Discussion Questions Unit 3

Question 1

Why would a scientist or medical professional want a microbial count? Give an example where microbial counts would be valuable.

Answer 1

Why Microbial Counts are Important:
1. Diagnosing Infections: Helps identify pathogens causing illness.

2. Food Safety: Ensures food is safe to eat by checking for harmful microbes.
3. Water Quality Testing: Monitors drinking water for contamination.
4. Environmental Monitoring: Assesses the health of ecosystems.

Example: Urinary Tract Infections (UTIs): A doctor might perform a microbial count on urine to check for high levels of bacteria, like E. coli, to confirm a UTI and determine the best treatment.

Question 2

Given specific information, can you ID the type of microbial count performed by the scientist?

a. Dr. Bowen used an indirect measurement which relied upon a spectrophotometer to measure the amount of cloudiness in the tube. He chose it because it was quick test but a disadvantage was that it couldn’t tell between living or dead cells. What technique am I?

Answer 2

Turbidity (cloudiness)

Question 3

Given specific information, can you ID the type of microbial count performed by the scientist?

b) Waste management scientist, Dr. Who, used a series of tubes with liquid and nutrient agar plates to determine the number of microorganisms from the original sewage sample. This allowed Dr. Who to determine what it took to get the microbe number to zero so that the sample could be flushed into the Pacific Ocean.

Answer 3

Serial Dilution & Viable plate counts

Question 4

A scientist describes an organism as a chemoheterotrophic, aerotolerant, mesophilic, facultatively halophilic coccus. Describe the cell’s metabolic and structural features in plain English.

Answer 4

Chemoheterotroph: uses organic molecules as carbon & energy

Aerotolerant: doesn’t use oxygen but low levels of oxygen can be present

Mesophilic: can live in a temperature range of room temperature to body temperature

Facultative halophile: can survive at normal to high salt concentration

Coccus: round or spherical in shape

Question 5

Energy source:

Answer 5

Light: phototroph

Chemical: chemotroph

Question 6

Electron source:

Answer 6

Organic: organotroph

Inorganic: lithotroph

Question 7

Carbon source:

Answer 7

Organic: heterotroph

CO2: autotroph

Question 8

The filamentous bacterium Beggiatoa gets its carbon from carbon dioxide and its electrons and energy from hydrogen sulfide. What is its nutritional classification?

Answer 8

Chemolithoautotroph
Chemo- : chemical energy
-litho- : inorganic electron
-autotroph: carbon is co2

Question 9

Temperature terms:

Answer 9

Thermophile: likes above 45°C

Hyperthermophile: grows best at above 80°C

Mesophile: grows at 20-40°C

Psychrophile: grows at 0-15°C

Question 10

pH terms:

Answer 10

Alkalinophile: grows at greater than 8 pH (basic)

Neutrophile: grows at 6.5-7.5 pH

Acidophile: grows at less than 6 pH (acidic)

Question 11

Osmotic pressure terms:

Answer 11

Hypotonic: solution cell is in is less concentrated causes cells to swell and lyse

Isotonic: concentration = in cell and outside

Hypertonic: solution is more concentrated than cell causes cell to shrink or crenate

Question 12

Salt terms:

Answer 12

Halophile: salt loving

Question 13

Hydrostatic (water) pressure terms:

Answer 13

Barophile: thrives under high pressure (deep sea)

Question 14

Oxygen requirement terms:

Answer 14

Obligate aerobe: needs more than 21% oxygen

Obligate anaerobe: killed by any % of oxygen

Facultative anaerobe: can use or not use oxygen (0-21%)

Microaerophile: grows at 2-10% oxygen

Aerotolerant: tolerates oxygen but doesn’t use it

Question 15

Scientist studying deep sea bacteria in the Antarctic Ocean must take into consideration what environmental factors when trying to culture these bacterial species? What terms would you use to describe these bacterial species?

Answer 15

Water pressure: barophile (high pressure)
Temperature: psycrophile (cold)
pH: alkalinophile (8.1 slightly basic)
Salt: halophile (ocean is salty)
Oxygen: Obligate anaerobe (no oxygen down there)
If it is near a thermal vent:
Temperature: thermophile
pH: acidophile

Question 16

Sheep blood is suspended in an unknown solution X. You take a sample & make a wet mount. Under high power, you observe crenation of these cells. What term would describe unknown solution X?

Answer 16

Hypertonic (concentrated)

Question 17

A film of microorganisms is observed floating on the top of your vinegar. What term would describe these microbes?

Answer 17

Acidophile (likes acidic environments)

Question 18

Pasteurization is a technique that uses temperatures of about 72°C to neutralize potential pathogens in foods. What effect does this temperature have on the enzymes and cellular metabolism of pathogens? Why does the heat of pasteurization kill some microorganisms yet fail to affect thermophiles?

Answer 18

72°C exceeds the max temp for pathogens that are mesophiles (effect humans because they thrive in body temp). At this temp mesophiles proteins denature and metabolism stops.

Thermophiles thrive well in this temperature because they like the heat.

Question 19

If you were to streak for isolation from the biofilm, describe what your plate would look like after incubating the plate at the appropriate temperature. Explain your answer.

Answer 19

A streak for isolation should show many different types of colonies because a biofilm is a community of microbes

Question 20

Waste management scientist, Dr. Siri, wanted to extend the lifetime of the sewage pipes in the Seattle Public Works system. She noticed that the older pipes were laden with two inches of biofilm. What would be one potential way that she could design an experiment to either dismantle the biofilm or prevent it from starting?

Answer 20

Blocking cell receptors for quorum sensing -> disrupt communication

Amplify the quorum sensing signal -> population is too big -> dismantle

Question 21

Which selective/differential medium tests for halophiles?

Answer 21

Mannitol salt agar (MSA): because it contains 7.5% NaCl which halophiles love because they love salty environments

Question 22

What are the ingredients in CNA?

Answer 22

Colistin: disrupts outer membranes of gram negatives

Nalidixic acid: blocks DNA replication in some gram neg

(selects for gram positive)

Question 23

What are the ingredients in EMB?

Answer 23

Lactose, sucrose, peptone: energy source

Eosin Y and Methylene blue: dyes that inhibit gram positive

(selects for gram negative)

Question 24

What are the ingredients in MacConkey Agar?

Answer 24

Bile salts and Crystal violet: inhibit gram positives

Lactose: for energy

Neutral red: pH indicator that is red below pH 6.8 (colorless above = basic)

(selects for gram negative)

Question 25

What is the ingredients in MSA?

Answer 25

Mannitol: sugar alcohol fermented by some bacteria

7.5% NaCl: few organisms tolerate this high salt concentration

(selects for halophiles)

Question 26

What are the ingredients in Blood agar?

Answer 26

Peptones: for energy

Hemoglobin: can be hydrolyzed by some bacteria

(not selective)

Question 27

A scientist inoculates a bacterium into a complex nutrient slant tube using the stab & streak method. The bacterium forms only a few colonies on the slanted surface but grows prolifically (lots) in the depth of the agar. Describe the oxygen requirements of the bacterium.

Answer 27

Obligate anaerobe (because it doesn’t use oxygen)

or

Facultative anaerobe (because it can use or not use oxygen)

Question 28

For several weeks, faculty, students, and staff at Rayburn High School have been dealing with an epidemic of unsightly, painful boils and skin infections. Over 40 athletes have been too sore to play sports, and 13 students have been hospitalized. Nurses take clinical samples of the drainage of the infections from hospitalized students, and medical laboratory scientists culture the samples. Isolated bacterial colonies are circular, convex, and golden. The bacterium is Gram-positive, mesophilic, and facultatively halophilic and can grow with or without oxygen. The cells are spherical and remain attached in clusters.

a. What color are the Gram-stained cells?
b. What is the scientific description of the bacterium’s oxygen requirement?
c. What selective/differential medium could they have determined that the causative agent was facultatively halophilic? (Hint: think about which selective/differential media we used for lab.)

Answer 28

a. purple because they are gram positive
b. facultative anaerobe because it can grow with or without oxygen
c. MSA (mannitol) and a TSA control

Question 29

What do each of the mediums look like?
CNA
EMB
MSA
MacConkey
Blood agar

Answer 29

CNA: looks like TSA
EMB: dark red
MSA: bright red
MacConkey: light red
Blood agar: blood red