chapte 5: Enviromental Influences & Control fo Microbial Growth

Question 1

Explain what are extremophiles.

Answer 1

any ecological niche outside the “normal” growth conditions:

• Sea level
• Temperature (20-40C)
• A near-neutral pH
• 0.9% salt and ample nutrients

Question 2

why are extremophiles important?

Answer 2

environmental habitat that a species inhabits is based on the tolerance of that organism’s proteins and other macromolecular structures to the physical conditions within that niche.

Question 3

what parameters define any growth environment?

Answer 3

• temp.
• Pressure
• pH
• osmolarity
• oxygen

Question 4

Describe Mesophiles

Answer 4

growth temp. (around 15-45C)
typical "lab rat" (E.coli)
easy to grow
most human pathogens are mesophiles
Membranes are composed mostly of unsaturated lipids= more fluid membranes at lower temps.  (Typical lipid bilayer)

Question 5

Describe Psychrophiles

Answer 5

growth temp. (: ~0oC–20oC)
have more flexible proteins than mesophiles and require less energy
have commercial interest b/c of their ability to carry out reactions at low temps. useful for food processing and bioremediation.

Question 6

describe thermophiles/ hyperthermophiles

Answer 6

growth temp. ~40oC–80oC
- enzymes do not unfold as easily as mesophilic enzymes, they hold shape.
growth temp ~65oC–121oC ( found near thermal vents)
-have specially adapted membranes & protein sequences
-have chaperone proteins to help them unfold.

Question 7

what do thermophiles have to do with PCR technology

Answer 7

Thermophiles spieces adapt to growth at high temperatures (55C

Question 8

why is water activity important to microbial growth? what changes water activity?

Answer 8

• water is needed for microbial growth. Microbes can only use water that is not bound at any given instant to ions or other solutes in solution.
• interactions with solutes lower water activity, the more solutes there are in solution, the less water there is available for microbes to use for growth.

Question 9

How do cells protect themselves from osmotic stress?

Answer 9

Microbes have at least two other mechanisms to minimize osmotic stress across membranes.

• (Hypertonic medium= higher osmolarity than the cell), bacteria try to protect their internal water from leaving the cell by synthesizing or importing compatible solutes that increase intracellular osmolarity.
• cells contain pressure sensitive channels that can be used to leak solutes out of the cell (hypotonic medium=lower osmolarity than the cell)

Question 10

why do changes in [H+] affect cell growth?

Answer 10

[H+] affects protein structure and function. thus, enzymes have pH optima, minima, and maxima.

Question 11

What are and how do acidophiles manage to grow at the extremes of pH?

Answer 11

• bacteria and archaea that live in acidic environments (often lithotrophs).
• grow between pH -5.
• generally maintain an internal pH that is considerably more acidic than that of neutralophiles but still less acidic than their growth environment.
• ability to grow at this pH is due to altered membrane lipid profiles that decrease proton permeability.

Question 12

what is a D-value?

Answer 12

-efficacy of a given lethal agent/condition is measured in which the length of time it takes that agent to kill 90% of the population.

Question 13

List and explain various means by which humans can control microbial growth?

Answer 13

• heat: alters their membranes and denaturing proteins.
• autoclaves: moist-heat sterilization. Raise in temperature without damaging the items.
• pasteurization: uses heat but does not render the food sterile.
• Refrigeration and Freezing: slows down the growth of microorganisms significantly. freezing, may stop microbial growth and even kill susceptible organisms.
• filtration: physical separation
• sonication: use of high frequency ultrasound waves to disrupt cell structures.
• irradation:
• pressure

Question 14

what is a phenol coefficient?

Answer 14

Phenol, Joseph Lister. Reduces the incidence of surgical infection, but is no longer use as disinfectant, b/c of its toxicity.

• phenolics denature proteins, and are effective in the presence of organic material, and remain active surfaces long after application.
• Phenol coefficient: consists of inoculating a fixed # of bacteria into dilutions of the testing agent. Based on the highest dilutions (lowest concentration) of a disinfectant that will kill all the bacteria in a 10 min exposure but leaves survivors after only 5 mins of exposure.

Question 15

Neutrlophiles

Answer 15

Grow generally b/w pH 5-8.
Include most human pathogens
Adjusts metabolism to maintain internal pH slightly above neutality.

Question 16

Acidophiles

Answer 16

Grow b/w pH 0-5.
Generally maintains internal pH that is considerably more acidic than that of neutrophils. But less acidic than their environment.

Question 17

Alkaliphiles

Answer 17

Opposite end of pH spectrum

Grows best at pH ranging 9-11

Question 18

Strict aerobe

Answer 18

Organism that not only exists in oxygen but also uses oxygen as a terminal electron acceptor

Question 19

Strict anaerobes

Answer 19

Dies in present of oxygen.

Question 20

3 ways to remove oxygen

Answer 20

1. Oxygen reducing agent: thioglycolate
2. Anaerobe jar : palladium packet catalyze reaction
3. Special anaerobic glove box: atmosphere is removed by vacuum.

Question 21

Sterilization

Answer 21

Process by which all living cells, spores, and viruses are destroyed on an object.

Question 22

Disinfect

Answer 22

The killing of removal of disease producing organisms ms from inanimate surfaces.

• pathogens are killed but other microbes may survive.
• damage living tissues

Question 23

Antiseptic

Answer 23

Removing pathogens from the surface of living tissues (skin)

Question 24

Sanitation

Answer 24

Reducing the microbial population to safe levels by cleaning and disinfecting an object.

Question 25

Factors that influence efficiency of given chemical agent

Answer 25

• presence of organic matter
• kind of organisms present
• corrosiveness
• stability and surface tension.