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

Die Synthese verschiedener Carbonsäuren durch den Multienzymkomplex der Fettsäuresynthese aus Hefe und die Erklärung ihrer Bildung [ = Synthesis of various carboxylic acids by the fatty acid synthetase multienzyme complex of yeast and the explanation for their structure]

The purified multienzyme complex, fatty acid synthetase of yeast, produces palmityl-CoA and stearyl-CoA in equal amounts under standard conditions, with adequate NADPH, and a 1:2 ratio of acetyl-CoA and malonyl-CoA. Based on the known enzymatic properties of fatty acid synthetase a model which rationalizes the chain termination at the level of C16 and C18-acid is proposed. The model is based on two assumptions that are supported by experimental evidence: (a) the probability of any covalently enzyme-bound saturated acyl residue forming a product by transfer to CoA is determined by the relative velocities of the condensing and transferring reactions. (b) The growing alkan chain interacts with the enzyme protein only after a chain length of 13 carbon atoms has been attained; this interaction changes the relative velocities in favour of product formation by an energy increment of -0.9 kcal for each additional methylene group beyond the 13th. 3 To calculate the probability of product release at a particular chain length, an equation was derived from the model describing quantitatively the observed product distribution. 4 The formula suggests conditions under which either short acyl-CoA derivatives or exclusively stearyl-CoA can be produced. Synthesis under these conditions was examined experimentally and results indicated that the formula can be applied to a wide range of experimental conditions. 5 Because the condensation reaction in fatty acid synthesis is the rate limiting step under normal conditions, saturated acyl residues have the longest life-time as intermediates and consequently the highest probability of leaving the enzyme complex as an endproduct. The reduction reactions can be made rate limiting when the NADPH level drops. Under such circumstances β-ketoacyl-CoA's and α,β-unsaturated acyl-CoA's appear as endproducts. With NADH as electron donor the first reduction is slowed to such an extent that predominantly β-ketoacyl-CoA's derivatives are synthesized. 6 The possibility that the enzyme complex catalyses synthesis of short chain fatty acids and and β-ketoacids in vivo is discussed

Drusen Regression is Associated With Local Changes in Fundus Autofluorescence in Intermediate Age-Related Macular Degeneration

PURPOSE: To investigate the association of spontaneous drusen regression in intermediate age-related macular degeneration (AMD) with changes on fundus photography and fundus autofluorescence (FAF) imaging. DESIGN: Prospective observational case series. METHODS: Fundus images from 58 eyes (in 58 patients) with intermediate AMD and large drusen were assessed over 2 years for areas of drusen regression which exceeded the area of circle C1 (diameter 125μm; Age-Related Eye Disease Study grading protocol). Manual segmentation and computer-based image analysis were used to detect and delineate areas of drusen regression. Delineated regions were graded as to their appearance on fundus photographs and FAF images, and changes in FAF signals were graded manually and quantitated using automated image analysis. RESULTS: Drusen regression was detected in approximately half of study eyes using manual (48%) and computer-assisted (50%) techniques. At year 2, the clinical appearance of areas of drusen regression on fundus photography was mostly unremarkable, with a majority of eyes (71%) demonstrating no detectable clinical abnormalities, and the remainder (29%) showing minor pigmentary changes. However, drusen regression areas were associated with local changes in FAF that were significantly more prominent than changes on fundus photography. A majority of eyes (64–66%) demonstrated a predominant decrease in overall FAF signal, while 14–21% of eyes demonstrated a predominant increase in overall FAF signal. CONCLUSIONS: FAF imaging demonstrated that drusen regression in intermediate AMD was often accompanied with changes in local autofluorescence signal. Drusen regression may be associated with concurrent structural and physiological changes in the outer retina

Are there socioeconomic disparities in women having discussions on human papillomavirus vaccine with health care providers?

<p>Abstract</p> <p>Background</p> <p>Human papillomavirus (HPV) vaccine recommendation by a health care provider (HCP) is an important predictor of vaccine receipt. We examined whether being of a minority race/ethnicity, having lower income and education, and the lack of health insurance and a regular HCP are each associated with a lower likelihood of a discussion on HPV vaccine occurring between a woman and her HCP.</p> <p>Methods</p> <p>A sample of 1,631 women aged 18 years and older was drawn from the 2007 Health Information National Trends Survey. Given that only a subgroup of women who were aware of the HPV vaccine were asked if they had a discussion with their HCPs, we estimated a probit model correcting for sample selection.</p> <p>Results</p> <p>Among those aware of the HPV vaccine, 17.3% of respondents reported having discussions on the vaccine with their HCPs. Compared with Whites, African Americans were less likely to be aware of the HPV vaccine but more likely to have discussions with their HCPs concerning the vaccine. A statistically significant association between lower income and education levels and a lower likelihood of HPV vaccine awareness was observed, but low levels of income and education did not appear to affect the probability of having HPV vaccine discussions with HCPs.</p> <p>Conclusions</p> <p>Socioeconomically disadvantaged women did not show a lower propensity to have vaccine discussions with their HCPs, suggesting that HCPs can be a major catalyst in increasing vaccine receipt among the higher risk group. The results of the study suggest a two-pronged approach that seeks to raise vaccine awareness among socioeconomically disadvantaged women at the population level and encourages HCPs to intensify discussions about the HPV vaccine with patients.</p

DNA double-strand breaks: A potential causative factor for mammalian aging?

Aging is a pleiotropic and stochastic process influenced by both genetics and environment. As a result the fundamental underlying causes of aging are controversial and likely diverse. Genome maintenance and in particular the repair of DNA damage is critical to ensure longevity needed for reproduction and as a consequence imperfections or defects in maintaining the genome may contribute to aging. There are many forms of DNA damage with double-strand breaks (DSBs) being the most toxic. Here we discuss DNA DSBs as a potential causative factor for aging including factors that generate DNA DSBs, pathways that repair DNA DSBs, consequences of faulty or failed DSB repair and how these consequences may lead to age-dependent decline in fitness. At the end we compare mouse models of premature aging that are defective for repairing either DSBs or UV light-induced lesions. Based on these comparisons we believe the basic mechanisms responsible for their aging phenotypes are fundamentally different demonstrating the complex and pleiotropic nature of this process