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

Do children with reading difficulties experience writing difficulties? A meta-analysis

In this meta-analysis, we examined whether children identified with reading difficulties (RD) evidence writing difficulties. We included studies comparing children with RD with (a) typically developing peers matched on age (k = 87 studies) and (b) typically developing younger peers with similar reading capabilities (k = 24 studies). Children identified with RD scored lower on measures of writing than their same age peers (g = −1.25) when all writing scores in a study were included in the analysis. This same pattern occurred for specific measures of writing: quality (g = −0.95), output (g = −0.66), organization (g = −0.72), sentence skills (g = −0.78), vocabulary (g = −1.17), syntax (g = −1.07), handwriting (g = −0.64), and spelling (g = −1.42). Differences in the writing scores of children identified with RD and same age peers were moderated by whether the writing assessment was a norm-referenced or researcher-designed measure when all writing measures or just spelling were included in the analyses. Depth of orthography for studies involving European languages also moderated differences in the spelling scores of children identified with RD and same age peers. Finally, children identified with RD scored lower on writing than younger peers with similar reading capabilities (g = −0.94) and more specifically on spelling (−0.93). We concluded that children with RD experience difficulties with writing, providing support for theoretical propositions of reading and writing connections as well as the importance of writing instruction for these students. (PsycInfo Database Record (c) 2020 APA, all rights reserved