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PubMed2006

Epitheliocystis in fish.

Epitheliocystis is a condition affecting the gills and skin of fish, which has been reported from more than 50 freshwater and marine species. It is caused by intracellular Gram-negative bacteria. Mortalities have been associated with epitheliocystis infections in cultured fish. This review provides an update of our current understanding of this condition, including characterization of the pathogen using immunohistochemical and molecular studies. In most fish species the epitheliocystis agent was negative to an antibody specific for chlamydial genus-specific lipopolysaccharide antigen. Recently, four epitheliocystis agents from four different fish species have been characterized using molecular analysis. While they all belong to the order Chlamydiales, in a lineage separate from the Chlamydiaceae, they are distinct organisms and similarity analysis showed that they had highest similarity values with other chlamydia-like bacteria isolated from various sources, including humans or pig. This confirms the high diversity and host specificity of the pathogen. Further molecular analysis should result in an increased understanding of this condition. To date the pathogen has not been cultured, making experimental studies difficult. High stocking densities, presence of nutrients, season, temperature and fish age have been identified as potential risk factors for the manifestation of this condition.

Animals↗

PubMed2002

Sequence diversity in the major fimbrial subunit gene (flp-1) of Actinobacillus actinomycetemcomitans.

Cells of the periodontal pathogen Actinobacillus actinomycetemcomitans exhibit tight adherence to surfaces such as glass, plastic and hydroxyapatite, a property that probably plays an important role in the ability of this bacterium to colonize teeth and other surfaces. Tight adherence is mediated by long fibrils of bundled pili (fimbriae) that form on the surface of the cell. The flp-1 gene encodes the major pilin protein component of A. actinomycetemcomitans fimbriae. In this study we compared flp-1 DNA sequences from 43 strains of A. actinomycetemcomitans isolated in Europe, Japan and the United States and identified seven distinct flp-1 allelic classes. DNA and predicted protein sequences were almost completely conserved within each flp-1 class but were highly divergent between classes. Most amino acid substitutions occurred in the C-terminus of the pilin protein, a region that has been shown to be important for the bundling and adhesive properties of the pili. flp-1 classes correlated with serotypes and 16S rRNA genotypes in most strains. At least five strains showed evidence of horizontal transfer of flp-1 between strains of different serotypes and 16S rRNA genotypes. Four of the seven flp-1 classes were present in geographically diverse isolates. Strains representing all seven flp-1 classes, but not a strain carrying a transposon insertion in flp-1, bound avidly to polystyrene in an in vitro adherence assay. Strains representing six of the seven flp-1 classes were isolated from localized juvenile periodontitis patients, suggesting that phylogenetically diverse strains carry pathogenic potential. Our findings provide a framework for future biochemical, immunological and genetic studies of A. actinomycetemcomitans fimbriae.

Actinobacillus Infections↗

PubMed2005

Arcanobacterium pyogenes: molecular pathogenesis of an animal opportunist.

Arcanobacterium pyogenes is a commensal and an opportunistic pathogen of economically important livestock, causing diseases as diverse as mastitis, liver abscessation and pneumonia. This organism possesses a number of virulence factors that contribute to its pathogenic potential. A. pyogenes expresses a cholesterol-dependent cytolysin, pyolysin, which is a haemolysin and is cytolytic for immune cells, including macrophages. Expression of pyolysin is required for virulence and this molecule is the most promising vaccine candidate identified to date. A. pyogenes also possesses a number of adherence mechanisms, including two neuraminidases, the action of which are required for full adhesion to epithelial cells, and several extracellular matrix-binding proteins, including a collagen-binding protein, which may be required for adhesion to collagen-rich tissue. A. pyogenes also expresses fimbriae, which are similar to the type 2 fimbriae of Actinomyces naeslundii, and forms biofilms. However, the role of these factors in the pathogenesis of A. pyogenes infections remains to be elucidated. A. pyogenes also invades and survives within epithelial cells and can survive within J774A.1 macrophages for up to 72 h, suggesting an important role for A. pyogenes interaction with host cells during pathogenesis. The two component regulatory system, PloSR, up-regulates pyolysin expression and biofilm formation but down-regulates expression of proteases, suggesting that it may act as a global regulator of A. pyogenes virulence. A. pyogenes is a versatile pathogen, with an arsenal of virulence determinants. However, most aspects of the pathogenesis of infection caused by this important opportunistic pathogen remain poorly characterized.

Actinomycetaceae↗

PubMed2004

Foundations for a Phase III human immunodeficiency virus vaccine trial: A decade of Thai-U.S. Army collaborative research.

As part of the response of the Royal Thai Army to the outbreak of human immunodeficiency virus (HIV) in Thailand, a collaboration was established with the U.S. Army to jointly work toward the development of vaccines for the prevention of HIV infection. During the first decade of this collaboration, studies have been carried out in the diverse disciplines that are crucial to providing the foundations for efficacy trials of candidate HIV vaccines. Studies of host, pathogen, and vaccine interventions included studies of viral diversity, epidemiology, disease course, potential vaccine cohorts, and Phase I/II clinical trials. Collaborations were expanded to other Thai institutions and to overseas partners, resulting in the Thai AIDS Vaccine Evaluation Group. The efforts of these collaborations resulted in the development of candidate vaccines specifically designed for use in Thailand, and sequential evaluations that have lead to the threshold of the world's next and largest efficacy trial of HIV vaccines.

AIDS Vaccines↗

PubMed1992

Diversity among Streptomyces Strains Causing Potato Scab.

Eighty Streptomyces isolates, including 35 potato scab-inducing strains and 12 reference strains of Streptomyces scabies, were physiologically characterized by a total of 329 miniaturized tests. Overall similarities of all strains were determined by numerical taxonomy, with the unweighted average linkage (UPGMA) algorithm and simple matching (S(sm)) and Jaccard (S(j)) coefficients used as measures for similarity. Three cluster groups (A to C) were defined at a similarity level of 80.1% (S(sm)); these groups contained 14 clusters and 24 unclustered strains defined at a similarity level of 86.5% (S(sm)). Cluster group A contained strains phenotypically related to S. griseus or S. exfoliatus, whereas cluster group B contained strains which were phenotypically related to S. violaceus or S. rochei. The majority of the pathogenic isolates and reference strains were assigned to S. violaceus (57%) and S. griseus (22%). A DNA probe derived from the rRNA operon of S. coelicolor IMET 40271 was used to detect restriction fragment length polymorphisms (RELPs) among 40 pathogenic and nonpathogenic Streptomyces isolates. Southern blots revealed a high degree of diversity among the pathogenic strains tested. No significant correlation between numerical classification and RFLP grouping of Streptomyces strains could be revealed. The results obtained suggest that RFLP data are of minor importance in classification of Streptomyces species and that genes for pathogenicity determinants are spread among different Streptomyces species by mobilizable elements.

Journal Article↗

PubMed2025

Comparative Genomic Analysis of Six Mycoplasma Gallisepticum Strains: Insights into Genetic Diversity and Antibiotic Resistance.

Mycoplasma gallisepticum (MG) is a significant pathogen that causes respiratory diseases, which have had a substantial economic impact on the poultry industry. Despite the resistance of MG to antibiotics, it is imperative to identify genetic diversity in order to develop countermeasures. In this study, the genomes of six MG strains were examined to gain deeper insights into the mutations. The data pertaining to Variant Annotation and Mutation Analysis using SnpEff, along with the calculation of mutation rates as the ratio of total mutations to the length of the genomic regions analyzed, were thoroughly examined. The comprehensive evaluation yielded a total of 25,942 variants across the six strains, underscoring substantial genetic diversity. Notably, strain S6 exhibited a preponderance of frameshift mutations. A notable finding was the presence of a mutation in the MsbA gene shared by all six strains. Furthermore, five of the six strains, with the exception of strain F99 Lab, exhibited a mutation at position 5158, which impacts a multidrug transport system. Notably, strain ATCC exhibits a distinctive mutation at position 942, while strain S6 displays a unique mutation at position 6855, which is linked to efflux ABC transporter components. Furthermore, a substantial degree of genetic variation was observed among the CrmA, GapA, and vlhA genes among the various strains. High-impact changes, such as insertions and deletions, exhibited a higher frequency in CrmA, particularly in strain S6. Conversely, nonsynonymous variations demonstrated a heightened prevalence in GapA, particularly in strain F99 Lab. The vlhA gene exhibited a spectrum of effects, ranging from synonymous mutations to high-impact mutations such as stop-gains and frameshifts, particularly in strains k5111a and k4602. The functional variations observed among the strains can be attributed to these mutations, which have the potential to alter gene expression or protein function. Furthermore, substantial mutations in the dxr and rpoC genes were associated with antibiotic resistance. These mutations underscore the ongoing evolutionary adaptations of M. gallisepticum. Consequently, there is an imperative for the revision of treatment protocols and the formulation of targeted vaccines to regulate resistance within the poultry industry.

Mycoplasma gallisepticum↗

PubMed2005

Heat shock proteins as endogenous adjuvants in sterile and septic inflammation.

Heat shock proteins (HSPs) have been reported to stimulate the immune system via innate receptors. However, the role of HSPs as endogenous adjuvants has been challenged by reports claiming that pure HSPs are not innate ligands; it is only the bacterial molecules trapped by the HSPs that can signal the innate immune system. In this review, we discuss data suggesting that both views, in essence, are correct; pure HSPs are indeed innate immunostimulators, but HSPs can also function as transducers of pathogen signals. In other words, HSPs perform diverse functions in two alternative modes of inflammation: sterile inflammation, which results from endogenous stimuli and is necessary for body maintenance, and septic inflammation, which protects us from environmental pathogens. Endogenous HSPs are key players in the modulation of these two modes of inflammation, and as such, they are potential targets for new and more efficient therapies for cancer, infections, and autoimmunity.

Animals↗

PubMed2005

Clostridium bacteraemia characterised by 16S ribosomal RNA gene sequencing.

BACKGROUND: Owing to problems in accurate species identification of the diverse genus clostridium, the epidemiology and pathogenicity of many species are not fully understood. Moreover, previous studies on clostridium bacteraemia have been limited and relied only on phenotypic species identification. AIMS: To characterise the epidemiology, disease spectrum, and outcome of clostridium bacteraemia using 16S ribosomal RNA (rRNA) gene sequencing. METHOD: During a four year period (1998-2001), all cases of clostridium bacteraemia were prospectively studied and all "non-perfringens" clostridium isolates identified to the species level by 16S rRNA gene sequencing. RESULTS: Fifty one blood culture isolates were identified as Clostridium perfringens and 17 belonged to 11 other clostridium species. The first case of C disporicum infection and two cases of clostridium bacteraemia in children with intussusception were also described. Of the 68 clostridium isolates from 68 different patients, 38 were associated with clinically relevant bacteraemia. The gastrointestinal and hepatobiliary tracts were common sites of both underlying disease and portal of entry in these patients. Clostridium perfringens accounted for 79% of all clinically relevant bacteraemia, with the remainder caused by a diversity of species. The attributable mortality rate of clinically relevant clostridium bacteraemia was 29%. Younger age and underlying gastrointestinal/hepatobiliary tract disease were associated with mortality (p < 0.05). CONCLUSIONS: Patients with clinically relevant clostridium bacteraemia should be investigated for the presence of underlying disease processes in the gastrointestinal or hepatobiliary tracts. 16S rRNA gene analysis will continue to be useful in further understanding the pathogenicity of various clostridium species.

Adult↗

PubMed1998

Genetic epidemiology of parasitic protozoa and other infectious agents: the need for an integrated approach.

This paper emphasises the relevance of the concepts and methods of evolutionary genetics for studying the epidemiology of parasitic protozoa and other pathogenic agents. Population genetics and phylogenetic analysis both contribute to identifying the relevant evolutionary and epidemiologically discrete units of research (Discrete typing units = DTUs), that can be equated to distinct phylogenetic lines. It is necessary (i) to establish that a given species represents a reliable DTU; (ii) to see whether a given species is further structured into lower DTUs that correspond to either clonal lineages or to cryptic species, and could exhibit distinct biomedical properties (virulence, resistance to drugs, etc). DTUs at the species and subspecies level can be conveniently identified by specific genetic markers or sets of genetic markers ("tags") for epidemiological follow-up. For any kind of pathogen (protozoa, fungi, bacteria, viruses), DTUs represent the relevant units of research, not only for epidemiology, but also, for other applied researches (clinical study, pathogenicity, vaccine and drug design, immunology, etc). The development of an "integrated genetic epidemiology of infectious diseases", that would explore the respective role of, and the interactions between, the genetic diversity (and its biological consequences) of the pathogen, the host and the vector (in the case of vector-borne diseases) is called for.

Animals↗

PubMed2003

Thymic selection does not limit the individual MHC diversity.

The number of different major histocompatibility (MHC) molecules expressed per individual is widely believed to represent a trade-off between maximizing the detection of foreign antigens, and minimizing the loss of T cell clones due to self-tolerance induction. Using a mathematical model we here show that this argument fails to explain why individuals typically express of the order of 1020 different MHC molecules. Expression of extra MHC types decreases the number of clones surviving negative selection, but increases the number of positively selected clones. Based on experimental parameter estimates, we show that the number of clones in the functional T cell repertoire would in fact increase if the MHC diversity within an individual were to exceed its normal value, until more than one hundred different MHC molecules would be expressed. Since additional MHC types also increase the number of presented pathogen peptides, resistance against pathogens only decreases at unrealistically high MHC diversities exceeding 1,500 different MHC molecules per individual.

Animals↗

PubMed2005

Intestinal bacteria and development of the B-lymphocyte repertoire.

Vertebrates have a large antibody repertoire with diverse antigen specificities, poised to react to invading pathogens, such as bacteria, viruses and helminths. In some species, microbes such as these are required for development of both diverse antibody and B-lymphocyte repertoires. Recent studies demonstrate that B-lymphocyte expansion, selection and somatic diversification of Ig genes are regulated in these species, in part, by the interaction between commensal intestinal bacteria and gut-associated lymphoid tissue (GALT). These findings indicate that the commensal microbiota can shape the repertoire of peripheral B lymphocytes and can potentially influence the health of the host. Here, how the interactions between commensal microbiota and lymphoid cells of GALT might affect the development of the peripheral B-lymphocyte repertoire is discussed.

Animals↗

PubMed2000

Sequence diversity of a fragment of the 16S RNA gene from Helicobacter pylori.

Helicobacter pylori is one of the most common bacterial pathogens. It is the main cause of gastric and duodenal ulcers and has been associated with other diseases. The organism seems to be more genetically diverse than other bacterial pathogens, and the source of these differences awaits explanation. The sequence of a fragment of the 16S rRNA gene was determined for ten strains of H. pylori to examine the contribution of point mutation within a conserved gene. There were few differences between the sequences from the various strains and it was concluded that such differences were not the most important source of diversity.

Base Sequence↗

PubMed2006

Phylogenomic analysis of non-ribosomal peptide synthetases in the genus Aspergillus.

Fungi from the genus Aspergillus are important saprophytes and opportunistic human fungal pathogens that contribute in these and other diverse ways to human well-being. Part of their impact on human well-being stems from the production of small molecular weight secondary metabolites, which may contribute to the ability of these fungi to cause invasive fungal infections and allergic diseases. In this study, we identified one group of enzymes responsible for secondary metabolite production in five Aspergillus species, the non-ribosomal peptide synthetases (NRPS). Hidden Markov models were used to search the genome databases of A. fumigatus, A. flavus, A. terreus, A. nidulans, and A. oryzae for domains conserved in NRPS proteins. A genealogy of adenylation domains was utilized to identify orthologous and unique NRPS among the Aspergillus species examined, as well as gain an understanding of the potential evolution of Aspergillus NRPS. mRNA abundance of the 14 NRPS identified in the A. fumigatus genome was analyzed using real-time reverse transcriptase PCR in different environmental conditions to gain a preliminary understanding of the possible functions of the NRPSs' peptide products. Our results suggest that Aspergillus species contain conserved and unique NRPS genes with a complex evolutionary history. This result suggests that the genus Aspergillus produces a substantial diversity of non-ribosomally synthesized peptides. Further analysis of these genes and their peptide products may identify important roles for secondary metabolites produced by NRPS in Aspergillus physiology, ecology, and fungal pathogenicity.

Amino Acid Sequence↗

PubMed2006

Neuroprotection in vascular dementia.

Vascular dementia (VaD) is the second most common form of dementia after Alzheimer's disease (AD), and one of the major causes of mental and physical disability in developed countries. As such, the identification and implementation of strategies which prevent the development of the condition or enable improvements in patients with VaD are healthcare objectives of the first order. VaD is now regarded as a combined group of clinical-pathological entities rather than one disease, that is, multiple pathogenic mechanisms and lesion types underlie a cognitive impairment of vascular origin. The clinical diagnosis of VaD is complex and difficult because of the heterogeneous nature of its clinical presentation and progression and the low sensitivity of existing clinical criteria. Moreover, there is growing evidence of the epidemiological significance of mixed forms of dementia, and that ischemic processes may precipitate and exacerbate cognitive impairment in AD. Numerous compounds have been proposed as potentially useful in the treatment of patients with VaD, comprising vasodilatative, antithrombotic, hemorrheological, nootropic, antiserotoninergic and, most recently, antiglutamatergic and cholinergic approaches. In spite of some initially favorable reports based on the use of memantine, donepezil and galantamine, there is as yet no conclusive evidence of a definitive treatment for VaD. Unsatisfactory results from VaD drug trials may be attributed in part to the diversity of the patients included (underlying pathogenic mechanisms, number, type, and location of vascular lesions), and to methodological limitations in the design of the trials (outcome measures, end-points, size, follow-up period). The treatment of modifiable vascular risk factors - hypertension, diabetes mellitus, hypercholesterolemia and heart disease - is an important strategy for the reduction of the risk of dementia, and is likely to slow the progress of cognitive decline.

Animals↗

PubMed2002

Preservation of clonal heterogeneity of the Pneumocystis carinii-specific CD4 T cell repertoire in HIV infected, asymptomatic individuals.

The loss of CD4 lymphocytes in HIV disease associates with opportunistic infections. Since diverse CD4 T cell clones respond to an opportunistic pathogen, we asked whether CD4 depletion deletes selected clones in the repertoire (vertical depletion) or it affects all clones by reducing the cell number in each progeny without affecting the overall number of clones (horizontal depletion). Understanding this point may help explain the mode of CD4 depletion and the mode of immunoreconstitution after therapy. Therefore we examined the CD4 T cell repertoire specific for Pneumocystis carinii, a relevant opportunistic pathogen in AIDS, in HIV-infected, asymptomatic individuals. We identified two patients of 36 asymptomatics for lack of proliferation to P. carinii, suggesting selective depletion of specific CD4 cells. To investigate clonal heterogeneity of P. carinii-responsive CD4 lymphocytes, specific CD4 T cell lines were generated and studied by TCR BV gene family usage and CDR3 length analysis (spectratyping). Clonal heterogeneity was similar in antigen-specific CD4 lines generated from P. carinii non-responding HIV seropositives and from controls. Thus, despite undetectable response to the pathogen, residual specific cells probably prevent overt infection and, when expanded in vitro, exhibit a clonal diversity similar to normal controls. These findings suggest a horizontal, rather than vertical, depletion in these asymptomatic patients.

AIDS-Related Opportunistic Infections↗

PubMed2003

Genetic diversity within honeybee colonies prevents severe infections and promotes colony growth.

Multiple mating by social insect queens increases the genetic diversity among colony members, thereby reducing intracolony relatedness and lowering the potential inclusive fitness gains of altruistic workers. Increased genetic diversity may be adaptive, however, by reducing the prevalence of disease within a nest. Honeybees, whose queens have the highest levels of multiple mating among social insects, were investigated to determine whether genetic variation helps to prevent chronic infections. I instrumentally inseminated honeybee queens with semen that was either genetically similar (from one male) or genetically diverse (from multiple males), and then inoculated their colonies with spores of Ascosphaera apis, a fungal pathogen that kills developing brood. I show that genetically diverse colonies had a lower variance in disease prevalence than genetically similar colonies, which suggests that genetic diversity may benefit colonies by preventing severe infections.

Animals↗

PubMed2006

Structural congruence among membrane-active host defense polypeptides of diverse phylogeny.

A requisite for efficacious host defense against pathogens and predators has prioritized evolution of effector molecules thereof. A recent multidimensional analysis of physicochemical properties revealed a novel, unifying structural signature among virtually all classes of cysteine-containing antimicrobial peptides. This motif, termed the gamma-core, is seen in host defense peptides from organisms spanning more than 2.6 billion years of evolution. Interestingly, many toxins possess the gamma-core signature, consistent with discoveries of their direct antimicrobial activity. Many microbicidal chemokines (kinocidins) likewise contain iterations of the gamma-core motif, reconciling their antimicrobial efficacy. Importantly, these polypeptide classes have evolved to target and modulate biomembranes in protecting respective hosts against unfavorable interactions with potential pathogens or predators. Extending on this concept, the current report addresses the hypothesis that antimicrobial peptides, kinocidins, and polypeptide toxins are structurally congruent and share a remarkably close phylogenetic relationship, paralleling their roles in host-pathogen relationships. Analyses of their mature amino acid sequences demonstrated that cysteine-stabilized antimicrobial peptides, kinocidins, and toxins share ancient evolutionary relatedness stemming from early precursors of the gamma-core signature. Moreover, comparative 3-D structure analysis revealed recurring iterations of antimicrobial peptide gamma-core motifs within kinocidins and toxins. However, despite such congruence in gamma-core motifs, the kinocidins diverged in overall homology from microbicidal peptides or toxins. These findings are consistent with observations that chemokines are not toxic to mammalian cells, in contrast to many antimicrobial peptides and toxins. Thus, specific functions of these molecular effectors may be governed by specific configurations of structural modules associated with a common gamma-core motif. These concepts are consistent with the hypothesis that the gamma-core is an archetype determinant in polypeptides that target or regulate with biological membranes, with specific iterations optimized to unique or cognate host defense contexts. Quantitative and qualitative data suggest these protein families emerged through both parallel and divergent processes of modular evolution. Taken together, the current and prior findings imply that the gamma-core motif contributes to conserved structures and functions of host defense polypeptides. The presence of this unifying molecular signature in otherwise diverse categories of membrane-active host defense peptides implies an ancient and essential role for such a motif in effector molecules governing host-pathogen relationships.

Amino Acid Sequence↗

PubMed2006

Pyoverdine siderophores: from biogenesis to biosignificance.

Pyoverdines are a group of structurally related siderophores produced by fluorescent Pseudomonas species. Recent genomic and biochemical data have shed new light on the complex molecular steps of pyoverdine biogenesis and explained the chemical diversity of these compounds. In the opportunistic pathogen Pseudomonas aeruginosa, pyoverdine is necessary for infection in several different disease models. The occurrence of pyoverdine-defective strains in chronic infections of patients with cystic fibrosis and the extremely high sequence diversity of genes involved in pyoverdine synthesis and uptake indicate that pyoverdine production is subject to high evolutionary pressure. Pyoverdine-dependent iron transport is also crucial for biofilm development, further expanding the importance of these siderophores in Pseudomonas biology.

Bacterial Proteins↗