Multiparametric quantification of bacterial cells using digital holographic microscopy

The detection and quantification of the physical properties of bacterial cells are crucial for advancing precision microbiology. Here, we use digital holographic microscopy (DHM) to measure the dry mass of individual Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli) cells with high throughput and rapid acquisition. We demonstrate that by processing quantitative phase images with polynomial background correction, Gaussian filtering, and adaptive masking, we are able to obtain, not only the dry mass of individual bacterial cells, but also detailed morphological information. These features allow the discrimination between single and clustered cocci, as well as the identification of elongation patterns in bacilli, that may provide relevant indicators of bacterial growth and physiological state. Finally, we compare the DHM dry mass distribution with those obtained by nanomechanical mass spectrometry (NMS), highlighting the potential and limitations of each technique.