Inhibition of Bacterial Conjugation by Phage M13 and Its Protein g3p: Quantitative Analysis and Model

Conjugation is the main mode of horizontal gene transfer that spreads antibiotic resistance among bacteria. Strategies for inhibiting conjugation may be useful for preserving the effectiveness of antibiotics and preventing the emergence of bacterial strains with multiple resistances. Filamentous bacteriophages were first observed to inhibit conjugation several decades ago. Here we investigate the mechanism of inhibition and find that the primary effect on conjugation is occlusion of the conjugative pilus by phage particles. This interaction is mediated primarily by phage coat protein g3p, and exogenous addition of the soluble fragment of g3p inhibited conjugation at low nanomolar concentrations. Our data are quantitatively consistent with a simple model in which association between the pili and phage particles or g3p prevents transmission of an F plasmid encoding tetracycline resistance. We also observe a decrease in the donor ability of infected cells, which is quantitatively consistent with a reduction in pili elaboration. Since many antibiotic-resistance factors confer susceptibility to phage infection through expression of conjugative pili (the receptor for filamentous phage), these results suggest that phage may be a source of soluble proteins that slow the spread of antibiotic resistance genes

Completion of a Stand‐Alone Versus Coach‐Supported Trial of a Web‐Based Program for Distressed Relationships

Objective To assess program completion of the online OurRelationship program with varying levels of paraprofessional support in an effort to further examine the role of coach support in self‐help couple interventions. Background Although the OurRelationship program for distressed couples has been found to statistically improve relationship and individual functioning, the program's provision of paraprofessional coach support limits its dissemination and implementation. Method Using an interrupted time series design, we compared completion rates of those who enrolled in a trial of OurRelationship with no coach support (n = 529 couples) to completion rates of a previous trial of OurRelationship in which couples were randomized to receive either one (n = 179 couples) or four (n = 177 couples) calls with a coach. Results Individuals were statistically less likely to complete the OurRelationship program when they were not provided a coach than they were when provided with either one or four coach calls. Analyses of moderators of completion rates revealed that a coach was generally equally helpful across demographic factors and measures of baseline relationship and individual functioning; however, coaching was especially helpful for Hispanic individuals and those without elevated depressive symptoms at baseline. Conclusions Even a single call with a coach yields higher completion of an online program for relationship distress. Implications The findings highlight the growing need for tests of alternate types of program support, such as automated support, in an effort to reduce program costs and increase potential for dissemination without negatively affecting program completion rates