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At least 847 records · Page 47Linked to original sources
PubMed2000

Cytokine gene expression in innately susceptible BALB/c mice and relatively resistant C57BL/6 mice during infection with virulent Burkholderia pseudomallei.

Production of cytokines including gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) is an important early-stage host response following infection with intracellular pathogens. Development of immunity to these pathogens is determined to a large extent by the timing and relative level of expression of the cytokines. Numerous studies have shown that early cytokine responses involving interleukin-12 (IL-12) and IFN-gamma are important for resistance to intracellular pathogens, whereas responses involving IL-4 and IL-10 increase host susceptibility. These often-indistinct early cytokine responses influence the differentiation of naïve CD4(+) T helper cells, which later develop into what have commonly been termed Th1- and Th2-type cells. The characterization of CD4(+) T-helper-cell responses as Th1 or Th2 type is based largely on the cytokine profiles during the specific phase and has been used in recent years to account for the innate resistance and susceptibility of different inbred strains of mice to several intracellular pathogens. Studies investigating cytokine production in terms of CD4(+) T-helper-cell polarization in Burkholderia pseudomallei infection have not been undertaken. In this study, we used semiquantitative reverse transcription-PCR to assess induction of cytokine mRNA in liver and spleen of B. pseudomallei-susceptible BALB/c and relatively resistant C57BL/6 mice following infection with virulent B. pseudomallei. The levels of mRNA for IFN-gamma, TNF-alpha, IL-1beta, IL-6, IL-10, and IL-12 increased in both BALB/c and C57BL/6 mice 24 to 36 h after infection. A comparison of BALB/c and C57BL/6 responses revealed the relative levels of expression of mRNA for several of these cytokines, including IFN-gamma, were greater in BALB/c mice, suggesting a role for endotoxic shock and cytokine-mediated immunopathology in the development of acute melioidosis. Early induction of mRNA for the cytokines classically associated with development of Th1- and Th2-type responses was absent or minimal, and induction levels in both strains of mice were similar. During the specific phase, cytokine mRNA profiles occurred as a combination of Th1- and Th2-type patterns. Collectively, these results demonstrate that cytokine mRNA responses in BALB/c and C57BL/6 mice following infection with virulent B. pseudomallei do not develop as polarized Th1- or Th2-type profiles. Considering the role of TNF-alpha and IFN-gamma in the processes of endotoxic shock, these results also indicate that selected cytokines, while important for resistance to B. pseudomallei infection, are also potential contributors to immunopathology and the development of acute fulminating disease.

Animals↗
PubMed2005

Identification and characterization of pathogenic Yersinia enterocolitica isolates by PCR and pulsed-field gel electrophoresis.

Approximately 550 to 600 yersiniosis patients are reported annually in Sweden. Although pigs are thought to be the main reservoir of food-borne pathogenic Yersinia enterocolitica, the role of pork meat as a vehicle for transmission to humans is still unclear. Pork meat collected from refrigerators and local shops frequented by yersiniosis patients (n=48) were examined for the presence of pathogenic Yersinia spp. A combined culture and PCR method was used for detection, and a multiplex PCR was developed and evaluated as a tool for efficient identification of pathogenic food and patient isolates. The results obtained with the multiplex PCR were compared to phenotypic test results and confirmed by pulsed-field gel electrophoresis (PFGE). In all, 118 pork products (91 raw and 27 ready-to-eat) were collected. Pathogenic Yersinia spp. were detected by PCR in 10% (9 of 91) of the raw pork samples (loin of pork, fillet of pork, pork chop, ham, and minced meat) but in none of the ready-to-eat products. Isolates of Y. enterocolitica bioserotype 4/O:3 were recovered from six of the PCR-positive raw pork samples; all harbored the virulence plasmid. All isolates were recovered from food collected in shops and, thus, none were from the patients' home. When subjected to PFGE, the six isolates displayed four different NotI profiles. The same four NotI profiles were also present among isolates recovered from the yersiniosis patients. The application of a multiplex PCR was shown to be an efficient tool for identification of pathogenic Y. enterocolitica isolates in naturally contaminated raw pork.

Adolescent↗
PubMed1983

[Immunologic profile of a patient with lymphocutaneous sporotrichosis].

Sporotrichosis is characterized by a wide range of clinical manifestations from mild fixed cutaneous forms to systemic dissemination of the disease, despite an apparent regular pattern of virulence of the etiological agent, S. schenckii. These facts suggest that immunological mechanisms of the host could play an important role on the pathogenesis of the mycosis. On this basis, an immunologic survey was carried out in patients with lymphocutaneous sporotrichosis. Cell-mediated immunity was evaluated by means of lymphocyte transformation stimulated with phytohaemagglutinin and the response to several intradermal reaction antigens. Lymphocyte blastic transformation was normal as compared with a control group. All patients were positive at least against one of the antigens tested. These results indicate that this group of patients did not show any cell-mediated immunity deficiency. Serum immunoglobulins (IgG, IgM, IgA), and C3 measured to evaluate humoral immunity, were also within normality. Since many cases of sporotrichosis cure with the administration of potassium iodine, whose mechanisms of therapeutic activity are unknown, a possible impairment in the management of iodine was investigated, with the premise that iodine enhances the host defenses rather than acting against the fungus. Thyroid function tests performed in all patients to support this hypothesis, gave normal results. These data permit to conclude that susceptibility to sporotrichosis in the affected patients does not depend on gross abnormal humoral and/or cell-mediated immunity, and their response to potassium iodine is not related to deficient thyroid function.

Adolescent↗
PubMed1987

A potassium thiocyanate extract vaccine prepared from Pasteurella multocida 3:A protects rabbits against homologous challenge.

Potassium thiocyanate extracts of a virulent Pasteurella multocida 3:A rabbit isolate were prepared and used as a vaccine in rabbits. The extract contained protein, carbohydrate, hyaluronic acid, lipopolysaccharide, DNA, and RNA. The protein and lipopolysaccharide profiles of the extract were similar to those of the P. multocida cell membrane. Rabbits were vaccinated intranasally (i.n.) or intramuscularly (i.m.) four times at 1- or 3-week intervals and challenged i.n. with the homologous P. multocida 2 weeks after the last vaccination. Rabbits vaccinated with the extract by the i.n. route developed persisting serum immunoglobulin G (IgG) and nasal IgA antibodies, whereas rabbits immunized by the i.m. route produced persisting serum IgG and transient nasal IgA antibodies. The extract prevents the death of rabbits which were vaccinated by either route and challenged. Vaccination by the i.n. route in rabbits reduced the numbers of virulent P. multocida in nasal cavities and lungs and the prevalence and severity of rhinitis and pneumonia. These i.n.-vaccinated rabbits were also resistant to virulent P. multocida colonization in liver, spleen, uterus, and tympanic bullae. Similarly, i.m. vaccination in rabbits resulted in a reduction in the severity of rhinitis; the numbers of virulent P. multocida in lungs; and the prevalence of colonization in liver, spleen, uterus, and tympanic bullae. Vaccination by the i.n. route was superior to that by the i.m. route in that there was a significant reduction in the severity of pneumonia and numbers of virulent P. multocida in nasal cavities and lungs. Rabbits vaccinated with the extract without challenge showed no lesions.

Administration, Intranasal↗
PubMed2006

Impact of intestinal colonization and invasion on the Entamoeba histolytica transcriptome.

A genome-wide transcriptional analysis of Entamoeba histolytica was performed on trophozoites isolated from the colon of six infected mice and from in vitro culture. An Affymetrix platform gene expression array was designed for this analysis that included probe sets for 9435 open reading frames (ORFs) and 9066 5' and 3' flanking regions. Transcripts were detected for > 80% of all ORFs. A total of 523 transcripts (5.2% of all E. histolytica genes) were significantly changed in amebae isolated from the intestine on Days 1 and 29 after infection: 326 and 109 solely on Days 1 and 29, and 88 on both days. Quantitative real-time reverse transcriptase PCR confirmed these changes in 11/12 genes tested using mRNA isolated from an additional six mice. Adaptation to the intestinal environment was accompanied by increases in a subset of cell signaling genes including transmembrane kinases, ras and rho family GTPases, and calcium binding proteins. Significant decreases in mRNA abundance for genes involved in glycolysis and concomitant increases in lipases were consistent with a change in energy metabolism. Defense against bacteria present in the intestine (but lacking from in vitro culture) was suggested by alterations in mRNA levels of genes similar to the AIG1 plant antibacterial proteins. Decreases in oxygen detoxification pathways were observed as expected in the anaerobic colonic lumen. Of the known virulence factors the most remarkable changes were a 20-35-fold increase in a cysteine proteinase four-like gene, and a 2-3-fold decrease in two members of the Gal/GalNAc lectin light subunit family. Control of the observed changes in mRNA abundance in the intestine might potentially rest with four related proteins with DNA binding domains that were down-regulated 6-16-fold in the intestinal environment. In conclusion, the first genome-wide analysis of the transcriptome of E. histolytica demonstrated that the vast majority of genes are transcribed in trophozoites, and that in the host intestine trophozoites altered the expression of mRNAs for genes implicated in metabolism, oxygen defense, cell signaling, virulence, antibacterial activity, and DNA binding.

Animals↗
PubMed2001

Correlation of genetic variability with safety of mumps vaccine Urabe AM9 strain.

The Urabe AM9 strain of mumps vaccine live is known for its genetic instability and some vaccines derived from this strain were withdrawn from the market due to an excessive number of vaccine-associated parotitis and meningitis cases. To identify the molecular basis of this instability, we determined complete nucleotide sequences of several stocks of the Urabe strain used for vaccine production by different manufacturers and of two clinical isolates from cases of vaccine-associated meningitis. In contrast to previously published studies relating the Lys335 --> Glu mutation in the viral HN gene with neurovirulence of mumps virus, we could not confirm any association of this mutation with the safety of mumps vaccine. Each of the three vaccine stocks studied had its own characteristic profile of mutations that was identified by cDNA sequencing and quantitated by mutant analysis by PCR and restriction enzyme cleavage. Determination of the mutational profile of mumps vaccine lots could allow vaccine manufacturers to characterize seed viruses and monitor the consistency of vaccine production to prevent emergence of virulent revertants.

Amino Acid Substitution↗
PubMed1984

Isolation and characterization of monoclonal antibodies to Bordetella pertussis.

Monoclonal antibodies to Bordetella pertussis were produced by fusion of mouse myeloma cells and spleen cells of immunized mice. Cell lines were examined for specific antibody production against several crude antigen preparations and lipopolysaccharide. Cross reactivity of monoclonal antibodies was assessed by enzyme immunoassay using cell lysates prepared from Bordetella spp. and several other bacteria. Reactivity of monoclonal antibodies to cell surface components was determined by immunofluorescence microscopy. Monoclonal antibodies represent useful probes to study the antigenic profile and distribution of antigens among various species of Bordetella, as well as specific tools to study the structure and function of B. pertussis virulence factors.

Animals↗
PubMed2003

Plaque as a biofilm: pharmacological principles of drug delivery and action in the sub- and supragingival environment.

Dental plaque is the diverse microbial community, embedded in a matrix of host and bacterial polymers, growing on teeth as a biofilm. Dental plaque develops naturally, and contributes to the host defences by preventing colonization by exogenous species. The composition of dental plaque varies at distinct surfaces as a result of the inherent biological and physical properties at these sites; the balance of the predominant bacterial populations shifts in disease. Plaque has an open architecture, with channels traversing from the biofilm surface through to the enamel. This structure affects the movement of molecules within plaque, and gradients in key determinants develop. Bacteria growing on a surface display a novel phenotype; one consequence of which is an increased resistance to antimicrobial agents. Resistance can result from restricted inhibitor penetration (diffusion-reaction theory), slower bacterial growth rates, transfer of resistance genes, suboptimal environmental conditions for inhibitor activity, and the expression of a resistant phenotype. Such biofilm-associated traits, coupled with the pharmacokinetic profile of orally delivered antimicrobial agents (high concentrations for short periods/lower concentrations for longer periods), affect the mode of action and efficacy of antimicrobials. Agents with a broad spectrum of activity in laboratory studies may display a far narrower inhibitory profile under the conditions prevailing in the mouth. This may result in a selective inhibition of species implicated in disease, or reduced production of virulence factors, while preserving the benefits associated with a resident oral microflora.

Administration, Topical↗
PubMed1999

Genetic diversity among Escherichia coli O149:K91 strains isolated from pigs with diarrhoea determined by randomly amplified polymorphic DNA analysis.

The genetic relatedness among 72 Escherichia coli strains of serotype O149:K91 isolated from pigs with diarrhoea was investigated by randomly amplified polymorphic DNA (RAPD) analysis. Fimbrial and toxic virulence markers of the isolates were also tested. Amplification with primer 1254 resulted in three different RAPD types whereas primer 1290 generated one RAPD profile only. Based on the RAPD and fimbrial/toxin types the strains were classified into five distinct groups.

Animals↗
PubMed1989

Effect of iron restriction on the outer membrane proteins of Actinobacillus (Haemophilus) pleuropneumoniae.

The outer membrane protein profile of Actinobacillus (Haemophilus) pleuropneumoniae grown under iron-restricted and iron-replete conditions was studied by polyacrylamide gel electrophoresis and immunoblotting. A virulent serotype 1 isolate synthesized a novel protein with an apparent molecular weight of 105,000 (105K) and increased the synthesis of a 76K protein under iron-restricted conditions. Both proteins were synthesized within 15 min of establishment of iron-restricted conditions. Proteins of equivalent molecular weights could also be induced by iron restriction in serotype 2, 3, 4, 5, and 7 isolates of A. pleuropneumoniae. Convalescent-phase sera from serotype 1-infected pigs contained antibodies which recognized both the 105K and 76K proteins from all six serotypes examined, indicating that these proteins were expressed in vivo and were immunologically conserved. Cells expressing the 105K and 76K proteins also displayed an enhanced ability to bind Congo red and hemin, suggesting that one or both of these proteins functioned to acquire complexed iron during in vivo growth.

Actinobacillus↗
PubMed1997

Cellular changes and cytokine expression in the ilea of gnotobiotic piglets resulting from peroral Salmonella typhimurium challenge.

Two stable rough mutants of Salmonella spp. were studied as live peroral vaccines. The SF1591 mutant of S. typhimurium (Ra chemotype) protected germ-free piglets against subsequent infection with virulent smooth S. typhimurium LT2, whereas a deep-rough mutant of S. minnesota mR595 (Re chemotype) did not. We investigated cytokine and leukocyte profiles in the ilea of gnotobiotic piglets colonized for 1 week either with rough mutants alone or with rough mutants followed by S. typhimurium LT2. The ileal mucosae of piglets associated with strain SF1591 alone were not inflamed. Villi contained activated macrophages, and enterocytes expressed transforming growth factor beta (TGF-beta). Subsequent infection of piglets with S. typhimurium LT2 resulted in immigration of alphabeta T cells and immunoglobulin A (IgA) response. In contrast, the ileal mucosae of piglets associated with strain mR595 alone expressed heat shock proteins and inflammatory cytokines but not TGF-beta. Acellular villi contained numerous gammadelta T cells but no alphabeta T cells. After subsequent challenge with the LT2 strain, most piglets died of sepsis. Intestinal mucosae contained IgG but no IgA. These findings suggest the importance of cytokine signals in the regulation of intestinal responses against Salmonella infection.

Animals↗
PubMed2000

Absence of SpeB production in virulent large capsular forms of group A streptococcal strain 64.

Passage in human blood of group A streptococcal isolate 64p was previously shown to result in the enhanced expression of M and M-related proteins. Similarly, when this isolate was injected into mice via an air sac model for skin infection, organisms recovered from the spleens showed both increased expression of M and M-related proteins and increased skin-invasive potential. We show that these phenotypic changes were not solely the result of increased transcription of the mRNAs encoding the M and M-related gene products. Rather, the altered expression was associated with posttranslational modifications of the M and M-related proteins that occur in this strain, based on the presence or absence of another virulence protein, the streptococcal cysteine protease SpeB. The phenotypic variability also correlates with colony size variation. Large colonies selected by both regimens expressed more hyaluronic acid, which may explain differences in colony morphology. All large-colony variants were SpeB negative and expressed three distinct immunoglobulin G (IgG)-binding proteins in the M and M-related protein family. Small-colony variants were SpeB positive and bound little IgG through their M and M-related proteins because these proteins, although made, were degraded or altered in profile by the SpeB protease. We conclude that passage in either human blood or a mouse selects for a stable, phase-varied strain of group A streptococci which is altered in many virulence properties.

Antigens, Bacterial↗
PubMed2005

The BvgAS signal transduction system regulates biofilm development in Bordetella.

The majority of Bordetella sp. virulence determinants are regulated by the BvgAS signal transduction system. BvgAS mediates the control of multiple phenotypic phases and a spectrum of gene expression profiles specific to each phase in response to incremental changes in the concentrations of environmental signals. Studies highlighting the critical role of this signaling circuitry in the Bordetella infectious cycle have focused on planktonically growing bacterial cells. It is becoming increasingly clear that the major mode of bacterial existence in the environment and within the body is a surface-attached state known as a biofilm. Biofilms are defined as consortia of sessile microorganisms that are embedded in a matrix. During routine growth of Bordetella under agitating conditions, we noticed the formation of a bacterial ring at the air-liquid interface of the culture tubes. We show here that this surface adherence property reflects the ability of these organisms to form biofilms. Our data demonstrate that the BvgAS locus regulates biofilm development in Bordetella. The results reported in this study suggest that the Bvg-mediated control in biofilm development is exerted at later time points after the initial attachment of bacteria to the different surfaces. Additionally, we show that these biofilms are highly tolerant of a number of antimicrobials, including the ones that are currently recommended for treatment of veterinary and human infections caused by Bordetella spp. Finally, we discuss the significance of the biofilm lifestyle mode as a potential contributor to persistent infections.

Adaptation, Physiological↗
PubMed2000

Molecular characteristics and epidemiological significance of Shiga toxin-producing Escherichia coli O26 strains.

Fifty-five Shiga toxin (Stx)-producing Escherichia coli (STEC) O26:H11 and O26:H(-) strains isolated from humans between 1965 and 1999 in Germany and the Czech Republic were investigated for their chromosomal and plasmid characteristics. All motile (n = 23) and nonmotile (n = 32) STEC O26 strains were shown to possess the identical flagellin subunit-encoding gene (fliC). We observed a striking recent shift of the stx genotype from stx(1) to stx(2) among the STEC O26 isolates. While stx(1) was the exclusive genotype identified in our collection until 1994, 94% of the isolates obtained after 1997 possessed stx(2) either alone (71%) or together with stx(1) (23%). Plasmid profiling demonstrated a remarkable heterogeneity with respect to plasmid sizes and combinations. Southern blot analysis of plasmid DNA with probes specific to potential accessory virulence genes revealed considerable additional variability in gene composition and arrangement. Pulsed-field gel electrophoresis (PFGE) differentiated 16 subgroups among the 55 STEC O26 strains. Using these techniques we demonstrate the emergence of a new clonal subgroup characterized by PFGE pattern A and a unique combination of virulence markers including stx(2) and a single, approximately 90-kb plasmid harboring the enterhemorrhagic E. coli hlyA and etp genes. The proportion of PFGE subgroup A strains among STEC O26 isolates rose from 30% in 1996 to more than 50% in 1999. Four clusters of infections with the clonal subgroup A were identified. We conclude that the STEC serogroup O26 is diverse and that pathogenic clonal subgroups can rapidly emerge during short intervals. The extensive genetic diversity of STEC O26 provides a basis for molecular subtyping of this important non-O157 STEC serogroup.

Bacterial Toxins↗
PubMed2001

Prospects offered by genome studies for combating meningococcal disease by vaccination.

Meningococcal disease was first recognised and Neisseria meningitidis isolated as the causative agent over 100 years ago, but despite more than a century of research, attempts to eliminate this distressing illness have so far been thwarted. The main problem lies in the fact that N. meningitidis usually exists as a harmless commensal inhabitant of the human nasopharynx, the pathogenic state being the exception rather than the norm. As man is its only host, the meningococcus is uniquely adapted to this ecological niche and has evolved an array of mechanisms for evading clearance by the human immune response. Progress has been made in combating the disease by developing vaccines that target specific pathogenic serogroups of meningococci. However, a fully comprehensive vaccine that protects against all pathogenic strains is still just beyond reach. The publication of the genome sequences of two meningococcal strains, one each from serogroups A and B and the imminent completion of a third illustrates the extent of the problems to be overcome, namely the vast array of genetic mechanisms for the generation of meningococcal diversity. Fortunately, genome studies also provide new hope for solutions to these problems in the potential for a greater understanding of meningococcal pathogenesis and possibilities for the identification of new vaccine candidates. This review describes some of the approaches that are currently being used to exploit the information from meningococcal genome sequences and seeks to identify future prospects for combating meningococcal disease.

Clinical Trials as Topic↗
PubMed2006

Insights from the genome of the biotrophic fungal plant pathogen Ustilago maydis.

Ustilago maydis is a ubiquitous pathogen of maize and a well-established model organism for the study of plant-microbe interactions. This basidiomycete fungus does not use aggressive virulence strategies to kill its host. U. maydis belongs to the group of biotrophic parasites (the smuts) that depend on living tissue for proliferation and development. Here we report the genome sequence for a member of this economically important group of biotrophic fungi. The 20.5-million-base U. maydis genome assembly contains 6,902 predicted protein-encoding genes and lacks pathogenicity signatures found in the genomes of aggressive pathogenic fungi, for example a battery of cell-wall-degrading enzymes. However, we detected unexpected genomic features responsible for the pathogenicity of this organism. Specifically, we found 12 clusters of genes encoding small secreted proteins with unknown function. A significant fraction of these genes exists in small gene families. Expression analysis showed that most of the genes contained in these clusters are regulated together and induced in infected tissue. Deletion of individual clusters altered the virulence of U. maydis in five cases, ranging from a complete lack of symptoms to hypervirulence. Despite years of research into the mechanism of pathogenicity in U. maydis, no 'true' virulence factors had been previously identified. Thus, the discovery of the secreted protein gene clusters and the functional demonstration of their decisive role in the infection process illuminate previously unknown mechanisms of pathogenicity operating in biotrophic fungi. Genomic analysis is, similarly, likely to open up new avenues for the discovery of virulence determinants in other pathogens.

Fungal Proteins↗