Plasmid carriage can limit bacteria-phage coevolution.

Coevolution with bacteriophages is a major selective force shaping bacterial populations and communities. A variety of both environmental and genetic factors has been shown to influence the mode and tempo of bacteria-phage coevolution. Here, we test the effects that carriage of a large conjugative plasmid, pQBR103, had on antagonistic coevolution between the bacterium Pseudomonas fluorescens and its phage, SBW25ϕ2. Plasmid carriage limited bacteria-phage coevolution; bacteria evolved lower phage-resistance and phages evolved lower infectivity in plasmid-carrying compared with plasmid-free populations. These differences were not explained by effects of plasmid carriage on the costs of phage resistance mutations. Surprisingly, in the presence of phages, plasmid carriage resulted in the evolution of high frequencies of mucoid bacterial colonies. Mucoidy can provide weak partial resistance against SBW25ϕ2, which may have limited selection for qualitative resistance mutations in our experiments. Taken together, our results suggest that plasmids can have evolutionary consequences for bacteria that go beyond the direct phenotypic effects of their accessory gene cargo.

Bacteriophages limit the existence conditions for conjugative plasmids.

UNLABELLED: Bacteriophages are a major cause of bacterial mortality and impose strong selection on natural bacterial populations, yet their effects on the dynamics of conjugative plasmids have rarely been tested. We combined experimental evolution, mathematical modeling, and individual-based simulations to explain how the ecological and population genetics effects of bacteriophages upon bacteria interact to determine the dynamics of conjugative plasmids and their persistence. The ecological effects of bacteriophages on bacteria are predicted to limit the existence conditions for conjugative plasmids, preventing persistence under weak selection for plasmid accessory traits. Experiments showed that phages drove faster extinction of plasmids in environments where the plasmid conferred no benefit, but they also revealed more complex effects of phages on plasmid dynamics under these conditions, specifically, the temporary maintenance of plasmids at fixation followed by rapid loss. We hypothesized that the population genetic effects of bacteriophages, specifically, selection for phage resistance mutations, may have caused this. Further mathematical modeling and individual-based simulations supported our hypothesis, showing that conjugative plasmids may hitchhike with phage resistance mutations in the bacterial chromosome. IMPORTANCE: Conjugative plasmids are infectious loops of DNA capable of transmitting DNA between bacterial cells and between species. Because plasmids often carry extra genes that allow bacteria to live in otherwise-inhospitable environments, their dynamics are central to understanding bacterial adaptive evolution. The plasmid-bacterium interaction has typically been studied in isolation, but in natural bacterial communities, bacteriophages, viruses that infect bacteria, are ubiquitous. Using experiments, mathematical models, and computer simulations we show that bacteriophages drive plasmid dynamics through their ecological and evolutionary effects on bacteria and ultimately limit the conditions allowing plasmid existence. These results advance our understanding of bacterial adaptation and show that bacteriophages could be used to select against plasmids carrying undesirable traits, such as antibiotic resistance.

The contextual development of healthy living centres services: an examination of food-related initiatives.

The Healthy Living Centre (HLC) programme was designed to address the wider determinants of health, in particular social exclusion and socio-economic disadvantage, through targeting services at the most deprived local communities. This paper draws on data collected during an in-depth process evaluation of six Scottish HLC case study sites. Food-related services, which were found to cross-cut all the sites, were used to address social exclusion and to promote health. Three types of service, each linked to a social model of health, were found to be in operation: those which enhance skills; those which promote social inclusion; and those which influence food accessibility. The paper illustrates how food-related services have developed in the case study HLCs to take account of the differing needs of the communities and neighbourhoods that have been targeted. Consideration is then given to how HLCs adapt to meet the practicalities of improving health while addressing social exclusion through targeting health inequalities.

Counselling for postnatal depression in the voluntary sector.

The study aimed to investigate the effectiveness of counselling and therapy offered by the voluntary sector for women with postnatal depression or distress. Twenty-seven women accepted for individual counselling or therapy were assessed at baseline, and 3 and 6 months after therapy. They were assessed using standardized measures of depression, parenting stress, marital relationship and maternal self-efficacy. Data were collected by home interviews by an independent researcher. The study sample was representative of those referred for therapy. Scores on measures of depression, parenting self-efficacy and parenting stress decreased significantly over time. Scores of marital satisfaction did not change. The scores of 16 out of 27 (60%) had fallen to below 14 on the Edinburgh Postnatal Depression Scale. There was no difference between those having individual or group therapy. It is not feasible, logistically or ethically, to carry out a randomized controlled trial of counselling which is negotiated between client and therapist. The results from this prospective study of support given by the voluntary sector suggest that it can be effective in alleviating symptoms of postnatal depression.