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Effective modelling of the fate and transport of water-borne pathogens is needed to support federally required pollution-reduction plans, for water quality improvement planning, and to protect public health. Lack of understanding of microbial-particle interactions in water bodies has sometimes led to the assumption that bacteria move in surface waters not associated with suspended mineral and organic particles, despite a growing body of evidence suggesting otherwise. Limited information exists regarding the factors driving interactions between micro-organisms and particles in surface waters. This review discusses cellular, particle and environmental factors potentially influencing interactions and in-stream transport. Bacterial attachment in the aquatic environment can be influenced by properties of the cell such as genetic predisposition and physiological state, surface structures such as flagella and fimbriae, the hydrophobicity and electrostatic charge of the cell surface, and the presence of outer-membrane proteins and extracellular polymeric substances. The mechanisms and degree of attachment are also affected by characteristics of mineral and organic particles including the size, surface area, charge and hydrophobicity. Environmental conditions such as the solution chemistry and temperature are also known to play an important role. Just as the size and surface of chemical particles can be highly variable, bacterial attachment mechanisms are also diverse., (© 2015 The Society for Applied Microbiology.)

Aim: A standard procedure does not exist to distinguish between attached and unattached micro-organisms. In this study, we compared two methods to quantify between Escherichia coli attached to clay particles and E. coli freely suspended in solution: flow cytometry (attachment assay and viability assay) and settling (or centrifugation followed by settling)., Methods and Results: Methods were tested using three environmental strains collected from swine facilities (A, B and C) and one purchased modified pathogenic strain (ATCC 43888); four clay particles: Hectorite, Kaolinite, Ca-Montmorillonite, Montmorillonite K-10; and a range of surface area ratios (particle surface area to E. coli surface area). When comparing the two methods, the per cent attached obtained from the flow cytometry was lower, but not significantly different from the per cent attached obtained from the settling method for all conditions except when the particle was Hectorite or Montmorillonite K-10; when the strain was C; and when the surface area ratio was below 100. Differences between the methods are likely because traditional culture-based methods cannot detect the viable but nonculturable (VBNC) population, whereas flow cytometry can detect the fraction of VBNC with intact membranes., Conclusion: Our results indicate that flow cytometry is a rapid and culture-independent method for differentiating between attached and unattached micro-organisms., Significance and Impact of the Study: Flow cytometry is useful for laboratory-based studies of micro-organism-particle interactions., (© 2014 The Society for Applied Microbiology.)