BIOL241 Study Guide - Final Guide: Micrococcus, Foodborne Illness, Tryptophan
24 Oct 2017
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Experiment 1: direct microscopic count of microorganisms in milk. Milk is composed of the following types of microorganisms: gram-positive, non-motile, microaerophilic, anaerobic rods, anaerobic cocci, lactobacillus, micrococcus, streptococcus. Advantages to method: results are available rapidly, minimum equipment required, morphology can be determined, slides kept as permanent record. Disadvantages to method: counts are not accurate on low-count milk, dead cells are counted, continuous examinations are tiring, debris may be confused with bacteria cells. Individual bacteria and clumps of bacteria can be counted. Materials: slidebrite remove fat globules, 0. 14% methylene blue stain stain, 95% ethanol decolourization, remove slidebrite, water remove stain, remove ethanol, stop decolourization. Microscope factor = the relationship of the field to a milliliter: use stage micrometer to measure diameter of oil immersion field. Standard plate count: agar-plate method for estimating bacterial populations. Total # colonies formed = # viable microorganisms in diluted sample. Advantages of plate count method: counts only viable organisms, accurate for milk with low bacterial content.
