in these organizations follow a center periphery pattern rather than a hierarchical logic and that perceptions of culture vary more by verbal network than by formal hierarchy. The perceptions of culture of central groups in one organization are much like those of peripheral groups in another. In all four hospitals, structurally equivalent social networks are more important in predicting subcultures than are hierarchical groupings and hierarchy has a limited impact on the development of verbal networks. These findings suggest the value of an amoeba rather than a pyramid metaphor in interpreting the cultures and relational structures of organizations.

Isolamento de amebas de vida livre a partir de água mineral engarrafada

Foram isoladas amebas dos gêneros Vahlkampfia, Glaeseria, Acanthamoeba, Filamoeba, Amoeba, Platyamoeba e Hartmanella de dez diferentes marcas de água mineral engarrafadas, servidas no Rio de Janeiro, RJ (Brasil). Somente uma das marcas foi negativa para protozoários, enquanto que de todas as outras foram isoladas amebas de vida livre. O significado desses resultados é discutido como um indicador de qualidade da água mineral usada comercialmente, destacando-se o fato de que alguns desses microorganismos são potencialmente patogênicos.

Isolamento de amebas de vida livre potencialmente patogênicas em poeira de hospitais

OBJETIVO: Observar a ocorrência de amebas de vida livre dos gêneros Acanthamoeba e Naegleria em amostras de poeira coletadas em hospitais. MÉTODOS: Foram coletadas 132 amostras de poeira em dois hospitais do município de Presidente Prudente, São Paulo. Os locais da coleta foram: Unidade de Terapia Intensiva, Centro Cirúrgico, Isolamento de Moléstias Infecciosas, Berçário, Emergência e Cozinha. As amostras foram semeadas em três meios de cultura: meio de ágar não nutriente com Escherichia coli, meio de ágar infusão de soja e microcultivo em meio de Pavlova modificado por Giazzi. As amebas isoladas foram identificadas segundo critérios morfológicos. RESULTADOS: O índice geral de positividade para amebas de vida livre, potencialmente patogênicas, dos gêneros Acanthamoeba e Naegleria, foi de 45,5%, sendo positivas 41,6% das amostras de poeira coletadas no hospital universitário e 50% no hospital estadual. Obtiveram-se 45,5% de positividade do gênero Acanthamoeba e 3,8% para amebas do gênero Naegleria. CONCLUSÕES: As amebas de vida livre, potencialmente patogênicas, estavam presentes em todos os ambientes estudados dos dois hospitais, sendo que as espécies do gênero Acanthamoeba foram as isoladas com maior freqüência.

Biodiversity of amoebae and amoebae-resisting bacteria in a drinking water treatment plant

The complex ecology of free-living amoebae (FLA) and their role in spreading pathogenic microorganisms through water systems have recently raised considerable interest. In this study, we investigated the presence of FLA and amoebae-resisting bacteria (ARB) at various stages of a drinking water plant fed with river water. We isolated various amoebal species from the river and from several points within the plant, mostly at early steps of water treatment. Echinamoeba- and Hartmannella-related amoebae were mainly recovered in the drinking water plant whereas Acanthamoeba- and Naegleria-related amoebae were recovered from the river water and the sand filtration units. Some FLA isolates were recovered immediately after the ozonation step, thus suggesting resistance of these microorganisms to this disinfection procedure. A bacterial isolate related to Mycobacterium mucogenicum was recovered from an Echinamoeba-related amoeba isolated from ozone-treated water. Various other ARB were recovered using co-culture with axenic Acanthamoeba castellanii, including mycobacteria, legionella, Chlamydia-like organisms and various proteobacteria. Noteworthy, a new Parachlamydia acanthamoebae strain was recovered from river water and from granular activated carbon (GAC) biofilm. As amoebae mainly multiply in sand and GAC filters, optimization of filter backwash procedures probably offers a possibility to better control these protists and the risk associated with their intracellular hosts

Lausannevirus Seroprevalence among Asymptomatic Young Adults.

Objectives: The giant Lausannevirus was recently identified as a parasite of amoeba that replicates rapidly in these professional phagocytes. This study aimed at assessing Lausannevirus seroprevalence among asymptomatic young men in Switzerland and hopefully identifying possible sources of contact with this giant virus. Methods: The presence of anti-Lausannevirus antibodies was assessed in sera from 517 asymptomatic volunteers who filled a detailed questionnaire. The coreactivity between Lausannevirus and amoeba-resisting bacteria was assessed. Results: Lausannevirus prevalence ranged from 1.74 to 2.51%. Sporadic condom use or multiple sexual partners, although frequent (53.97 and 60.35%, respectively), were not associated with anti-Lausannevirus antibodies. On the contrary, frequent outdoor sport practice as well as milk consumption were significantly associated with positive Lausannevirus serologies (p = 0.0066 and 0.028, respectively). Coreactivity analyses revealed an association between Criblamydia sequanensis (an amoeba-resisting bacterium present in water environments) and Lausannevirus seropositivity (p = 0.001). Conclusions: Lausannevirus seroprevalence is low in asymptomatic Swiss men. However, the association between virus seropositivity and frequent sport practice suggests that this member of the Megavirales may be transmitted by aerosols and/or exposure to specific outdoor environments. Milk intake was also associated with seropositivity. Whether the coreactivity observed for C. sequanensis and Lausannevirus reflects a common mode of acquisition or some unexpected cross-reactivity remains to be determined. © 2013 S. Karger AG, Basel.

Predator-prey chemical warfare determines the expression of biocontrol genes by rhizosphere-associated Pseudomonas fluorescens.

Soil bacteria are heavily consumed by protozoan predators, and many bacteria have evolved defense strategies such as the production of toxic exometabolites. However, the production of toxins is energetically costly and therefore is likely to be adjusted according to the predation risk to balance the costs and benefits of predator defense. We investigated the response of the biocontrol bacterium Pseudomonas fluorescens CHA0 to a common predator, the free-living amoeba Acanthamoeba castellanii. We monitored the effect of the exposure to predator cues or direct contact with the predators on the expression of the phlA, prnA, hcnA, and pltA genes, which are involved in the synthesis of the toxins, 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin, hydrogen cyanide, and pyoluteorin, respectively. Predator chemical cues led to 2.2-, 2.0-, and 1.2-fold increases in prnA, phlA, and hcnA expression, respectively, and to a 25% increase in bacterial toxicity. The upregulation of the tested genes was related to the antiprotozoan toxicity of the corresponding toxins. Pyrrolnitrin and DAPG had the highest toxicity, suggesting that bacteria secrete a predator-specific toxin cocktail. The response of the bacteria was elicited by supernatants of amoeba cultures, indicating that water-soluble chemical compounds were responsible for induction of the bacterial defense response. In contrast, direct contact of bacteria with living amoebae reduced the expression of the four bacterial toxin genes by up to 50%, suggesting that protozoa can repress bacterial toxicity. The results indicate that predator-prey interactions are a determinant of toxin production by rhizosphere P. fluorescens and may have an impact on its biocontrol potential.

Host tissue destruction by Entamoeba histolytica: molecules mediating adhesion, cytolysis, and proteolysis

Entamoeba histolytica, the protozoan parasite causing human amoebisis, has recently been found to comprise two genetically distinct forms, potentially pathogenic and constitutively nonpathogenic ones. Host tissue destruction by pathogenic forms is belived to result from cell functions mediaed by a lectin-type adherence receptor, a pore-forming peptide involved in host cell lysis, and abundant expression of cysteine proteinase(s). Isolation and molecular cloning of these amoeba products have provided the tools for structural analyses and manipulations of cell functions including comparisons between pathogenic and nonpathogenic forms.

Insight into cross-talk between intra-amoebal pathogens.

Abstract: Background: Amoebae are phagocytic protists where genetic exchanges might take place between amoeba-resistant bacteria. These amoebal pathogens are able to escape the phagocytic behaviour of their host. They belong to different bacterial phyla and often show a larger genome size than human-infecting pathogens. This characteristic is proposed to be the result of frequent gene exchanges with other bacteria that share a sympatric lifestyle and contrasts with the genome reduction observed among strict human pathogens.Results: We sequenced the genome of a new amoebal pathogen, Legionella drancourtii, and compared its gene content to that of a Chlamydia-related bacterium, Parachlamydia acanthamoebae. Phylogenetic reconstructions identified seven potential horizontal gene transfers (HGTs) between the two amoeba-resistant bacteria, including a complete operon of four genes that encodes an ABC-type transporter. These comparisons pinpointed potential cases of gene exchange between P. acanthamoebae and Legionella pneumophila, as well as gene exchanges between other members of the Legionellales and Chlamydiales orders. Moreover, nine cases represent possible HGTs between representatives from the Legionellales or Chlamydiales and members of the Rickettsiales order.Conclusions: This study identifies numerous gene exchanges between intracellular Legionellales and Chlamydiales bacteria, which could preferentially occur within common inclusions in their amoebal hosts. Therefore it contributes to improve our knowledge on the intra-amoebal gene properties associated to their specific lifestyle.

Early expression of the type III secretion system of Parachlamydia acanthamoebae during a replicative cycle within its natural host cell Acanthamoeba castellanii.

The type three secretion system (T3SS) operons of Chlamydiales bacteria are distributed in different clusters along their chromosomes and are conserved at both the level of sequence and genetic organization. A complete characterization of the temporal expression of multiple T3SS components at the transcriptional and protein levels has been performed in Parachlamydia acanthamoebae, replicating in its natural host cell Acanthamoeba castellanii. The T3SS components were classified in four different temporal clusters depending on their pattern of expression during the early, mid- and late phases of the infectious cycle. The putative T3SS transcription units predicted in Parachlamydia are similar to those described in Chlamydia trachomatis, suggesting that T3SS units of transcriptional expression are highly conserved among Chlamydiales bacteria. The maximal expression and activation of the T3SS of Parachlamydia occurred during the early to mid-phase of the infectious cycle corresponding to a critical phase during which the intracellular bacterium has (1) to evade and/or block the lytic pathway of the amoeba, (2) to differentiate from elementary bodies (EBs) to reticulate bodies (RBs), and (3) to modulate the maturation of its vacuole to create a replicative niche able to sustain efficient bacterial growth.

Proteomics fingerprinting of phagosome maturation and evidence for the role of a Galpha during uptake.

Phagocytosis, whether of food particles in protozoa or bacteria and cell remnants in the metazoan immune system, is a conserved process. The particles are taken up into phagosomes, which then undergo complex remodeling of their components, called maturation. By using two-dimensional gel electrophoresis and mass spectrometry combined with genomic data, we identified 179 phagosomal proteins in the amoeba Dictyostelium, including components of signal transduction, membrane traffic, and the cytoskeleton. By carrying out this proteomics analysis over the course of maturation, we obtained time profiles for 1,388 spots and thus generated a dynamic record of phagosomal protein composition. Clustering of the time profiles revealed five clusters and 24 functional groups that were mapped onto a flow chart of maturation. Two heterotrimeric G protein subunits, Galpha4 and Gbeta, appeared at the earliest times. We showed that mutations in the genes encoding these two proteins produce a phagocytic uptake defect in Dictyostelium. This analysis of phagosome protein dynamics provides a reference point for future genetic and functional investigations.

Discovery of new intracellular pathogens by amoebal coculture and amoebal enrichment approaches.

Intracellular pathogens such as legionella, mycobacteria and Chlamydia-like organisms are difficult to isolate because they often grow poorly or not at all on selective media that are usually used to cultivate bacteria. For this reason, many of these pathogens were discovered only recently or following important outbreaks. These pathogens are often associated with amoebae, which serve as host-cell and allow the survival and growth of the bacteria. We intend here to provide a demonstration of two techniques that allow isolation and characterization of intracellular pathogens present in clinical or environmental samples: the amoebal coculture and the amoebal enrichment. Amoebal coculture allows recovery of intracellular bacteria by inoculating the investigated sample onto an amoebal lawn that can be infected and lysed by the intracellular bacteria present in the sample. Amoebal enrichment allows recovery of amoebae present in a clinical or environmental sample. This can lead to discovery of new amoebal species but also of new intracellular bacteria growing specifically in these amoebae. Together, these two techniques help to discover new intracellular bacteria able to grow in amoebae. Because of their ability to infect amoebae and resist phagocytosis, these intracellular bacteria might also escape phagocytosis by macrophages and thus, be pathogenic for higher eukaryotes.

Novel Chlamydiales strains isolated from a water treatment plant.

Chlamydiae are obligate intracellular bacteria infecting free-living amoebae, vertebrates and some invertebrates. Novel members are regularly discovered, and there is accumulating evidence supporting a very important diversity of chlamydiae in the environment. In this study, we investigated the presence of chlamydiae in a drinking water treatment plant. Samples were used to inoculate Acanthamoeba monolayers (Acanthamoeba co-culture), and to recover autochthonous amoebae onto non-nutritive agar. Chlamydiae were searched for by a pan-chlamydia 16S rRNA gene PCR from both Acanthamoeba co-cultures and autochthonous amoebae, and phylotypes determined by 16S rRNA gene sequencing. Autochthonous amoebae also were identified by 18S rRNA gene amplification and sequencing. From a total of 79 samples, we recovered eight chlamydial strains by Acanthamoeba co-culture, but only one of 28 amoebae harboured a chlamydia. Sequencing results and phylogenetic analysis showed our strains belonging to four distinct chlamydial lineages. Four strains, including the strain recovered within its natural host, belonged to the Parachlamydiaceae; two closely related strains belonged to the Criblamydiaceae; two distinct strains clustered with Rhabdochlamydia spp.; one strain clustered only with uncultured environmental clones. Our results confirmed the usefulness of amoeba co-culture to recover novel chlamydial strains from complex samples and demonstrated the huge diversity of chlamydiae in the environment, by identifying several new species including one representing the first strain of a new family.