Lab 8-Enterobacteriaceae and water analysis Flashcards
Enterobacteriacaea is a taxonomic family name given to a group of common intestinal bacteria. True / False
True
MacConkey’s agar is selective for pathogenic bacteria and EMB is selective for benign bacteria.
True / False
False
Boiling contaminated water for 10 minutes effectively destroyed all of the coliform bacteria in
our laboratory experiments.True / False
True
Both MacConkey’s agar and EMB agar are differential and selective media used
to culture and help identify Gram-negative Enterobacteriaceae.True / False
True
Crystal violet and bile salts impart the differential characteristics to MacConkey’s agar.
True / False
True
Enterobaceteriaceae grown on EMB and which produce a heavy dark precipitate often
exhibiting green iridescence can be presumptively classified as what?
E. coli
Enterobacteriaceae grown on EMB and which produce a heavy dark precipitate often
exhibiting green iridescence can be presumptively classified as what?
robust lactose fermenters (such as E. coli)
Isolated colonies from an environmental sample that generate dark green colonies on EMB and
bright pink colonies on MacConkey’s media likely represent what?
-None of these
- Carbohydrate fermentation characteristic of most pathogenic gut bacteria
- Fecal organisms in the sample being tested
- Carbohydrate fermentation characteristic of most skin pathogens
Klebsiella pneumoniae is a normal flora enteric organism that has emerged as an important
opportunistic pathogen in hospital settings. Based on reading exercise 4-6 in your lab manual
and your observations in lab, which of the following would you predict concerning the growth of
K. pneumonia on EMB and MacConkey agar?
K. pneumonia would grow - producing darkly pigmented colonies on EMB and pink colonies
on MacConkey’s agar.
If microbes fail to grow on MacConkey’s agar, which of the following is a likely reason?
They are not able to ferment lactose.
Using the Coliscan easy gel system we assessed water samples for the presence of which of the
following (circle all that apply)?
Fecal coliform count
Purple / dark blue colonies in Coliscan media represent what?
Glucuronidase and Galactosidase activity indicative of fecal coliform bacteria such as E. coli.
Which of the following techniques can be used to safely sanitize water to make it potable (circle
all that apply)?
- Treatment with 0.05% bleach (a final concentration of 0.05%)
- Treatment with 5 drops of iodine per / 100 ml of water
- Boiling for 10 minutes
What is the acceptable titer of coliform microorganisms in potable water?
100 coliform bacteria / 1 liter.
Why is there so much attention given to classifying Gram negative organisms based on their
ability to ferment lactose?
Because heavy lactose fermentation is indicative of organisms that are often associated with
fecal contamination and poor sanitization which in turn, indicates an increased risk of
transmission of enteric pathogens.
