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Results for “Virulence factor”

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PubMed1993

Differential regulation of Bordetella pertussis virulence factors.

Bordetella pertussis, the causative agent of whooping cough, regulates its virulence factors coordinately according to environmental parameters such as temperature and certain chemicals. A regulatory locus has been characterized which is essential for this regulation. This bvg locus codes for a two-component regulatory system composed of the sensor protein BvgS and the transcriptional activator protein BvgA. It has been shown that the BvgA and BvgS proteins are sufficient for the transcriptional regulation of some virulence factors such as the filamentous haemagglutinin (FHA) involved in adhesion. The recent identification of new regulatory mutants demonstrates that the regulation of some virulence factors such as the pertussis toxin (PTX) and the adenylate cyclase toxin (CYA) is more complex and involves additional regulatory factor(s). This finding suggests that the regulation of the various virulence factors is coordinated at the highest level of regulation, but there may be differences in the fine regulation of some of the factors such as the adhesins and the toxins.

Bacterial Proteins↗

PubMed2003

Evidence that intracellular beta1-2 mannan is a virulence factor in Leishmania parasites.

The protozoan parasite Leishmania mexicana proliferates within macrophage phagolysosomes in the mammalian host. In this study we provide evidence that a novel class of intracellular beta1-2 mannan oligosaccharides is important for parasite survival in host macrophages. Mannan (degree of polymerization 4-40) is expressed at low levels in non-pathogenic promastigote stages but constitutes 80 and 90% of the cellular carbohydrate in the two developmental stages that infect macrophages, non-dividing promastigotes, and lesion-derived amastigotes, respectively. Mannan is catabolized when parasites are starved of glucose, suggesting a reserve function, and developmental stages having low mannan levels or L. mexicana GDPMP mutants lacking all mannose molecules are highly sensitive to glucose starvation. Environmental stresses, such as mild heat shock or the heat shock protein-90 inhibitor, geldanamycin, that trigger the differentiation of promastigotes to amastigotes, result in a 10-25-fold increase in mannan levels. Developmental stages with low mannan levels or L. mexicana mutants lacking mannan do not survive heat shock and are unable to differentiate to amastigotes or infect macrophages in vitro. In contrast, a L. mexicana mutant deficient only in components of the mannose-rich surface glycocalyx differentiates normally and infects macrophages in vitro. Collectively, these data provide strong evidence that mannan accumulation is important for parasite differentiation and survival in macrophages.

Animals↗

PubMed1989

[Immunobiologic activity of Bordetella pertussis strains defective in various virulence factors].

The immunobiological properties of mutant strains, selectively deprived of certain antigens (hemagglutinin, B. pertussis toxin, dermonecrotic toxin, hemolysin, adenylate cyclase), have been studied with the aim of finding out the relationship between the presence of certain antigens in microbial strains and their protective properties. The results of these studies suggest that the protective potency of pertussis vaccine may be related to the presence of some antigenic substances, including those not pertaining to the known factors of virulence.

Adenylate Cyclase Toxin↗

PubMed1990

Molecular aspects of some virulence factors of Haemophilus somnus.

Several virulence factors of Haemophilus somnus have been investigated, but to a varying extent. It is known that some isolates are more virulent than others. Factors associated with virulence include attachment to vaginal epithelial cells, turbinate cells or embryos; serum resistance; growth stimulation by normal flora; interference with phagocyte function; Fc receptors; and toxicity for several bovine cell types. Lipooligosaccharide and Fc receptors have been investigated at the molecular level and studies are in progress to relate their molecular structure to virulence.

Animals↗

PubMed1995

Comparison of expression of virulence factors by Escherichia coli causing cystitis and E. coli colonizing the periurethra of healthy girls.

The prevalence of virulence factors possessed by Escherichia coli colonizing the periurethra was examined and compared with that of E. coli causing urinary tract infection. One hundred two E. coli isolates obtained from the periurethra and urine of 7 non-sexually active girls at risk for cystitis were characterized for genetic relatedness and examined for expression of six virulence factors. Expression of virulence factors in colonizing clones of E. coli were compared with expression in clones from symptomatic infection. All virulence factors except P adhesin were commonly expressed by colonizing clones of E. coli that did not go on to infect the urinary tract. Although P adhesin-expressing E. coli were commonly isolated from episodes of cystitis, the presence of P adhesin on periurethral E. coli did not usually predict subsequent infection. By itself, expression of virulence factors on periurethral E. coli is not enough to predict subsequent infection.

Agglutination Tests↗

PubMed2000

Decreased virulence of a strain of Pseudomonas aeruginosa O12 overexpressing a chromosomal type 1 beta-lactamase could be due to reduced expression of cell-to-cell signaling dependent virulence factors.

Pseudomonas aeruginosa produces a large variety of virulence factors and is characterized by its capacity to rapidly develop resistance when exposed to antibiotics. In order to evaluate a possible correlation between acquired resistance to antibiotics and virulence, we examined the virulence of four isogenic variants of P. aeruginosa O12 that differ in their resistance phenotypes to various beta-lactam antibiotics in a mouse model of acute pneumonia. Strains overproducing a chromosomal type 1 beta-lactamase were less virulent in both immunocompetent and immunosuppressed animals. Whereas the production of the exopolysaccharide alginate was similar between the four strains, extracellular virulence factors (elastase, rhamnolipid) that are controlled by the cell-to-cell signaling system circuit were detected in reduced amounts in the supernatant of the two isolates overproducing type 1 beta-lactamase. These results suggest that strains overexpressing the chromosomal type 1 beta-lactamase could be less virulent because of a reduction of cell-to-cell signaling dependent virulence factor production.

Alginates↗

PubMedDate not supplied

[Significance of Pseudomonas aeruginosa virulence factors in acute and chronic Pseudomonas aeruginosa infections].

The virulence of Pseudomonas aeruginosa is multifactorial and caused by several extracellular enzymes and other substances. The importance of these virulence factors for the pathogenesis of human P. aeruginosa infections is dependent on the type of infection. For acute, systemic infections in immunocompromised patients, exotoxin A, alkaline protease and elastase are essential virulence factors. In localized infections (e.g., cystic fibrosis) they seem to be of minor importance, since they are neutralized by specific antibodies in immune complexes, and in the case of exotoxin A cleavage by proteinases from polymorphonuclear leukocytes occurs. The rhamnolipid of P. aeruginosa which has been detected in sputa of patients with cystic fibrosis evades the host's immune response and has to be regarded as a potential virulence factor together with the phenazine pigments, also in chronic P. aeruginosa infections.

ADP Ribose Transferases↗

PubMed1987

[Significance of Pseudomonas aeruginosa virulence factors for acute and chronic Pseudomonas aeruginosa infections].

The virulence of Pseudomonas aeruginosa is multifactorial and caused by several extracellular enzymes and other substances. The importance of these virulence factors for the pathogenesis of human P. aeruginosa infections is dependent on the type of infection. For acute, systemic infections in immunocompromised patients, exotoxin A, alkaline protease and elastase are essential virulence factors. In localized infections (e. g., cystic fibrosis) they seem to be of minor importance, since they are neutralized by specific antibodies in immune complexes, and in the case of exotoxin A cleavage by proteinases from polymorphonuclear leukocytes occurs. The rhamnolipid of P. aeruginosa which has been detected in sputa of patients with cystic fibrosis evades the host's immune response and has to be regarded as a potential virulence factor together with the phenazine pigments, also in chronic P. aeruginosa infections.

ADP Ribose Transferases↗

PubMed1997

Superantigens as virulence factors in autoimmunity and immunodeficiency diseases.

Virulence factors are microbial products that are known to be harmful to the host and may assist in the pathogenesis of the micro-organism. Superantigens, including those produced by bacteria and viruses, clearly act as virulence factors. The clinical effects of superantigens can be not only acute but also chronic and complex. Recent evidence suggests that superantigens may play a central role in the pathogenesis of autoimmune and immunodeficiency disorders. It is our contention that superantigens, as environmental factors, can change a controllable disease into one that becomes relentless for susceptible individuals. To illustrate the detrimental effects of superantigens on disease outcome, modulation of experimental allergic encephalomyelitis by superantigen, as well as the potential role of superantigens in human immunodeficiency virus pathogenesis will be discussed. The information presented may provide valuable insight into the role of superantigens in autoimmunity and human immunodeficiency virus infection.

Animals↗

PubMed2000

Putative virulence factors of Aspergillus fumigatus.

Various putative virulence factors of Aspergillus fumigatus have been studied over the past decades. A. fumigatus gliotoxin is a potent inhibitor of the mucociliary system. Several fungal metabolites interfere with phagocytosis and opsonization including toxins, 'conidial inhibitory factor', 'A. fumigatus diffusible product' and 'complement inhibitory factor'. A. fumigatus can bind specifically to different host tissues components, whereas toxins give a general and significant immunosuppressive effect on host defences. Circumstantial evidence links the production of elastinolytic proteases with the ability to cause disease. However, none of the reports demonstrates conclusively a decisive role for any of the virulence factors described thus far. It is conceivable that proteolytic enzyme activities such as those expressed by AFAlp are one of a number of factors, each with a minor effect, that combine to facilitate disease progression.

Aspergillosis↗

PubMed1991

Virulence factors in Bacteroides fragilis group.

Attempts were made to study the virulence factors in some strains of B. fragilis group in the rat model. Subcutaneous wound abscesses could be produced by 10(9) CFU/ml of live cells of all the five species of B. fragilis group tested. For determination of virulence factor cellular components (capsular polysaccharide and lipopolysaccharide) of B. fragilis were separated using gel filtration technique and injected in rats. Abscesses could be produced only by capsular polysaccharide fraction suggesting it to be the virulence factor. Studies with transmission electron microscope showed presence of capsular polysaccharide in B. fragilis and B. thetaiotaomicron, it was doubtful in B. distasonis and absent in B. ovatus and B. vulgatus. This suggested that virulence factors other than capsular polysaccharide may be responsible for pyogenic lesions in the noncapsulated species of B. fragilis group. The abscess could not be produced by 10(9) CFU/ml of heat killed cells of non-capsulated B. ovatus and B. vulgatus indicating that in live bacteria, a heat labile factor was responsible for the development of abscess.

Abscess↗

PubMed1998

Disparate findings on the role of virulence factors of Enterococcus faecalis in mouse and rat models of peritonitis.

The role of Enterococcus faecalis in polymicrobial peritonitis is still debated. Virulence factors expressed in some enterococcal strains might be involved in the pathogenicity of these organisms. To clarify their role, three of these virulence factors (cytolysin, gelatinase, and aggregation substance) were studied in six isogenic strains of E. faecalis expressing various combinations of these factors. Since the pathogenic effects of enterococci are only moderate, the expression of their virulence might vary from one animal species to another and from one type of infection to another. Therefore, we evaluated these effects in two animal models, i.e., a systemic infection in mice in which we assessed the virulence of the strains in 50% lethal dose studies and a model of compartmentalized infection in rats in which the microbiologic and inflammatory effects of the strains were evaluated in monomicrobial or polymicrobial infection. In mice, significant differences were observed in the cumulative survival curves depending on the virulence factors (P < 0.0001 [log rank test]). In rats, monomicrobial infection induced only mild changes. In polymicrobial peritonitis, the virulence factors mainly increased the inflammatory response while the changes observed in the microbiologic response were minimal. The combination of two virulence factors did not significantly increase the severity of infection either in the mice model or the polymicrobial rat model. These data argue for species and model dependence of the role of the virulence factors studied here and suggest that other important factors may be involved in the pathogenicity of enterococci.

Animals↗

PubMed2005

Microarray analysis of Bacillus cereus group virulence factors.

Bacillus cereus, B. thuringiensis and B. anthracis are closely related medically and economically important bacterial species that belong to the B. cereus group. Members of the B. cereus group carry genes encoding several important virulence factors, including enterotoxins, phospholipases and exotoxins. Since it is difficult to differentiate among B. cereus group members, and because Bacillus virulence factors are very important for pathogenesis, we explored the use of microarray-based detection of virulence factor genes as a tool for strain identification and for determining virulence. Our method requires an initial multiplex PCR amplification step, followed by identification of the PCR amplicons by hybridization to an oligonucleotide microarray containing genes for all three types of Bacillus virulence factors including B. anthracis virulence factors. The DNA chip described here contains 21 identical arrays used for analysis of seven samples in triplicates. Using the arrays, we found that virulence factors are present in several combinations in the strains analyzed. This work also demonstrates the potential of oligonucleotide microarrays for medical, food safety and biodefense analysis of microbial pathogens.

Bacillus cereus↗

PubMed2005

E. coli virulence factors in children with neurogenic bladder associated with bacteriuria.

The value of E. coli virulence factors in patients with neurogenic bladder has not been established. The aim of this study is to correlate E. coli virulence factors with asymptomatic and symptomatic UTI in children with neurogenic bladder. Fifty E. coli strains, which were collected in sequence, underwent analysis in relation to: the association to pyuria, serotype (O:H), the presence of genes and expression of fimbriae P, type 1, S and hemagglutinin Dr, the presence of the gene and production of hemolysins and cytotoxins (CNF1). We also analyzed the cell adherence capability and pattern and presence of usp (uropathogenic-specific protein). Pyuria was present in most of the positive urine cultures, with 86% AB and 97% UTI. Low rates of uropathogenic strains were observed in the two groups, with 18% AB and 21% UTI. Type 1 fimbria predominated in 44% of the E. coli strains. Of the bacteria studied, 30% (15 strains) exhibited papG genotypes (11 class II and 4 class III). Of these, 12/15 patients presented AB. Production of hemolysins was detected in 38% of the strains (16 AB and 3 UTI) and usp in only 18% of the strains, with 8 AB and 1 UTI. Adherence tests demonstrated the adhesive capacity in all samples analyzed. Neither group (AB or symptomatic UTI) presented a statistically significant difference in relation to the virulence factors studied. E. coli clones that caused symptomatic UTI in children with neurogenic bladder expressed few virulence factors, with no statistically significant difference in comparison to the AB group.

Bacterial Adhesion↗

PubMed2005

Brucella lipopolysaccharide acts as a virulence factor.

Brucella is a facultative intracellular bacterium responsible for brucellosis. Virulence factors involved in Brucella replication and Brucella's strategies to circumvent the immune response are under investigation. VirB proteins that form the type IV secretion system and that are involved in intracellular replication are considered as one of Brucella's virulence factors. In addition to this secretion system, bacterial outer membrane components have also been described as being implicated in Brucella survival in the host. For example, this bacterium possesses an unconventional non-endotoxic lipopolysaccharide that confers resistance to anti-microbial attacks and modulates the host immune response. These properties make lipopolysaccharide an important virulence factor for Brucella survival and replication in the host.

Animals↗

PubMed2006

MvirDB--a microbial database of protein toxins, virulence factors and antibiotic resistance genes for bio-defence applications.

Knowledge of toxins, virulence factors and antibiotic resistance genes is essential for bio-defense applications aimed at identifying 'functional' signatures for characterizing emerging or engineered pathogens. Whereas genetic signatures identify a pathogen, functional signatures identify what a pathogen is capable of. To facilitate rapid identification of sequences and characterization of genes for signature discovery, we have collected all publicly available (as of this writing), organized sequences representing known toxins, virulence factors, and antibiotic resistance genes in one convenient database, which we believe will be of use to the bio-defense research community. MvirDB integrates DNA and protein sequence information from Tox-Prot, SCORPION, the PRINTS virulence factors, VFDB, TVFac, Islander, ARGO and a subset of VIDA. Entries in MvirDB are hyperlinked back to their original sources. A blast tool allows the user to blast against all DNA or protein sequences in MvirDB, and a browser tool allows the user to search the database to retrieve virulence factor descriptions, sequences, and classifications, and to download sequences of interest. MvirDB has an automated weekly update mechanism. Each protein sequence in MvirDB is annotated using our fully automated protein annotation system and is linked to that system's browser tool. MvirDB can be accessed at http://mvirdb.llnl.gov/.

Bacterial Proteins↗

PubMed1994

Virulence factors in clinical and food isolates of Aeromonas species.

Virulence factors were compared in 15 Aeromonas spp. isolated from faeces of patients with Aeromonas-associated gastroenteritis and in 81 strains isolated from food. Strains from food did not show differences in the distribution of virulence factors when compared with strains isolated from faeces. However, 88.8% of Aeromonas strains isolated from food were capable of producing possible virulence factors. Characterization of 28 autoagglutinating (AA+) Aeromonas spp. indicated that the human strains differed from the food strains in hemagglutinating and hemolytic capacities. These results suggest that autoagglutination associated with hemagglutinating and hemolytic capacities in food strains may be a helpful indicator of potential pathogenicity.

Acriflavine↗

PubMed2001

Virulence factors of Escherichia coli isolated from urine of diabetic women with asymptomatic bacteriuria: correlation with clinical characteristics.

Since Escherichia coli isolated from compromised patients with symptomatic urinary tract infections (UTIs) express fewer virulence factors than those isolated from healthy controls, the question arises whether this is also the case for diabetic patients with asymptomatic bacteriuria (ASB). Polymerase chain reaction (PCR) assays were conducted on 111E. coli strains, isolated from the urine of diabetic women with ASB, using primers for the major subunit A and the G-adhesin (I, II, and III) of P fimbriae, type 1 fimbriae, S fimbriae, afimbrial adhesin, cytotoxic necrotizing factor (CNF), and aerobactin. Phenotypically, hemolysis, mannose-sensitive hemagglutination, mannose-resistant hemagglutination and O:K:H-serotypes were determined. Furthermore, we investigated the associations between virulence factors and patient characteristics (including deterioration of renal function). Type 1 fimbriae were the most prevalent virulence factor (86% by genotyping and 59% phenotypically). Except for a lower prevalence of known uropathogenic O-serotypes, we found the same number of virulence factors in our compromised patient group as listed in the literature in noncompromised patients with ASB. Certain virulence factors (type 1 and S fimbriae and CNF) of the causative E. coli correlated with the risk of a decline in renal function. In conclusion, the number of virulence factors in E. coli isolated from the urine of diabetic women with ASB are comparable with the results found in other (noncompromised) patients with ASB. Furthermore, certain virulence factors of E. coli might contribute to a decline in renal function.

Adult↗