Bacterial Nutrition & Metabolism

Question 1

Bacteria grow in living animals?

Answer 1

Treponema Pallidum

• causes syphilis
• needs to be grown in rabbit testes
• loses infectivity if grown in primary cell culture

Mycobacterium Leprae

• causes leprosy
• grown in mice & nine-banded armadillo

Question 2

Techniques to isolate specific organisms?

Answer 2

Enrichment cultures, selective medium, differential medium

Question 3

Enrichment Medium

Answer 3

• Liquid medium favors growth
• minimal conditions
• ex. Azotobacter- nonvolatile nitrates to fix nitrogen

Question 4

Selective medium

Answer 4

• agar plates, selects one and/or inhibits others

- takes advantage of specific metabolic requirements or specific set of conditions that inhibit growth.

Question 5

Differential Medium

Answer 5

• agar plate, colonies of desired orgsm have distinct appearance.
• NOT necessarily selective

Question 6

Blood Agar (selective, differential, promotes, inhibits)

Answer 6

S: no
D: Hemolysis patterns
P: Many bacteria
I: -

Question 7

Eosin Methylene Blue (EMB) (selective, differential, promotes, inhibits)

Answer 7

S: dyes inhibit growth
D: lactose fermentation, purple or metallic green
P: enteric gram - rods
I: gram +

Question 8

Mannitol Salt (selective, differential, promotes, inhibits)

Answer 8

S: high Mannitol (5%) inhibits growth
D: Mannitol fermentation, yellow around colonies
P: Gram + (staph)
I: gram -

Question 9

MacConkey (MAC) (selective, differential, promotes, inhibits)

Answer 9

S: Bile salts and crystal violet inhibit growth
D: Lactose fermentation, Dark pink colonies due to pH indicator
P: Gram-
I: Gram +

Question 10

Which medium promotes gram -?

Answer 10

• EMB: enteric gram-

- MAC

Question 11

which medium promotes gram +?

Answer 11

Mannitol salt

Question 12

Blood Agar hemolysis patterns?

Answer 12

A. beta (complete)
-clear zone around colony
-ex. S. pyrogenes
B. alpha (partial)
-indistinct zone of partial RBC lysis around colony, greenish to brownish discoloratoin
-S. pneumonia, viridans group of streptococci.
C. gamma (no hemolysis)

Question 13

Eosin Methylene Blue bacterial growth?

Answer 13

A. Ecoli- ferments lactose
B. P aeruginosa- no fermentation
C. e. aeruginosa- weak fermentation
D. S aureus- inhibited by eosin and Methylene blue (gram +)

Question 14

Mannitol Fermentation bacterial growth?

Answer 14

yellow, Staphylococcus aureus

Question 15

MacConkey growth?

Answer 15

lactose fermentation (pink)

Question 16

Obligate Anaerobes

Answer 16

cannot survive in the presence of O2

Question 17

Obligate Aerobes

Answer 17

cannot survive in the absence of 02

Question 18

Facultative anaerobes or aerobes

Answer 18

can survive in the presence or absence of oxygen

Question 19

Examples of Obligate anaerobes

Answer 19

ex. Bacteriodes fragilis: common in abdominal abcesses

ex. clostridium tetani: causative agent of tetanus

Question 20

Why is 02 lethal?

Answer 20

1. auto-oxidation of flavines generate superoxide radical -O2
   - highly toxic!
2. Lack enzymes that dispose of -02
   
   • superoxide dismutase
   • catalase

Question 21

Examples of Obligate Aerobes

Answer 21

Ex. Pseudomonas aeruginosa: cause nosocomial infections

ex. bacillus anthracis: biological warfare, bioterrorism potential

Question 22

Why is 02 required?

Answer 22

• cannot generate enough energy from glycolysis, Krebs cycle is essential!
• lack PFK (F6P–>F16BP)
• Make triose P using Pentose shunt
• creates an ATP deficit that can only be offset by oxidative phosphorylation.

Question 23

Why is iron critical for bacteria?

Answer 23

1. cofactor for enzyme
   
   • sulfur containing enzymes
   • electron carriers

Question 24

In what state does Iron exist in the envirn?

Answer 24

ferric state Fe3+ as insoluble hydroxides, carbonates and phosphates

Question 25

How is iron found in cells?

Answer 25

Bound to cellular proteins

Question 26

How does Iron get into the cell?

Answer 26

1. Bacteria make Siderophores which scavenge Fe3+. 2. Membrane R bind the siderophores 3. Transport proteins takes up the complex and moves it into the cell. Fe3+-->Fe2+ (useful form).

Question 27

Importance of Iron update systems?

Answer 27

1. Iron updates systems are redundant- 4 distinct systems in E. Coli 2. Loss of high affinity may lead to loss of ability to cause disease

Question 28

Comparative Metabolism

Answer 28

- similar pathways in bacteria and mammals. | - diff good for diagnosis NOT useful for therapy

Question 29

Which bacteria can ferment lactose?

Answer 29

E. Coli, normal component of the gut S. dysenteriae indicates disease E. Coli resistant to acid

Question 30

Which bacteria cannot ferment lactose?

Answer 30

Shigella- inhibited by even low concentrations of acid. | Inadequate food consumption-->decreased gastric acid secretion-->infection w/ Shigella

Question 31

What product does Enterobacter aerogenes produce and what type of bacteria is it?

Answer 31

-acetonin -gram - rod Normally present in field water If ecoli present the contaminate sewage

Question 32

How does yeast produce ethanol?

Answer 32

pyruvic acid-->ethanol (not med. useful)

Question 33

How does bacteria make ethanol?

Answer 33

pyruvate-->acetyl coa-->acetaldehyde-->ethanol

Question 34

How do bacteria use pyruvic acid?

Answer 34

make proprionic acid + CO2 (no medical relevance) (CO2 generates holes in swiss cheese)

Question 35

what is an important diff btw humans and bacteria?

Answer 35

peptidoglycan - give bacterial cells wall rigidity - determines bact shape & protecs cytop. membrane

Question 36

What is the structure of peptidoglycan?

Answer 36

NAG-NAM-NAG-NAM-ETC

Question 37

What type of bacteria can vertical cross link peptidoglycan?

Answer 37

Gram + NOT gram - | thus have thicker walls, retain gram stain crystal violet, walls are porous

Question 38

what determines the thickness of the cells wall?

Answer 38

- peptidoglycan vertical cross-links | - antibiotics affect crosslinking thus are lethal.

Question 39

What are the steps in pepitdoglycan synthesis?

Answer 39

1. peptidoglycan monomer 2. extension of glycan chain 3. cross-linking of glycan strands.

Question 40

What does the drug Fofsomycin prevent?

Answer 40

- prevents formation of peptidoglycan monomer - NAM cannot make NAG - Antagonizes Phosphoenolpyruvate

Question 41

What the Cycloserine prevent?

Answer 41

-It blocks the formation of DALA -DALA-DALA during the production of NAM

Question 42

What does Bacitracin target?

Answer 42

Blocks the linking of NAG and NAM pentapeptide

Question 43

What do the antibiotics: B-lactams (penicillins, cephalosporins) and vanocomycin block?

Answer 43

Binds to transpeptidase, thus cannot catalyze cross-linking

Question 44

What are the phases of growth in culture?

Answer 44

1. Lag (enzyme productin) 2. Exponential or Logarithmic (doubling time) 3. Stationary (growing=dying)

Question 45

What is the doubling time?

Answer 45

(mean generation time) - the amount of time it take to double (Td) - smaller is faster

Question 46

What is the instantaneous growth rate (alpha)?

Answer 46

td=0.69 (1/alpha) | -larger is faster

Question 47

what is the exponential growth rate (u)?

Answer 47

td=1/u | -larger is faster

Question 48

What is the optimal temperature of psychrophiles?

Answer 48

- 5 to 30C | ex. listeria monocytogenes, which has causes disease from inadequately pasteurized cheese.

Question 49

what is the optimal temperature for mesophiles?

Answer 49

10 to 40C | pathogens grow well at body temperature

Question 50

what is the optimal temp for Thermophiles?

Answer 50

25 to 100C | ex. Thermus acquaticus, source of Tap polymerase