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

Traditional dietary pattern of South America is linked to breast cancer: an ongoing case-control study in Argentina

Introduction Several studies have shown the effect of dietary patterns on breast cancer risk, but none has been conducted in Argentina. The aim of this study was to extract dietary patterns from Food Frequency Questioner, to estimate their effect on breast cancer occurrence while taking into account aggregation factors (family history of breast cancer) and to explore the sensitivity of the estimates to changes in the assumptions. Methods A principal component exploratory factor analysis was applied to identify dietary patterns, which were then included as covariates in a multilevel logistic regression. Family history of BC was considered as a clustering variable. A multiple probabilistic sensitivity analysis was also performed. Results The study included 100 cases and 294 controls. Four dietary patterns were identified. Traditional (fat meats, bakery products, and vegetable oil and mayonnaise) (OR III tertile vs I 3.13, 95 % CI 2.58?3.78), Rural (processed meat) (OR III tertile vs I 2.02, 95 % CI 1.21?3.37) and Starchy (refined grains) (OR III tertile vs I 1.82, 95 % CI 1.18?2.79) dietary patterns were positively associated with BC risk, whereas the Prudent pattern (fruit and non-starchy vegetables) (OR III tertile vs I 0.56, 95 % CI 0.41?0.77) showed a protective effect. For Traditional pattern, the median bias-adjusted ORs (3.52) were higher than the conventional (2.76). Conclusions While the Prudent pattern was associated with a reduced risk of BC, Traditional, Rural and Starchy patterns showed a promoting effect. Despite the threats to validity, the nature of associations was not strongly affected.Fil: Tumas, Natalia. Universidad Nacional de Cordoba. Facultad de Medicina. Escuela de Nutricion. Cat.de Estadistica y Bioestasdística; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones y Estudio sobre Cultura y Sociedad; ArgentinaFil: Niclis, Camila. Universidad Nacional de Cordoba. Facultad de Medicina. Escuela de Nutricion. Cat.de Estadistica y Bioestasdística; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aballay, Laura. Universidad Nacional de Cordoba. Facultad de Medicina. Escuela de Nutricion. Cat.de Estadistica y Bioestasdística; ArgentinaFil: Osella, Alberto. Laboratorio di Epidemiologia E Biostatistica; ItaliaFil: Diaz, María del Pilar. Universidad Nacional de Cordoba. Facultad de Medicina. Escuela de Nutricion. Cat.de Estadistica y Bioestasdística; Argentin