Heterotrophic plate counts of surface water samples by using impedance methods

Academic Article


  • Membrane filtration, spread plating, and pour plating are conventional methods used to determine the heterotrophic plate counts of water samples. Impedance methods were investigated as an alternative to conventional methods, since sample dilution is not required and the bacterial count can be estimated within 24 h. Comparisons of impedance signals obtained with different water samples revealed that capacitance produced faster detection times than conductance. Moreover, the correlation between heterotrophic plate count and detection time was highest (r = 0.966) when capacitance was used. Linear and quadratic regressions of heterotrophic plate count and impedance detection time were affected by incubation temperatures. Regressions between heterotrophic plate counts based on conventional methods and detection times of water samples incubated at ≤25°C had R2 values of 0.878 to 0.933. However, regressions using detection times of water samples incubated at ≥30°C had lower R2 values, even though water samples produced faster detection times. Comparisons between broth-based versions of R2A medium and plate count agar revealed that the latter correlated highly with heterotrophic plate count, provided that water samples were incubated at 25°C and impedance measurements were conducted with the capacitance signal (r = 0.966). When the linear regression of this relationship was tested with 100 water samples, the correlation between predicted and actual log10 CFU milliliter-1 was 0.869. These results indicate that impedance methods provide a suitable alternative to conventional methods.
  • Authors

    Digital Object Identifier (doi)

    Author List

  • Noble PA; Ashton E; Davidson CA; Albritton WL
  • Start Page

  • 3287
  • End Page

  • 3291
  • Volume

  • 57
  • Issue

  • 11