Biomedical subjects

Katherine M E Turner

Publications and source records attributed to Katherine M E Turner.

4 recordsLinked to original sources

PubMed2007

The secret life of the multilocus sequence type.

Such are the challenges, and the potential, presented by complete genome sequences that the eventual erosion of the boundaries between biochemistry, ecology, bioinformatics, population biology, epidemiology and medical microbiology will perhaps be the most profound legacy of the genomics revolution. The development of nucleotide sequence-based typing schemes (multilocus sequence typing (MLST)) represents a similar synthesis, for this technique both matches the practical requirements for a highly portable standard for strain characterisation whilst also being firmly grounded in the population biology principles of multilocus enzyme electrophoresis (MLEE). Contrary to recent claims that population biology analyses of public health-oriented MLST data 'obscures its utility in applied microbiology' [Maiden MC. Multilocus sequence typing of bacteria. Annu Rev Microbiol 2006;60:561-88.], we argue that such an emphasis is essential for full interpretation of the data. Here we note a pertinent case in point; how a consideration of the rates of genetic recombination can help to explain why MLST data tend to correlate with virulence properties in some species (Neisseria meningitidis) but not in others (Staphylococcus aureus). We also discuss how the argument applies to the identification of recently emerged methicillin-resistant S. aureus (MRSA) clones using MLST. We conclude with a speculative rationale for promoting the 'clonal complexes' of S. aureus to species status.

Bacterial Typing Techniques↗

PubMed2006

Modelling bacterial speciation.

A central problem in understanding bacterial speciation is how clusters of closely related strains emerge and persist in the face of recombination. We use a neutral Fisher-Wright model in which genotypes, defined by the alleles at 140 house-keeping loci, change in each generation by mutation or recombination, and examine conditions in which an initially uniform population gives rise to resolved clusters. Where recombination occurs at equal frequency between all members of the population, we observe a transition between clonal structure and sexual structure as the rate of recombination increases. In the clonal situation, clearly resolved clusters are regularly formed, break up or go extinct. In the sexual situation, the formation of distinct clusters is prevented by the cohesive force of recombination. Where the rate of recombination is a declining log-linear function of the genetic distance between the donor and recipient strain, distinct clusters emerge even with high rates of recombination. These clusters arise in the absence of selection, and have many of the properties of species, with high recombination rates and thus sexual cohesion within clusters and low rates between clusters. Distance-scaled recombination can thus lead to a population splitting into distinct genotypic clusters, a process that mimics sympatric speciation. However, empirical estimates of the relationship between sequence divergence and recombination rate indicate that the decline in recombination is an insufficiently steep function of genetic distance to generate species in nature under neutral drift, and thus that other mechanisms should be invoked to explain speciation in the presence of recombination.

Bacteria↗

PubMed2006

Developing a realistic sexual network model of chlamydia transmission in Britain.

BACKGROUND: A national chlamydia screening programme is currently being rolled out in the UK and other countries. However, much of the epidemiology remains poorly understood. In this paper we present a stochastic, individual based, dynamic sexual network model of chlamydia transmission and its parameterisation. Mathematical models provide a theoretical framework for understanding the key epidemiological features of chlamydia: sexual behaviour, health care seeking and transmission dynamics. RESULTS: The model parameters were estimated either directly or by systematic fitting to a variety of appropriate data sources. The fitted model was representative of sexual behaviour, chlamydia epidemiology and health care use in England. We were able to recapture the observed age distribution of chlamydia prevalence. CONCLUSION: Estimating parameters for models of sexual behaviour and transmission of chlamydia is complex. Most of the parameter values are highly correlated, highly variable and there is little empirical evidence to inform estimates. We used a novel approach to estimate the rate of active treatment seeking, by combining data sources, which improved the credibility of the model results. The model structure is flexible and is broadly applicable to other developed world settings and provides a practical tool for public health decision makers.

Adolescent↗

PubMed2005

The re-emergence of syphilis in the United Kingdom: the new epidemic phases.

OBJECTIVE: The objective of this study was to characterize the resurgence of infectious syphilis in the United Kingdom between 1997 and 2003. STUDY: The authors conducted a retrospective analysis of routine surveillance data from genitourinary medicine clinics and data collected through enhanced surveillance. RESULTS: Between 1997 and 2002, diagnoses of primary, secondary, and early latent syphilis made at genitourinary medicine clinics increased by 213% in heterosexual males, 1412% in men who have sex with men (MSM), and 22% in females. These increases have been driven by a series of outbreaks, the largest of which were seen in Manchester (528) and London (1222) up to the end of October 2003. All the outbreaks have been geographically localized and the majority of cases occurred in MSM. A high percentage of concurrent HIV infection was reported, and oral sex was often reported as a route of transmission. CONCLUSIONS: Syphilis has re-emerged in response to behavior change, probably driven by changes in the HIV epidemic. The future course of the epidemic is difficult to predict and control remains elusive.

Adolescent↗