02_Bacterial Growth Flashcards Preview

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Flashcards in 02_Bacterial Growth Deck (31)
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1

This deck is complete. It contains info from both lecture and notes.

This deck is complete. It contains info from both lecture and notes.

2

What is generation time?

• Time for population to double

3

What limits bacterial growth?

• nutrient limits
• toxic metabolic byproducts
• anti-biotics of other organisms
• immune system
• environmental conditions

4

What are the major nutrient requirements for bacterial growth?

• Carbon for all molecules
• Nitrogen (proteins and DNA) (from amino acids, NH4, and nitrate)
• Phosphorus (phospholipids and DNA)
• Sulfur (proteins)
• Iron (enzymes)

5

What are the major nutrient sources?

• Glucose
• Other sugars
• Amino acids
• Lipids
• Organic acids and alcohols

6

Note: some energy sources are also used as building materials for cells (ex: glucose provides energy and a carbon source)

Note: depending on the species, some amino acids are “essential”

Note: some energy sources are also used as building materials for cells (ex: glucose provides energy and a carbon source)

Note: depending on the species, some amino acids are “essential”

7

How does a bacteria absorb a protein?

• amino acids and peptides can be taken up.
• Proteins are too big
• Pathogens secrete proteases

8

How does a bacteria absorb DNA and RNA?

• secrete nucleases
• use the C, N, and P sources for other compounds or for their own DNA

9

How do bacteria absorb phospholipids? What building materials do phsopholipids provide for bacteria?

• produce phospholipases that act on host cell membranes or lung surfactant
• Provides bacteria with C, N, and P

10

What happens if a bacteria is low in phosphorus or iron?

• induces phospholipase production
• phospholipids yields
• Host cell lysis by phospholipase activity yields iron

11

What are the iron sources in the host?

• dietary iron
• extracellular: transferring; lactoferrin
• intracellular: ferritin
• proteins and hemoproteins

12

What role does iron play in host-pathogen relationships?

• host makes iron-binding factors that make iron unavailable for microbial invaders
• bacteria and fungi make iron chelators (siderophores) that can extract iron from host reserves

13

What are siderophores?

• small molecules secreted by bacteria that bind to iron and remove it from the host
• iron chelators

14

Summary of nutrient acquisition by bacteria

Hemolysins
Phospholipases
Proteases
DNases
Siderophores
Plus: Bacteria have dozens of transporters

15

Pathogenesis results from microbes accessing host nutrients. Microflora are “provided for” by the host. The host also gets vitamins from the microflora (such as vitamin K and B12)

Pathogenesis results from microbes accessing host nutrients. Microflora are “provided for” by the host. The host also gets vitamins from the microflora (such as vitamin K and B12)

16

What are growth factors (as opposed to nutrients)?

• growth factors are organic compounds that are not metabolized to supply energy but are used to make metabolites that the bacterium cannot synthesize themselves.
• Example:
o E coli can grow without growth factors on glucose, NH4, and inorganic ions
o However, many host-associated microbes require one or more specific growth factors in addition to the carbon source

17

What is the term “fastidious” in bacteriology? What are examples?

• requirement of some bacteria for specific growth factors
• This can be diagnostic
o Lactobacilli require purines, pyrimidines, vitamins, and select amino acids
o E coli can synthesize everything that it needs
o Haemophilus goes only on medium containing heme and NAD+

18

What are the physical requirements for bacterial growth?

• Temperature
• pH
• Osmotic conditions (high salt and sugar inhibit bacterial growth)

19

At what temperature do most bacteria grow best at?
Explain Leprosy bacteria as a reduced temperature bacteria
Explain Listeria bacteria as a reduced temperature bacteria
Explain Legionella as a high temperature bacteria.

• 37 degrees (body temp)
• Myobacterium leprae. Leprosy grows on the skin but does not infect internal organs
• Listeria can grow at 4 degrees and is a cause of food poisoning
• Legionella grows in hot water heaters, so they need to be at least 120 degrees

20

What is pH for pathogenic growth? What is a common bacteria in canned foods?

• 6 to 8; 7.4 is optimal
• this is the point of pickled and fermented foods
o only non-pathogenic bacteria grow at the pH of pickles and sauerkraut
• Clostridium Botulinum grows in canned foods that are not acidic

21

How do bacteria survive the stomach?

• H Pylori secrete urease with raises immediate local stomach pH (creates a pH buffer zone)
• Breakdown of urea to NH3

22

Bacteria are somewhat resistant to osmosis due to their cell walls, but there is still a limit. High salt and high sugar foods inhibit bacterial growth.

Bacteria are somewhat resistant to osmosis due to their cell walls, but there is still a limit. High salt and high sugar foods inhibit bacterial growth.

23

What are some common growth mediums?

• peptone (digested meat broth) with glucose
• agar
• Blood agar (supports 90% of pathogens)

24

How is infection determined?

• size of bacteria population
o CSF should have no bacteria
o Urine may have some bacteria

25

Why is counting bacteria important?

• determine infection
• determine antibiotic efficacy
• other research measurements

26

What are the ways to measure bacteria levels?

1. optical measurements of cell mass
a. scattered light, reduced light transmission, turbidity (Light turbid 10^6 and very turbid 10^8)
2. metabolic activity (CO2, ATP production, redox, dyes of electron transport chain)
3. direct counting with microscope (if you can see them, it usually indicates infection) (note this counts both viable and non-viable cells)
4. Viable plate counts (colony forming units from diluted, then calculate undiluted)
5. Sample dilution

27

How do you calculate the original number of colonies in a dilution experiment?

• count the number of colonies / the dilution factor

28

What is responsible for the lag phase?

• when bacteria are first inoculated, first they increase cell mass, proteins, and RNA before dividing.
• They may also be getting used to the new medium

29

What is the log or exponential phase?

• generation time dependent
• Balanced growth occurs: 1) cell mass doubles 2) cell divides

30

What is the stationary phase?

• Log phase slows due to pH, oxygen tension, growth medium, temp changes
• Number of viable cells remains constant
• Steady state of birth and death