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

Resilience assessment in complex supply networks

Resilience has been widely used as one of the core elements to deal with and to respond to major disruptions. Therefore, building resilient supply networks has become an important issue for managers, stakeholders, and researchers. However, the complexity arises when large numbers of companies are networked together to achieve some collaborative advantage. The combination of large-scale interdependencies and unpredictable behavior creates new challenges for managing risk. Different actors make decisions at different times and consequently with different sets of information guiding them. The network resilience results from the interaction of all network components. The presence of interdependence between nodes in different networks makes the resilience assessment more difficult, since the failure of nodes in one network may cause a disruption at its dependent node in another network. Traditional theories and approaches do not fully address the technical and managerial challenges of today’s supply chains. Hence, one challenge faced by researchers is how to assess the resilience. The main objective of this chapter is to define and formalize a method for a holistic resilience assessment in complex supply networks