Search PubMed⌕ Search

Biomedical subjects

M C Maiden

Publications and source records attributed to M C Maiden.

At least 19 recordsLinked to original sources
PubMed2001

Exploring the evolution of diversity in pathogen populations.

Pathogen biodiversity is an under-exploited source of inference regarding disease processes and the evolution of pathogens and pathogenesis. In addition, the structure of pathogen populations, especially for diverse organisms such as the meningococcus, has implications for public health interventions including vaccination and antibiotic use. The predominant paradigm for interpreting bacterial diversity has been the clonal population structure, which has been modified by the incorporation of the effects of horizontal genetic exchange. Multilocus models of variable antigens, which explore the effects of immune selection, provide alternative explanations for structured diversity in pathogen populations.

Antigenic Variation↗
PubMed2001

Database-driven multi locus sequence typing (MLST) of bacterial pathogens.

MOTIVATION: Multi Locus Sequence Typing (MLST) is a newly developed typing method for bacteria based on the sequence determination of internal fragments of seven house-keeping genes. It has proved useful in characterizing and monitoring disease-causing and antibiotic resistant lineages of bacteria. The strength of this approach is that unlike data obtained using most other typing methods, sequence data are unambiguous, can be held on a central database and be queried through a web server. RESULTS: A database-driven software system (mlstdb) has been developed, which is used by public health laboratories and researchers globally to query their nucleotide sequence data against centrally held databases over the internet. The mlstdb system consists of a set of perl scripts for defining the database tables and generating the database management interface and dynamic web pages for querying the databases. AVAILABILITY: http://www.mlst.net.

Bacteria↗
PubMed2001

Sequence type analysis and recombinational tests (START).

UNLABELLED: The 32-bit Windows application START is implemented using Visual Basic and C(++) and performs analyses to aid in the investigation of bacterial population structure using multilocus sequence data. These analyses include data summary, lineage assignment, and tests for recombination and selection. AVAILABILITY: START is available at http://outbreak.ceid.ox.ac.uk/software.htm. CONTACT: keith.jolley@ceid.ox.ac.uk

Databases, Nucleic Acid↗
PubMed2001

Multilocus sequence typing system for Campylobacter jejuni.

The gram-negative bacterium Campylobacter jejuni has extensive reservoirs in livestock and the environment and is a frequent cause of gastroenteritis in humans. To date, the lack of (i) methods suitable for population genetic analysis and (ii) a universally accepted nomenclature has hindered studies of the epidemiology and population biology of this organism. Here, a multilocus sequence typing (MLST) system for this organism is described, which exploits the genetic variation present in seven housekeeping loci to determine the genetic relationships among isolates. The MLST system was established using 194 C. jejuni isolates of diverse origins, from humans, animals, and the environment. The allelic profiles, or sequence types (STs), of these isolates were deposited on the Internet (http://mlst.zoo.ox.ac.uk), forming a virtual isolate collection which could be continually expanded. These data indicated that C. jejuni is genetically diverse, with a weakly clonal population structure, and that intra- and interspecies horizontal genetic exchange was common. Of the 155 STs observed, 51 (26% of the isolate collection) were unique, with the remainder of the collection being categorized into 11 lineages or clonal complexes of related STs with between 2 and 56 members. In some cases membership in a given lineage or ST correlated with the possession of a particular Penner HS serotype. Application of this approach to further isolate collections will enable an integrated global picture of C. jejuni epidemiology to be established and will permit more detailed studies of the population genetics of this organism.

Alleles↗
PubMed2001

Phenotypic and genotypic approaches to characterization of isolates of Neisseria meningitidis from patients and their close family contacts.

Characterization of isolates of Neisseria meningitidis obtained from patients with meningococcal disease or from pharyngeal swabs of asymptomatic carriers can be achieved by several approaches which provide different levels of discrimination. A total of 45 gram negative, oxidase-positive diplococcus strains isolated from 15 individuals with meningococcal disease and 30 of their family contacts were examined by three approaches: serological typing, multilocus enzyme electrophoresis (MLEE), and multilocus sequence typing (MLST). For 10 of the 15 patient and contact groups, all of the isolates were confirmed as meningococci, and the bacteria obtained from the patients and contacts, including their mother or principal caregiver in the case of children, were indistinguishable by all three methods. In the remaining five groups the isolates from the patients were distinct from those recovered from the contacts, and in three examples, in two separate groups, the contacts were shown by MLST to be carrying strains of Neisseria lactamica. The data obtained from the three techniques were consistent, although complete serological typing was possible for only a minority of isolates. Both MLEE and MLST established the genetic relationships of the isolates and identified members of known hypervirulent lineages, but MLST was faster than MLEE and had the additional advantages that it could be performed on noninfective material distributed by mail and that the results from different laboratories could be compared via the internet (http://mlst.zoo.ox.ac.uk).

Adolescent↗
PubMed2001

Sequence typing confirms that Campylobacter jejuni strains associated with Guillain-Barré and Miller-Fisher syndromes are of diverse genetic lineage, serotype, and flagella type.

Guillain-Barré syndrome (GBS) and Miller-Fisher syndrome (MFS) are correlated with prior infection by Campylobacter jejuni in up to 40% of cases. Nucleotide sequence-based typing of 25 C. jejuni isolates associated with neuropathy permitted robust comparisons with equivalent data from approximately 800 C. jejuni isolates not associated with neuropathy. A total of 13 genetic lineages and 20 flaA short variable region nucleotide sequences were present among the 25 isolates. A minority of isolates (4 of 25) had the flaA short variable region nucleotide sequences that were previously proposed as a marker for GBS-associated isolates. These 4 isolates probably represented the Penner serotype 19 lineage, which has been proposed to have an association with GBS.

Bacterial Typing Techniques↗
PubMed2001

Molecular techniques for the investigation of meningococcal disease epidemiology.

Meningococcal disease remains a major cause of childhood morbidity and mortality world wide and no comprehensive vaccine is available against the causative organism, Neisseria meningitidis. Molecular studies of the diversity of this bacterium have provided a number of key insights into its biology, which have implications for control of meningococcal disease. These have included the identification of hyperinvasive lineages and the correlation of genetic type with antigenic type and disease epidemiology. In practical terms, such studies have enabled the application of DNA-based technologies in the development of improved methods for diagnosis and epidemiological monitoring. These data are of especial importance with the current, and ongoing, development and introduction of new meningococcal vaccines.

Antigens, Bacterial↗
PubMed2000

Carriage of serogroup W-135, ET-37 meningococci in The Gambia: implications for immunisation policy?

We found high levels of symptomless carriage of a hyperinvasive Neisseria meningitidis strain (electrophoretic type 37 [ET-37], serogroup W-135) during a vaccine trial in Gambian children in 1996. Serogroup C, ET-37 complex meningococci cause 30-40% of meningococcal disease in countries such as the UK, and have a point prevalence of 0.5-1.0%. The recent Haj-associated spread of serogroup W-135, ET-37 complex meningococci, which has been accompanied by numerous secondary cases, might be explained by the apparently raised carriage rates reported here.

Bacterial Vaccines↗
PubMed2000

High-throughput sequencing in the population analysis of bacterial pathogens of humans.

High-throughput nucleotide sequence determination technologies present new opportunities for studies of bacterial pathogens by enabling the accumulation of large volumes of biodiversity information from isolate collections. Population studies, which combine these data with epidemiological, phylogenetic, and evolutionary concepts, provide insights into the behaviour of pathogens that are unavailable from other approaches as they address questions of relevance to pathogenesis from the perspective of the infectious organism rather from that of the host. Hypothesis-driven analyses applied to these data permit the determination of microbial population diversity and structure, the identification of the mechanisms of genetic change in bacterial populations, and the generation of models of pathogen evolution. The nucleotide sequence-based population studies performed to date demonstrate a spectrum of nucleotide sequence diversity, population structure, and evolutionary mechanisms among pathogenic bacteria. The rapid development of nucleotide sequence determination and analysis techniques provides the tools necessary for the prosecution of population studies on an increasing number of bacterial pathogens.

Bacteria↗
PubMed2000

Carried meningococci in the Czech Republic: a diverse recombining population.

Population and evolutionary analyses of pathogenic bacteria are frequently hindered by sampling strategies that concentrate on isolates from patients with invasive disease. This is especially so for the gram-negative diplococcus Neisseria meningitidis, a cause of septicemia and meningitis worldwide. Meningococcal isolate collections almost exclusively comprise organisms originating from patients with invasive meningococcal disease, although this bacterium is a commensal inhabitant of the human nasopharynx and very rarely causes pathological effects. In the present study, molecular biology-based techniques were used to establish the genetic relationships of 156 meningococci isolated from healthy young adults in the Czech Republic during 1993. None of the individuals sampled had known links to patients with invasive disease. Multilocus sequence typing (MLST) showed that the bacterial population was highly diverse, comprising 71 different sequence types (STs) which were assigned to 34 distinct complexes or lineages. Three previously identified hyperinvasive lineages were present: 26 isolates (17%) belonged to the ST-41 complex (lineage 3); 4 (2.6%) belonged to the ST-11 (electrophoretic type [ET-37]) complex, and 1 (0.6%) belonged to the ST-32 (ET-5) complex. The data were consistent with the view that most nucleotide sequence diversity resulted from the reassortment of alleles by horizontal genetic exchange.

Adolescent↗
PubMed1999

Crystal structure of an Fab fragment in complex with a meningococcal serosubtype antigen and a protein G domain.

Many pathogens present highly variable surface proteins to their host as a means of evading immune responses. The structure of a peptide antigen corresponding to the subtype P1.7 variant of the porin PorA from the human pathogen Neisseria meningitidis was determined by solution of the X-ray crystal structure of the ternary complex of the peptide (ANGGASGQVK) in complex with a Fab fragment and a domain from streptococcal protein G to 1.95 A resolution. The peptide adopted a beta-hairpin structure with a type I beta-turn between residues Gly4P and Gly7P, the conformation of the peptide being further stabilised by a pair of hydrogen bonds from the side-chain of Asn2P to main-chain atoms in Val9P. The antigen binding site within the Fab formed a distinct crevice lined by a high proportion of apolar amino acids. Recognition was supplemented by hydrogen bonds from heavy chain residues Thr50H, Asp95H, Leu97H and Tyr100H to main-chain and side-chain atoms in the peptide. Complementarity-determining region (CDR) 3 of the heavy chain was responsible for approximately 50 % of the buried surface area formed by peptide-Fab binding, with the remainder made up from CDRs 1 and 3 of the light chain and CDRs 1 and 2 of the heavy chain. Knowledge of the structures of variable surface antigens such as PorA is an essential prerequisite to a molecular understanding of antigenic variation and its implications for vaccine design.

Amino Acid Sequence↗
PubMed1999

Bacterial population genetics, evolution and epidemiology.

Asexual bacterial populations inevitably consist of an assemblage of distinct clonal lineages. However, bacterial populations are not entirely asexual since recombinational exchanges occur, mobilizing small genome segments among lineages and species. The relative contribution of recombination, as opposed to de novo mutation, in the generation of new bacterial genotypes varies among bacterial populations and, as this contribution increases, the clonality of a given population decreases. In consequence, a spectrum of possible population structures exists, with few bacterial species occupying the extremes of highly clonal and completely non-clonal, most containing both clonal and non-clonal elements. The analysis of collections of bacterial isolates, which accurately represent the natural population, by nucleotide sequence determination of multiple housekeeping loci provides data that can be used both to investigate the population structure of bacterial pathogens and for the molecular characterization of bacterial isolates. Understanding the population structure of a given pathogen is important since it impacts on the questions that can be addressed by, and the methods and samples required for, effective molecular epidemiological studies.

Bacteria↗
PubMed1999

Use of streptococcal protein G in obtaining crystals of an antibody Fab fragment in complex with a meningococcal antigen.

Crystals have been obtained of an antibody Fab fragment grown in the presence of a single domain from streptococcal protein G and a ten amino-acid peptide corresponding to the P1.7 serosubtype antigen from the human pathogen Neisseria meningitidis. Crystal trials using the Fab fragment and peptide antigen alone were unsuccessful, but the inclusion of a protein G domain provided an additional variable that generated suitable crystals. Crystals are in space group P21 with unit-cell parameters a = 43.60, b = 63.42, c = 89.63 A, beta = 98.58 degrees and a data set has been collected to 2.9 A resolution using synchrotron radiation. The inclusion of protein G is likely to be of general utility for the crystallization of Fab-antigen complexes.

Amino Acid Sequence↗
PubMed1999

The relative contributions of recombination and mutation to the divergence of clones of Neisseria meningitidis.

Multilocus sequence typing (MLST) is a recently developed nucleotide sequence-based method for the definitive assignment of isolates within bacterial populations to specific clones. MLST uses the same principles as multilocus enzyme electrophoresis and provides data that can be used to investigate aspects of the population genetics and evolution of bacterial species. We used an MLST data set consisting of the sequences of approximately 450-bp fragments from seven housekeeping loci from a large strain collection of Neisseria meningitidis to estimate the relative impact of recombination compared with point mutation in the diversification of N. meningitidis clonal complexes. 126 meningococcal isolates were assigned to 10 clonal complexes, 9 of which contained minor clonal variants. The allelic variation within each complex was classified as a recombinational exchange or a putative point mutation through a comparison of the sequences of each variant allele with that of the allele typically found in the clonal complex. The nine clonal complexes contained a total of 23 allelic variants, and analysis of the sequences of these variant alleles revealed that a single nucleotide site in a meningococcal housekeeping gene is at least 80-fold more likely to change as a result of recombination than as a result of mutation. This value is estimated to be 10-50-fold for Escherichia coli and approximately 50-fold for Streptococcus pneumoniae.

Alleles↗
PubMed1999

The influence of recombination on the population structure and evolution of the human pathogen Neisseria meningitidis.

The extent to which recombination disrupts the bifurcating treelike phylogeny and clonal structure imposed by binary fission on bacterial populations remains contentious. Here, we address this question with a study of nucleotide sequence data from 107 isolates of the human pathogen Neisseria meningitidis. Gene fragments from 12 house-keeping loci distributed around the meningococcal chromosome were analyzed, showing that (1) identical alleles are disseminated among genetically diverse isolates, with no evidence for linkage disequilibrium; (2) different loci give distinct and incongruent phylogenetic trees; and (3) allele sequences are incompatible with a bifurcating treelike phylogeny at all loci. These observations are consistent with the hypothesis that meningococcal populations comprise organisms assembled from a common gene pool, with alleles and allele fragments spreading independently, together with the occasional importation of genetic material from other species. Further, they support the view that recombination is an important genetic mechanism in the generation new meningococcal clones and alleles. Consequently, for anything other than the short-term evolution of this species, a bifurcating treelike phylogeny is not an appropriate model.

Alleles↗