This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Noble, P A Articles by Albritton, W L Search for Related Content PubMed PubMed Citation Articles by Noble, P A Articles by Albritton, W L Agricola Articles by Noble, P A Articles by Albritton, W L

 Previous Article  |  Next Article 

Appl Environ Microbiol. 1991 November; 57(11): 3287-3291

Heterotrophic plate counts of surface water samples by using impedance methods.

Department of Applied Microbiology and Food Science, University of Saskatchewan, Saskatoon, Canada.

ABSTRACT

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 less than or equal to 25 degrees C had R2 values of 0.878 to 0.933. However, regressions using detection times of water samples incubated at greater than or equal to 30 degrees 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 degrees 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.