Microbial Growth And Control

Question 1

Explain the statement “Bacteria Grow”

Answer 1

• # of cells are increasing ( ^ reproductive process)
• Before a bacteria cell can divide into 2 daughter, the parent cell must make a copy of its genetic chromosome (DNA replication)

Question 2

Why is the log scale used for the y-axis of bacterial growth curves?

Answer 2

-its easier to predict growth linearly compared to exponentially, due to the unchanging slow as time increases on the x-asis

Question 3

State and explain the 4 phases of bacterial growth

Answer 3

1) Lag phase: # of cells are constant/no division
- microbe is adapting to culture conditions (synthesis of needed enzymes

2) Exponential phase (log phase): rapid growth (binary fission)
- Increase in nutrients and decrease in waste=growth
- sporulation occurs at the end of this phase

3) stationary phase: # of cells are constant, growth rate=death rate
- decrease in nutrients, increase in waste

4) Decline/death phase: # of cells decrease, rate of death> rate of growth
- substantial increase in wastes, substantial decrease in nutrients

Question 4

Some growth curves have only 3 phases. Which phase is not always present in a bacterial growth curve? Why?

Answer 4

• Lag phase

- Some bacteria don’t need to adapt to their environment. But may need to develop enzymes to metabolize the nutrients

Question 5

What is the equation for the exponential growth of bacteria. Explain what each term means

Answer 5

N(t) = N(0) x 2 ^t/d)

N(t)= total number of cells at time t

N(0)= the number of cells to start with at time 0

t= time that has passes

D=doubling time

Question 6

Define Sanitizer

Answer 6

• an agent that reduces the number of microbes to a safe level

Question 7

Define disinfectant

Answer 7

• an agent applied to inanimate objects to reduce the microbial load

Question 8

Define antiseptic

Answer 8

-an agent applied to human tissues to reduce microbial load

Question 9

define antimicrobial agent

Answer 9

-an agent that could be antiseptic, disinfectant, or antibiotics

Question 10

Define sterilant

Answer 10

• an agent that destroys all microbes including bacterial endospores

Question 11

Define Batericidal

Answer 11

-an agent that destroys all vegetative bacterial cells

Question 12

Define bacteriostatic

Answer 12

-an agent that prevents vegetative bacterial cells from reproducing

Question 13

Define Virucidal

Answer 13

-an agent that inactivates virus particles so they cannot infect

Question 14

Define fungistatic

Answer 14

-an agent that stops fungi from reproducing

Question 15

Define Sporicidal

Answer 15

• aka sterilant

- it kills all bacterial endospores and other microbes

Question 16

Define degerming agent

Answer 16

• physically removing microbes

Question 17

Define cleaner

Answer 17

• an agent that removes dirt and decrease microbes

Question 18

What is a phenolic? Explain how they work

Answer 18

• disinfecting agent
• denatures proteins and disrupt plasma membranes of microbes
  
  • effective in the presence of organic material and remain active on surfaces long after application

-general types of chem disinfectants: Phenolics, halogens, alcohols, hydrogen peroxide

Question 19

Explain how hexachlorophene works

Answer 19

• antiseptic agent that works by disrupting plasma membranes of microbes
• can also be used as a disinfectant

Question 20

Explain how chlorhexidine works

Answer 20

• an antiseptic agent that disrupts the plasma membranes of microbes
• also can be used as a disinfectant

Question 21

Name some examples of halogen based control agents and explain how they work

Answer 21

• Iodine, betadine
  
  • disrupts protein synthesis and membranes
  • oxidizes proteins
• Chlorine
  
  • powerful oxidizer (DNA, proteins, membranes)

Question 22

How do alcohol-based antiseptics and disinfectants work? Explain the relationship between water and alcohol-based antiseptic effectiveness.

Answer 22

• Alcohol based antiseptics needs to be between 60-95% alcohol to kill organisms. Too little or too much concentration will not be able to kill the microorganism
• needs water to be effective

Question 23

What is a quat? How do they work?

Answer 23

• super soap/detergent that is considered a disinfectants and antiseptic
• denatures proteins and disrupts plasma membranes

Question 24

What is the oligodynamic effect? Which chemicals does the term oligodynamic effect apply?

Answer 24

• describes how specific agents such as heavy metals, help denature proteins at very low concentrations
• silver ions

Question 25

What are 2 examples of antiseptics based upon the oligodynamic effect

Answer 25

• silver nitrate: used as drops to prevent neonatal gonorrheal infection
• silver sulfadiazine: antiseptic cream on burns to prevent infection

Question 26

Name 3 organic acids used as preservatives. How do they work?

Answer 26

• Sorbic acid, Benzoic acid, and calcium propionate

- controls molds and bacteria in food

Question 27

How does ethylene oxide work? What is it used for?

Answer 27

• chemically reactive gas that modifies the proteins, lipids, and DA in the chamber by alkylating proteins, DNA, RNA.
• used on heat-sensitive medical instruments like plastic probes
• long exposure time needed

Question 28

Most resistant to least resistant microbes

Answer 28

1) Endospores
2) Myobacteria
3) Cyst of Protozoa
4) vegetative Protozoa
5) Gram - bacteria
6) Fungi, including fungal spores
7) Viruses without envelopes
8) Gram + bacteria
9) Virusus with lipid evelopes

Question 29

What are some factors that affect bacterial growth?

Answer 29

• Physical conditions
  
  • temp, pH, osmotic pressure
• chemical conditions
  
  • CHNOPS (macronutrients)
  • inorganic elements: Na, Cl, K
  • gases