| 1. |
- Åhlund, Monika K, et al.
(författare)
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Directed screen of Francisella novicida virulence determinants using Drosophila melanogaster
- 2010
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Ingår i: Infection and Immunity. - : ASM International. - 0019-9567 .- 1098-5522. ; 78:7, s. 3118-3128
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Tidskriftsartikel (refereegranskat)abstract
- Francisella tularensis is a highly virulent, facultative intracellular human pathogen whose virulence mechanisms are not well understood. Occasional outbreaks of tularemia and the potential use of F. tularensis as a bioterrorist agent warrant better knowledge about the pathogenicity of this bacterium. Thus far, genome-wide in vivo screens for virulence factors have been performed in mice, all however restricted by the necessity to apply competition-based, negative-selection assays. We wanted to individually evaluate putative virulence determinants suggested by such assays and performed directed screening of 249 F. novicida transposon insertion mutants by using survival of infected fruit flies as a measure of bacterial virulence. Some 20% of the genes tested were required for normal virulence in flies; most of these had not previously been investigated in detail in vitro or in vivo. We further characterized their involvement in bacterial proliferation and pathogenicity in flies and in mouse macrophages. Hierarchical cluster analysis of mutant phenotypes indicated a functional linkage between clustered genes. One cluster grouped all but four genes of the Francisella pathogenicity island and other loci required for intracellular survival. We also identified genes involved in adaptation to oxidative stress and genes which might induce host energy wasting. Several genes related to type IV pilus formation demonstrated hypervirulent mutant phenotypes. Collectively, the data demonstrate that the bacteria in part use similar virulence mechanisms in mammals as in Drosophila melanogaster but that a considerable proportion of the virulence factors active in mammals are dispensable for pathogenicity in the insect model.
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| 2. |
- Waldenström, Jonas, et al.
(författare)
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Migrating birds and tickborne encephalitis virus
- 2007
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Ingår i: Emerging Infectious Diseases. - : Centers for Disease Control and Prevention (CDC). - 1080-6040 .- 1080-6059. ; 13:8, s. 1215-8
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Tidskriftsartikel (refereegranskat)abstract
- During spring and autumn 2001, we screened 13,260 migrating birds at Ottenby Bird Observatory, Sweden, and found 3.4% were infested with ticks. Four birds, each a different passerine species, carried tickborne encephalitis virus (TBEV)-infected ticks (Ixodes ricinus). Migrating birds may play a role in the geographic dispersal of TBEV-infected ticks.
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| 3. |
- Widerström, Micael, 1958-
(författare)
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Molecular epidemiology of coagulase-negative staphylococci in hospitals and in the community
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background Coagulase-negative staphylococci (CoNS) and in particular Staphylococcus epidermidis have emerged as major pathogens primarily causing nosocomial infections in patients with indwelling medical devices. These infections are often caused by multidrug-resistant strains of S. epidermidis (MDRSE). Other clinical entities due to CoNS are lower urinary tract infections (UTI) in women and native valve endocarditis. The purpose of this work was to investigate the frequency of antibiotic resistance and the molecular epidemiology of both hospital and community-associated isolates of S. epidermidis in order to examine if certain clones are related to MDRSE infections. Furthermore, we aimed to explore if specific clones of S. saprophyticus are associated with UTI in women. Methods A total of 359 hospital-associated methicillin-resistant isolates of CoNS obtained from 11 hospitals in northern Europe and 223 community-associated staphylococcal isolates were examined. Furthermore, 126 isolates of S. saprophyticus isolated from women with uncomplicated UTI from five different locations in northern Europe were analyzed. Pulsed-field gel electrophoresis (PFGE) was used for genotyping. Additionally, some of the S. epidermidis isolates were analyzed with multilocus sequence typing (MLST). Antibiotic susceptibility was determined for all isolates by the disc diffusion test. Results 293 of the 359 (82%) hospital-associated and 124 of the 223 (56%) community-associated isolates belonged to the species S. epidermidis. Among the hospital-associated S. epidermidis isolates, two dominating PFGE types (type A and B) were distinguished, comprising 78 (27%) and 51 (17%) isolates, respectively. Type A, which was detected in a Norwegian and eight Swedish hospitals, corresponded with a novel sequence type (ST215). Type B was discovered in a German, a Danish and seven Swedish hospitals and corresponded with ST2. In contrast, community-associated isolates of S. epidermidis were genetically extremely diverse with no predominating genotype, and showed a low rate of antibiotic resistance; only two (1.6%) methicillin-resistant strains were detected. Among 126 analyzed isolates of S. saprophyticus, 47 different PFGE profiles were identified. Several clusters of genetically highly related isolates were detected among isolates obtained from different locations and periods of time. Conclusion We have demonstrated the occurrence, persistence and potential dissemination of two multidrug-resistant S. epidermidis (MDRSE) genotypes, including a novel sequence type (ST215), within hospitals in northern Europe. Community-associated isolates of S. epidermidis showed a low rate of methicillin-resistance and were genetically heterogeneous. These results indicate that MDRSE by large are confined to the hospital setting in our region. Moreover, although the S. saprophyticus population was quite heterogeneous, indistinguishable isolates of S. saprophyticus causing lower UTI in women were identified in different countries 11 years apart, indicating the persistence and geographical spread of some clones of S. saprophyticus.
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| 4. |
- Rydén, Patrik, 1969-, et al.
(författare)
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Outbreaks of tularemia in a boreal forest region depends on mosquito prevalence
- 2012
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Ingår i: Journal of Infectious Diseases. - : Oxford University Press (OUP). - 0022-1899 .- 1537-6613. ; 205:2, s. 297-304
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Tidskriftsartikel (refereegranskat)abstract
- Background. We aimed to evaluate the potential association of mosquito prevalence in a boreal forest area with transmission of the bacterial disease tularemia to humans, and model the annual variation of disease using local weather data.Methods. A prediction model for mosquito abundance was built using weather and mosquito catch data. Then a negative binomial regression model based on the predicted mosquito abundance and local weather data was built to predict annual numbers of humans contracting tularemia in Dalarna County, Sweden.Results. Three hundred seventy humans were diagnosed with tularemia between 1981 and 2007, 94% of them during 7 summer outbreaks. Disease transmission was concentrated along rivers in the area. The predicted mosquito abundance was correlated (0.41, P < .05) with the annual number of human cases. The predicted mosquito peaks consistently preceded the median onset time of human tularemia (temporal correlation, 0.76; P < .05). Our final predictive model included 5 environmental variables and identified 6 of the 7 outbreaks.Conclusions. This work suggests that a high prevalence of mosquitoes in late summer is a prerequisite for outbreaks of tularemia in a tularemia-endemic boreal forest area of Sweden and that environmental variables can be used as risk indicators.
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| 5. |
- Elfving, Karin, et al.
(författare)
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Dissemination of Spotted Fever Rickettsia Agents in Europe by Migrating Birds
- 2010
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- Migratory birds are known to play a role as long-distance vectors for many microorganisms. To investigate whether this is true of rickettsial agents as well, we characterized tick infestation and gathered ticks from 13,260 migratory passerine birds in Sweden. A total of 1127 Ixodes spp. ticks were removed from these birds and the extracted DNA from 957 of them was available for analyses. The DNA was assayed for detection of Rickettsia spp. using real-time PCR, followed by DNA sequencing for species identification. Rickettsia spp. organisms were detected in 108 (11.3%) of the ticks. Rickettsia helvetica, a spotted fever rickettsia associated with human infections, was predominant among the PCR-positive samples. In 9 (0.8%) of the ticks, the partial sequences of 17kDa and ompB genes showed the greatest similarity to Rickettsia monacensis, an etiologic agent of Mediterranean spotted fever-like illness, previously described in southern Europe as well as to the Rickettsia sp. IrITA3 strain. For 15 (1.4%) of the ticks, the 17kDa, ompB, gltA and ompA genes showed the greatest similarity to Rickettsia sp. strain Davousti, Rickettsia japonica and Rickettsia heilongjiangensis, all closely phylogenetically related, the former previously found in Amblyomma tholloni ticks in Africa and previously not detected in Ixodes spp. ticks. The infestation prevalence of ticks infected with rickettsial organisms was four times higher among ground foraging birds than among other bird species, but the two groups were equally competent in transmitting Rickettsia species. The birds did not seem to serve as reservoir hosts for Rickettsia spp., but in one case it seems likely that the bird was rickettsiemic and that the ticks had acquired the bacteria from the blood of the bird. In conclusion, migratory passerine birds host epidemiologically important vector ticks and Rickettsia species and contribute to the geographic distribution of spotted fever rickettsial agents and their diseases.
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| 6. |
- Johansson, Anders, 1966-, et al.
(författare)
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Francisella tularensis : Tularemia
- 2012
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Ingår i: BSL3 and BSL4 agents. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 9783527317158 - 9783527645114 ; , s. 309-311
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Bokkapitel (refereegranskat)abstract
- This practical guide gives some starting points to manage biological safety issues with Francisella tularensis.
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| 7. |
- Lindgren, Marie, et al.
(författare)
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The Francisella tularensis LVS ΔpdpC mutant exhibits a unique phenotype during intracellular infection
- 2013
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Ingår i: BMC Microbiology. - : BioMed Central. - 1471-2180. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Background: A prerequisite for the virulence of the facultative intracellular bacterium Francisella tularensis is effective intramacrophage proliferation, which is preceded by phagosomal escape into the cytosol, and ultimately leads to host cell death. Many components essential for the intracellular life cycle are encoded by a gene cluster, the Francisella pathogenicity island (FPI), constituting a type VI secretion system.Results: We characterized the FPI mutant ΔpdpC of the live vaccine strain (LVS) of F. tularensis and found that it exhibited lack of intracellular replication, incomplete phagosomal escape, and marked attenuation in the mouse model, however, unlike a phagosomally contained FPI mutant, it triggered secretion of IL-1β, albeit lower than LVS, and markedly induced LDH release.Conclusions: The phenotype of the ΔpdpC mutant appears to be unique compared to previously described F. tularensis FPI mutants.
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| 8. |
- Eneslätt, Kjell, et al.
(författare)
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Vaccine-mediated mechanisms controlling replication of Francisella tularensis in human peripheral blood mononuclear cells using a co-culture system
- 2018
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Ingår i: Frontiers in Cellular and Infection Microbiology. - : Frontiers Media S.A.. - 2235-2988. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Cell-mediated immunity (CMI) is normally required for efficient protection against intracellular infections, however, identification of correlates is challenging and they are generally lacking. Francisella tularensis is a highly virulent, facultative intracellular bacterium and CMI is critically required for protection against the pathogen, but how this is effectuated in humans is poorly understood. To understand the protective mechanisms, we established an in vitro co-culture assay to identify how control of infection of F. tularensis is accomplished by human cells and hypothesized that the model will mimic in vivo immune mechanisms. Non-adherent peripheral blood mononuclear cells (PBMCs) were expanded with antigen and added to cultures with adherent PBMC infected with the human vaccine strain, LVS, or the highly virulent SCHU S4 strain. Intracellular numbers of F. tularensis was followed for 72 h and secreted and intracellular cytokines were analyzed. Addition of PBMC expanded from naïve individuals, i.e., those with no record of immunization to F. tularensis, generally resulted in little or no control of intracellular bacterial growth, whereas addition of PBMC from a majority of F. tularensis-immune individuals executed static and sometimes cidal effects on intracellular bacteria. Regardless of infecting strain, statistical differences between the two groups were significant, P < 0.05. Secretion of 11 cytokines was analyzed after 72 h of infection and significant differences with regard to secretion of IFN-γ, TNF, and MIP-1β was observed between immune and naïve individuals for LVS-infected cultures. Also, in LVS-infected cultures, CD4 T cells from vaccinees, but not CD8 T cells, showed significantly higher expression of IFN-γ, MIP-1β, TNF, and CD107a than cells from naïve individuals. The co-culture system appears to identify correlates of immunity that are relevant for the understanding of mechanisms of the protective host immunity to F. tularensis.
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| 9. |
- Golovliov, Igor, et al.
(författare)
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An In Vitro Co-culture Mouse Model Demonstrates Efficient Vaccine-Mediated Control of Francisella tularensis SCHU S4 and Identifies Nitric Oxide as a Predictor of Efficacy
- 2016
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Ingår i: Frontiers in Cellular and Infection Microbiology. - : Frontiers Media SA. - 2235-2988. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Francisella tularensis is a highly virulent intracellular bacterium and cell-mediated immunity is critical for protection, but mechanisms of protection against highly virulent variants, such as the prototypic strain F. tularensis strain SCHU S4, are poorly understood. To this end, we established a co-culture system, based on splenocytes from naive, or immunized mice and in vitro infected bone marrow-derived macrophages that allowed assessment of mechanisms controlling infection with F. tularensis. We utilized the system to understand why the clpB gene deletion mutant, Delta clpB, of SCHU S4 shows superior efficacy as a vaccine in the mouse model as compared to the existing human vaccine, the live vaccine strain (LVS). Compared to naive splenocytes, Delta clpB-, or LVS-immune splenocytes conferred very significant control of a SCHU S4 infection and the Delta clpB-immune splenocytes were superior to the LVS-immune splenocytes. Cultures with the Delta clpB-immune splenocytes also contained higher levels of IFN-gamma, IL-17, and GM-CSF and nitric oxide, and T cells expressing combinations of IFN-gamma, TNF-alpha, and IL-17, than did cultures with LVS-immune splenocytes. There was strong inverse correlation between bacterial replication and levels of nitrite, an end product of nitric oxide, and essentially no control was observed when BMDM from iNOS(-/-) mice were infected. Collectively, the co-culture model identified a critical role of nitric oxide for protection against a highly virulent strain of F. tularensis.
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| 10. |
- Eliasson, Henrik, et al.
(författare)
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Kinetics of the immune response associated with tularemia : comparison of an enzyme-linked immunosorbent assay, a tube agglutination test, and a novel whole-blood lymphocyte stimulation test
- 2008
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Ingår i: Clinical and Vaccine Immunology. - 1556-6811 .- 1556-679X. ; 15:8, s. 1238-1243
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Tidskriftsartikel (refereegranskat)abstract
- We have developed and evaluated a novel and simplified whole-blood lymphocyte stimulation assay that focuses on the measurement of gamma interferon after 24 h of stimulation with whole-cell tularemia antigen and a tularemia enzyme-linked immunosorbent assay (ELISA) based on highly purified lipopolysaccharide antigen. Comparison of the kinetics of the two assays and those of the traditional tube agglutination test shows that the cellular immune response can be detected earlier by the lymphocyte stimulation assay. This test already shows a high proportion of positive results during the first week after the onset of the disease, may be applicable in everyday laboratory practice, and has the potential of changing routine diagnostics for tularemia. The new ELISA has a high sensitivity and becomes positive to a high degree during the second week of disease.
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