MMG Lab 13
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- How do federal/food/water organizations monitor samples?
- -using standard plate count
- What are some methods of plate count technique?
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-membrane filtration technique
-spread plate technique
-pour plate technique - What happens in membrane filtration technique?
- -cells in a liquid sample are concentrated on a filter membrane which is than applied to agar plate surface
- How is the spread plate technique done?
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-a small volume of smaple (0.1ml) is spread over an agar plate with suitable applicator
-may be diluted or undiluted volume - What are the ways pour plate techniques are done?
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1) sample added to petri dish and molten, tempered agar added
2) sample added directly to a tube of tempered agar which is then dispensed into a petri dish
*object in both: prep of countable plate for calc of number of microbial cells - What is a countable plate?
- -After colonies grow, there should be between 30 and 300 colony forming units (CFU)
- What affects the final number and types of microorganisms found in a finished food product?
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-general environment from which food obtained
-microbial content of food in unprocessed state
-sanitary conditions during processing
-adequacy of subsequent packaging, handling, and storage conditions - Describe the microorganisms that typically make up the flora in milk.
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-Gram +
-nonmotile
-aerobic
-microaerophilic or faculatative anaerobic rods or cocci - What generas are usually found as the flora in milk?
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-Lactobacillus sp
-Listeria sp
-Microbacterium sp
-Micrococcus sp
-Streptococcus sp - What is the most reliable indication of milks sanitary quality?
- -bacterial count
- What are some advantages to plate counts in terms of milk?
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-can show how many bacteria are in milk
-can show pathogens that may only apear as one colony and would normally be overlooked
-can show good bacteria such as Lactobacillus in yogurt - What are the U.S. Public Health Services guidlines for Grade A raw milk, and Grade A milk products
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-100,000/ml
-20000/ml - What factors affect the numbers and types of bacteria found in water?
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-organic matter present
-presence of toxic substances
-saline content
-environmental factors such as pH, temp, and aeration - Where do the highest numbers of heterotrophic forms exist in water?
- -on the bottoms and banks of rivers and lakes where organic matter predominates
- When is water considered unsafe?
- -when some condition makes the water unsafe for recreation or consumption or upsets the natural balance of plants and animals living in or near that water
- What are two types of pollution?
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-toxic or unsightly chemicals
-pathogenic microorganisms - What are some diseases caused by fecal water contamination?
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-typhoid fever, cholera, Bacillary dysentery caused from bacteria
-Poliomyelitis, hepatitis caused by viruses
-amoebic dysentery caused by protozoa - What are indicator organisms?
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-microbes which are not only commonly found in association with pathogenic species
-usually found in much higher numbers than pathogens and easier to find
-their presence in water implies presence of enteric pathogens in a water supply -
What is the most commonly sough indicator organisms in drinking water?
Why is this? -
+Escherichia coli
-small Gr - bacilli
-does NOT contain spores
-ferments lactose in presence of bile with acid and gas production - What is a common bacteria found in fecal matter AND naturally on plants and soil?
- -Enterobacter aerogenes which is similar to E coli
- What are two bacterium that indicate animal fecal contamination?
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-Enterococcus faecalis
-Enterococcus faecium - What are the two water testing techniques?
-
-membrane filtration
-spread plate - What is the membrane filtration method used for?
-
-used to recover indicator organisms
-filter 100 ml water and put filter on surface of agar medium
-use two types of agar plates for specific growth - What are the two types of plates used in membrane filtration and what grows on each?
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-mEndo agar for E. coli
-KF Streptococcus agar to grow E. faecalis and E. faecium - Why is the KF plate called Streptococcus?
- -Enterococcus used the be grouped with Streptococcus, but now it isn't, but the name hasn't changed
- What is the purpose of plate count in water sampling?
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-used to determine the concentration of heterotrophic organisms in water
-water added directly to 2 PCA (Plate count Agar) and incubated at two different temps - Why is PCA plates used for water sampling rather than TSA?
- -it is a more dilute form of nutrients to match a watery habitat
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What are the two temperatures that the plates are incubated at?
What designates contamination? -
-25 C
-37 C
*can not have over 500 heterotropic cells/ml - From the plates, how would you calculate FC?
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-use mEndo plate for E. coli
-divide CFU per 100 ml - How would you calculate FS from water plating?
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-use KF Streptococcus plate for enterococcal indicator
-find CFU/100ml - How would you find the FC:FS ratio?
- -Find both FC and FS. Divide FC by the FS number.
- When is the FC:FS ratio considered contamination and what does this come from?
-
>4.1 human
0.7-4.1 human and animal
<0.7 animal - Using CFU, how do you find CFU per ml in a sample?
- -multiply CFU x 1/FDF