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  • 1
    Publication Date: 2016-04-20
    Description: Several Gram-positive pathogens scavenge host-derived heme to satisfy their nutritional iron requirement. However, heme is a toxic molecule capable of damaging the bacterial cell. Gram-positive pathogens within the phylum Firmicutes overcome heme toxicity by sensing heme through HssRS, a two-component system that regulates the heme detoxification transporter HrtAB. Here we show that heme sensing by HssRS and heme detoxification by HrtAB occur in the insect pathogen Bacillus thuringiensis . We find that in B. thuringiensis , HssRS directly regulates an operon, hrmXY , encoding hypothetical membrane proteins that are not found in other Firmicutes with characterized HssRS and HrtAB systems. This novel HssRS-regulated operon or its orthologs BMB171_c3178 and BMB171_c3330 are required for maximal heme resistance. Furthermore, the activity of HrmXY is not dependent on expression of HrtAB. These results suggest that B. thuringiensis senses heme through HssRS and induces expression of separate membrane-localized systems capable of overcoming different aspects of heme toxicity.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 2
    Publication Date: 2016-08-05
    Description: Shiga toxin-encoding Escherichia coli (STEC) regroup strains that carry genes encoding Shiga toxin (Stx). Among intestinal pathogenic E. coli , enterohaemorrhagic E. coli (EHEC) constitute the major subgroup of virulent STEC. EHEC cause serious human disease such as haemorrhagic colitis and haemolytic-uremic syndrome. While EHEC have evolved from enteropathogenic E. coli , hybrids with enteroaggregative E. coli have recently emerged. Of note, some enteroinvasive E. coli also belong to the STEC group. While the LEE (locus of enterocyte effacement) is a key and prominent molecular determinant in the pathogenicity, neither all EHEC nor STEC contain the LEE, suggesting that they possess additional virulence and colonisation factors. Currently, nine protein secretion systems have been described in diderm-lipopolysaccharide bacteria (archetypal Gram-negative) and can be involved in the secretion of extracellular effectors, cell-surface proteins or assembly of cell-surface organelles, such as flagella or pili. In this review, we focus on the secretome of STEC and related enteropathotypes, which are relevant to the colonisation of biotic and abiotic surfaces. Considering the wealth of potential protein trafficking mechanisms, the different combinations of colonisation factors and modulation of their expression is further emphasised with regard to the ecophysiology of STEC.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 3
    Publication Date: 2016-06-17
    Description: Coagulase-negative staphylococci are thought to act as reservoirs of antibiotic resistance genes that can be transferred to Staphylococcus aureus , thus hindering the combat of this bacterium. In this work, we analyzed the presence of plasmids conferring resistance to the antibiotic mupirocin—widely used to treat and prevent S. aureus infections in hospital environments—in nosocomial S. haemolyticus strains. About 12% of the 75 strains tested were resistant to mupirocin, and this phenotype was correlated with the presence of plasmids. These plasmids were shown to be diverse, being either conjugative or mobilizable, and capable of transferring mupirocin resistance to S. aureus . Our findings reinforce that S. haemolyticus , historically and mistakenly considered as a less important pathogen, is a reservoir of resistance genes which can be transferred to other bacteria, such as S. aureus , emphasizing the necessity of more effective strategies to detect and combat this emergent opportunistic pathogen.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 4
    Publication Date: 2016-05-08
    Description: Legionella feeleii is a Gram-negative pathogenic bacterium that causes Pontiac fever and pneumonia in humans. When L. feeleii serogroup 1 (ATCC 35072) was cultured on BCYE agar plates, two types of colonies were observed and exhibited differences in color, opacity and morphology. Since the two colony types are white rugose and brown translucent, they were termed as white rugose L. feeleii (WRLf) and brown translucent L. feeleii (BTLf), respectively. They exhibited different growth capacities in BYE broth in vitro , and it was found that WRLf could transform to BTLf. Under the electron microscope, it was observed that WRLf secreted materials which could be stained with ruthenium red, which was absent in BTLf. When U937 macrophages and HeLa cells were infected with the bacteria, WRLf manifested stronger internalization ability than BTLf. Intracellular growth in murine macrophages and Acanthamoeba cells was affected by the level of initial phagocytosis. WRLf was more resistant to human serum bactericidal action than BTLf. After being inoculated to guinea pigs, both organisms caused fever in the animals. These results suggest that ruthenium red-stained materials secreted in the surroundings may play a crucial role in determining L. feeleii colony morphology and virulence traits.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 5
    Publication Date: 2016-02-25
    Description: An RNAi system based on T7 RNA polymerase (TRNAP) was designed and examined in Aspergillus fumigatus . This system consists of two elements; an inducible T7RNAP expressing cassette and an AMA1-based episomal RNAi plasmid. These constructs were transformed into the A. fumigatus protoplasts and the efficiency of this system was tested in downregulation of alb1 gene. Upon the induction of T7RNAP expression, the recombinant T7RNAP was able to recognize T7 promoters, which were located on the episomal plasmid and in opposite direction. As a result, the bidirectional transcription of alb1 fragment led to the silencing of the target gene. However, our results demonstrated that this silencing system is unstable and may not be applicable in preparation of RNAi libraries.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 6
    Publication Date: 2016-05-20
    Description: A simple diagnosis of the presence or absence of an infection is an uninformative metric when individuals differ considerably in their tolerance to different infection loads or resistance to rates of disease progression. Models that incorporate the relationship between the progression of the infection with the potential alternate outcomes provide a far more powerful predictive tool than diagnosis alone. The global decline of amphibians has been amplified by Batrachochytrium dendrobatidis , a pathogen that can cause the fatal disease chytridiomycosis. We measured the infection load and observed signs of disease in Litoria aurea . Receiver operating characteristic curves were used to quantify the dissimilarity between the infection loads of L. aurea that showed signs associated with chytridiomycosis and those that did not. Litoria aurea had a 78% probability of developing chytridiomycosis past a threshold of 68 zoospore equivalents (ZE) per swab and chytridiomycosis occurred within a variable range of 0.5–490 ZE. Studies should incorporate a species-specific threshold as a predictor of chytridiomycosis, rather than a binary diagnosis. Measures of susceptibility to chytridiomycosis must account not only for the ability of B. dendrobatidis to increase its abundance on the skin of amphibians but also to determine how each species tolerates these infection loads.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 7
    Publication Date: 2016-12-29
    Description: Sporisorium scitamineum is the fungus that causes sugarcane smut disease. Despite of the importance of sugarcane for Brazilian agribusiness and the persistence of the pathogen in most cropping areas, genetic variation studies are still missing for Brazilian isolates. In this study, sets of isolates were analyzed using two molecular markers (AFLP and telRFLP) and ITS sequencing. Twenty-two whips were collected from symptomatic plants in cultivated sugarcane fields of Brazil. A total of 41 haploid strains of compatible mating types were selected from individual teliospores and used for molecular genetic analyses. telRFLP and ITS analyses were expanded to six Argentine isolates, where the sugarcane smut was first recorded in America. Genetic relationship among strains suggests the human-mediated dispersal of S. scitamineum within the Brazilian territory and between the two neighboring countries. Two genetically distinct groups were defined by the combined analysis of AFLP and telRFLP. The opposite mating-type strains derived from single teliospores were clustered together into these main groups, but had not always identical haplotypes. telRFLP markers analyzed over two generations of selfing and controlled outcrossing confirmed the potential for emergence of new variants and occurrence of recombination, which are relevant events for evolution of virulence and environmental adaptation.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 8
    Publication Date: 2016-07-15
    Description: Invertebrate animal species that can withstand temperatures as high as 37°C, the human body temperature, are limited. In the present study, we utilized the two-spotted cricket, Gryllus bimaculatus , which lives in tropical and subtropical regions, as an animal model of human pathogenic bacterial infection. Injection of Pseudomonas aeruginosa or Staphylococcus aureus into the hemolymph killed crickets. Injected P. aeruginosa or S. aureus proliferated in the hemolymph until the cricket died. The ability of these pathogenic bacteria to kill the crickets was blocked by the administration of antibiotics. S. aureus gene-knockout mutants of virulence factors, including cvfA, agr and srtA , exhibited decreased killing ability compared with the parent strain. The dose at which 50% of crickets were killed by P. aeruginosa or S. aureus was not decreased at 37°C compared with that at 27°C. Injection of Listeria monocytogenes , which upregulates toxin expression at 37°C, killed crickets, and the dose at which 50% of crickets were killed was decreased at 37°C compared with that at 27°C. These findings suggest that the two-spotted cricket is a useful model animal for evaluating the virulence properties of various human pathogenic bacteria at variable temperature including 37°C.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 9
    Publication Date: 2016-06-23
    Description: Auranofin is an FDA-approved gold-containing compound used for the treatment of rheumatoid arthritis. Recent reports of antimicrobial activity against protozoa and bacteria indicate that auranofin targets the reductive enzyme thioredoxin reductase (TrxR). We evaluated auranofin as well as five auranofin analogs containing N- heterocyclic carbenes (instead of the triethylphosphane present in auranofin) and five gold-carbene controls for their ability to inhibit or kill Helicobacter pylori in vitro . Auranofin completely inhibited bacterial growth at 1.2 μM. Purified H. pylori TrxR was inhibited by auranofin in a cell-free assay (IC 50 ~88 nM). The most active gold(I)- N- heterocyclic carbene compounds exhibited MICs comparable to auranofin against H. pylori (2 μM), while also exhibiting lower toxicities for human embryonic kidney cells (HEK-293T cells). Median toxic concentrations (TC 50 ) were 13–20-fold higher compared to auranofin indicating that they were less cytotoxic. The N- heterocyclic carbene analogs maybe well tolerated, but further evaluation is needed in vivo . Finally, auranofin was synergistic with the antibiotic amoxicillin, suggesting that targeting both the reductive enzyme TrxR and cell wall synthesis may be effective against H. pylori infections.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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  • 10
    Publication Date: 2016-05-12
    Description: Pseudomonas aeruginosa is an opportunistic pathogen, known to develop robust biofilms. Its biofilm development increases when antibiotics are presented at subminimal inhibitory concentrations (MICs) for reasons that remain unclear. In order to identify genes that affect biofilm development under such a sublethal antibiotic stress condition, we screened a transposon (Tn) mutant library of PAO1, a prototype P. aeruginosa strain. Among ~5000 mutants, a fiuA gene mutant was verified to form very defective biofilms in the presence of sub-MIC carbenicillin. The fiuA gene encodes ferrichrome receptor A, involved in the iron acquisition process. Of note, biofilm formation was not decreased in the pchpvd mutant defective in the production of pyochelin and pyoverdine, two well-characterized P. aeruginosa siderophore molecules. Moreover, fiuA , a non-polar fiuA deletion mutant, produced a significantly decreased level of elastase, a major virulence determinant. Mouse airway infection experiments revealed that the mutant expressed significantly less pathogenicity. Our results suggest that the fiuA gene has pleiotropic functions that affect P. aeruginosa biofilm development and virulence. The targeting of FiuA could enable the attenuation of P. aeruginosa virulence and may be suitable for the development of a drug that specifically controls the virulence of this important pathogen.
    Keywords: Pathogens & Pathogenicity
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
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