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

Disease control and prevention in China in the 20th century and prospects for the new millennium

In the first part of the paper, the main achievements and experience of disease control and prevention in China during last 50 years are described. Infectious diseases and parasitosis have been successfully controlled and prevented and people’s health enhanced owing to the establishment of an effective system of public health, the launch of a campaign called “Patriotic Public Health”, immunization planning, and the improvement of economic and environmental conditions. In the second part, the challenges to public health in China are presented. The threat from old and emerging infectious diseases, especially sexually transmitted diseases, a sustained increase in the prevalence of chronic non-infectious diseases (cardiovascular diseases tumors and diseases of the respiratory system), environmental problems and the health problems of aging are discussed. Finally, strategies for disease control and prevention in the new century is suggested