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33 Cards in this Set

  • Front
  • Back
How do federal/food/water organizations monitor samples?
-using standard plate count
What are some methods of plate count technique?
-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?
-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?
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?
-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.
-Gram +
-microaerophilic or faculatative anaerobic rods or cocci
What generas are usually found as the flora in milk?
-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?
-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
What factors affect the numbers and types of bacteria found in water?
-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?
-toxic or unsightly chemicals
-pathogenic microorganisms
What are some diseases caused by fecal water contamination?
-typhoid fever, cholera, Bacillary dysentery caused from bacteria
-Poliomyelitis, hepatitis caused by viruses
-amoebic dysentery caused by protozoa
What are indicator organisms?
-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?
-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?
-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?
-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
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?
-use mEndo plate for E. coli
-divide CFU per 100 ml
How would you calculate FS from water plating?
-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