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At least 397 records · Page 22Linked to original sources
PubMed2006

Does genetic diversity hinder parasite evolution in social insect colonies?

Polyandry is often difficult to explain because benefits of the behaviour have proved elusive. In social insects, polyandry increases the genetic diversity of workers within a colony and this has been suggested to improve the resistance of the colony to disease. Here we examine the possible impact of host genetic diversity on parasite evolution by carrying out serial passages of a virulent fungal pathogen through leaf-cutting ant workers of known genotypes. Parasite virulence increased over the nine-generation span of the experiment while spore production decreased. The effect of host relatedness upon virulence appeared limited. However, parasites cycled through more genetically diverse hosts were more likely to go extinct during the experiment and parasites cycled through more genetically similar hosts had greater spore production. These results indicate that host genetic diversity may indeed hinder the ability of parasites to adapt while cycling within social insect colonies.

Animals↗
PubMed2005

Molecular epidemiology of emergent multidrug-resistant Salmonella enterica serotype Typhimurium strains carrying the virulence resistance plasmid pUO-StVR2.

OBJECTIVES: To evaluate the incidence of a distinct multidrug-resistant (MDR) grouping of Salmonella serotype Typhimurium strains carrying the hybrid virulence resistance plasmid pUO-StVR2, and its possible evolution in the region where it was first detected [Principality of Asturias (PA), Spain]. METHODS: pUO-StVR2-containing isolates were tentatively identified by two genetic markers: the bla(OXA-30) gene and the class 1 integron InH:2000 bp/bla(OXA-30)-aadA1a. Positive isolates were examined for resistance profile (RP), plasmid content, virulence profile (VP) and genomic polymorphisms using macrorestriction-PFGE. RESULTS: A total of 182 out of 248 Typhimurium clinical isolates recorded in the PA over 2001-02 were ampicillin-resistant and could be distributed into several MDR groupings. A MDR grouping carrying pUO-StVR2, with a defined RP (AMP/bla(OXA-30), CHL/catA1, [STR-SPT]/[strA/B,aadA1a], SUL/[sul1,sul2], TET/tet(B), qacEDelta1, merA, +/-TMP/dfrA12, and containing InH), was represented by 49 isolates. The VPs of these isolates (24 genes screened) differed from that of the type strain LT2 by the absence of the sopE1 and pef genes. Macrorestriction analysis established six combined XbaI/BlnI PFGE profiles, and supported a clonal relationship among most of the isolates. CONCLUSIONS: During 2001-02, the isolates carrying pUO-StVR2 constituted the second most frequent S. Typhimurium MDR grouping recorded in the PA, preceded only by the pandemic pentaresistant DT104. Polymorphisms on the genomic DNA, different phage types, different plasmid profiles and the detection of trimethoprim resistance in one isolate encoded by an additional plasmid, were consistent with both intra-cluster evolution and horizontal transfer of the hybrid plasmid.

Ampicillin Resistance↗
PubMed2026

Plasticity in a bacterial global regulatory switch that drives a shift in antibiotic resistance and virulence.

Antibiotic resistance and expression of virulence factors impact the outcome of infection by Pseudomonas aeruginosa. Pathogenesis is often modelled using the PAO1 reference strain but laboratory lineages vary in the sequence and activity of MexT, a global regulator impacting virulence, biofilm formation, and ciprofloxacin resistance. We defined the impact of active versus inactive MexT in PAO1 and observed transcriptomic changes affecting the expression of ~900 genes. Phenotyping revealed altered metabolism, antibiotic resistance, and virulence, resulting in striking variation across a 'single' model organism. We propose that antibiotic resistance promotes plasticity in mexT accounting for variation across lineages. We introduced antibiotic resistance into clinical P. aeruginosa isolates and observed mutations in mexT when selective pressure was removed, supporting the proposed evolutionary pathway. Overall, we have demonstrated the transcriptomic basis of MexT as a phenotypic switch in PAO1 and implicated antibiotic resistance as a cause of changes in mexT. Furthermore, MexS/MexT-regulated efflux is implicated in the antibiotic stress response and virulence, helping identify the mechanisms for rapid phenotypic switching through mexT and confirming that PAO1 is unlike most isolates. Improved understanding of the regulatory changes linked to antibiotic resistance is particularly relevant to P. aeruginosa where cycles of antibiotic treatment are common.

antibiotic resistance↗
PubMed2004

Diverse evolutionary mechanisms shape the type III effector virulence factor repertoire in the plant pathogen Pseudomonas syringae.

Many gram-negative pathogenic bacteria directly translocate effector proteins into eukaryotic host cells via type III delivery systems. Type III effector proteins are determinants of virulence on susceptible plant hosts; they are also the proteins that trigger specific disease resistance in resistant plant hosts. Evolution of type III effectors is dominated by competing forces: the likely requirement for conservation of virulence function, the avoidance of host defenses, and possible adaptation to new hosts. To understand the evolutionary history of type III effectors in Pseudomonas syringae, we searched for homologs to 44 known or candidate P. syringae type III effectors and two effector chaperones. We examined 24 gene families for distribution among bacterial species, amino acid sequence diversity, and features indicative of horizontal transfer. We assessed the role of diversifying and purifying selection in the evolution of these gene families. While some P. syringae type III effectors were acquired recently, others have evolved predominantly by descent. The majority of codons in most of these genes were subjected to purifying selection, suggesting selective pressure to maintain presumed virulence function. However, members of 7 families had domains subject to diversifying selection.

Base Composition↗
PubMed2004

Expansion of quasispecies diversity but no evidence for adaptive evolution of SHIV during rapid serial transfers among seronegative macaques.

Four successive, rapid serial passages of the nonpathogenic, CCR5-tropic simian-human immunodeficiency virus SHIV(SF162) in rhesus macaques resulted in an increase in acute plasma viremia with each passage and the emergence of a pathogenic isolate SHIV(SF162P3) in one of the passage three transfer animals (macaque T353). To explore the mechanism(s) underlying increased virulence of SHIV(SF162) upon in vivo passage, the evolution of the HIV-1 envelope gene was characterized in plasma and PBMC samples obtained from animals before (week 1) and after (week 3) the time of virus transfer. We found no evidence in support of adaptive evolution of the HIV gp120 during rapid serial passage; however, the animals which later received passage virus had more diverse quasispecies. SHIV(SF162P3)-like gp120 sequences were first detected in macaque T353 at week 6, after seroconversion. These sequence changes increased in frequency and number at later time points. The first sequence change conferred neutralization escape but not an increase in viral infectivity that could account for the apparent increase in replicative capacity of the later passage viruses. Collectively, our data argue against any host-specific adaptation of the HIV-1 envelope gp120 as the basis for the generation of more aggressive SHIV variants during rapid serial transfers in seronegative macaques, and support the model of quasispecies diversity as a predictor of pathogenesis. Envelope sequence changes accumulate principally in response to immune pressure exerted by the host, generating viral variants that can persist in the presence of a strong host immune response.

Amino Acid Sequence↗
PubMed1999

Alternative mechanism of cholera toxin acquisition by Vibrio cholerae: generalized transduction of CTXPhi by bacteriophage CP-T1.

Horizontal transfer of genes encoding virulence factors has played a central role in the evolution of many pathogenic bacteria. The unexpected discovery that the genes encoding cholera toxin (ctxAB), the main cause of the profuse secretory diarrhea characteristic of cholera, are encoded on a novel filamentous phage named CTXPhi, has resulted in a renewed interest in the potential mechanisms of transfer of virulence genes among Vibrio cholerae. We describe here an alternative mechanism of cholera toxin gene transfer into nontoxigenic V. cholerae isolates, including strains that lack both the CTXPhi receptor, the toxin coregulated pilus (TCP), and attRS, the chromosomal attachment site for CTXPhi integration. A temperature-sensitive mutant of the V. cholerae generalized transducing bacteriophage CP-T1 (CP-T1ts) was used to transfer a genetically marked derivative of the CTX prophage into four nontoxigenic V. cholerae strains, including two V. cholerae vaccine strains. We demonstrate that CTXPhi transduced by CP-T1ts can replicate and integrate into these nontoxigenic V. cholerae strains with high efficiency. In fact, CP-T1ts transduces the CTX prophage preferentially when compared with other chromosomal markers. These results reveal a potential mechanism by which CTXPhi(+) V. cholerae strains that lack the TCP receptor may have arisen. Finally, these findings indicate an additional pathway for reversion of live-attenuated V. cholerae vaccine strains.

Attachment Sites, Microbiological↗
PubMed2003

Comparison of the genome sequences of Listeria monocytogenes and Listeria innocua: clues for evolution and pathogenicity.

Listeria monocytogenes, an invasive opportunistic, food-borne pathogen, remains one of the leading causes of mortality from food-borne infections. The recently determined complete genome sequences of L. monocytogenes strain EGDe and of that of the closely related non-pathogenic species Listeria innocua strain CLIP11262 enhance our knowledge of the genetic basis of the virulence of L. monocytogenes and advance our understanding of the evolution of these Listeria species. Both genomes encode a high number of surface, transport and regulatory proteins. Comparison of the genome organisation revealed a perfect synteny between the two Listeria genomes. Comparison with other closely related bacteria also showed a high conservation in genome organisation among the Listeria, Staphylococcus and Bacillus group of low G+C content bacteria. Distinct G+C content of a number of strain-specific genes suggests intensive lateral gene transfer. The identification of a 55-kb locus encoding proteins with high homology to Salmonella enterica serovar Typhimurium vitamin B(12) synthesis proteins as well as those necessary for degradation of ethanolamine and propanediol further indicates acquisition of a complete metabolic pathway by horizontal gene transfer and a probable role of this locus in anaerobic growth in the host.

Anaerobiosis↗
PubMed2000

Mutualism, parasitism and competition in the evolution of coviruses.

Coviruses are viruses with the property that their genetic information is divided up among two or more different viral particles. I model the evolution of coviruses using information on both viral virulence and the interactions between viruses and molecules that parasitize them: satellite viruses, satellite RNAs and defective interfering viruses. The model ultimately, and inevitably contains within it single-species dynamics as well as mutualistic, parasitic, cooperative and competitive relationships. The model shows that coexistence between coviruses and the self-sufficient viruses that spawned them is unlikely, in the sense that the quantitative conditions for coexistence are not easy to satisfy I also describe an abrupt transition from mutualistic two-species to single-species dynamics, showing a new sense in which questions such as 'Is a lichen one species or two?' can be given a definite answer.

Animals↗
PubMed1994

Involvement of cell wall glucans in the genesis and persistence of the inflammatory reaction caused by the fungus Paracoccidioides brasiliensis.

The role of cell wall polysaccharides in leucocyte recruitment and granuloma formation in paracoccidioidomycosis was investigated. The inflammatory cells recruitment to the peritoneal cavity in rats inoculated with cell wall fraction (CW-265 or F1-265) from an avirulent strain of Paracoccidioides brasiliensis (Pb265), was greater than that observed for the cell wall fraction (CW-HC or F1-HC) recovered from the virulent strain (PbHC). Moreover, the inoculation of F1-HC and F1-265 into the subcutaneous layer of mice resulted in the formation of nodular and not progressive granulomatous lesions. The size and mean time of evolution of these lesions was proportional to the degree of virulence of the sample from which they were derived. Analyses showed that both F1 fractions contained beta-glucan and chitin. Only beta-glucan was able to trigger attraction and concentric organization of polymorphonuclear neutrophils and macrophages at the inflammatory foci, and the difference in the concentration of this compound in the cell walls of PbHC and Pb265 could explain the inflammatory capacity exhibited by the two strains of P. brasiliensis.

Animals↗
PubMed2000

Enterotoxigenic Escherichia coli--an overview.

Enterotoxigenic Escherichia coli is an important cause of traveler's diarrhea and diarrheal illnesses in children in the developing world. In this presentation we will focus on the main virulence attributes of this pathogenic category of E. coli, and discuss the evolution of studies conducted in our laboratory.

Diarrhea↗
PubMed2003

Molecular evolution of the dotA gene in Legionella pneumophila.

The molecular evolution of dotA, which is related to the virulence of Legionella pneumophila, was investigated by comparing the sequences of 15 reference strains (serogroups 1 to 15). It was found that dotA has a complex mosaic structure. The whole dotA gene of Legionella pneumophila subsp. pneumophila serogroups 2, 6, and 12 has been transferred from Legionella pneumophila subsp. fraseri. A discrepancy was found between the trees inferred from the nucleotide and deduced amino acid sequences of dotA, which suggests that multiple hits, resulting in synonymous substitutions, have occurred. Gene phylogenies inferred from three different segments (the 5'-end region, the central, large periplasmic domain, and the 3'-end region) showed impressively dissimilar topologies. This was concordant with the sequence polymorphisms, indicating that each region has experienced an independent evolutionary history, and was evident even within the same domain of each strain. For example, the PP2 domain was found to have a heterogeneous structure, which led us hypothesize that the dotA gene of L. pneumophila may have originated from two or more different sources. Comparisons of synonymous and nonsynonymous substitutions demonstrated that the PP2 domain has been under strong selective pressure with respect to amino acid change. Split decomposition analysis also supported the intragenic recombination of dotA. Multiple recombinational exchange within the dotA gene, encoding an integral cytoplasmic membrane protein that is secreted, probably provided increased fitness in certain environmental niches, such as within a particular biofilm community or species of amoebae.

Bacterial Proteins↗
PubMed2001

Common mechanisms for pathogens of plants and animals.

The vast evolutionary gulf between plants and animals--in terms of structure, composition, and many environmental factors--would seem to preclude the possibility that these organisms could act as receptive hosts to the same microorganism. However, some pathogens are capable of establishing themselves and thriving in members of both the plant and animal kingdoms. The identification of functionally conserved virulence mechanisms required to infect hosts of divergent evolutionary origins demonstrates the remarkable conservation in some of the underlying virulence mechanisms of pathogenesis and is changing researchers' thinking about the evolution of microbial pathogenesis.

Animals↗
PubMed1996

Regulation of virulence gene expression in pathogenic Listeria.

Dynamic interactions between host and pathogen are characteristic of infections caused by intracellular bacteria. This has favoured the evolution of highly effective control systems by which these pathogens regulate the expression of different virulence factors during sequential steps of the infection process. In the case of the facultative intracellular bacterium Listeria monocytogenes, these steps involve internalization by eukaryotic cells, lysis of the resulting phagosome, replication as well as movement within the host cytoplasm, direct cell-to-cell spread, and subsequent lysis of a double-membrane vacuole when entering neighbouring cells. Virulence factors which are involved in each of these steps have been identified and the expression of these factors is subject to a co-ordinate and differential control exerted by the major listerial virulence regulator PrfA. This protein belongs to the Crp/Fnr-family of transcriptional activators and recognizes specific target sequences in promoter regions of several listerial virulence genes. Differential expression of these genes during sequential steps of the infection seems to be at least partially mediated by different binding affinities of PrfA to its target sequences. Activity of PrfA-dependent genes and of prfA itself is under the control of several environmental variables which are used by the pathogen to recognize its transition from the free environment into a eukaryotic host.

Animals↗
PubMed2000

Horizontal gene transfer and the origin of species: lessons from bacteria.

In bacteria, horizontal gene transfer (HGT) is widely recognized as the mechanism responsible for the widespread distribution of antibiotic resistance genes, gene clusters encoding biodegradative pathways and pathogenicity determinants. We propose that HGT is also responsible for speciation and sub-speciation in bacteria, and that HGT mechanisms exist in eukaryotes.

Bacteria↗
PubMed2006

Evolutionary implications of Avian Infectious Bronchitis Virus (AIBV) analysis.

For developing efficient vaccines, it is essential to identify which amino acid changes are most important to the survival of the virus. We investigate the amino acid substitution features in the Avian Infectious Bronchitis Virus (AIBV) antigenic domain of a vaccine serotype (DE072) and a virulent viral strain (GA98) to better understand adaptive evolution of AIBV. In addition, the SARS Coronavirus (SARS-CoV) was also analyzed in the same way. It is interesting to find that extreme comparability exists between AIBV and SARS in amino acid substitution pattern. It suggests that amino acid changes that result in overall shift of residue charge and polarity should be paid special attention to during the development of vaccines.

Amino Acid Substitution↗
PubMed2000

Salmonella pathogenicity island 2.

Systemic infections by Salmonella enterica, such as typhoid fever, are a significant threat to human health. Recent studies indicate that the function of a type III secretion system encoded by Salmonella Pathogenicity Island 2 (SPI2) is central for the ability of S. enterica to cause systemic infections and for intracellular pathogenesis. This review summarizes approaches leading to the identification of SPI2, the molecular genetics and evolution of SPI2, and the current understanding of the regulation of gene expression. Recent studies have indicated that SPI2 is used by intracellular Salmonella to actively modify functions of the host cells. The role of SPI2 during pathogenesis of salmonellosis and current models regarding function will be discussed.

Animals↗
PubMed2001

The relevance of evolutionary genetics for identification of Trichinella sp. and other pathogens at the strain, subspecies and species levels.

In the specific field of Trichinella research, the impact of evolutionary methods has been until now limited. This is all the more distressing, since this group of parasites is characterized by hard taxonomical problems. Moreover, for the epidemiological tracking of Trichinella populations, high-discriminating genetic typing, conveniently analyzed by population genetic methods, could be of considerable help. With no additional efforts, many molecular data are already available and could be used for retrospective analyses able to solve many taxonomical problems. It is desirable that coming studies are specifically designed according to evolutionary genetics principles and the question under study (sample size, selection of the appropriate marker).

Animals↗