Enumeration of Coliforms and E.coli

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Enumeration of Coliforms and E. coli Objective The objective of this experiment was to compare and contrast several different enumeration methods, which were used to determine the approximate microbial populations in foods. The enumeration methods that are performed in this experiment are the spread plate, Petrifilm plate, and spiral plate for aerobic plate count, coliform, Petrifilm Violet Red Bile (VRB), and most probable number (MPN) techniques. Materials and Methods Please refer to the FDST (MIBO) 4030 Lab Manual for the materials and methods used for this experiment1. Results Table 1 Aerobic plate Method Coliform Forming Unit (cfu/mL) Spiral Plate 2.20E3 Spread Plate 1.80E4 Petrifilm Plate 2.01E4 When plotting the data for the Aerobic plate methods, that can be seen in Table 1, we discovered that the results range from 2.20E3 colony forming units/mL to 2.01E4 colony forming units/mL, which is a difference of almost 10 folds. The method with the least colony forming units per mL is the spiral plate method with 2.2E3, followed by the spread plate with 1.8E4, and lastly the Petrifilm plate method with the greatest count of 2.01E4. Table 2 Coliform Method Colony Forming Unit (cfu/mL) Solid Medium/Pour plate 1.40E2 Petrifilm VRB 2.00E2 MPN 2.10E2 The results for the coliform methods as seen above in Table 2 show that the colony forming units per mL do not vary as much; they only range from 1.40E2 to 2.10E2. The solid medium pour plate method has the lowest count with 1.40E2, followed by the Petrifilm VRB, with 2.0E2, and last with the highest count, the MPN (Most Probable Number) method with 2.1E2. Discussion When using the aerobic plate methods, our group used the 10–2 dilution for the spread plate and Petrifilm plate and 100 dilution for the spiral plate method due to the fact that they fell into the suitable colony counting range

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