BIOL241 Study Guide - Final Guide: Pasteurization, Indole Test, Arabitol
21 Apr 2016
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Experiment 1: direct microscopic count of microorganisms in milk. Milk is typically composed of gram positive, non-motile, microaerophilic or anaerobic rods or cocci: mainly lactobacillus, micrococcus, and streptococcus. Advantages of stained film on a milk sample are: fast, bacteria and clumps can be counted, little equipment is required, morphology can be looked at, slides can be preserved. Disadvantages of stained film on a milk sample are: counts cannot be accurate on low-count milk, includes dead cells which can skew results, extra debris in the milk may be confused with cells. Post-contamination may occur in processing and handling or infections from the cow. Pasteurized by htst (high-temp-short- time 72c for 15 sec or 79c for 20-25 sec) Higher numbers because it counts both living and dead cells so it is not effective for low counts. Lower numbers because it counts only cells that can grow under experiment conditions.
