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. http://www.3m.com/index.jhtml

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

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

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

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

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

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

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

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 days @ 25°C courtesy Jim Ralph

courtesy Jim Ralph

courtesy Jim Ralph

courtesy Jim Ralph

Use a texta to count colonies courtesy Jim Ralph

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