Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Case Formulation in Young People with Post-Traumatic Stress Disorder and First-Episode Psychosis

Background: Evidence based treatment interventions for young people with first-episode psychosis (FEP) and trauma histories is lacking. Although case formulation (CF) has been widely regarded in cognitive behavioural therapy manuals as beneficial, there is limited empirical research examining how clients and therapists experience the process. Aim: This study aimed to explore young people’s reactions to CF in treatment for PTSD (post-traumatic stress disorder) and FEP. Method: Semi-structured interviews were conducted with three participants (aged 19–20) with FEP and PTSD and their therapists, after they had completed a trauma-focused treatment program with a CF component. Transcripts were analysed using an interpretative phenomenological approach and themes were derived. Results: Two themes related to participants’ experiences were identified from the analysis: (1) Developing Insight; (2) A challenging experience; and two themes from the therapists: (1) Doing the case formulation; (2) Value of case formulation. Participants and therapists reported benefits in making connections between current symptoms and past trauma. Participants viewed the process as challenging. Conclusion: Results suggest a potential discrepancy between the experience of the case formulation process for clients and therapists

Mutations that adapt SARS-CoV-2 to mink or ferret do not increase fitness in the human airway

SARS-CoV-2 has a broad mammalian species tropism infecting humans, cats, dogs, and farmed mink. Since the start of the 2019 pandemic, several reverse zoonotic outbreaks of SARS-CoV-2 have occurred in mink, one of which reinfected humans and caused a cluster of infections in Denmark. Here we investigate the molecular basis of mink and ferret adaptation and demonstrate the spike mutations Y453F, F486L, and N501T all specifically adapt SARS-CoV-2 to use mustelid ACE2. Furthermore, we risk assess these mutations and conclude mink-adapted viruses are unlikely to pose an increased threat to humans, as Y453F attenuates the virus replication in human cells and all three mink adaptations have minimal antigenic impact. Finally, we show that certain SARS-CoV-2 variants emerging from circulation in humans may naturally have a greater propensity to infect mustelid hosts and therefore these species should continue to be surveyed for reverse zoonotic infections