title: Flow cytometry is a promising and rapid method for differentiating between freely suspended Escherichia coli and E. coli attached to clay particles.
abstract: OBJECTIVE
  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).
  
  
  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.
  
  
  CONCLUSIONS
  Our results indicate that flow cytometry is a rapid and culture-independent method for differentiating between attached and unattached micro-organisms.
  
  
  CONCLUSIONS
  Flow cytometry is useful for laboratory-based studies of micro-organism-particle interactions.
authors.affiliation: Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA, USA.
authors.forename: X
authors.initials: X
authors.lastname: Liang
authors.forename: M L
authors.initials: ML
authors.lastname: Soupir
authors.forename: S
authors.initials: S
authors.lastname: Rigby
authors.forename: L R
authors.initials: LR
authors.lastname: Jarboe
authors.forename: W
authors.initials: W
authors.lastname: Zhang
mesh_terms: D000538:Aluminum Silicates; D001546:Bentonite; D000077215:Clay; D004926:Escherichia coli / Q000302:isolation & purification*; D005434:Flow Cytometry / Q000379:methods*; D007616:Kaolin; D017640:Silicates
chemical_list: D000538:Aluminum Silicates; D017640:Silicates; C503188:montmorillonite K-10; C013547:hectorite; D001546:Bentonite; D007616:Kaolin; D000077215:Clay
keywords: E. coli; attachment; clay; flow cytometry; settling