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- Beal, Jacob, et al.
(author)
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Robust estimation of bacterial cell count from optical density
- 2020
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In: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Journal article (peer-reviewed)abstract
- 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.
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2. |
- Zhou, Yihui, et al.
(author)
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Chlorinated Paraffins in Human Milk from Urban Sites in China, Sweden, and Norway
- 2020
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 54:7, s. 4356-4366
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Journal article (peer-reviewed)abstract
- Short-, medium-, and long-chain chlorinated paraffins (SCCPs, MCCPs, and LCCPs) were analyzed in human milk from the Yangtze River Delta (YRD) and Scandinavia. Individual samples were collected from Shanghai, Jiaxing, and Shaoxing (China), Stockholm (Sweden), and Bodø (Norway) between 2010 and 2016. Mean concentrations (range) of SCCPs, MCCPs, and LCCPs in samples from the YRD were 124 [-1 fat, respectively, all of which were significantly (p < 0.05) higher than 15.9 (-1 fat, respectively, in samples from Scandinavia. MCCPs predominate in most samples, and LCCP concentrations exceed reported for polybrominated diphenyl ethers in human milk from the same regions. This study is the first to confirm LCCP exposure via breastfeeding. Principal component analysis showed that the YRD samples were more influenced by SCCPs than the Scandinavian samples, which mirror different exposures to CPs between the regions. Because of a large variation in concentrations among individuals, SCCP intake via breastfeeding indicated a potential health concern in the 90th percentile among Chinese infants. Further, CP concentrations in the YRD samples from first-time mothers were on average three times higher than from second-time mothers. In order to limit the worldwide CP contamination, the inclusion of SCCPs as persistent organic pollutants in the Stockholm Convention needs to be followed up, with the inclusion of MCCPs and LCCPs as well.
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