1. PETRIFILMTM PLATES http://www.3m.com/index.jhtml
flat dehydrated media on a sheet which forms a rehydrated gel when 1 ml ( or other volume as directed) of sample is added to the surface.
the sample is spread using a special PetrifilmTM spreader.
colonies are dyed and can be counted and examined after incubation.
PetrifilmTM plates have been designed for isolation and/or quantification of the following microbial groups:
aerobic plate count, coliform count, E. coli count, Enterobacteriaceae count, S. aureus count, yeast and mould count, and environmental Listeria detection.

4. APPLICATIONS Count (enumerate) bacteria Identify bacteria
Measure growth/death rates
Quantify levels of bacteria
Quantify levels of hygiene
Identify bacteria
E. coli, coliforms, Staph. aureas, Y&M
Indicators of faecal contamination
Contamination/purity of cultures
courtesy Jim Ralph

5. 3M TRICKS THAT MAKE LIFE EASIER
Petrifilm plates are:
pre-sterilised
complete – no additional chemicals are required
dehydrated – just add water
stable – last about a year
self-capping – prevents contamination and entraps gas
courtesy Jim Ralph

7. colonies stained pink with tetrazolium dye
Aerobic Plate Count
colonies stained pink with tetrazolium dye

8. Advantages:
no preparation of media
PetrifilmsTM can be stacked taking up very little room.
can be carried much more conveniently than traditional plates
easily sterilised

9. Example: Coliform Count Plates
Chemicals (violet red bile) prevent growth of most non-coliform bacteria
Dyes differentiate bacteria and plastic film entraps gas
Blue with gas  E. coli
Red with gas  colifom bacteria
Red / no gas  not a coliform bacterium
courtesy Jim Ralph

10. Petrifilm(TM) E. coli count plates, incorporating coliforms counts

11. E. Coli PetrifilmTM plates distinguishing coliforms and E.coli
Typical E. coli
=blue + gas
Typical coliforms = pink + gas

12. Example: Yeast & Mould Count Plates
Low ph prevents growth of most bacteria
Dye makes counting colonies easy
Case study
Pinch of bakers yeast in 100 ml water
Make 1/10 dilutions to a final dilution of 1/1,000,000 of original cell suspension
Plate out 1 ml onto Y&M plates
Incubate 5 25°C
courtesy Jim Ralph

13. courtesy Jim Ralph

14. courtesy Jim Ralph

15. courtesy Jim Ralph

16. Use a texta to count colonies
courtesy Jim Ralph

18. Acknowledgement
I thank 3M and Jim Ralph from Regency Tafe in SA for giving permission to use some slides.