Lab Quiz: Water Quality Testing Flashcards
Indicator organisms
organisms that indicate the pressence of contaminants
Coliforms
-(are commonly used as indicator organisms
-They are gram-negative non-endospore-forming rods from the bacterial family Enterobacteriaceae (enteric bacteria) that ferment lactose with acid and gas production within 48 hours at 35 degrees celsius.
Lactose fermentation
is visualized by a color change in the lactose media from pink to orange-yellow, and gas production is observed by the presence of gas collected in an inverted glass Durham tube in the media.
Drinking water typically must register…?
a coliform count of 1 cell per 100 mL of water
recreational water is considered acceptable for swimming as long as the coliform count…?
is 125 cells per 100mL of water.
Most coliforms are not what?
pathogenic
The presumptive Test
The initial test for water quality analysis. This tests for the presence of coliforms in a water sample (although not necessarily fecal coliforms) and enables an estimate of the number of coliforms present in a sample.
The confirmed Test
-A positive presumptive test is followed with a confirmed test
- This uses selective media: inhibits the group of certain organisms, while allowing the growth of others
-Also uses Differential media: visual change due to certain types of bacteria grown on them.
Brilliant Green Bile Broth (BGBB):
-selective medium that inhibits the growth of gram positive bacteria
-differential medium containing lactose and a Durham tube.
-Gas production captured by the Durham tube indicates contamination by coliforms
Eosin Methylene Blue agar(EMB):
-is a selective medium Inhibits the growth of gram-positive bacteria
- differential medium that changes color when coliform bacteria are grown on it
-coliforms colonies will have dark centers and a metallic green sheen. Any other colonies are non-coliforms
Macconkey (MAC):
-Is a selective medium that inhibits the growth of gram positive bacteria.
-differential medium changes color when coliform bacteria is grown in it
-pinkish-red with a pink hue to the surrounding agar. Other colonies are non-coliforms
The completed Test:
-if the confirmed test results are positive, a completed test is often performed to definitively establish the presence of coliforms.
-In the completed test, the positive sample colony from the EMB plates is gram-stained and used to inoculate one more lactose fermentation tube.
-identification of Gram-negative rods that ferment lactose with gas production absolutely confirms that the sample is a coliform.
