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At least 19 recordsLinked to original sources
PubMed2000

Neochlamydia hartmannellae gen. nov., sp. nov. (Parachlamydiaceae), an endoparasite of the amoeba Hartmannella vermiformis.

Free-living amoebae are increasingly being recognized to serve as vehicles of dispersal for various bacterial human pathogens and as hosts for a variety of obligate bacterial endocytobionts. Several Chlamydia-like Acanthamoeba endocytobionts constituting the recently proposed family Parachlamydiaceae are of special interest as potential human pathogens. In this study coccoid bacterial endocytobionts of a Hartmannella vermiformis isolate were analysed. Infection of H. vermiformis with these bacteria resulted in prevention of cyst formation and subsequent host-cell lysis. Transfection experiments demonstrated that the parasites were not capable of propagating within other closely related free-living amoebae but were able to infect the distantly related species Dictyostelium discoideum. Electron microscopy of the parasites revealed typical morphological characteristics of the Chlamydiales, including the existence of a Chlamydia-like life-cycle, but indicated that these endocytobionts, in contrast to Chlamydia species, do not reside within a vacuole. Comparative 16S rRNA sequence analysis showed that the endocytobiont of H. vermiformis, classified as Neochlamydia hartmannellae gen. nov., sp. nov., is affiliated to the family Parachlamydiaceae. Confocal laser scanning microscopy in combination with fluorescence in situ hybridization using rRNA-targeted oligonucleotide probes confirmed the intracellular localization of the parasites and demonstrated the absence of other bacterial species within the Hartmannella host. These findings extend our knowledge of the phylogenetic diversity of the Parachlamydiaceae and demonstrate for the first time that these endocytobionts can naturally develop within amoebae of the genus Hartmannella.

Animals↗
PubMed1995

Bacteriolytic activities of the free-living soil amoebae, Acanthamoeba castellanii, Acanthamoeba polyphaga and Hartmannella vermiformis.

Bacteriolytic activities of axenically grown free-living soil amoebae Acanthamoeba castellanii, Acanthamoeba polyphaga and Hartmannella vermiformis towards various Gram-positive and Gram-negative bacteria were determined. A spectrophotometric assay revealed that the specific bacteriolytic activities of both Acanthamoeba species were higher as those of the three Hartmannella strains. Bacillus megaterium, Bacillus subtilis, Chromatium vinosum, Micrococcus luteus and Pseudomonas fluorescens were more easily lysed than the other bacteria tested. Agrobacterium tumefaciens, Klebsiella aerogenes and Serratia marcescens were hardly affected at all by the amoebal bacteriolytic activities. Among the Gram-negative bacteria we observed differences in lysis sensitivity while the Gram-positive bacteria tested were sensitive to lysis. Isoelectric focusing (IEF) gel-electrophoresis in the pH range 3-10 was performed to separate the bacteriolytic isoenzymes of amoebae. Bacteriolytic patterns were shown by using an activity assay in which lysis bands were formed in the agar/bacteria gel-overlay. The activity assay revealed remarkable differences in typical banding patterns for bacteriolytic activities among amoebae. Distinct differences between typical pI points of bacteriolytic activities in Acanthamoeba and Hartmannella were shown. Bacteriolytic activities of Hartmannella were more pronounced and observed in the isoelectric points (pI) range of 4.0-9.3 while for Acanthamoeba the range was pI 4.5-8.9.

Acanthamoeba↗
PubMed1993

Impact of Chlorine and Heat on the Survival of Hartmannella vermiformis and Subsequent Growth of Legionella pneumophila.

Hartmannella vermiformis, a common amoebal inhabitant of potable-water systems, supports intracellular multiplication of Legionella pneumophila and is probably important in the transportation and amplification of legionellae within these systems. To provide a practical guide for decontamination of potable-water systems, we assessed the chlorine and heat resistance of H. vermiformis. H. vermiformis cysts and trophozoites were treated independently with chlorine at concentrations of 2.0 to 10.0 ppm for 30 min and then cocultured with L. pneumophila. Both cysts and trophozoites were sensitive to concentrations between 2.0 and 4.0 ppm and above (trophozoites somewhat more so than cysts), and 10.0 ppm was lethal to both forms. Hartmannellae treated with chlorine up to a concentration of 4.0 ppm supported the growth of legionellae. To determine whether heat would be an effective addendum to chlorine treatment of amoebae, hartmannellae were subjected to temperatures of 55 and 60 degrees C for 30 min and alternatively to 50 degrees C followed by treatment with chlorine at a concentration of 2 ppm. Fewer than 0.05% of the amoebae survived treatment at 55 degrees C, and there were no survivors at 60 degrees C. Pretreatment at 50 degrees C appeared to make hartmannella cysts more susceptible to chlorine but did not further reduce the concentration of trophozoites.

Journal Article↗
PubMed1998

Acanthamoeba keratitis with symbiosis of Hartmannella ameba.

PURPOSE: To report a case of severe amebic keratitis in which both Hartmannella and Acanthamoeba were isolated simultaneously from the same lesion. METHOD: Case report. The deep corneal lesion was scraped for cytopathology and isolation of the pathogens. We tested the in vitro sensitivities of the pathogens to several drugs. RESULTS: Cultures of the corneal scrapings and of the solution in the patient's contact lens storage case were positive for Acanthamoeba E9 cysts and trophozoites. Hartmannella ameba coexisted with Acanthamoeba in the cornea. When tested in vitro, Acanthamoeba trophozoites were sensitive to both miconazole nitrate and natamycin, while cysts were sensitive only to natamycin. However, the patient did not respond to these antiamebic drugs. CONCLUSIONS: This case suggests that Acanthamoeba is not the only origin of amebic keratitis. Hartmannella may also cause severe drug-resistant keratitis.

Acanthamoeba↗
PubMed1996

Amebic keratitis in a wearer of disposable contact lenses due to a mixed Vahlkampfia and Hartmannella infection.

PURPOSE: To support the hypothesis that Acanthamoeba is not a unique cause of amebic keratitis, we report a case of amebic keratitis in which viable Acanthamoeba could not be isolated from corneal tissue. Vahlkampfia and Hartmannella, two other genera of free-living ameba, were isolated, however, using prolonged culture. METHODS: A 24-year-old wearer of soft contact lenses had keratitis. Extensive histologic and microbiologic investigations were performed on corneal scrape, biopsy, and keratoplasty tissue. Contact lenses, storage case, and the home water supply, where contact lens hygiene was practiced, were examined for the presence of micro-organisms. RESULTS: No viruses, pathogenic bacteria, or fungi were detected from corneal tissue samples. Amebae were observed using light and electron microscopy, but these could not be unequivocally classified using immunocytochemical staining. Viable Vahlkampfia and Hartmannella, but no Acanthamoeba, were isolated from the corneal biopsy sample. Indirect immunofluorescence with a range of polyclonal rabbit antisera raised against axenically cultivated stains of the three amebal genera was unhelpful because of cross-reactivity. A diverse range of micro-organisms was present within the storage case, including the three amebal species. Amebic cysts also were associated with the contact lens. CONCLUSION: A mixed non-Acanthamoeba amebic keratitis has been identified in a wearer of soft contact lenses where lack of storage case hygiene provided the opportunity for the free-living protozoa Vahlkampfia and Hartmannella to be introduced to the ocular surface. When Acanthamoeba-like keratitis occurs, but where Acanthamoeba cannot be isolated using conventional laboratory culture methods, alternate means should be used to identify other amebae that may be present. Polyclonal immunofluorescent antibody staining was unreliable for generic identification of pathogenic free-living amebae in corneal tissue.

Adult↗
PubMed1997

Differences in isoenzyme patterns of axenically and monoxenically grown Acanthamoeba and Hartmannella.

Axenically and monoxenically grown Acanthamoeba castellanii, Acanthamoeba polyphaga and different isolates of Hartmannella vermiformis strains were examined by polyacrylamide isoelectric focusing in the pH range 3-10. Isoenzyme patterns of acid phosphatase (AP), propionyl esterase (PE), malate dehydrogenase (MDH), alcohol dehydrogenase (ADH), glucose phosphate isomerase (GPI) and phosphoglucomutase (PGM) were compared. Zymograms were used to reveal differences in typical isoenzyme patterns between axenically and monoxenically grown amoebae and to compare axenically grown A. castellanii, A. polyphaga and H. vermiformis. Comparison of zymograms for AP, PE and MDH between axenically grown Acanthamoeba and Hartmannella strains revealed different isoenzyme patterns. Acanthamoeba showed strong bands for ADH and extremely weak bands for GPI and PGM, while Hartmannella lacked ADH but possessed bands for GPI and PGM. Comparison of zymograms from axenically and monoxenically grown amoebae revealed a lower intensity and even lack of typical isoenzyme bands in lysates from monoxenic cultures. The observed changes in typical isoenzyme patterns induced by the bacterial substrate can influence the correct isoenzymatic typing of different strains in clinical and phylogenetic studies.

Acanthamoeba↗
PubMed2003

Cytopathogenicity of acanthamoeba, vahlkampfia and hartmannella: quantative & qualitative in vitro studies on keratocytes.

OBJECTIVES: To compare the cytopathogenicity of Vahlkampfia and Hartmannella clinical isolates with a type culture of Acanthamoeba castellanii. METHODS: The cytopathic effect produced during 24 h co-incubation with cultured keratocytes was assessed at set time intervals. Formal quantative studies involved image analysis of the area of cells remaining after 6 h. The mechanism of cytopathogenicity was elucidated using time-lapse video, light and scanning electron microscopy. The ability to produce cell damage in the absence of physical contact was studied using the transwell apparatus. The role of apotosis was also investigated. RESULTS: All three isolates produced near destruction of the keratocyte monolayer within 24 h, although initial cell destruction was more rapid with Acanthamoeba. For all three genera, the mechanism of cell damage involved physical attack and trogocytosis: cytopathic products were also implicated as cell damage was produced in the absence of physical contact, but apoptosis was not demonstrated. CONCLUSIONS: While the results do not prove that Vahlkampfia and Hartmannella are pathogens, they provide important evidence supporting the thesis that they cause keratitis by demonstrating that their ability to produce a cytopathic effect on keratocytes in vitro is similar in magnitude and mechanism to that of the known pathogen Acanthamoeba castellanii. The mechanisms by which small free-living amoebae produce cell damage is poorly understood. The ability of genera of amoebae other than Acanthamoeba to produce corneal infection remains controversial. In this study, the cytopathogenicity of Vahlkampfia and Hartmannella isolated from a case human keratitis are compared both quantitatively and qualitatively with that to the known pathogen Acanthamoeba castellanii. The results suggest that representatives of each of the 3 genera produce a similar degree of cytopathic effect on keratocytes after 24h of co-incubation and that a combination of physical and chemical factors are responsible.

Acanthamoeba↗
PubMed1994

Sequence variations in small-subunit ribosomal RNAs of Hartmannella vermiformis and their phylogenetic implications.

Evidence of associations between free-living amoebas and human disease has been increasing in recent years. Knowledge about phylogenetic relationships that may be important for the understanding of pathogenicity in the genera involved is very limited at present. Consequently, we have begun to study these relationships and report here on the phylogeny of Hartmannella vermiformis, a free-living amoeba that can harbor the etiologic agent of Legionnaires' disease. Our analysis is based on studies of small-subunit ribosomal RNA genes (srDNA). Nucleotide sequences were determined for nuclear srDNA from three strains of H. vermiformis isolated from the United Kingdom, Germany, and the United States. These sequences then were compared with a sequence previously obtained for a North American isolate by J. H. Gunderson and M. L. Sogin. The four genes are 1,840 bp long, with an average GC content of 49.6%. Sequence differences among the strains range are 0.38%-0.76%. Variation occurs at 19 positions and includes 2 single-base indels plus 14 monotypic and 3 ditypic single-base substitutions. Variation is limited to eight helix/loop structures according to a current model for srRNA secondary structure. Parsimony, distance, and bootstrap analyses used to examine phylogenetic relationships between the srDNA sequences of H. vermiformis and other eukaryotes indicated that Hartmannella sequences were most closely related to those of Acanthamoeba and the alga Cryptomonas. All ditypic sites were consistent with a separation between European and North American strains of Hartmannella, but results of other tests of this relationship were statistically inconclusive.

Acanthamoeba↗
PubMed2001

Development of 18S rRNA-targeted oligonucleotide probes for specific detection of Hartmannella and Naegleria in Legionella-positive environmental samples.

Aquatic protozoa are natural hosts of the human pathogen Legionella pneumophila. The fluorescence labeled 16S rRNA-targeted oligonucleotide probe LEGPNE1 has recently been shown to specifically detect extracellular legionellae as well as intracellular legionellae parasitizing protozoa. In this study we designed oligonucleotide probes which are complementary to distinct regions of the 18S rRNA of the Legionella host organisms of the genera Hartmannella and Naegleria. The specificity of the probes, HART498 and NAEG1088, was tested by in situ hybridization of various laboratory reference strains. In order to evaluate the fluorescent probes for environmental studies three selected Legionella-positive cold water habitats were examined for the presence of these protozoa. Traditional culture methods followed by morphological identification revealed an almost consistent presence of Naegleria spp. in cold water habitats. Other protozoa species including Acanthamoeba spp., Echinamoeba spp., Hartmannella spp., Platyamoeba placida, Saccamoeba spp., Thecamoeba quadrilineata, and Vexillifera spp. were found sporadically. Concomitant analysis of the pH, conductivity and temperature of the water samples revealed no preference of Legionella or the respective protozoa for certain environmental conditions. The specificity of the newly designed 18S rRNA probes demonstrates that they are valuable and rapid tools for the identification of culturable environmental protozoa.

Animals↗
PubMedDate not supplied

Characterization of an axenic strain of Hartmannella vermiformis obtained from an investigation of nosocomial legionellosis.

A free-living amoeba identified as Hartmannella vermiformis was isolated from a water sample obtained during an investigation of nosocomial legionellosis. Hartmannella vermiformis is known to support the intracellular multiplication of Legionella pneumophila. This strain of H. vermiformis, designated CDC-19, was cloned and established in axenic culture to develop a model for the study of the pathogenicity of legionellae. Isoenzyme patterns of axenically-cultivated strain CDC-19 were compared with two strains of H. vermiformis derived from the type strain, one axenic (ATCC 50236) and the other grown in the presence of bacteria (ATCC 30966). Enzyme patterns suggested that all three strains are assignable to the species H. vermiformis. Axenic H. vermiformis strain CDC-19 has been deposited with the American Type Culture Collection (ATCC 50237) and should prove useful in the study of protozoan-bacterial interaction.

Animals↗
PubMed2006

Quantitative detection of the free-living amoeba Hartmannella vermiformis in surface water by using real-time PCR.

A real-time PCR-based method targeting the 18S rRNA gene was developed for the quantitative detection of Hartmannella vermiformis, a free-living amoeba which is a potential host for Legionella pneumophila in warm water systems and cooling towers. The detection specificity was validated using genomic DNA of the closely related amoeba Hartmannella abertawensis as a negative control and sequence analysis of amplified products from environmental samples. Real-time PCR detection of serially diluted DNA extracted from H. vermiformis was linear for microscopic cell counts between 1.14 x 10(-1) and 1.14 x 10(4) cells per PCR. The genome of H. vermiformis harbors multiple copies of the 18S rRNA gene, and an average number (with standard error) of 1,330 +/- 127 copies per cell was derived from real-time PCR calibration curves for cell suspensions and plasmid DNA. No significant differences were observed between the 18S rRNA gene copy numbers for trophozoites and cysts of strain ATCC 50237 or between the copy numbers for this strain and strain KWR-1. The developed method was applied to water samples (200 ml) collected from a variety of lakes and rivers serving as sources for drinking water production in The Netherlands. Detectable populations were found in 21 of the 28 samples, with concentrations ranging from 5 to 75 cells/liter. A high degree of similarity (> or =98%) was observed between sequences of clones originating from the different surface waters and between these clones and the reference strains. Hence, H. vermiformis, which is highly similar to strains serving as hosts for L. pneumophila, is a common component of the microbial community in fresh surface water.

Animals↗
PubMed2004

Detection of Hartmannella sp, a free-living amoeba from Sungai Setiu, Terengganu.

Hartmannella sp is one of the free-living amoebae that have the ability to infect animal tissues because it has been found in human's nasal mucosa, dog's bronchial and turkey's intestine. Treatment for diseases inflicted by free-living amoebae is difficult because most of them infect and damage the host's tissues, so preventive measures are better to take rather than to cure the diseases. In this study, water taken from several stations namely Kampung Padang, Kampung Besut, Ibu Bekalan Setiu, Kampung Tasik, Kampung Guntung, Kampung Nyatoh, Kampung Penarik and Kampung Mangkok) along Sungai Setiu, Terengganu was examined for the presence of Hartmannella sp. The results of this study indicated that only Ibu Bekalan Setiu station was found positive to have the amoeba. Detail results on the water quality and nutrient contents measured in relation to the distribution of the amoeba at Ibu Bekalan Setiu station are presented and discussed.

Journal Article↗
PubMed1975

The inhibitory effect of glucose on the differentiation of trophic Hartmannella culbertsoni into viable cysts.

During encystation of Hartmannella culbertsoni induced by taurine or epinephrine, 60-70% of the reserve glycogen is degraded. Glycogen phosphorylase is activated and glycogen synthetase is inhibited after 6-8 hr of exposure to the encystation medium. The carbon skeleton of glycogen but not that of protein is utilised in the synthesis of cyst wall cellulose. Exogenously added glucose (225 and 550 mM) blocks encystation, degradation of glycogen and synthesis of cellulose. Cyclic AMP synthesis is also very much reduced in cells exposed to glucose.

Adenylyl Cyclases↗
PubMed2000

Signal transduction in the protozoan host Hartmannella vermiformis upon attachment to Legionella pneumophila.

Intracellular replication of the Legionnaires' disease bacterium, Legionella pneumophila, within protozoa plays a major role in bacterial ecology and pathogenesis. Invasion of the protozoan host Hartmannella vermiformis by L. pneumophila is mediated by attachment to the Gal/GalNAc lectin receptor, which is similar to the beta(2) integrin transmembrane receptors of mammalian cells. Bacterial invasion is associated with induction of a protein tyrosine phosphatase (PTPase) activity in H. vermiformis that results in tyrosine dephosphorylation of the lectin receptor and several cytoskeletal proteins. In this report, we show that entry of L. pneumophila into H. vermiformis is not required to induce tyrosine dephosphorylation of one of the cytoskeletal proteins, paxillin. Tyrosine dephosphorylation of paxillin is mediated at the level of bacterial attachment to the lectin receptor, and is blocked by inhibiting bacterial attachment to the lectin receptor. Attachment of L. pneumophila to the lectin receptor is not mediated by the type IV pilus, which is one of the bacterial ligands involved in attachment to protozoa. Interestingly, the lectin receptor in resting H. vermiformis is associated with several phosphorylated proteins that are dissociated upon bacterial attachment and invasion. We show that the L. pneumophila-induced PTPase activity in H. vermiformis and the associated tyrosine dephosphorylation of host proteins can be mimicked by the cytoskeletal disrupting agent, cytochalasin D. Taken together, our data indicate that attachment of L. pneumophila to the lectin receptor of H. vermiformis induces a PTPase activity, tyrosine dephosphorylation of the lectin and cytoskeletal proteins, dissociation of the lectin from its associated phosphorylated proteins, and most probably disassembly of the cytoskeleton. This novel L. pneumophila-protozoa interaction may be a bacterial strategy to invade protozoa and to be trafficked into a replicative 'niche', or to block differentiation of the protozoan host into a cyst in which L. pneumophila cannot replicate.

Actin Cytoskeleton↗
PubMed1997

Identification of a Gal/GalNAc lectin in the protozoan Hartmannella vermiformis as a potential receptor for attachment and invasion by the Legionnaires' disease bacterium.

The Legionnaire's disease bacterium, Legionella pneumophila, is a facultative intracellular pathogen which invades and replicates within two evolutionarily distant hosts, free-living protozoa and mammalian cells. Invasion and intracellular replication within protozoa are thought to be major factors in the transmission of Legionnaire's disease. Although attachment and invasion of human macrophages by L. pneumophila is mediated in part by the complement receptors CR1 and CR3, the protozoan receptor involved in bacterial attachment and invasion has not been identified. To define the molecular events involved in invasion of protozoa by L. pneumophila, we examined the role of protein tyrosine phosphorylation of the protozoan host Hartmannella vermiformis upon attachment and invasion by L. pneumophila. Bacterial attachment and invasion were associated with a time-dependent tyrosine dephosphorylation of multiple host cell proteins. This host cell response was highly specific for live L. pneumophila, required contact with viable bacteria, and was completely reversible following washing off the bacteria from the host cell surface. Tyrosine dephosphorylation of host proteins was blocked by a tyrosine phosphatase inhibitor but not by tyrosine kinase inhibitors. One of the tyrosine dephosphorylated proteins was identified as the 170-kD galactose/N-acetylgalactosamine-inhibitable lectin (Gal/GalNAc) using immunoprecipitation and immunoblotting by antibodies generated against the Gal/GalNAc lectin of the protozoan Entamoeba histolytica. This Gal/GalNAc-inhibitable lectin has been shown previously to mediate adherence of E. histolytica to mammalian epithelial cells. Uptake of L. pneumophila by H. vermiformis was specifically inhibited by two monovalent sugars, Gal and GalNAc, and by mABs generated against the 170-kD lectin of E. histolytica. Interestingly, inhibition of invasion by Gal and GalNAc was associated with inhibition of bacterial-induced tyrosine dephosphorylation of H. vermiformis proteins. High stringency DNA hybridization confirmed the presence of the 170-kD lectin gene in H. vermiformis. We conclude that attachment of L. pneumophila to the H. vermiformis 170-kD lectin is required for invasion and is associated with tyrosine dephosphorylation of the Gal lectin and other host proteins. This is the first demonstration of a potential receptor used by L. pneumophila to invade protozoa.

Acetylgalactosamine↗
PubMed1998

Identification of putative cytoskeletal protein homologues in the protozoan host Hartmannella vermiformis as substrates for induced tyrosine phosphatase activity upon attachment to the Legionnaires' disease bacterium, Legionella pneumophila.

The Legionnaires' disease bacterium, Legionella pneumophila, is a facultative intracellular pathogen that invades and replicates within two evolutionarily distant hosts, free living protozoa and mammalian cells. Invasion and intracellular replication within protozoa are thought to be major factors in the transmission of Legionnaires' disease. We have recently reported the identification of a galactose/N-acetyl-D-galactosamine (Gal/GalNAc) lectin in the protozoan host Hartmannella vermiformis as a receptor for attachment and invasion by L. pneumophila (Venkataraman, C., B.J. Haack, S. Bondada, and Y.A. Kwaik. 1997. J. Exp. Med. 186:537-547). In this report, we extended our studies to the effects of bacterial attachment and invasion on the cytoskeletal proteins of H. vermiformis. We first identified the presence of many protozoan cytoskeletal proteins that were putative homologues to their mammalian counterparts, including actin, pp125(FAK), paxillin, and vinculin, all of which were basally tyrosine phosphorylated in resting H. vermiformis. In addition to L. pneumophila-induced tyrosine dephosphorylation of the lectin, bacterial attachment and invasion was associated with tyrosine dephosphorylation of paxillin, pp125(FAK), and vinculin, whereas actin was minimally affected. Inhibition of bacterial attachment to H. vermiformis by Gal or GalNAc monomers blocked bacteria-induced tyrosine dephosphorylation of detergent-insoluble proteins. In contrast, inhibition of bacterial invasion but not attachment failed to block bacteria-induced tyrosine dephosphorylation of H. vermiformis proteins. This was further supported by the observation that 10 mutants of L. pneumophila that were defective in invasion of H. vermiformis were capable of inducing tyrosine dephosphorylation of H. vermiformis proteins. Entry of L. pneumophila into H. vermiformis was predominantly mediated by noncoated receptor-mediated endocytosis (93%) but coiling phagocytosis was infrequently observed (7%). We conclude that attachment but not invasion by L. pneumophila into H. vermiformis was sufficient and essential to induce protein tyrosine dephosphorylation in H. vermiformis. These manipulations of host cell processes were associated with, or followed by, entry of the bacteria by a noncoated receptor-mediated endocytosis. A model for attachment and entry of L. pneumophila into H. vermiformis is proposed.

Actins↗
PubMed1993

Attachment and entry of Legionella pneumophila in Hartmannella vermiformis.

Legionella pneumophila is an intracellular parasite of Hartmannella vermiformis. Attachment to the amebae and entry of L. pneumophila were studied by two quantitative assays: One used plate counts to measure the number of bacteria attaching to amebae at 4 degrees C; the other determined the number of intracellular bacteria by use of transmission electron microscopy (TEM). The attachment assay showed that L. pneumophila are inefficient in attachment to amebae. About 0.05% of the bacteria were bound after 1 h with a 10- to 40-fold increase over the next 11 h. Attachment of both virulent and avirulent strains of L. pneumophila occurred at a similar rate. Uptake of L. pneumophila was measured by counting intracellular bacteria using TEM. Limited numbers of virulent L. pneumophila were found intracellularly before 4 h, but the numbers increased logarithmically after this time. The number of amebae containing virulent L. pneumophila increased linearly during the 12-h co-incubation. Avirulent L. pneumophila were rarely detected within amebae throughout the 12-h incubation. Results indicate that entry, not attachment, of virulent L. pneumophila is the limiting step in infection of axenically grown H. vermiformis.

Animals↗