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

The Practice of collective bargaining

xix, 809 p.; 23 cm

Farmers' bulletin (United States. Dept. of Agriculture); no. 755 (rev.)

Revised edition. This report discusses birds commonly found in the southeastern United States with special regard to their diets and the impact these birds have on agriculture and insects in this region

Farmers' bulletin (United States. Dept. of Agriculture); no. 755

This report discusses birds commonly found in the southeastern United States with special regard to their diets and the impact these birds have on agriculture and insects in this region