Invasion of protozoa by Legionella pneumophila and its role in bacterial ecology and pathogenesis

The Legionella pneumophila collagen-like protein mediates sedimentation, autoaggregation, and pathogen-phagocyte interactions

Although only partially understood, multicellular behavior is relatively common in bacterial pathogens. Bacterial aggregates can resist various host defenses and colonize their environment more efficiently than planktonic cells. For the waterborne pathogen Legionella pneumophila, little is known about the roles of autoaggregation or the parameters which allow cell-cell interactions to occur. Here, we determined the endogenous and exogenous factors sufficient to allow autoaggregation to take place in L. pneumophila. We show that isolates from Legionella species which do not produce the Legionella collagen-like protein (Lcl) are deficient in autoaggregation. Targeted deletion of the Lcl-encoding gene (lpg2644) and the addition of Lcl ligands impair the autoaggregation of L. pneumophila. In addition, Lcl-induced autoaggregation requires divalent cations. Escherichia coli producing surface-exposed Lcl is able to autoaggregate and shows increased biofilm production. We also demonstrate that L. pneumophila infection of Acanthamoeba castellanii and Hartmanella vermiformis is potentiated under conditions which promote Lcl dependent autoaggregation. Overall, this study shows that L. pneumophila is capable of autoaggregating in a process that is mediated by Lcl in a divalent-cation-dependent manner. It also reveals that Lcl potentiates the ability of L. pneumophila to come in contact, attach, and infect amoebae.

Architecture and host interface of environmental chlamydiae revealed by electron cryotomography

Chlamydiae comprise important pathogenic and symbiotic bacteria that alternate between morphologically and physiologically different life stages during their developmental cycle. Using electron cryotomography, we characterize the ultrastructure of the developmental stages of three environmental chlamydiae: Parachlamydia acanthamoebae, Protochlamydia amoebophila and Simkania negevensis. We show that chemical fixation and dehydration alter the cell shape of Parachlamydia and that the crescent body is not a developmental stage, but an artefact of conventional electron microscopy. We further reveal type III secretion systems of environmental chlamydiae at macromolecular resolution and find support for a chlamydial needle-tip protein. Imaging bacteria inside their host cells by cryotomography for the first time, we observe marked differences in inclusion morphology and development as well as host organelle recruitment between the three chlamydial organisms, with Simkania inclusions being tightly enveloped by the host endoplasmic reticulum. The study demonstrates the power of electron cryotomography to reveal structural details of bacteria-host interactions that are not accessible using traditional methods.

VBNC Legionella pneumophila cells are still able to produce virulence proteins

Legionella pneumophila is the agent responsible for legionellosis. Numerous bacteria, including L. pneumophila, can enter into a viable but not culturable (VBNC) state under unfavorable environmental conditions. In this state, cells are unable to form colonies on standard medium but are still alive. Here we show that VBNC L. pneumophila cells, obtained by monochloramine treatment, were still able to synthesize proteins, some of which are involved in virulence. Protein synthesis was measured using (35)S-labeling and the proteomes of VBNC and culturable cells then compared. This analysis allowed the identification of nine proteins that were accumulated in the VBNC state. Among them, four were involved in virulence, i.e., the macrophage infectivity potentiator protein, the hypothetical protein lpl2247, the ClpP protease proteolytic subunit and the 27 kDa outer membrane protein. Others, i.e., the enoyl reductase, the electron transfer flavoprotein (alpha and beta subunits), the 50S ribosomal proteins (L1 and L25) are involved in metabolic and energy production pathways. However, resuscitation experiments performed with Acanthamoeba castellanii failed, suggesting that the accumulation of virulence factors by VBNC cells is not sufficient to maintain their virulence.

Microbial and physicochemical parameters associated with Legionella contamination in hot water recirculation systems

Hot water recirculation systems (HWRS) in hotels and nursing homes, which are common in countries such as Spain, have been related to outbreaks of legionellosis. To establish the relationships of microbial and physicochemical parameters, especially protozoa, with the occurrence of Legionella in HWRS, 231 samples from hotels and nursing homes were analysed for Legionella, protozoa, heterotrophic plate counts (HPC) at 22 and 37 °C, Pseudomonas, metals, temperature and others. Legionella pneumophila was the dominant species isolated, and 22 % were sg. 1. The sampling method became particularly important in order to define which factors were involved on the occurrence of Legionella. Results showed that the bacteria and the accompanying microbiota were more abundant in the first flush water whose temperature was lower. The bacteria occurred in those samples with high HPC and were inversely correlated with high temperatures. Multivariate regression showed that a concentration above 1 × 10(5) CFU/100 mL of HPC at 37 °C, Fe above 0.095 ppm and the presence of protozoa increased significantly the risk of Legionella colonization, while univariant regression showed that the presence of Cu above 0.76 ppm and temperature above 55 °C diminished it. Therefore, to reduce the risk associated with Legionella occurrence in HWRS these parameters should be taken into consideration.

Comparative Genomics Reveal That Host-Innate Immune Responses Influence the Clinical Prevalence of Legionella pneumophila Serogroups

Legionella pneumophila is the primary etiologic agent of legionellosis, a potentially fatal respiratory illness. Amongst the sixteen described L. pneumophila serogroups, a majority of the clinical infections diagnosed using standard methods are serogroup 1 (Sg1). This high clinical prevalence of Sg1 is hypothesized to be linked to environmental specific advantages and/or to increased virulence of strains belonging to Sg1. The genetic determinants for this prevalence remain unknown primarily due to the limited genomic information available for non-Sg1 clinical strains. Through a systematic attempt to culture Legionella from patient respiratory samples, we have previously reported that 34% of all culture confirmed legionellosis cases in Ontario (n = 351) are caused by non-Sg1 Legionella. Phylogenetic analysis combining multiple-locus variable number tandem repeat analysis and sequence based typing profiles of all non-Sg1 identified that L. pneumophila clinical strains (n = 73) belonging to the two most prevalent molecular types were Sg6. We conducted whole genome sequencing of two strains representative of these sequence types and one distant neighbour. Comparative genomics of the three L. pneumophila Sg6 genomes reported here with published L. pneumophila serogroup 1 genomes identified genetic differences in the O-antigen biosynthetic cluster. Comparative optical mapping analysis between Sg6 and Sg1 further corroborated this finding. We confirmed an altered O-antigen profile of Sg6, and tested its possible effects on growth and replication in in vitro biological models and experimental murine infections. Our data indicates that while clinical Sg1 might not be better suited than Sg6 in colonizing environmental niches, increased bloodstream dissemination through resistance to the alternative pathway of complement mediated killing in the human host may explain its higher prevalence.

Cellular microbiology and molecular ecology of Legionella-amoeba interaction

Legionella pneumophila is an aquatic organism that interacts with amoebae and ciliated protozoa as the natural hosts, and this interaction plays a central role in bacterial ecology and infectivity. Upon transmission to humans, L. pneumophila infect and replicate within alveolar macrophages causing pneumonia. Intracellular proliferation of L. pneumophila within the two evolutionarily distant hosts is facilitated by bacterial exploitation of evolutionarily conserved host processes that are targeted by bacterial protein effectors injected into the host cell by the Dot/Icm type VIB translocation system. Although cysteine is semi-essential for humans and essential for amoeba, it is a metabolically favorable source of carbon and energy generation by L. pneumophila. To counteract host limitation of cysteine, L. pneumophila utilizes the AnkB Dot/Icm-translocated F-box effector to promote host proteasomal degradation of polyubiquitinated proteins within amoebae and human cells. Evidence indicates ankB and other Dot/Icm-translocated effector genes have been acquired through inter-kingdom horizontal gene transfer.

Effector translocation by the Legionella Dot/Icm type IV secretion system

Legionella pneumophila is an opportunistic pathogen responsible for Legionnaires' disease. This bacterium survives and replicates within phagocytes by bypassing their bactericidal activity. Intracellular replication of L. pneumophila requires the Dot/Icm type IV secretion system made of approximately 27 proteins that presumably traverses the bacterial and phagosomal membranes. The perturbation of the host killing ability largely is mediated by the collective functions of the protein substrates injected into host cells via the Dot/Icm transporter. Proper protein translocation by Dot/Icm is determined by a number of factors, including signals recognizable by the translocator, chaperones that may facilitate the proper folding of substrates and transcriptional regulation and protein stability that determine the abundance and temporal transfer of the substrates. Although a large number of Dot/Icm substrates have been identified, investigation to understand the translocation is ongoing. Here we summarized the recent advancements in our understanding of the factors that determine the protein translocation activity of the Dot/Icm transporter.

Seasonal diversity of planktonic protists in Southwestern Alberta rivers over a 1-year period as revealed by terminal restriction fragment length polymorphism and 18S rRNA gene library analyses

The temporal dynamics of planktonic protists in river water have received limited attention despite their ecological significance and recent studies linking phagotrophic protists to the persistence of human-pathogenic bacteria. Using molecular-based techniques targeting the 18S rRNA gene, we studied the seasonal diversity of planktonic protists in Southwestern Alberta rivers (Oldman River Basin) over a 1-year period. Nonmetric multidimensional scaling analysis of terminal restriction fragment length polymorphism (T-RFLP) data revealed distinct shifts in protistan community profiles that corresponded to season rather than geographical location. Community structures were examined by using clone library analysis; HaeIII restriction profiles of 18S rRNA gene amplicons were used to remove prevalent solanaceous plant clones prior to sequencing. Sanger sequencing of the V1-to-V3 region of the 18S rRNA gene libraries from spring, summer, fall, and winter supported the T-RFLP results and showed marked seasonal differences in the protistan community structure. The spring library was dominated by Chloroplastidae (29.8%), Centrohelida (28.1%), and Alveolata (25.5%), while the summer and fall libraries contained primarily fungal clones (83.0% and 88.0%, respectively). Alveolata (35.6%), Euglenozoa (24.4%), Chloroplastida (15.6%), and Fungi (15.6%) dominated the winter library. These data demonstrate that planktonic protists, including protozoa, are abundant in river water in Southwestern Alberta and that conspicuous seasonal shifts occur in the community structure.

Exploitation of evolutionarily conserved amoeba and mammalian processes by Legionella

Legionella pneumophila proliferates within various protists and metazoan cells, where a cadre of ∼300 effectors is injected into the host cell by the defect in organelle trafficking/intracellular multiplication (Dot/Icm) type IVB translocation system. Interkingdom horizontal gene transfer of genes of protists and their subsequent convergent evolution to become translocated effectors has probably enabled L. pneumophila to adapt to the intracellular life within various protists and metazoan cells through exploitation of evolutionarily eukaryotic processes, such as endoplasmic reticulum-to-Golgi vesicle traffic, phosphoinositol metabolism, AMPylation, deAMPylation, prenylation, polyubiquitination, proteasomal degradation and cytosolic amino- and oligo-peptidases. This is highlighted by the ankyrin B (AnkB) F-box effector that exploits multiple conserved eukaryotic machineries to generate high levels of free amino acids as sources of carbon and energy essential for intracellular proliferation in protists and metazoan cells and for manifestation of pulmonary disease in mammals.

Detection of free-living amoebae by using multiplex quantitative PCR

Free-living amoebae (FLA) are protozoa found worldwide in soil and aquatic environments, which are able to colonize man-made water networks. Some FLA have the potential to be pathogenic and others might harbour pathogenic bacteria. Indeed, FLA feed on bacteria, but some bacteria could resist phagocytosis and either survive in FLA or even multiply within FLA. These bacteria are collectively named amoeba resistant bacteria (ARB). The best characterized example is Legionella pneumophila, for which FLA is the main reservoir in the environment. Not only could FLA be a reservoir that protects ARB, some bacteria might become more resistant to treatment and be more virulent. Thus, it is of medical significance to quantify FLA populations in soil, water or the environment. The main limitation for the quantification of FLA is that classical culture is not efficient and reliable for many genera and 'strains'. Thus, several PCR-based quantification methods have been published for various FLA. However, thus far, no method has been published to simultaneously quantify the main FLA genera in the same PCR reaction. In this study, we developed a multiplex qPCR method to detect both Amoebozoan (i.e. Acanthamoeba, Hartmannella and Echinamoeba) and Vahlkampfiidae (i.e. Vahlkampfia and Naegleria) using 18S ribosomal RNA as the target gene. This method was shown to be specific, reliable and sensitive, could be used for the quantification of FLA and is likely to be useful to anticipate risks due to FLA or pathogenic bacteria, such as L. pneumophila.

Contribution of amoebic coculture to recovery of Legionella isolates from respiratory samples: prospective analysis over a period of 32 months

We evaluated the contribution of amoebic coculture to the recovery of Legionella spp. from 379 respiratory samples. The sensitivity of axenic culture was 42.1%. The combination of axenic culture with amoebic coculture increased the Legionella isolation rate to 47.1%. Amoebic coculture was particularly efficient in isolating Legionella spp. from respiratory samples contaminated with oropharyngeal flora.

Comparison of potentially pathogenic free-living amoeba hosts by Legionella spp. in substrate-associated biofilms and floating biofilms from spring environments

This study compares five genera of free-living amoebae (FLA) hosts by Legionella spp. in the fixed and floating biofilm samples from spring environments. Detection rate of Legionella spp. was 26.9% for the floating biofilms and 3.1% for the fixed biofilms. Acanthamoeba spp., Hartmanella vermiformis, and Naegleria spp. were more frequently detected in floating biofilm than in fixed biofilm samples. The percentage of pathogenic Acanthamoeba spp. among all the genus Acanthamoeba detected positive samples was 19.6%. The potential pathogenic Naegleria spp. (for example, Naegleria australiensis, Naegleria philippinensis, and Naegleria italica) was 54.2% to all the Naegleria detected positive samples. In the study, 12 serotypes of possible pneumonia causing Legionella spp. were detected, and their percentage in all the Legionella containing samples was 42.4%. The FLA parasitized by Legionella included unnamed Acanthamoeba genotype, Acanthamoeba griffini, Acanthamoeba jacobsi, H. vermiformis, and N. australiensis. Significant differences were also observed between the presence/absence of H. vermiformis and Legionella parasitism in FLA. Comparisons between the culture-confirmed method and the PCR-based detection method for detecting FLA and Legionella in biofilms showed great variation. Therefore, using these analysis methods together to detect FLA and Legionella is recommended.

Increased persistence of Salmonella enterica serovar Typhi in the presence of Acanthamoeba castellanii

Salmonella enterica serovar Typhi (S. Typhi) is the etiological agent of the systemic disease typhoid fever. Transmission occurs via ingestion of contaminated food or water. S. Typhi is specific to humans, and no animal or environmental reservoirs are known. As the free-living amoeba Acanthamoeba castellanii is an environmental host for many pathogenic bacteria, this study investigates interactions between S. Typhi and A. castellanii by using cocultures. Growth of both organisms was estimated by cell count, viable count, flow cytometry, and fluorescence microscopy. Results indicate that S. Typhi can survive at least 3 weeks when grown with A. castellanii, as opposed to less than 10 days when grown as singly cultured bacteria under the same conditions. Interestingly, growth rates of amoebae after 14 days were similar in cocultures or when amoebae were singly cultured, suggesting that S. Typhi is not cytotoxic to A. castellanii. Bacteria surviving in coculture were not intracellular and did not require a physical contact with amoebae for their survival. These results suggest that S. Typhi may have a selective advantage when it is associated with A. castellanii and that amoebae may contribute to S. Typhi persistence in the environment.

Total and viable Legionella pneumophila cells in hot and natural waters as measured by immunofluorescence-based assays and solid-phase cytometry

A new method was developed for the rapid and sensitive detection of viable Legionella pneumophila. The method combines specific immunofluorescence (IF) staining using monoclonal antibodies with a bacterial viability marker (ChemChrome V6 cellular esterase activity marker) by means of solid-phase cytometry (SPC). IF methods were applied to the detection and enumeration of both the total and viable L. pneumophila cells in water samples. The sensitivity of the IF methods coupled to SPC was 34 cells liter(-1), and the reproducibility was good, with the coefficient of variation generally falling below 30%. IF methods were applied to the enumeration of total and viable L. pneumophila cells in 46 domestic hot water samples as well as in cooling tower water and natural water samples, such as thermal spring water and freshwater samples. Comparison with standard plate counts showed that (i) the total direct counts were always higher than the plate counts and (ii) the viable counts were higher than or close to the plate counts. With domestic hot waters, when the IF assay was combined with the viability test, SPC detected up to 3.4 × 10(3) viable but nonculturable L. pneumophila cells per liter. These direct IF methods could be a powerful tool for high-frequency monitoring of domestic hot waters or for investigating the occurrence of viable L. pneumophila in both man-made water systems and environmental water samples.

Usefulness of real-time PCR as a complementary tool to the monitoring of Legionella spp. and Legionella pneumophila by culture in industrial cooling systems

AIMS

This study was designed to evaluate the usefulness of quantification by real-time PCR as a management tool to monitor concentrations of Legionella spp. and Legionella pneumophila in industrial cooling systems and its ability to anticipate culture trends by the French standard method (AFNOR T90-431).

METHODS AND RESULTS

Quantifications of Legionella bacteria were achieved by both methods on samples from nine cooling systems with different water qualities. Proportion of positive samples for L. pneumophila quantified by PCR was clearly lower in deionized or river waters submitted to a biocide treatment than in raw river waters, while positive samples for Legionella spp. were quantified for almost all the samples. For some samples containing PCR inhibitors, high quantification limits (up to 4·80 × 10(5) GU l(-1) ) did not allow us to quantify L. pneumophila, when they were quantified by culture. Finally, the monitoring of concentrations of L. pneumophila by both methods showed similar trends for 57-100% of the samples.

CONCLUSIONS

These results suggest that, if some methodological steps designed to reduce inhibitory problems and thus decrease the quantification limits, could be developed to quantify Legionella in complex waters, the real-time PCR could be a valuable complementary tool to monitor the evolution of L. pneumophila concentrations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows the possibility of using real-time PCR to monitor L. pneumophila proliferations in cooling systems and the importance to adapt nucleic acid extraction and purification protocols to raw waters.

Intra-Vacuolar Proliferation of F. Novicida within H. Vermiformis

Francisella tularensis is a gram negative facultative intracellular bacterium that causes the zoonotic disease tularemia. Free-living amebae, such as Acanthamoeba and Hartmannella, are environmental hosts of several intracellular pathogens. Epidemiology of F. tularensis in various parts of the world is associated with water-borne transmission, which includes mosquitoes and amebae as the potential host reservoirs of the bacteria in water resources. In vitro studies showed intracellular replication of F. tularensis within A. castellanii cells. Whether ameba is a biological reservoir for Francisella in the environment is not known. We used Hartmannella vermiformis as an amebal model system to study the intracellular life of F. novicida. For the first time we show that F. novicida survives and replicates within H. vermiformis. The iglC mutant strain of F. novicida is defective for survival and replication not only within A. castellanii but also in H. vermiformis cells. In contrast to mammalian cells, where bacteria replicate in the cytosol, F. novicida resides and replicates within membrane-bound vacuoles within the trophozoites of H. vermiformis. In contrast to the transient residence of F. novicida within acidic vacuoles prior to escaping to the cytosol of mammalian cells, F. novicida does not reside transiently or permanently in an acidic compartment within H. vermiformis when examined 30 min after initiation of the infection. We conclude that F. tularensis does not replicate within acidified vacuoles and does not escape into the cytosol of H. vermiformis. The Francisella pathogenicity island locus iglC is essential for intra-vacuolar proliferation of F. novicida within H. vermiformis. Our data show a distinct intracellular lifestyle for F. novicida within H. vermiformis compared to mammalian cells.

Ecological behaviour of three serogroups of Legionella pneumophila within a model plumbing system

Three Legionella pneumophila strains isolated from water samples and belonging to serogroups (sgs) 1, 6 and 9 were analysed for their capacity to colonise an experimental model simulating a domestic hot water distribution system. Ecological factors that could influence the persistence of the sgs such as intracellular life within protozoan hosts and bacterial interference by the production of antagonistic compounds were also studied. Viable counts of L. pneumophila increased both in the planktonic and in the sessile phases. Sg 6 showed a marked prevalence during the whole experiment and exhibited the highest host infection efficiency. Sg 1 was significantly less represented, but showed the highest capacity to reproduce in the protozoan hosts. Sg 9 was poorly represented and less adapted to intracellular life. Among the 14 bacteria constantly isolated in the system, five (35.7%) produced antagonistic substances against Legionella, with differences according to the bacterial strain and L. pneumophila sgs.

Do free-living amoebae in treated drinking water systems present an emerging health risk?

There is an expanding body of evidence that free-living amoebae (FLA) increase both the numbers and virulence of water-based, human-pathogenic, amoeba-resisting microorganisms (ARM). Legionella spp., Mycobacterium spp., and other opportunistic human pathogens are known to be both ARM and also the etiologic agents of potentially fatal human lung infections. However, comparatively little is known about the FLA that may facilitate ARM growth in drinking water. This review examines the available literature on FLA in treated drinking water systems; in total 26 studies from 18 different countries. FLA were reported to breakthrough the water treatment barrier and enter distribution systems, in addition to the expected post-treatment system ingress. Once in the distribution system there is evidence of FLA colonization and regrowth especially in reservoirs and in-premise plumbing storage tanks. At the point of use the average FLA detection rate was 45% but highly variable (n = 16, σ = 31) due to both differences in both assay methods and the type of water systems examined. This review reveals that FLA are consistently detected in treated drinking water systems around the world and present a yet unquantified emerging health risk. However, more research is urgently required before accurate risks assessments can be undertaken to assess the impacts on human health, in households and institutions, due to exposure to FLA facilitated pathogenic ARM.

Salmonella transcriptional signature in Tetrahymena phagosomes and role of acid tolerance in passage through the protist

Salmonella enterica Typhimurium remains undigested in the food vacuoles of the common protist, Tetrahymena. Contrary to its interaction with Acanthamoeba spp., S. Typhimurium is not cytotoxic to Tetrahymena and is egested as viable cells in its fecal pellets. Through microarray gene expression profiling we investigated the factors in S. Typhimurium that are involved in its resistance to digestion by Tetrahymena. The transcriptome of S. Typhimurium in Tetrahymena phagosomes showed that 989 and 1282 genes were altered in expression compared with that in water and in LB culture medium, respectively. A great proportion of the upregulated genes have a role in anaerobic metabolism and the use of alternate electron acceptors. Many genes required for survival and replication within macrophages and human epithelial cells also had increased expression in Tetrahymena, including mgtC, one of the most highly induced genes in all three cells types. A ΔmgtC mutant of S. Typhimurium did not show decreased viability in Tetrahymena, but paradoxically, was egested at a higher cell density than the wild type. The expression of adiA and adiY, which are involved in arginine-dependent acid resistance, also was increased in the protozoan phagosome. A ΔadiAY mutant had lower viability after passage through Tetrahymena, and a higher proportion of S. Typhimurium wild-type cells within pellets remained viable after exposure to pH 3.4 as compared with uningested cells. Our results provide evidence that acid resistance has a role in the resistance of Salmonella to digestion by Tetrahymena and that passage through the protist confers physiological advantages relevant to its contamination cycle.

The role of fimV and the importance of its tandem repeat copy number in twitching motility, pigment production, and morphology in Legionella pneumophila

Twitching motility, a flagella-independent type of translocation of bacteria over moist surfaces, requires an array of proteins, including FimV. To investigate the role of this protein in twitching motility in Legionella pneumophila, we have generated a knockout mutant of fimV and characterized its phenotypic effects. In addition to a major reduction in twitching motility, deletion of the fimV gene caused a number of other phenotypic effects including decreased protective pigment formation, and it also affected cell morphology. Since fimV contains a variable number of tandem repeats, which can vary according to the origin of a given strain, we have examined the importance of this variability found within the coding region of this gene. By complementing the knockout strain with constructs containing a different number of this tandem repeat, we have been able to also show that repeat copy number is important in the functioning of this gene.

Molecular characterization of the Dot/Icm-translocated AnkH and AnkJ eukaryotic-like effectors of Legionella pneumophila

Although most Dot/Icm-translocated effectors of Legionella pneumophila are not required for intracellular proliferation, the eukaryotic-like ankyrin effectors, AnkH and AnkJ are required for intracellular proliferation. In this report, we show that the IcmSW chaperones are essential for translocation of AnkJ but not AnkH. The 10 C-terminal residues and the ANK domains of AnkH and AnkJ are required for translocation. Our data indicate that the two ANK domains of AnkH are critical domains required for the function of the effector in intracellular replication of L. pneumophila. The ankH and ankJ mutants are severely defective in intrapulmonary proliferation in mice. Expression of AnkH and AnkJ fusions within HEK293 cells show a punctuate distribution in the cytosol but no association with endocytic vesicles, the Golgi apparatus or the endoplasmic reticulum. Interestingly, the defect in intracellular proliferation of the ankH or ankJ mutants is rescued in HEK293 cells expressing the respective protein. We conclude that AnkH and AnkJ are effectors translocated by the Dot/Icm system by distinct mechanisms and modulate distinct cytosolic processes in the host cell.

Detection of bacterial endosymbionts in clinical acanthamoeba isolates

PURPOSE

To determine the presence of 4 clinically relevant bacterial endosymbionts in Acanthamoeba isolates obtained from patients with Acanthamoeba keratitis (AK) and the possible contribution of endosymbionts to the pathogenesis of AK.

DESIGN

Experimental study.

PARTICIPANTS

Acanthamoeba isolates (N = 37) recovered from the cornea and contact lens paraphernalia of 23 patients with culture-proven AK and 1 environmental isolate.

METHODS

Acanthamoeba isolates were evaluated for the presence of microbial endosymbionts belonging to the bacterial genera Legionella, Pseudomonas, Mycobacterium, and Chlamydia using molecular techniques (polymerase chain reaction and sequence analysis, fluorescence in situ hybridization) and transmission electron microscopy. Corneal toxicity and virulence of Acanthamoeba isolates with and without endosymbionts were compared using a cytopathic effect (CPE) assay on human corneal epithelial cells in vitro. Initial visual acuity, location and characteristics of the infiltrate, time to detection of the infection, and symptom duration at presentation were evaluated in all patients.

MAIN OUTCOME MEASURES

Prevalence and potential pathobiology of bacterial endosymbionts detected in Acanthamoeba isolates recovered from AK.

RESULTS

Twenty-two (59.4%) of the 38 cultures examined contained at least 1 bacterial endosymbiont. One isolate contained 2 endosymbionts, Legionella and Chlamydia, confirmed by fluorescence in situ hybridization. Corneal toxicity (CPE) was significantly higher for Acanthamoeba-hosting endosymbionts compared with isolates without endosymbionts (P<0.05). Corneal pathogenic endosymbionts such as Pseudomonas and Mycobacterium enhanced Acanthamoeba CPE significantly more than Legionella (P<0.05). In the presence of bacterial endosymbionts, there was a trend toward worse initial visual acuity (P>0.05), central location (P<0.05), absence of radial perineuritis (P<0.05), delayed time to detection (P>0.05), and longer symptom duration at presentation (P>0.05).

CONCLUSIONS

Most Acanthamoeba isolates responsible for AK harbor 1 or more bacterial endosymbionts. The presence of endosymbionts enhances the corneal pathogenicity of Acanthamoeba isolates and may impact detection time and clinical features of AK.

Transcriptional down-regulation and rRNA cleavage in Dictyostelium discoideum mitochondria during Legionella pneumophila infection

Bacterial pathogens employ a variety of survival strategies when they invade eukaryotic cells. The amoeba Dictyostelium discoideum is used as a model host to study the pathogenic mechanisms that Legionella pneumophila, the causative agent of Legionnaire's disease, uses to kill eukaryotic cells. Here we show that the infection of D. discoideum by L. pneumophila results in a decrease in mitochondrial messenger RNAs, beginning more than 8 hours prior to detectable host cell death. These changes can be mimicked by hydrogen peroxide treatment, but not by other cytotoxic agents. The mitochondrial large subunit ribosomal RNA (LSU rRNA) is also cleaved at three specific sites during the course of infection. Two LSU rRNA fragments appear first, followed by smaller fragments produced by additional cleavage events. The initial LSU rRNA cleavage site is predicted to be on the surface of the large subunit of the mitochondrial ribosome, while two secondary sites map to the predicted interface with the small subunit. No LSU rRNA cleavage was observed after exposure of D. discoideum to hydrogen peroxide, or other cytotoxic chemicals that kill cells in a variety of ways. Functional L. pneumophila type II and type IV secretion systems are required for the cleavage, establishing a correlation between the pathogenesis of L. pneumophila and D. discoideum LSU rRNA destruction. LSU rRNA cleavage was not observed in L. pneumophila infections of Acanthamoeba castellanii or human U937 cells, suggesting that L. pneumophila uses distinct mechanisms to interrupt metabolism in different hosts. Thus, L. pneumophila infection of D. discoideum results in dramatic decrease of mitochondrial RNAs, and in the specific cleavage of mitochondrial rRNA. The predicted location of the cleavage sites on the mitochondrial ribosome suggests that rRNA destruction is initiated by a specific sequence of events. These findings suggest that L. pneumophila specifically disrupts mitochondrial protein synthesis in D. discoideum during the course of infection.

Free-living freshwater amoebae differ in their susceptibility to the pathogenic bacterium Legionella pneumophila

Legionella pneumophila is known as a facultative intracellular parasite of free-living soil and freshwater amoebae, of which several species have been shown to support the growth of the pathogenic bacteria. We report for the first time the behaviour of two strains (c2c and Z503) of the amoeba Willaertia magna towards different strains of L. pneumophila serogroup 1 and compared it with Acanthamoeba castellanii and Hartmannella vermiformis, known to be L. pneumophila permissive. In contrast to the results seen with other amoebae, W. magna c2c inhibited the growth of one strain of Legionella (L. pneumophila, Paris), but not of others belonging to the same serogroup (L. pneumophila, Philadelphia and L. pneumophila, Lens). Also, the different L. pneumophila inhibited cell growth and induced cell death in A. castellanii, H. vermiformis and W. magna Z503 within 3-4 days while W. magna c2c strain remained unaffected even up to 7 days. Electron microscopy demonstrated that the formation of numerous replicative phagosomes observed within Acanthamoeba and Hartmannella is rarely seen in W. magna c2c cocultured with L. pneumophila. Moreover, the morphological differences were observed between L. pneumophila cultured either with Willaertia or other amoebae. These observations show that amoebae are not all equally permissive to L. pneumophila and highlight W. magna c2c as particularly resistant towards some strains of this bacterium.

A Dot/Icm-translocated ankyrin protein of Legionella pneumophila is required for intracellular proliferation within human macrophages and protozoa

The Dot/Icm type IV secretion system of Legionella pneumophila translocates numerous bacterial effectors into the host cell and is essential for bacterial proliferation within macrophages and protozoa. We have recently shown that L. pneumophila strain AA100/130b harbours 11 genes encoding eukaryotic-like ankyrin (Ank) proteins, a family of proteins involved in various essential eukaryotic cellular processes. In contrast to most Dot/Icm-exported substrates, which have little or no detectable role in intracellular proliferation, a mutation in ankB results in a severe growth defect in intracellular replication within human monocyte-derived macrophages (hMDMs), U937 macrophages and Acanthamoeba polyphaga. Single cell analyses of coinfections of hMDMs have shown that the intracellular growth defect of the ankB mutant is totally rescued in cis within communal phagosomes harbouring the wild type strain. Interestingly, distinct from dot/icm structural mutants, the ankB mutant is also rescued in trans within cells harbouring the wild type strain in a different phagosome, indicating that AnkB is a trans-acting secreted effector. Using adenylate cyclase fusions to AnkB, we show that AnkB is translocated into the host cell via the Dot/Icm secretion system in an IcmSW-dependent manner and that the last three C-terminal amino acid residues are essential for translocation. Distinct from the dot/icm structural mutants, the ankB mutant-containing phagosomes exclude late endosomal and lysosomal markers and their phagosomes are remodelled by the rough endoplasmic reticulum. We show that at the postexponential phase of growth, the LetA/S and PmrA/B Two Component Systems confer a positive regulation on expression of the ankB gene, whereas RpoS, LetE and RelA suppress its expression. Our data show that the eukaryotic-like AnkB protein is a Dot/Icm-exported effector that plays a major role in intracellular replication of L. pneumophila within macrophages and protozoa, and its expression is temporally controlled by regulators of the postexponential phase of growth.

The PmrA/PmrB two-component system of Legionella pneumophila is a global regulator required for intracellular replication within macrophages and protozoa

To examine the role of the PmrA/PmrB two-component system (TCS) of Legionella pneumophila in global gene regulation and in intracellular infection, we constructed pmrA and pmrB isogenic mutants by allelic exchange. Genome-wide microarray gene expression analyses of the pmrA and pmrB mutants at both the exponential and the postexponential phases have shown that the PmrA/PmrB TCS has a global effect on the expression of 279 genes classified into nine groups of genes encoding eukaryotic-like proteins, Dot/Icm apparatus and secreted effectors, type II-secreted proteins, regulators of the postexponential phase, stress response genes, flagellar biosynthesis genes, metabolic genes, and genes of unknown function. Forty-one genes were differentially regulated in the pmrA or pmrB mutant, suggesting a possible cross talk with other TCSs. The pmrB mutant is more sensitive to low pH than the pmrA mutant and the wild-type strain, suggesting that acidity may trigger this TCS. The pmrB mutant exhibits a significant defect in intracellular proliferation within human macrophages, Acanthamoeba polyphaga, and the ciliate Tetrahymena pyriformis. In contrast, the pmrA mutant is defective only in the ciliate. Despite the intracellular growth defect within human macrophages, phagosomes harboring the pmrB mutant exclude late endosomal and lysosomal markers and are remodeled by the rough endoplasmic reticulum. Similar to the dot/icm mutants, the intracellular growth defect of the pmrB mutant is totally rescued in cis within communal phagosomes harboring the wild-type strain. We conclude that the PmrA/PmrB TCS has a global effect on gene expression and is required for the intracellular proliferation of L. pneumophila within human macrophages and protozoa. Differences in gene regulation and intracellular growth phenotypes between the pmrA and pmrB mutant suggests a cross talk with other TCSs.

Microscopic and molecular studies of the diversity of free-living protozoa in meat-cutting plants

The diversity of free-living protozoa in five meat-cutting plants was determined. Light microscopy after enrichment culturing was combined with sequencing of PCR-amplified, denaturing gradient gel electrophoresis (DGGE)-separated 18S rRNA gene fragments, which was used as a fast screening method. The general results of the survey showed that a protozoan community of amoebae, ciliates, and flagellates was present in all of the plants. Protozoa were detected mainly in floor drains, in standing water on the floor, on soiled bars of cutting tables, on plastic pallets, and in out-of-use hot water knife sanitizers, but they were also detected on surfaces which come into direct contact with meat, such as conveyer belts, working surfaces of cutting tables, and needles of a meat tenderizer. After 7 days of incubation at refrigerator temperature, protozoa were detected in about one-half of the enrichment cultures. Based on microscopic observations, 61 morphospecies were found, and Bodo saltans, Bodo spp., Epistylis spp., Glaucoma scintillans, Petalomonas spp., Prodiscophrya collini, and Vannella sp. were the most frequently encountered identified organisms. Sequencing of DGGE bands resulted in identification of a total of 49 phylotypes, including representatives of the Amoebozoa, Chromalveolata, Excavata, Opisthokonta, and Rhizaria. Sequences of small heterotrophic flagellates were affiliated mainly with the Alveolata (Apicomplexa), Stramenopiles (Chrysophyceae), and Rhizaria (Cercozoa). This survey showed that there is high protozoan species richness in meat-cutting plants and that the species included species related to known hosts of food-borne pathogens.

Application of unstable Gfp variants to the kinetic study of Legionella pneumophila icm gene expression during infection

An unstable type of green fluorescent protein (Gfp) tagged with a C-terminal extension, which is a target for tail-specific protease, was used as a reporter gene in Legionella pneumophila. To analyse Gfp expression in legionellae, transcriptional fusions of unstable gfp with the Legionella-specific icm (intracellular multiplication) promoters (P(icmS), P(icmT) and P(icmQ)) were constructed. Infection studies using J774.1 macrophages as the host, and L. pneumophila strains carrying P(icmS)-gfp, P(icmT)-gfp and P(icmQ)-gfp fusions, indicated that the icmS, icmT and icmQ genes could be expressed intracellularly. Expression of icmS, icmT and icmQ genes in infected cells was examined by flow cytometry. Furthermore, fluorescent intracellular legionellae were detected directly by confocal microscopy. Real-time quantitative RT-PCR revealed the differences in the gene expression of icmS, and that of icmT and icmQ, during infection. Expression of icmS was high in the late stage of infection, while that of icmT and icmQ was high in the early phase only. We show that unstable gfp is a useful reporter gene whose expression in legionellae can be followed in real-time, and that it allows analysis of promoter activities in legionellae and monitoring of the infection process.

Role for the Ankyrin eukaryotic-like genes of Legionella pneumophila in parasitism of protozoan hosts and human macrophages

Legionella pneumophila is a ubiquitous organism in the aquatic environment where it is capable of invasion and intracellular proliferation within various protozoan species and is also capable of causing pneumonia in humans. In silico analysis showed that the three sequenced L. pneumophila genomes each contained a common multigene family of 11 ankyrin (ank) genes encoding proteins with approximately 30-35 amino acid tandem Ankyrin repeats that are involved in protein-protein interactions in eukaryotic cells. To examine whether the ank genes are involved in tropism of protozoan hosts, we have constructed isogenic mutants of L. pneumophila in ten of the ank genes. Among the mutants, the DeltaankH and DeltaankJ mutants exhibit significant defects in robust intracellular replication within A. polyphaga, Hartmanella vermiformis and Tetrahymena pyriformis. A similar defect is also exhibited in human macrophages. Most of the ank genes are upregulated by L. pneumophila upon growth transition into the post-exponential phase in vitro and within Acanthamoeba polyphaga, and this upregulation is mediated, at least in part, by RpoS. Single-cell analyses have shown that upon co-infection of the wild-type strain with the ankH or ankJ mutant, the replication defect of the mutant is rescued within communal phagosomes harbouring the wild-type strain, similar to dot/icm mutants. Therefore, at least two of the L. pneumophila eukaryotic-like Ank proteins play a role in intracellular replication of L. pneumophila within amoeba, ciliated protozoa and human macrophages. The Ank proteins may not be involved in host tropism in the aquatic environment. Many of the L. pneumophila eukaryotic-like ank genes are triggered upon growth transition into post-exponential phase in vitro as well as within A. polyphaga. Our data suggest a role for AnkH and AnkJ in modulation of phagosome biogenesis by L. pneumophila independent of evasion of lysosomal fusion and recruitment of the rough endoplasmic reticulum.

Colonization of Legionella species in hotel water systems in Turkey

BACKGROUND

The goal of this study was to evaluate the prevalence of Legionella species in hotel water distribution systems in Alanya, Turkey, which is an important tourism center.

METHODS

Water and swab samples were obtained from 52 Turkish hotels from August 2003 to September 2005. Water samples were collected in 100 mL sterile containers and were concentrated by membrane filters with a pore size of 0.45 microm. Heat treatment was used to eliminate other microorganisms from the samples, which were then spread on buffered charcoal yeast extract alpha agar plates and glycine, vancomycin, polymyxin, cycloheximide agar plates. Cysteine-dependent colonies were identified by latex agglutination.

RESULTS

In all, 491 water and swab samples were analyzed. The results of all samples were negative for Legionella in 16 (30.8%) hotels. Legionella species (92.5% of which were Legionella pneumophila) were detected in 93 (18.9%) of the samples. The most frequently isolated species were L pneumophila serogroups 6 (63.5%) and 1 (21.5%).

CONCLUSIONS

Legionella pneumophila serogroup 6 was the most common isolate detected in Turkish hotel water systems in our study. The result of Legionella urinary antigen tests, which are the diagnostic tests most often used to identify legionnaires' disease, may be negative in people infected with L pneumophila serogroup 6. We suggest that clinicians should apply the whole spectrum of laboratory methods for the detection of legionnaires' disease in patients with pneumonia of unknown origin and history of travel to Alanya, Turkey.

Phylogenetic study of legionella species in pristine and polluted aquatic samples from a tropical Atlantic forest ecosystem

Legionella species are ubiquitous bacteria in aquatic environments. To examine the effect of anthropogenic impacts and physicochemical characteristics on the Legionellaceae population, we collected water from two sites in the Itanhaém River system in the Atlantic Forest of Brazil. One sample was collected from an upstream pristine region, the other from a downstream estuarine region moderately affected by untreated domestic sewage. Cultures on a selective medium failed to isolate Legionella species. Culture-independent methods showed that water from the estuarine aquatic habitat contained DNA sequences homologous to the 16S ribosomal DNA gene of Legionella pneumophila and non-pneumophila species. In pristine water, only two sequences related to L. pneumophila were detected. The results suggest that salinity and anthropogenic factors, such as wastewater discharge, favor a diversity of Legionella species, whereas pristine freshwater selects for Legionella pneumophila.

Do contaminated dental unit waterlines pose a risk of infection?

OBJECTIVES

To review the evidence that the dental unit waterlines are a source of occupational and healthcare acquired infection in the dental surgery.

DATA

Transmission of infection from contaminated dental unit waterlines (DUWL) is by aerosol droplet inhalation or rarely imbibing or wound contamination in susceptible individuals. Most of the organisms isolated from DUWL are of low pathogenicity. However, data from a small number of studies described infection or colonisation in susceptible hosts with Legionella spp., Pseudomonas spp. and environmental mycobacteria isolated from DUWL. The reported prevalence of legionellae in DUWL varies widely from 0 to 68%. The risk from prolonged occupational exposure to legionellae has been evaluated. Earlier studies measuring surrogate evidence of exposure to legionellae in dental personnel found a significant increase in legionella antibody levels but in recent multicentre studies undertaken in primary dental care legionellae were isolated at very low rate and the corresponding serological titres were not above background levels. Whereas, a case of fatal Legionellosis in a dental surgeon concluded that the DUWL was the likely source of the infection. The dominant species isolated from dental unit waterlines (DUWL) are Gram-negative bacteria, which are a potent source of cell wall endotoxin. A consequence of indoor endotoxin exposure is the triggering or exacerbation of asthma. Data from a single large practice-based cross-sectional study reported a temporal association between occupational exposure to contaminated DUWL with aerobic counts of >200cfu/mL at 37 degrees C and development of asthma in the sub-group of dentists in whom asthma arose following the commencement of dental training.

SOURCES

Medline 1966 to February 2007 was used to identify studies for this paper.

STUDY SELECTION

Design criteria included randomised control trials, cohort, and observational studies in English.

CONCLUSIONS

Although the number of published cases of infection or respiratory symptoms resulting from exposure to water from contaminated DUWL is limited, there is a medico-legal requirement to comply with potable water standards and to conform to public perceptions on water safety.

Rapid escape of the dot/icm mutants of Legionella pneumophila into the cytosol of mammalian and protozoan cells

The Legionella pneumophila-containing phagosome evades endocytic fusion and intercepts endoplasmic reticulum (ER)-to-Golgi vesicle traffic, which is believed to be mediated by the Dot/Icm type IV secretion system. Although phagosomes harboring dot/icm mutants are thought to mature through the endosomal-lysosomal pathway, colocalization studies with lysosomal markers have reported contradictory results. In addition, phagosomes harboring the dot/icm mutants do not interact with endocytosed materials, which is inconsistent with maturation of the phagosomes in the endosomal-lysosomal pathway. Using multiple strategies, we show that the dot/icm mutants defective in the Dot/Icm structural apparatus are unable to maintain the integrity of their phagosomes and escape into the cytoplasm within minutes of entry into various mammalian and protozoan cells in a process independent of the type II secretion system. In contrast, mutants defective in cytoplasmic chaperones of Dot/Icm effectors and rpoS, letA/S, and letE regulatory mutants are all localized within intact phagosomes. Importantly, non-dot/icm L. pneumophila mutants whose phagosomes acquire late endosomal-lysosomal markers are all located within intact phagosomes. Using high-resolution electron microscopy, we show that phagosomes harboring the dot/icm transporter mutants do not fuse to lysosomes but are free in the cytoplasm. Inhibition of ER-to-Golgi vesicle traffic by brefeldin A does not affect the integrity of the phagosomes harboring the parental strain of L. pneumophila. We conclude that the Dot/Icm transporter is involved in maintaining the integrity of the L. pneumophila phagosome, independent of interception of ER-to-Golgi vesicle traffic, which is a novel function of type IV secretion systems.

Cryptococcus neoformans mates on pigeon guano: implications for the realized ecological niche and globalization

The ecological niche that a species can occupy is determined by its resource requirements and the physical conditions necessary for survival. The niche to which an organism is most highly adapted is the realized niche, whereas the complete range of habitats that an organism can occupy represents the fundamental niche. The growth and development of Cryptococcus neoformans and Cryptococcus gattii on pigeon guano were examined to determine whether these two species occupy the same or different ecological niches. C. neoformans is a cosmopolitan pathogenic yeast that infects predominantly immunocompromised individuals, exists in two varieties (grubii [serotype A] and neoformans [serotype D]), and is commonly isolated from pigeon guano worldwide. By contrast, C. gattii often infects immunocompetent individuals and is associated with geographically restricted environments, most notably, eucalyptus trees. Pigeon guano supported the growth of both species, and a brown pigment related to melanin, a key virulence factor, was produced. C. neoformans exhibited prolific mating on pigeon guano, whereas C. gattii did not. The observations that C. neoformans completes the life cycle on pigeon guano but that C. gattii does not indicates that pigeon guano could represent the realized ecological niche for C. neoformans. Because C. gattii grows on pigeon guano but cannot sexually reproduce, pigeon guano represents a fundamental but not a realized niche for C. gattii. Based on these studies, we hypothesize that an ancestral Cryptococcus strain gained the ability to sexually reproduce in pigeon guano and then swept the globe.

A comparison of the growth and starvation responses of Acanthamoeba castellanii and Hartmannella vermiformis in the presence of suspended and attached Escherichia coli K12

The growth and starvation responses of Acanthamoeba castellanii and Hartmannella vermiformis were investigated in the presence and absence of Escherichia coli on an agar surface or within shaken suspensions. The amoebae perceived all the suspended systems to be unfavourable for growth, despite being challenged with high levels of prey, and as a consequence they exhibited a starvation response. However, the response differed between species, with A. castellanii producing characteristic cysts and H. vermiformis producing round bodies. These amoebic forms were reactivated into feeding trophozoites in the presence of bacterial aggregates, which formed in the suspended systems after 68 h of incubation. In contrast, both species of amoebae grew well in the presence of attached E. coli at a concentration of 1 x 10(6) cells cm(-2) of agar and yielded specific growth rates of c. 0.04 h(-1). Starvation responses were induced at the end of the growth phase, and these were equivalent to those recorded in the suspended systems. We conclude that, when suspended, amoebae in the 'floating form' cannot feed effectively on suspended prey, and hence the starvation response is initiated. Thus the majority of amoebic feeding is via trophozoite grazing of attached bacterial prey.

Solar disinfection of poliovirus and Acanthamoeba polyphaga cysts in water – a laboratory study using simulated sunlight

AIMS

To determine the efficacy of solar disinfection (SODIS) in disinfecting water contaminated with poliovirus and Acanthamoeba polyphaga cysts.

METHODS AND RESULTS

Organisms were subjected to a simulated global solar irradiance of 850 Wm(-2) in water temperatures between 25 and 55 degrees C. SODIS at 25 degrees C totally inactivated poliovirus after 6-h exposure (reduction of 4.4 log units). No SODIS-induced reduction in A. polyphaga cyst viability was observed for sample temperatures below 45 degrees C. Total cyst inactivation was only observed after 6-h SODIS exposure at 50 degrees C (3.6 log unit reduction) and after 4 h at 55 degrees C (3.3 log unit reduction).

CONCLUSIONS

SODIS is an effective means of disinfecting water contaminated with poliovirus and A. polyphaga cysts, provided water temperatures of 50-55 degrees C are attained in the latter case.

SIGNIFICANCE AND IMPACT OF THE STUDY

This research presents the first SODIS inactivation curve for poliovirus and provides further evidence that batch SODIS provides effective protection against waterborne protozoan cysts.

Interaction between Mycobacterium avium subsp. paratuberculosis and environmental protozoa

Background

Interactions between Mycobacterium avium subsp. paratuberculosis (Map) and free-living protozoa in water are likely to occur in nature. The potential impact of ingestion of Map by two naturally occurring Acanthamoeba spp. on this pathogen's survival and chlorine resistance was investigated.

Results

Between 4.6 and 9.1% of spiked populations of three Map strains (NCTC 8578, B2 and ATCC 19698), which had been added at a multiplicity of infection of 10:1, were ingested by Acanthamoeba castellanii CCAP 1501/1B and A. polyphaga CCAP 1501/3B during co-culture for 3 h at 25°C. Map cells were observed to be present within the vacuoles of the amoebae by acid-fast staining. During extended co-culture of Map NCTC 8578 at 25°C for 24 d with both A. castellanii and A. polyphaga Map numbers did not change significantly during the first 7 days of incubation, however a 1–1.5 log₁₀ increase in Map numbers was observed between days 7 and 24 within both Acanthamoeba spp. Ingested Map cells were shown to be more resistant to chlorine inactivation than free Map. Exposure to 2 μg/ml chlorine for 30 min resulted in a log₁₀ reduction of 0.94 in ingested Map but a log₁₀ reduction of 1.73 in free Map (p < 0.001).

Conclusion

This study demonstrated that ingestion of Map by and survival and multiplication of Map within Acanthamoeba spp. is possible, and that Map cells ingested by amoebae are more resistant to inactivation by chlorine than free Map cells. These findings have implications with respect to the efficacy of chlorination applied to Map infected surface waters.

La légionellose

Although one does not find the origin of the contamination in the human half of the cases of legionellosis, one knows that this disease is the consequence of the almost obligatory contamination of the networks of installations of hot water by Legionella pneumophila, and the inhalation by the man of infected droplets. Pathology generally consists of a relatively serious pneumopathy. The control of the level of contamination of the various producing hydrous installations of aerosols is imperative to avoid the serious medical consequences, which cannot be prevented by an action on the human target. The majority of the currently identified tanks are the air and cool towers and the distribution networks of hot water. The taking into account of this risk in the hospitals or thermal led to the implementation of many measurements of disinfection and control, which start to show a certain effectiveness on which has occurred of new cases in these establishments, today in clear reduction.

Detection of Legionella spp. by fluorescent in situ hybridization in dental unit waterlines

AIMS

To confirm the presence of viable Legionella spp. in dental unit waterlines (DUWL) using fluorescent in situ hybridization (FISH) and compare this method with culture approach and also to validate the utility of an enrichment to increase FISH sensitivity.

METHODS AND RESULTS

Water samples from 40 dental units were analysed. Three different techniques for detecting Legionella spp. were compared: (i) culture approach, (ii) direct FISH and (iii) FISH with a previous R2A medium enrichment (R2A/FISH). The FISH detection was confirmed by PCR. The use of the direct FISH does not improve significantly the detection of legionellae when compared with the culture. On the contrary, when R2A/FISH was performed, sensitivity was, respectively, two- and threefold higher than that with the direct FISH and culture approach. Using R2A/FISH, 63% of water samples analysed showed a contamination by legionellae.

CONCLUSIONS

Legionellae detection by direct FISH and R2A/FISH in dental unit water is possible but is more rapid and more sensitive (R2A/FISH) than the culture approach.

SIGNIFICANCE AND IMPACT OF THE STUDY

R2A/FISH showed that several pathogens present in DUWL are viable but may not be culturable. Unlike PCR, R2A/FISH is designed to detect only metabolically active cells and therefore provides more pertinent information on infectious risk.

Pathogenese, Diagnostik und Therapie der Legionella-Infektion

Legionella species are ubiquitous in aquatic environments. About 50 years ago they entered the engineered (technical) environment, i.e. warm water systems with zones of stagnation. Since that time they represent a hygienic problem. After transmission to humans via aerosols legionellae might cause Legionella pneumonia (legionnaires' disease) or influenza-like respiratory infections (Pontiac fever). Epidemiological data suggest that Legionella strains might differ substantially in their virulence properties. Although the molecular basis is not understood L. pneumophila serogroup 1 especially MAb 3/1-positive strains cause the majority of infections. The main virulence feature is the ability to multiply intracellularly. After uptake into macrophages legionellae multiply in a specialized vacuole and finally lyse their host cells. Several bacterial factors like surface components, secretion systems and iron uptake systems are involved in this process. Since the clinical picture of Legionella pneumonia does not allow differentiation from pneumoniae caused by other pathogens, microbiological diagnostic methods are needed to establish the diagnosis. Cultivation of legionellae from clinical specimens, detection of antigens and DNA in patients' samples and detection of antibodies in serum samples are suitable methods. However, none of the diagnostic tests presently available offers the desired quality with respect to sensitivity and specificity. Therefore, the standard technique is to use several diagnostic tests in parallel. Advantages and disadvantages of the diagnostic procedures are discussed. Therapeutic options for Legionella infections are newer macrolides like azithromycin and chinolones (ciprofloxacin, levofloxacin and moxifloxacin).

Multiplication intra-amibienne de Legionella pneumophila et rôle potentiel des amibes dans la transmission de la légionellose

Legionnaires' disease is one of the major infectious risks related to hospital water systems. It is commonly accepted, that the disease is transmitted to man mostly by inhalation of water aerosols contaminated by Legionella pneumophila. The ability of L. pneumophila to multiply intracellularly within some amoebae better explains the ecology, the pathogenicity, and the virulence of this bacterium against human alveolar macrophages. The presence of these amoebae in water systems located where cases of Legionnaire's disease broke out, partly explains the difficulty in eradicating Legionella. Some studies also show that amoebae can play a major role in the transmission of the disease to man. Some other studies point out that inhaled amoebae could be involved in the pathogenesis of Legionnaire's disease. Future strategies to prevent the transmission of Legionella will probably have to include efficient treatments against amoebae.

Acute Pneumonia and Importance of Atypical Bacteria

The term and concept of atypical pneumonia appeared in the 1940s following observations of penicillin-resistant pneumonia [1]. Despite the identification of a large number of microorganisms, the challenge of isolating so-called ‘atypical’ bacteria is the principal cause of failure of the etiologic diagnosis of pneumonia. These pathogenic agents in the tracheobronchial tree include a large variety of bacteria, viruses and even protozoa. Among atypical bacteria, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella pneumoniae, Bordetella pertussis, and Coxiella burnetii are the most widespread. Numerous other bacteria are emerging pathogenic species whose virulence is currently being evaluated. Clinical examination only provides a diagnostic orientation in a restricted number of cases. The availability of rapid and specific microbiologic examination improves the diagnostic performance for this type of pneumonia (Table 1) [2]. Since most of these bacteria are intracellular, diagnosis is based principally on serology.

Characterization of Acanthamoeba–microsphere association by multiparameter flow cytometry and confocal microscopy

BACKGROUND

Acanthamoebae, in common with other protozoa, readily endocytose particulate material, which in turn may lead to the spread of infectious disease.

METHODS

Evaluation and quantification of plain and carboxylate FITC-microsphere association with acanthamoebal trophzoites was undertaken using a combination of flow cytometry and confocal microscopy. Trophozoites from strains and species of Acanthamoeba were exposed to plain and carboxylate FITC-microspheres. Microsphere size and aspects such as trophozoite starvation, maturity, and exposure to metabolic inhibitors were assessed.

RESULTS

All species and strains of Acanthamoeba readily endocytosed plain and carboxylate microspheres. Starving trophozoites significantly increased binding and potential ingestion of microspheres, whereas trophozoites of increasing maturity lost such abilities. Trophozoites showed a significant preference for 2.0- and 3.0-microm-diameter microspheres when compared with other sizes, which in turn could occupy much of the cytoplasm. The physiological inhibitors sodium azide, 2,4-dinitrophenol, and cytochalasin B reduced microsphere association with trophozoites; however, some microspheres still bound and associated with trophozoites after inhibitor exposure, a manifestation of both active and inactive agent involvement in microsphere endocytosis.

CONCLUSIONS

Even though the origins of microsphere binding by acanthamoebal trophozoite remains shrouded, the combination of flow cytometry and confocal microscopy supported synergistic quantification and qualification of trophozoite-microsphere endocytosis.

Fitness of human enteric pathogens on plants and implications for food safety

The continuous rise in the number of outbreaks of foodborne illness linked to fresh fruit and vegetables challenges the notion that enteric pathogens are defined mostly by their ability to colonize the intestinal habitat. This review describes the epidemiology of produce-associated outbreaks of foodborne disease and presents recently acquired knowledge about the behavior of enteric pathogens on plants, with an emphasis on Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes. The growth and survival of enteric pathogens on plants are discussed in the light of knowledge and concepts in plant microbial ecology, including epiphytic fitness, the physicochemical nature of plant surfaces, biofilm formation, and microbe-microbe and plant-microbe interactions. Information regarding the various stresses that affect the survival of enteric pathogens and the molecular events that underlie their interactions in the plant environment provides a good foundation for assessing their role in the infectious dose of the pathogens when contaminated fresh produce is the vehicle of illness.

Acute Pneumonia and Importance of Atypical Bacteria

The diagnosis of pulmonary infection caused by Mycoplasma and Chlamydia pneumoniae, Coxiella burnetii, and different species of Legionella, is often long and challenging although they are the major etiologic agents of pneumonia. For this reason, the treatment of these infections remains probabilistic. Advances in new diagnostic techniques, such as PCR sequencing, show the relative predominance of atypical organisms and serves to identify emerging pathogenic agents. Moreover, these techniques should clarify the correlation between common and atypical pathogens.

Legionella contamination in hot water of Italian hotels

A cross-sectional multicenter survey of Italian hotels was conducted to investigate Legionella spp. contamination of hot water. Chemical parameters (hardness, free chlorine concentration, and trace element concentrations), water systems, and building characteristics were evaluated to study risk factors for colonization. The hot water systems of Italian hotels were strongly colonized by Legionella; 75% of the buildings examined and 60% of the water samples were contaminated, mainly at levels of > or =10(3) CFU liter(-1), and Legionella pneumophila was the most frequently isolated species (87%). L. pneumophila serogroup 1 was isolated from 45.8% of the contaminated sites and from 32.5% of the hotels examined. When a multivariate logistic model was used, only hotel age was associated with contamination, but the risk factors differed depending on the contaminating species and serogroup. Soft water with higher chlorine levels and higher temperatures were associated with L. pneumophila serogroup 1 colonization, whereas the opposite was observed for serogroups 2 to 14. In conclusion, Italian hotels, particularly those located in old buildings, represent a major source of risk for Legionnaires' disease due to the high frequency of Legionella contamination, high germ concentration, and major L. pneumophila serogroup 1 colonization. The possible role of chlorine in favoring the survival of Legionella species is discussed.