Bacterial colonies are then counted, and the number of CFUs (colony forming units) in the original undiluted sample is calculated.
#Serial dilution lab report microbiology serial
In this method, serial dilutions of the food are plated on general purpose and/or differential/selective growth media. One of the most common methods of determining the amount of bacteria in a food product is a standard plate count. Standard Plate Count and Serial Dilution Techniques typhimirium), and Yersinia enterocolitica. Microorganisms of concern in milk include Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, Mycobacterium bovis, Mycobacterium tuberculosis, Salmonella species (most common: S. This is why UHT milk can be left unopened at room temperature for long periods of time. If done aseptically, UHT (ultra high temperature) pasteurization can sterilize foods. If this milk is stored at 4✬ (refrigerator temperature) the bacteria are prevented from multiplying, but if the milk is left out at room temperature, the bacteria will reproduce and the milk will spoil. Milk that has undergone a regular pasteurization procedure can still contain bacteria. As discussed in Lab 7, regular pasteurization is the process used to reduce microbial loads to acceptable levels in foods like milk and fruit juices. Several different kinds of bacteria may be present in milk, most commonly the genera Lactobacillus, Micrococcus, and Streptococcus. Milk contains carbohydrates, minerals, fats, vitamins, and proteins, and is therefore susceptible to breakdown by a wide variety of microorganisms. In this lab, you will examine bacteria found in milk, chicken, and in other assorted food materials. coli suggests feces are present, indicating that serious pathogens, such as Salmonella species and Campylobacter species, could also be present. coli, are often used as indicator species, as they are not commonly found growing in nature in the absence of fecal contamination. A subset of these bacteria are the fecal coliforms, which are found at high levels in human and animal intestines. Coliform bacteria are Gram-negative non-spore forming bacteria that are capable of fermenting lactose to produce acid and gas. In many cases, small numbers of pathogenic bacteria are not dangerous, but improper storage and/or cooking conditions can allow these bacteria to multiply to dangerous levels.įecal contamination of water (and through water, contamination of food materials) is another one of the ways in which pathogens can be introduced.
Pathogens can be introduced into foods at any stage: during growth/production at the farm, during processing (grinding, chopping, milling, etc.), during handling and packaging, and when the food is prepared in the kitchen.
#Serial dilution lab report microbiology how to
Learn how to do a standard plate count.Standard Plate Count and Serial Dilution Techniques.
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