Applications and challenges for single-bacteria analysis by flow cytometry

Flow cytometry (FCM) is a powerful technique for single-bacteria analysis via simultaneous light-scattering and fluorescence measurements. By offering high-throughput, quantitative, and multiparameter analysis at the single-cell level, FCM has gained an increased popularity in microbiological research, food safety monitoring, water quality control, and clinical diagnosis. Here we will review the recent applications of flow cytometry in areas such as (1) total bacterial cell count, (2) bacterial viability analysis, (3) specific bacterial detection and identification, (4) characterization of physiological changes under environmental perturbations, and (5) biological function studies. Nevertheless, despite these widespread applications, challenges still remain for the detection of small sizes of bacteria and biochemical features that cannot be brightly stained via fluorescence. Recent improvement in FCM instrumentation will be discussed, and particularly the development of high sensitivity flow cytometry for advanced analysis of single bacterial cells will be highlighted.