Lecture 2 (8/22/13)

Question 1

What does a weak cell wall result in?

Answer 1

Osmotic lysis.

Question 2

How is the bacterial cell wall weakened? *Hint: see image*

Answer 2

Precursors get transported outside the cell. Existing peptide bonds are broken by autolysins. Transpeptidases mediate cross-linking. Penicillin-binding protein prevents the cross-linking of both strands.

Question 3

How do bacteria replicate?

Answer 3

asexually by binary fission

Question 4

What formula is used to deterimine the population of replicating bacteria?

Answer 4

P = 2ⁿ

Question 5

When the starting inoculum contains more than one cell, what formula can be used to deterimin the population of bacteria?

Answer 5

P = P₀ X 2ⁿ

Question 6

What are the different phases found on a bacterial growth curve?

Answer 6

Log Phase: when microbial numbers are low and just beginning to increase

Exponential Phase: when microbial numbers are steadily increasing

Stationary Phase: when microbial numbers are steady and stationary with not decrease or increase in growth

Question 7

Name a few ways one can go about counting bacteria. Explain each.

Answer 7

Microscopic: count individual bacteria under a microscope

Colony-counting: count the colonies of bactera (NOTE: you don’t know for sure if it was one bacterial cell, you only know the number of colonies)

Turbidometric: can use a spectrophotometer to make a suspension of a certain number of organisms and can use this to compare to the colony-couting or microscopic-counting methods; using this methods makes it easier to get a more accurate count of bacteria at different stages of growth

Question 8

Bacteria require what three resources?

Answer 8

Macro-elements: C,H,O,N,P,S,K,Mg,Ca,Fe [Anacronym: King (K) James ate Magnificent (Mg) CHOPS in the CaFe

Vitamins and Cofactors: pantothenic acid, folic acid, niacin, B vitamins, vitamin K

Trace elements: Mn, Cu, Zn, Ni

Question 9

What are a few sources of bacterial nutrition?

Answer 9

peptones, infusions, extracts of proteins,
sugars, alcohols, carbohydrates
blood, serum, yeast extract, purified biochemicals,
mineral salts

Question 10

What are the three types of culture media? Explain each.

Answer 10

Liquid (broth): nutrient (infusions from animal/plant tissues); selective enrichment (promotes growth of desired organisms and inhibits growth of unwanted organisms)

Solid (agar): general nutrient (infusions from animal/plant tissues); enriched non-selective (supplements added eg. blood, chocolate, vitamins); selective (contains inhibitors eg. dyes, salts, antibiotics); selective differential (support chemical reactions that differentiate organisms and contain an indicator to interpret the reaction)

Semi-solid: used for special purposes, eg. to detect motility; i.e. gelatin; substrate utlization

Question 11

Discuss the properties of agar.

Answer 11

The prinicple ingredient is a complex polysaccaride

Derived from a red algal seaweed

First used as a solidifying agent in oriental foods

Food and technical grade agar melts at 92⁰C and solidifies at 42⁰C.
Several grades of highly purified agar are referred to as agarose
and are used extensively in immunology and molecular biology.
Some ultra pure agarose grades remain liquid at mammalian body
temperature.

Not a usable nutrient by most bacteria

agarose: more purified agar form with varying salt concentrations

Question 12

Psychrophilic

Answer 12

capable of growth and reproduction in cold temperatures

Question 13

Mesophilic

Answer 13

grows best in moderate temperature, neither too hot nor too cold

Question 14

Thermophilic

Answer 14

Requiring high temperatures for normal development

Question 15

Alkalophilic

Answer 15

thrive in alkaline environments

Question 16

Acidophilic

Answer 16

grows best in acidic conditions

Question 17

Xerophilic

Answer 17

adapted for life with a limited supply of water

Question 18

Capnophilic

Answer 18

thrive in the presence of high concentrations of carbon dioxide, or which require the presence of carbon dioxide to survive.

Question 19

What factors have an influene on bacterial growth?

Answer 19

Temperature: psychrophilic, mesophilic, thermophilic

Hydrogen ion concentrations: alkalophilic, acidophilic

Water activity: some fungi xerophilic

Atmosphere: aerobic, anaerobic, capnophilic

Question 20

What are the various oxygen requirement of bacteria?

Answer 20

Oxygen is required for growth: aerobic, microaerophilic, capnophilic

Oxygen is not required or utilized for growth: obligately anaerobic, aerotolerant anaerobe

Oxygen is not required but can be utilized for growth: facultative anaerobe

Question 21

Name a few methods used to limit microbial growth.

Answer 21

Refrigeration (4-100C)
Freezing (-200C)
Boiling (1000C)
Pasteurization (720C, 15 sec)
Acidification (< pH5.6)
Increasing osmotic pressure (salt, sugar)
Oxygen removal (aerobes only)
Drying
Gamma irradiation
Hydrostatic pressure
Chemical additives

Question 22

Name a few methods used to preserve bacteria.

Answer 22

Continuous passage
Refrigeration
Freezing (- 800C)
Lyophilization

Question 23

Name a few sterilization methods used with bacteria.

Answer 23

Moist heat (autoclave:1210C, 15 min)
Dry heat (1600C, 1-2 hrs.)
Incineration (10000C)
Alcohol flame
Gamma irradiation
UV light
Membrane filtration
Chemical

Question 24

Know and understand this table.

Question 25

What are three elements of containment of bacteria?

Answer 25

Lab practices and techniques

Safety equipment (i.e. Biological Safety Cabinets, sealed centrifuge containers, personal protective clothing, pipetting devices)

Facilities (i.e. design, vents, directional air flow, pressure, airlocks, drains, pest control, controlled access)