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PubMed2005

The pbgPE operon in Photorhabdus luminescens is required for pathogenicity and symbiosis.

Photorhabdus is a genus of gram-negative Enterobacteriaceae that is pathogenic to insect larvae while also maintaining a mutualistic relationship with nematodes from the family Heterorhabditis, where the bacteria occupy the gut of the infective juvenile (IJ) stage of the nematode. In this study we describe the identification and characterization of a mutation in the pbgE1 gene of Photorhabdus luminescens TT01, predicted to be the fifth gene in the pbgPE operon. We show that this mutant, BMM305, is strongly attenuated in virulence against larvae of the greater wax moth, Galleria mellonella, and we report that BMM305 is more sensitive to the cationic antimicrobial peptide, polymyxin B, and growth in mildly acidic pH than the parental strain of P. luminescens. Moreover, we also show that the lipopolysaccharide (LPS) present on the surface of BMM305 does not appear to contain any O antigen. Complementation studies reveal that the increased sensitivity to polymyxin B and growth in mildly acidic pH can be rescued by the in trans expression of pbgE1, while the defects in O-antigen assembly and pathogenicity require the in trans expression of pbgE1 and the downstream genes pbgE2 and pbgE3. Finally, we show that BMM305 is defective in symbiosis as this mutant is unable to colonize the gut of the IJ stage of the nematode. Therefore, we conclude that the pbgPE operon is required for both pathogenicity and symbiosis in P. luminescens.

Animals↗
PubMed2002

Phylogenetic analysis identifies the invertebrate pathogen Helicosporidium sp. as a green alga (Chlorophyta).

Historically, the invertebrate pathogens of the genus Helicosporidium were considered to be either protozoa or fungi, but the taxonomic position of this group has not been considered since 1931. Recently, a Helicosporidium sp., isolated from the blackfly Simulium jonesi Stone & Snoddy (Diptera: Simuliidae), has been amplified in the heterologous host Helicoverpa zea. Genomic DNA has been extracted from gradient-purified cysts. The 185, 28S and 5.8S regions of the Helicosporidium rDNA, as well as partial sequences of the actin and beta-tubulin genes, were amplified by PCR and sequenced. Comparative analysis of these nucleotide sequences was performed using neighbour-joining and maximum-parsimony methods. All inferred phylogenetic trees placed Helicosporidium sp. among the green algae (Chlorophyta), and this association was supported by bootstrap and parsimony jackknife values. Phylogenetic analysis focused on the green algae depicted Helicosporidium sp. as a close relative of Prototheca wickerhamii and Prototheca zopfii (Chlorophyta, Trebouxiophyceae), two achlorophylous, pathogenic green algae. On the basis of this phylogenetic analysis, Helicosporidium sp. is clearly neither a protist nor a fungus, but appears to be the first described algal invertebrate pathogen. These conclusions lead us to propose the transfer of the genus Helicosporidium to Chlorophyta, Trebouxiophyceae.

Actins↗
PubMed1996

Identification of the antigenic determinants of factors 8, 9, and 34 of genus Candida.

We investigated the antigenic determinants of factors 8, 9, and 34 of the genus Candida among pathogenic yeasts by enzyme-linked immunosorbent assay (ELISA) using mannans of Saccharomyces cerevisiae wild type and mutant types, mnn 1-mnn 4 and mnn 2. Results of ELISA including antisera against the antigenic factors of genus Candida (Candida Check, latron; FAbs) indicated that these three types of mannan distinctly react with FAbs 34, 8 and 9, respectively. To identify the recognition sites of these FAbs, we compared the ability of various oligosaccharides to inhibit the binding of the mannans to FAbs. The results indicated that FAb 34 preferentially recognizes linear side chains containing a non-reducing terminal alpha-1,3-linked mannose residue, Man(alpha)1 --> 3Man(alpha)1 --> (2Man(alpha)1 --> )n(2Man) (n > or = 0), and that one of the recognition sites of FAb 9 is linear alpha-1,6-linked oligomannosyl series, Man(alpha)1 --> (6Man(alpha)1 --> )n(6Man) (n > or = 2). On the other hand, the recognition site of FAb 8 apparently consisted of two alpha-1,2-linked oligomannosyl side chains and an alpha-1,6-linked mannose residue that originated from the mannan backbone, Man(alpha)1 --> 2Man(alpha)1 --> 2(Man(alpha)1 -->2Man(alpha)1 --> 6)Man.

Antigens, Fungal↗
PubMed2006

Acanthamoeba isolates belonging to T1, T2, T3, T4 and T7 genotypes from environmental freshwater samples in the Nile Delta region, Egypt.

The free-living amoebae of the genus Acanthamoeba include non-pathogenic and pathogenic species and has been recently classified into 15 different genotypes, T1-T15. In this study, a survey was conducted in order to determine the presence and pathogenic potential of free-living amoebae of Acanthamoeba genus in freshwater sources associated with human activities in the Nile Delta region, Egypt. Identification of Acanthamoeba was based on the morphology of cyst and trophozoite forms and PCR amplification with a genus specific primer pair. The pathogenic potential of Acanthamoeba isolates was characterized using temperature and osmotolerance assays and PCR reactions with two primer pairs specific to Acanthamoeba pathogenesis. Isolates genotypes were also determined after ribosomal DNA sequencing. These data revealed that isolates belong to T1, T2, T3, T4 and T7 genotypes. As expected, T4 isolates exhibited the most pathogenic traits and were osmotolerant, temperature tolerant and expressed extracellular serine proteases. This is the first report presenting environmental distribution of Acanthamoeba genotypes in Egypt.

Acanthamoeba↗
PubMed1984

[Hemolytic effect of Listeria innocua on sheep erythrocytes].

The influence of culture medium composition on hemolytic effects produced by Listeria innocua on sheep blood agar has been investigated. Neither alpha- nor beta-hemolysis could be observed around L. innocua colonies grown on sheep erythrocyte agar lacking glucose. However, green zones of hemolytic phenomena were observed around colonies grown on such agar which contained 0,6% (w/v) glucose. By using L. innocua cell suspensions and culture filtrates this glucose-associated hemolysis only occurred in media which were weakly buffered (1 m M Na-PBS). This hemolytic phenomenon was attributed to the resulting acidification of the culture medium caused by the metabolic breakdown of glucose by Listeria. The results of this study demonstrate the necessity of including adequate buffer conditions when assaying the hemolytic property of a Listeria strain. It was found that the addition of 20 mM Na-PBS to the assay medium was sufficient to eliminate artificial "acidic-hemolysis". Moreover, the hemolysis observed with known hemolytic Listeria strains was unaffected by this buffering, as was in fact the case even when conditions of higher buffering capacity were employed. By testing in this manner, no evidence has been found which would suggest the existence of an hemolysin, either intra- or extracellular, produced by Listeria innocua. An accurate method for the determination of hemolysis caused by strains of the genus Listeria is proposed. This method of assaying hemolysis in a liquid grown medium has proven effective in determining the hemolytic properties of strains which appeared negative or questionable on blood agar as well as strains which in virulence tests were negative. The ability to accurately assess the hemolytic properties of Listeria strains, is essential in determining the association of Listeria hemolysin with pathogenicity of this genus. Together with current investigations on the genetics of hemolysin production by Listeria the determination of hemolytic activities will eventually allow to understand better the pathogenic principle of hemolytic strains of Listeria monocytogenes.

Agar↗
PubMedDate not supplied

[The pathogenicity factors in different representatives of the genus Citrobacter].

No trustworthy distinctions were revealed under the comparative analysis of properties of bacteria of Citrobacter genus from 3 studied ecological groups (from patients with diarrhea, from healthy persons and patients with extraenteric pathological process). It allows the finding of potentially partogenic bacteria of Citrobacter genus in patients with diarrhea to be considered the manifestation of dysbacteriosis.

Anti-Bacterial Agents↗
PubMed2003

Is a black-pigmented Corynebacterium species an opportunistic pathogen during pregnancy? Literature review and report of 3 new cases.

Isolation of black-pigmented Corynebacterium species from human clinical samples has been reported, although rarely. Review of the medical literature revealed 3 reports of culture isolation of these unusual bacteria. All were recovered from the female genital tract, and 1 case was associated with spontaneous abortion. Genetic characterization of these isolates indicates that they are similar and probably represent a novel pathogen in the genus Corynebacterium. We report 3 additional bacterial isolates sharing similar phenotypic and/or genotypic characteristics that were recovered from the genital tract of women who had complications of pregnancy. Similarities in these cases suggest that this newly recognized Corynebacterium species might be an opportunistic pathogen in pregnancy.

Adult↗
PubMed2006

Development potential of rifalazil and other benzoxazinorifamycins.

Rifalazil and other benzoxazinorifamycins (new chemical entities [NCEs]) are rifamycins that contain a distinct planar benzoxazine ring. Rifalazil has excellent antibacterial activity, high intracellular levels and high tissue penetration, which are attributes that favour its use in treating diseases caused by the obligate intracellular pathogens of the genus Chlamydia. Recent studies have shown that rifalazil has efficacy in the treatment of human sexually transmitted disease caused by Chlamydia trachomatis. The extraordinary potency of rifalazil and other NCEs, such as ABI-0043, extends to the related microorganism, C. pneumoniae, a respiratory pathogen that can disseminate and persist chronically in the vasculature, resulting in increased plaque formation in animal studies. A pivotal clinical trial with rifalazil has been initiated for the treatment of peripheral arterial disease. Other opportunities include gastric ulcer disease caused by Helicobacter pylori and antibiotic-associated colitis caused by infection with Clostridium difficile in the colon. The NCEs could prove to be valuable as follow-on compounds in these indications, as rifampin replacements in antibacterial combination therapy or as stand-alone topical antibacterials (e.g., to treat acne). Neither rifalazil nor NCEs appear to induce the cytochrome P450 3A4, an attribute of rifampin that can result in adverse events due to drug-drug interactions.

Animals↗
PubMed1990

[The molecular basis of the virulence of Yersinia].

Pathogenic bacteria of the genus Yersinia (Y. enterocolitica, Y. pseudotuberculosis and Y. pestis) are pathogens of the invasive type. Although they provoke diseases as different as plague and enterocolitis, the molecular bases of their virulence appear to be surprisingly similar: a 70 kb plasmid confers a degree of resistance to the primary immune response and the presence or absence of chromosome encoded functions modulates virulence. The knowledge of the virulence functions that now emerges suggests the conversion of Y. enterocolitica as a life carrier.

Bacterial Proteins↗
PubMed2002

Ranaviruses (family Iridoviridae): emerging cold-blooded killers.

Although possessing novel replicative and structural features, the family Iridoviridae has not been as extensively studied as other families of large, DNA-containing viruses (e.g., poxviridae and herpesviridae). This oversight most likely reflects the inability of iridoviruses to infect mammals and birds, and their heretofore low pathogenicity among cold-blooded animals and invertebrates. In fact, the original frog virus isolates (e.g., frog viruses 1-3) would likely have been considered orphan viruses since they were isolated from apparently healthy frogs. However, recent disease outbreaks among commercially and recreationally important fish, cultured and wild frogs, and endangered salamanders has challenged this benign view and have implicated several members of the genus Ranavirus as pathogens. This review explores three facets of ranavirus biology. In the first the salient features of ranavirus replication are summarized using frog virus 3 as a model. Secondly, criteria for characterizing new ranavirus isolates, based on biochemical (viral protein profiles, DNA restriction fragment length polymorphisms, and nucleotide sequence analysis), ecological (host range, tissue tropism), and clinical considerations, are detailed. Lastly, the principal agents of ranavirus-mediated disease and immune responses to these viruses are discussed. In light of the above, it is clear that ranaviruses are no longer orphan viruses, and that they have a significant impact on diverse populations of ectothermic animals.

Amphibians↗
PubMed2006

Variant antigen gene expression in malaria.

Pathogens of the genus Plasmodium are unicellular parasites that infect a variety of animals, including reptiles, birds and mammals. All Plasmodium species target host erythrocytes and replicate asexually within this niche. In humans, proliferation within erythrocytes causes disease symptoms ranging from asymtomatic infection to severe disease, including mild to severe febrile and respiratory symptoms, profound anaemia and obstruction of blood flow. The most serious form of human malaria is caused by Plasmodium falciparum, a pathogen that is responsible for several million deaths annually throughout the developing world. Malaria parasites succeed in evading the host immune response to establish long-term, persistent infections, thus increasing the efficiency by which they are transmitted to the mosquito vector. The ability to evade the host immune system, in particular the avoidance of antibody-mediated immunity against parasite-encoded surface proteins, is the result of amplification of extensive repertoires of multicopy, hypervariable gene families that encode infected erythrocyte or merozoite surface proteins. Via switching between antigenically diverse genes within these large families, populations of parasites have the capacity for rapid variation in antigenicity and virulence over the course of an infection. Here we review the amplification and generation of antigenic diversity within the Plasmodium variant gene families, as well as discuss the mechanisms underlying their tightly controlled gene expression and antigenic switching.

Animals↗
PubMed2003

Lipid rafts, caveolae, caveolin-1, and entry by Chlamydiae into host cells.

Obligate intracellular bacterial pathogens of the genus Chlamydia are reported to enter host cells by both clathrin-dependent and clathrin-independent processes. C. trachomatis serovar K recently was shown to enter cells via caveolae-like lipid raft domains. We asked here how widespread raft-mediated entry might be among the Chlamydia. We show that C. pneumoniae, an important cause of respiratory infections in humans that additionally is associated with cardiovascular disease, and C. psittaci, an important pathogen in domestic mammals and birds that also infects humans, each enter host cells via cholesterol-rich lipid raft microdomains. Further, we show that C. trachomatis serovars E and F also use these domains to enter host cells. The involvement of these membrane domains in the entry of these organisms was indicated by the sensitivity of their entry to the raft-disrupting agents Nystatin and filipin, and by their intracellular association with caveolin-1, a 22-kDa protein associated with the formation of caveolae in rafts. In contrast, caveolin-marked lipid raft domains do not mediate entry of C. trachomatis serovars A, 36B, and C, nor of LGV serovar L2 and MoPn. Finally, we show that entry of each of these chlamydial strains is independent of cellular expression of caveolin-1. Thus, entry via the Nystatin and filipin-sensitive pathway is dependent on lipid rafts containing cholesterol, rather than invaginated caveolae per se.

Anti-Bacterial Agents↗
PubMed2005

The Cf-4 and Cf-9 resistance genes against Cladosporium fulvum are conserved in wild tomato species.

The Cf-4 and Cf-9 genes originate from the wild tomato species Lycopersicon hirsutum and L. pimpinellifolium and confer resistance to strains of the leaf mold fungus Cladosporium fulvum that secrete the Avr4 and Avr9 elicitor proteins, respectively. Homologs of Cf-4 and Cf-9 (Hcr9s) are located in several clusters and evolve mainly through sequence exchange between homologs. To study the evolution of Cf genes, we set out to identify functional Hcr9s that mediate recognition of Avr4 and Avr9 (designated Hcr9-Avr4s and Hcr9-Avr9s) in all wild tomato species. Plants responsive to the Avr4 and Avr9 elicitor proteins were identified throughout the genus Lycopersicon. Open reading frames of Hcr9s from Avr4- and Avr9-responsive tomato plants were polymerase chain reaction-amplified. Several Hcr9s that mediate Avr4 or Avr9 recognition were identified in diverged tomato species by agroinfiltration assays. These Hcr9-Avr4s and Hcr9-Avr9s are highly identical to Cf-4 and Cf-9, respectively. Therefore, we conclude that both Cf-4 and Cf-9 predate Lycopersicon speciation. These results further suggest that C. fulvum is an ancient pathogen of the genus Lycopersicon, in which Cf-4 and Cf-9 have been maintained by selection pressure imposed by C. fulvum.

Amino Acid Sequence↗
PubMed2003

Human metapneumovirus: a newly emerging respiratory pathogen.

PURPOSE OF REVIEW: The present review focuses on the recent discovery, and clinical and epidemiological features of a virus associated with respiratory tract infections. RECENT FINDINGS: In June 2001, researchers in The Netherlands reported the discovery of a virus associated with respiratory tract disease in infants and children. Genetic studies of this newly discovered viral pathogen revealed that it was a paramyxovirus. This virus is the first human pathogen in the Genus Metapneumovirus and was called human metapneumovirus (hMPV). hMPV may be a common respiratory virus. Seroepidemiologic studies in The Netherlands suggested that, by age 5 years, nearly all individuals have been exposed to hMPV. The results of several studies suggest that hMPV may account for about 10% of respiratory tract infections in which a common respiratory virus, such as respiratory syncytial virus, or influenza or parainfluenza viruses, could not be detected. hMPV has been detected in patients with either upper or lower respiratory tract disease, or both. Symptoms associated with hMPV include cough, dyspnea, wheeze, and hypoxia. This newly recognized pathogen has been detected in children and adults. Epidemiological findings suggest that it may circulate worldwide and may have a seasonal distribution. SUMMARY: hMPV is a newly emerging respiratory pathogen and may be the cause of a significant proportion of both upper and lower respiratory tract infection in infants, children, and adults.

Adolescent↗