The evolution and determination of plasmid transfer rate and subsequent effect on competition

Horizontal gene transfer by conjugation is one of the processes that determines the persistence, prevalence and transmission of antibiotic resistance genes that can be found on bacterial plasmids. In order to appropriately tackle the spread of antibiotic resistance we must therefore understand how plasmid dynamics function in complex microbial communities. Various aspects of plasmid dynamics and how they contribute to the spread of antibiotic resistance are unclear and require attention. For example, plasmid transfer rates vary widely, but the ways in which environmental, plasmid and host factors explain this variation and the relative importance of each factor is unclear. In addition, the evolutionary forces that differentially affect plasmids and hosts to determine specific transfer rates have not been fully explored; in particular, the effects of host-plasmid conflicts in non-selective conditions and the impact of the relationship between plasmid cost on host growth and plasmid transfer rate. A theoretical understanding of transfer rates must then be placed within the context of the other parameters that affect plasmid dynamics (e.g. plasmid cost, loss etc.) to make assertions on plasmid persistence and prevalence, and theoretical results must be compared with experimental data in increasing microbial complexity. Experiments are rarely conducted using multiple species and the impacts and interactions of plasmid presence on a community have yet to be explored fully in the lab. The first data chapter of this thesis (chapter 2) seeks to address the question of how transfer rate variation can be attributed to various environmental variables in addition to the effects of plasmid, donor and recipient identities. A meta-analysis of published transfer rates was therefore conducted and the variation assessed by applying series of multivariate linear models to the data. Over three quarters of the variation from the meta-analysis could be explained, with plasmid repression and media type explaining the most variation. The results also identify the recipient identity as an important variable that explains up to 34\% of the variation. Given the variation in transfer rates, the next chapter (chapter 3) asks how the various selection pressures on host and plasmid may interact to determine specific rates of transfer. In particular, it asks how the costs of plasmid transfer impact transfer rates, and how host-plasmid conflicts in transfer rate may subsequently affect plasmid prevalence. Adaptive dynamics and invasion analyses were applied to simple conjugation models under selective and non-selective conditions, and using different plasmid transfer-cost relationships. The findings were then combined to model the effects that host-plasmid conflicts in non-selective conditions may have on transfer rates and plasmid prevalence. The results of separate analyses demonstrate the role of the recipient in controlling transfer rates, and show that plasmid-controlled transfer rate can be predicted with only three parameters (host growth rate, plasmid loss rate and the cost of plasmid transfer on growth). Low frequency genetic variation in transfer rate is predicted to accumulate, which can facilitate rapid adaptation to changing conditions. Further modelling showed that in order to substantially affect plasmid prevalence (and corresponding cumulative costs a plasmid has on a population in non-selective conditions) a host may need to decrease the transfer rate by several orders of magnitude, indicating that hosts must have strong control mechanisms to be valuable. In the final data chapter (chapter 4) I ask if and how plasmid dynamics focusing on the interaction of plasmid presence and inter-species competition in simple microbial communities can be predicted using independently measured parameters. In particular, how does the rate of plasmid transfer impact species competitive advantage and the outcomes of competition? A series of experiments were conducted to estimate parameters for two plasmids and two bacterial species for use in a simplified two-species bacterial conjugation model to make predictions of competitive advantage. These predictions were then compared with a series of corresponding competition assays. The effects of the plasmid distribution on competition and the presence of multiple species on plasmid stability in the community were also noted and described. The model accurately predicted many of the experimental results, but deviated from those results where specific parameters were over or underestimated. The results emphasise the importance of appropriate parameter measurement. Plasmid presence reduced the competitive ability of each host and incurred higher costs from the plasmid with a higher transfer rate. These effects were limited or exacerbated dependent on whether the plasmid was able to successfully invade the other species where it incurred similar costs. These results demonstrate the complex effects of plasmid transfer, cost and host interactions on plasmid dynamics in a microbial community and the competitive dynamics of that community. These results show that transfer rates are highly variable according to environmental conditions and that, while the majority of the variation can be assigned to some variables, additional work is required to evaluate the effects of particular variables, such as temperature and the effects of plasmid-host coevolution. While this work demonstrates how selective pressures act on transfer rates, more work is also required to link particular observed transfer rates to the conditions in which they evolve. The results highlight the importance of the variable and potentially conflicting selection pressures on host and plasmid that combine to determine the rate of transfer, emphasising the sometimes neglected role of the recipient. The relationship between plasmid cost and plasmid transfer rate is identified as a key part of transfer rate evolution and also requires future attention to describe this relationship in order to fully understand how plasmid transfer rates are constructed. These results increase our understanding of the factors that affect plasmid dynamics, have implications for the way we consider and handle the spread of antibiotic resistance, and provide direction for future research opportunities.Open Acces

Prevalence and costs of treating uncomplicated stage 1 hypertension in primary care: a cross-sectional analysis.

BACKGROUND: Treatment for uncomplicated stage 1 hypertension is recommended in most international guidelines but there is little evidence to indicate that therapy is beneficial. AIM: To estimate the prevalence of this condition in an untreated population and the potential costs of initiating therapy in such patients. DESIGN AND SETTING: Cross-sectional study of anonymised patient records in 19 general practices in the West Midlands, UK. METHOD: Data relating to patient demographics, existing cardiovascular disease (CVD), and risk factors (blood pressure and cholesterol) were extracted from patient records. Patients with a blood pressure of 140/90-159/99 mmHg, no CVD, and <20% 10-year cardiovascular risk were classified as having uncomplicated stage 1 hypertension. Missing data were imputed. The prevalence of untreated, uncomplicated stage 1 hypertension was estimated using descriptive statistics and extrapolated using national data. The cost of achieving blood pressure control in this population was examined in a cost-impact analysis using published costs from previous studies. RESULTS: Of the 34 975 patients (aged 40-74 years) in this study, untreated, uncomplicated stage 1 hypertension was present in 2867 individuals (8.2%, 95% confidence interval [CI] = 7.9 to 8.5). This is equivalent to 1 892 519 patients in England and Wales, for whom the additional cost of controlling blood pressure, according to guidelines, was estimated at £106-229 million per annum, depending on the health professional delivering care. CONCLUSION: Untreated, uncomplicated stage 1 hypertension is relatively common, affecting 1 in 12 patients aged 40-74 years in primary care. Current international guidelines and pay-for-performance targets, if followed, will incur significant costs for a patient benefit that is debatable.This work forms part of a larger programme on stroke prevention in primary care supported by the National Institute for Health Research (NIHR) (RP-PG-0606-1153). James P Sheppard holds a Medical Research Council Strategic Skills PostDoctoral Fellowship. Richard J McManus holds an NIHR Professorship. The views and opinions expressed are those of the authors and do not necessarily reflect those of the NHS, NIHR, or the Department of Health

Diagnosis and management of resistant hypertension

High blood pressure (hypertension) is one of the most important risk factors for cardiovascular disease,1 2 which is a significant cause of morbidity and mortality worldwide.3 Recent surveys from developed countries suggest that the prevalence of hypertension ranges from 20-30%, with 51-80% receiving treatment but only 27-66% with adequate blood pressure control.4 One subset of uncontrolled hypertensives who do not respond to treatment are known as resistant hypertensives. This article will describe how resistant hypertension is defined, its prevalence and prognosis, methods to diagnose it effectively in routine practice and strategies to effectively manage patients diagnosed with the condition

Impact of Changes to National Hypertension Guidelines on Hypertension Management and Outcomes in the United Kingdom.

In recent years, national and international guidelines have recommended the use of out-of-office blood pressure monitoring for diagnosing hypertension. Despite evidence of cost-effectiveness, critics expressed concerns this would increase cardiovascular morbidity. We assessed the impact of these changes on the incidence of hypertension, out-of-office monitoring and cardiovascular morbidity using routine clinical data from English general practices, linked to inpatient hospital, mortality, and socio-economic status data. We studied 3 937 191 adults with median follow-up of 4.2 years (49% men, mean age=39.7 years) between April 1, 2006 and March 31, 2017. Interrupted time series analysis was used to examine the impact of changes to English hypertension guidelines in 2011 on incidence of hypertension (primary outcome). Secondary outcomes included rate of out-of-office monitoring and cardiovascular events. Across the study period, incidence of hypertension fell from 2.1 to 1.4 per 100 person-years. The change in guidance in 2011 was not associated with an immediate change in incidence (change in rate=0.01 [95% CI, -0.18-0.20]) but did result in a leveling out of the downward trend (change in yearly trend =0.09 [95% CI, 0.04-0.15]). Ambulatory monitoring increased significantly in 2011/2012 (change in rate =0.52 [95% CI, 0.43-0.60]). The rate of cardiovascular events remained unchanged (change in rate =-0.02 [95% CI, -0.05-0.02]). In summary, changes to hypertension guidelines in 2011 were associated with a stabilisation in incidence and no increase in cardiovascular events. Guidelines should continue to recommend out-of-office monitoring for diagnosis of hypertension

Predicting out-of-office blood pressure level using repeated measurements in the clinic: an observational cohort study.

OBJECTIVES: Identification of people with lower (white-coat effect) or higher (masked effect) blood pressure at home compared to the clinic usually requires ambulatory or home monitoring. This study assessed whether changes in SBP with repeated measurement at a single clinic predict subsequent differences between clinic and home measurements. METHODS: This study used an observational cohort design and included 220 individuals aged 35-84 years, receiving treatment for hypertension, but whose SBP was not controlled. The characteristics of change in SBP over six clinic readings were defined as the SBP drop, the slope and the quadratic coefficient using polynomial regression modelling. The predictive abilities of these characteristics for lower or higher home SBP readings were investigated with logistic regression and repeated operating characteristic analysis. RESULTS: The single clinic SBP drop was predictive of the white-coat effect with a sensitivity of 90%, specificity of 50%, positive predictive value of 56% and negative predictive value of 88%. Predictive values for the masked effect and those of the slope and quadratic coefficient were slightly lower, but when the slope and quadratic variables were combined, the sensitivity, specificity, positive and negative predictive values for the masked effect were improved to 91, 48, 24 and 97%, respectively. CONCLUSION: Characteristics obtainable from multiple SBP measurements in a single clinic in patients with treated hypertension appear to reasonably predict those unlikely to have a large white-coat or masked effect, potentially allowing better targeting of out-of-office monitoring in routine clinical practice.This study presents independent research commissioned by the National Institute for Health Research (NIHR) under its Programme Grants for Applied Research funding scheme (RP-PG-1209–10051). R.J.Mc.M. holds an NIHR Professorship. J.S. was funded by the NIHR Birmingham and Black Country Collaboration for Leadership in Applied Health Research and Care during part of this work, but now holds a Medical Research Council Strategic Skills Postdoctoral Fellowship. B.W. is a NIHR Senior Investigator and is supported by the NIHR UCL Hospitals Biomedical Research Centre. The TASMINH2 trial was funded by the UK Department of Health Policy Research Programme and the National Coordinating Centre for Research Capacity Development. The views and opinions expressed are those of the authors and do not necessarily reflect those of the NHS, NIHR, or the Department of Health. All equipment used in the study was purchased commercially

Modern Management and Diagnosis of Hypertension in the United Kingdom: Home Care and Self-care

BackgroundThe effective diagnosis and management of hypertension is one of the most important parts of cardiovascular prevention internationally and this is no different in the United Kingdom. Approximately 14% of the UK population currently receive treatment for hypertension. Recent UK guidelines from the National Institute of Health and Care Excellence have placed greater emphasis on the utilization of out-of-office measurement of blood pressure to more accurately diagnose hypertension.ObjectiveThe aim of the present study was to provide a state-of-the-art review of the evidence for screening, diagnosing, and managing hypertension, as implemented in the United Kingdom, with an emphasis on the role of self-monitored and ambulatory blood pressure monitoring in routine clinical care.MethodConsideration was given to the use of ambulatory and home monitoring to confirm a diagnosis of hypertension and the use of self-monitoring and self-management to monitor and guide treatment. The evidence for the use of self-monitoring in patients with hypertension was examined, both in isolation, and in combination with lifestyle and treatment interventions.FindingsThere is a place for self-monitored blood pressure in specific underresearched populations such as the elderly, specialist conditions, ethnic groups, and during pregnancy and this is discussed here.ConclusionsThe evidence supporting the use of out-of-office monitoring in all aspects of routine clinical care has increased substantially in recent years and is reflected in increased utilization by patients and clinicians alike. Several areas require further research but it is clear that out-of-office monitoring is here to stay and is fast becoming an important part of hypertension management in the United Kingdom