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34 Cards in this Set
- Front
- Back
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What are plate count and MPN methods limited by? |
The volume of sample that can be tested |
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In the usual form, the MPN test for assessing coliform counts is based on? |
A maximum volume of 5 ml (5*ml) per sample |
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What are plate counts limited to? |
volumes under 0.2 ml |
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What is the US drinking water standards of coliform |
1 coliform per 100 ml |
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What is a method to quantitatively concentrate cells in a dilute sample |
Draw the sample through the membrane filter |
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What is a filter |
Micropore membrane with a proe size of 0.45 micro meters |
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When can bacteria grow on the filter |
If the filter is placed onto a solid medium with appropriate nutrients |
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What does the medium do if it is selective |
Specific target organisms grow on the filter |
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What happens if a medium is diagnostic |
Color and colony morpology are indicators of species identity |
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Waht are the two types of media we are using |
Eosine Methyene Blue (EMB) R2A |
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What is the EMB selective for |
Gram negative species |
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What is the EMB diagnostic for |
Most coliforms |
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What are the characteristics of coliforms |
Gram negative Rod Shaped Faculatively Anaerobic Produce acid and gas from lactose |
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Where do the gram-negative bacteria reside |
Mammalian digestive tract |
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What is the gram-negative bacteria indicative of |
Fecal or sewage contamination when found in water |
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What inhibits the gram-positive bacteria in EMB media |
Dyes eosine Y and methylene blue |
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Organisms that can ferment the lactose in the medium with a high production of acid develop what type of colonies |
Dark purple
Blue-black Brown Which are probable coliforms |
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A green metallic sheen on the EMB medium indicative of what |
Vigoroous lactose fermentation typical of many fecal coliforms
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What colonies do weak fermenters develop |
Pink colonies (They are possible, rather than probable coliforms) |
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Coliform counts are very high or low in drinking water |
Low |
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Why must large volumes be filtered in order to recover coliforms |
Because coliform counts are very low in drinking water |
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Is the R2A medium selective |
No |
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What does the R2A medium allow |
Development of slow growing hetertrophic water bacteria
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What does R2A medium give you an idea of |
Bacterial content of "clean water" |
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What is an additional advantage of membrane filter method |
Colonies are isolated on the plates |
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What cna be done after isolate colonies on plate |
Specific identifications made of colonies with subsequent tests |
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Procedure |
1) Unwrap and assemble 2) Sterilize forceps , membrane filter on fritted glass base, place reservoir on the base and clamp two parts together. Attach the filter flask to a vaccum source 3) Add measured water 4) Apply vaccum until entire sample pulled through membrane. Release vaccum, remove the filter reservoir lay filter Bacteria Side Up onto the desired medium taking care to prevent air pockets form forming under the filter 5) Incubate EMB plates for 48 hours. Incubate at room temperature for 5 days and count colonies |
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What are the parts of the sterilized filter housing |
Reservoir Fritted based Filter flask |
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If filtering have multiple volumes what to do |
Begin with smallest volume and work upwards |
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What do you do with small volumes (less than 5 ml) that tend to be condensed on filter and give poor seperation of colonies |
First add to 9 ml of sterile saline then filter entire quantity |
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Should the filter be placed on the medium bacteria side up or down |
Up |
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How long and at what temperature should we incubate EMB plates for |
37 degrees 48 hours |
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What conditions should we incubate R2A plates for |
Room temperature 5 day |
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For the total heterotrophic bacteria of the R2A plates what should we count |
All bacterial colonies |
