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Total Plate Count

Total Plate Count

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Total Plate Count

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  1. Total Plate Count Lab 1

  2. TPC • Rough estimate of total microbial content of food • Limitation • Fastidious organisms may not grow • Incubation temperature not ideal for all organisms • Oxygen content eliminates anaerobes, and may suppress microaerophiles • Molds and yeast require longer incubation periods • Fermented foods have a higher content of microbes than is preferred

  3. Overview Ground beef/cheese 11g/99ml peptone water Blender/Stomacher Cheese- 10-7 Meat -10-5 TSA not PCA 35ºC for 48 hr Slow growing organisms

  4. 2 min 2 min Spread plates Petrifilms

  5. Petrifilms • Quick plating method • Contains a dye to make it easier to observe live cells • TETRAZOLIUM dye is reduced by growing cells to produce a red color • You are counting red dots when using petrifilms • Disadvantages- No colony morphology and expensive

  6. 2 1 How to work with a Petrifilm 1 ml onto center

  7. 3 4 Place spreader with ridge side down onto center of Petrifilm Press center of device Let top flap down

  8. Release spreader and allow to dry Results of TPC Petrifilm

  9. Second and Third Period • Count colonies by rules (p. 9-12) and follow flowchart (p. 32) • Calculate the total plate count by dividing your value by the dilution factor X volume plate • Morphological and microscopic evaluations CFU dilution factor X volume plated

  10. 1. Colony shape and size: round, irregular, punctiform (tiny) 2. Margin (edge): entire (smooth), undulate (wavy), lobate (lobed) 3. Elevation: convex, umbonate, flat, raised 4. Color: color or pigment, plus opaque, translucent, shiny or dull 5. Texture: moist, mucoid, dry (or rough). Gram Stain Air dry specimen, heat fix Crystal Violet – 1 min Gram’s Iodine – 1 min Acetone Alcohol – quickly decolorize (3-5 sec) Safranin – 1 min Note cell shape and size Purple = +, Pink = – Evaluations COLONY MORPHOLOGY CELL MORPHOLOGY

  11. Lab Setup • Each group will have either cheese or ground meat • Within each group, one student blends the sample and the other will stomach a similar sample • Lab Report due Friday, April 8th • If you have any questions contact me at gramp.1@osu.edu