Exercise 15: Bacterial Examination of Water

What is the day 1 of the experiment called?

Presumptive testing using most probable number (MPN)

What is water routinely tested for?

coliform bacteria

Where is coliform bacteria often found in?

feces

What family are coliforms a member of?

Enterobacteriaceae

Because coliforms are part of enterobacteriacaea, what does that mean in regards to gram stain, morphology, and fermentation?

Gram negative rods that ferment lactose with gas production

The presence of coliform in water can indicate what?

fecal contamination

The day 1 presumptive test consist of multiple-tube of what test and what is it looking for?

Lactose fermentation with gas production

does the multiple tube lactose fermentation test confirm fecal contaminaiton?

Does NOT confirm, bit it is suggestive

What does the Most Probable Number method estimate?

number of microbes present in water sample

How many tubes do you need in total and how much of sample goes into each group

3 groups of 3 tubes (9 total), 10ml, 1ml, 0.1ml

What is included in each tube and whats its purpose?

durham tube to detect gas production from lactose fermentation

What is day 2 of the experiment called?

Confirmed Test

What 2 3-zone streak plate tests are used for day 2?

EMB (eosin methylene blue) agar and Endo Agar plate

What is day 3 of the test called?

Completed test

What is EMB plate selective and differential for?

selective for gram negatives and differential for lactose fermenters

What is the endo agar plate selective and differential for?

selective for gram negatives and differential for lactose fermenters

In an endo agar plate, what does E.coli produce?

pink/red colonies with a metallic sheen

The method of examining water for bacterial contamination by passing water through a filter with pores that are 0.45μm

membrane filter technique

with the membrane filter technique, what passes through and what does not?

captures bacteria (does not retain viruses) that was in the water, lets the water pass through

with the filter that caught the bacteria, when placed into a mENDO agar (pink), what shows if there is TOTAL colifrorms present?

pink shows total coliform by a golden sheen

with the filter that caught the bacteria, when placed into a mFc agar (light blue), what shows if there is FECAL colifrorms present?

darker blue colonies