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Petrifilm Counts with the Apogee BioCount System: Minimum Incubation Time

Petrifilm Counts with the Apogee BioCount System: Minimum Incubation Time. Joy Elbert and J. D. Hendrix Kennesaw State University. BioCount: A software program that uses image analysis technology to determine the number of microbial colonies in a petri dish.

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Petrifilm Counts with the Apogee BioCount System: Minimum Incubation Time

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  1. Petrifilm Counts with the Apogee BioCount System:Minimum Incubation Time Joy Elbert and J. D. Hendrix Kennesaw State University

  2. BioCount: A software program that uses image analysis technology to determine the number of microbial colonies in a petri dish. Determines the number of colonies with accuracy and precision comparable to a manual count. Background

  3. Previous Study • Saadat and Hendrix determined that the BioCount system accurately counted total aerobic colonies on Petrifilm media • Parameters were optimized to allow the program to detect an accurate number of colonies on the Petrifilm media

  4. Petrifilm • Developed By 3M • Rehydratable sample-ready media • Used for environmental and industrial purposes • 24 hour incubation required to count colonies accurately • Selective and/or differential medium

  5. Current Methods • Require a diluted sample of the microorganism spread evenly over the surface of a medium • Cells or groups of cells form colonies (“Colony Forming Units”) • The initial number of microorganisms can be calculated

  6. Objectives • Establish culture and dilution parameters to give a reproducible count of 20 - 200 colonies per film • Determine the minimum incubation time needed to detect colonies on Petrifilm • Compare manual and automated counts of colonies at different incubation times

  7. Procedure • Turbid broth cultures of Escherichia coli (24 hr, 37°C in tryptic soy broth) were diluted 10-5, 10-6, 10-7, 10-8, and 10-9 • 0.5 ml samples were plated on 3M Petrifilm (“Total Aerobic” films) and incubated at 37°C for time intervals between 6 and 24 hr • Colony counts were determined by manual and automated methods

  8. Results • Optimal dilution was determined on films incubated for 24 hr • At 10-7 dilution the colonies remained in the range of 50 to 80 (0.5 ml volume plated)

  9. Results

  10. Results

  11. Results

  12. Results

  13. Results • The t-test was used to determine if there was a significant difference between the manual and automated counts • For 29 films counted:t = 0.38 • There was no significant difference between manual and automated counts

  14. Conclusions • To detect Escherichia coli colonies on total aerobic Petrifilm, a minimum incubation time of 12 hr is required • There was no significant difference between manual and automated counts • Using automated counting is more rapid than manual counting, but it does not decrease the minimum incubation time needed to form the bacterial colonies

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