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33 Cards in this Set
- Front
- Back
How do federal/food/water organizations monitor samples?
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-using standard plate count
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What are some methods of plate count technique?
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-membrane filtration technique
-spread plate technique -pour plate technique |
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What happens in membrane filtration technique?
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-cells in a liquid sample are concentrated on a filter membrane which is than applied to agar plate surface
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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 |
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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 |
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What is a countable plate?
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-After colonies grow, there should be between 30 and 300 colony forming units (CFU)
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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 |
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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 |
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What generas are usually found as the flora in milk?
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-Lactobacillus sp
-Listeria sp -Microbacterium sp -Micrococcus sp -Streptococcus sp |
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What is the most reliable indication of milks sanitary quality?
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-bacterial count
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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 |
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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 |
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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 |
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Where do the highest numbers of heterotrophic forms exist in water?
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-on the bottoms and banks of rivers and lakes where organic matter predominates
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When is water considered unsafe?
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-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
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What are two types of pollution?
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-toxic or unsightly chemicals
-pathogenic microorganisms |
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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 |
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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 |
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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 |
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What is a common bacteria found in fecal matter AND naturally on plants and soil?
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-Enterobacter aerogenes which is similar to E coli
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What are two bacterium that indicate animal fecal contamination?
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-Enterococcus faecalis
-Enterococcus faecium |
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What are the two water testing techniques?
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-membrane filtration
-spread plate |
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What is the membrane filtration method used for?
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-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 |
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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 |
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Why is the KF plate called Streptococcus?
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-Enterococcus used the be grouped with Streptococcus, but now it isn't, but the name hasn't changed
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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 |
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Why is PCA plates used for water sampling rather than TSA?
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-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 |
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From the plates, how would you calculate FC?
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-use mEndo plate for E. coli
-divide CFU per 100 ml |
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How would you calculate FS from water plating?
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-use KF Streptococcus plate for enterococcal indicator
-find CFU/100ml |
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How would you find the FC:FS ratio?
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-Find both FC and FS. Divide FC by the FS number.
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When is the FC:FS ratio considered contamination and what does this come from?
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>4.1 human
0.7-4.1 human and animal <0.7 animal |
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Using CFU, how do you find CFU per ml in a sample?
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-multiply CFU x 1/FDF
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