Flow cytometry applications in physiological study and detection of foodborne microorganisms

Flow cytometry (FCM) provides a sophisticated technique for research on microorganisms to determine physiological characteristics on a single-cell basis. The ability of multiparametric analysis in conjunction with fluorescent dyes allows analysis and differentiation of mixed cultures as well as the identification of heterogeneities within populations with regard to structure and function. The acquisition-speed of FCM permits large numbers of cells to be analysed and hence the detection of even rare events with high statistical significance. This review focuses on different FCM approaches with special attention to food microbiology. Fluorochrome application for assessment of bacterial structure and metabolism is discussed. Factors like membrane integrity and potential or enzymatic activity are relevant indicators of cell viability, the knowledge of which is important to elucidate the potential of spoilage organisms or pathogens to grow in foods. Overall population susceptibilities after inactivation treatments are dependent on the physiological state distributions of subpopulations, which can be determined by FCM. Subsequent cell sorting allows correlation of subpopulation patterns with outgrowth potential. Application of flow cytometry in the food industry for detection of spoilage and pathogenic microorganisms is becoming more feasible due to improved instrumentation and labelling of cells.