Lecture 9: Control of Microorganisms

Question 1

Define sterilization, disinfection, and sanitization

Answer 1

1) Sterilization: The process by which all living organisms are either destroyed or removed from an object or habitat. Kills spores.
2) Disinfection: The substantial removal of the total microbial population and the destruction of potential pathogens. Does not kill spores.
3) Sanitization: The microbial population is reduced to the levels that are considered safe by public health standards

Question 2

Define antisepsis and chemotherapy

Answer 2

1) Antisepsis: The destruction or inhibition of microorganisms on a living tissue. (ex: cleaning a wound)
2) Chemotherapy: The use of chemical agents to kill or inhibit the growth of microorganisms within host tissue.

Question 3

1) Define biocide
2) What are the two things biocides include?

Answer 3

1) A chemical or physical agent that inactivates microorganisms
2) Disinfectants and antiseptics

Question 4

Describe the difference between biocidal and biostatic

Answer 4

1) Biocidal: the agent itself kills the microbe
2) Biostatic: pauses the microbe to let immune system kill it

Question 5

What are the 4 main methods of microbial control? Include which has the broadest range of effects.

Answer 5

1) Physical agents
2) Chemical agents: broadest range of effects
3) Mechanical removal methods
4) Biological agents.

Question 6

1) How is the effectiveness of a killing agent assessed?
2) In order to do this, what must be known?
3) What is minimum inhibitory concentration?

Answer 6

1) Time kill experiments, which measure the fraction of killed organisms in a given interval of time
2) We must know when microorganisms are dead
3) The lowest concentration of a killing agent that will inhibit visible growth

Question 7

1) Define ‘viable but non-culturable’ (VBNC)
2) Define ‘active but non-culturable’ (ABNC)

Answer 7

1)VBNC: Cells maintain capacity for basic metabolic processes despite inability to be cultured (can’t divide)
2) ABNC: Alternative term that takes into account whether the cells are still alive

Question 8

What are VBNC and ABNC a response to?

Answer 8

A long-term survival strategy in response to environmental stress

Question 9

What (6) factors influence the effectiveness of antimicrobial agents? Describe them

Answer 9

1) Population size: Larger population size takes longer to die
2) Population composition: Resistance varies between strains
3) Concentration of antimicrobial agent: Sometimes less is more; using too much could keep them from dying.
4) Contact time: Longer contact is deadlier
5) Temperature: Higher temperature increases efficacy
6) Local environment: The surroundings can dictate efficacy (ex: pH, biofilms)

Question 10

1) Define biofilm
2) What do biofilms protect?
3) What makes bacteria in a biofilm different?
4) When are biofilms problematic?

Answer 10

1) A complex community of microbes anchored to a surface
2) Protects a subset of the population
3) Bacteria in a biofilm are physiologically different
4) Problematic for medical equipment; must keep biofilms from forming on them.

Question 11

1) What are the two types of heat (as a method of microbial control)?
2) Which is more effective?

Answer 11

1) Moist heat and dry heat
2) Moist heat

Question 12

1) Give 2 examples of moist heat as an antimicrobial mechanism
2) What does moist heat do?

Answer 12

1) Pasteurization and autoclaving
2) Degrades nucleic acids, denatures enzymes/ proteins, disrupts membranes

Question 13

Define pasteurization and its two types

Answer 13

1) Pasteurization: Mild heat (72C) is sufficient to kill pathogenic microbes
2) High temp vs ultra-high temp
-ultra high temp only for a few seconds

Question 14

1) How does dry heat sterilize?
2) How does dry heat kill microbes?
3) Does dry heat corrode glassware? Is it fast or slow?
4) Give 3 examples of dry heat

Answer 14

1) By incineration
2) Oxidation of cell constituents and denaturation of proteins
3) Doesn’t corrode glassware or metal, but is slow and not suitable for some materials
4) Hot-air sterilization, flaming, dry heat incineration

Question 15

Define and describe the two types of liquid antimicrobial filters

Answer 15

1) Depth filters: Fibrous or granular materials bonded into a thick layer filled with twisting channels
-Made of diatomaceous earth, unglazed porcelain, asbestos
2) Membrane filters: Porous membranes of various sizes
-Screens out microbes and liquid is forced through

Question 16

1) What is commonly used filter microbes out of the air?
2) Give 3 examples of when this filter is used

Answer 16

1) High-efficiency particulate air (HEPA): fiberglass depth filter
2) Used to sterilize air in: biosafety cabinets, research labs, and industry

Question 17

Describe the new type of air filtration that could be used in hospitals and airplanes of the future

Answer 17

Micron-scale sheets of graphene form a two-layer air filter that traps pathogens and then kills them with a modest burst of electricity

Question 18

What are the two types of antimicrobial radiation? Describe them. Include which doesn’t penetrate and which is used for lab supplies.

Answer 18

1) Ultraviolet radiation
-Lethal, but doesn’t penetrate
-Effective for surfaces and water, but can degrade plastic
2) Ionizing radiation:
-Excellent sterilizing agent
-Kills spores, but not always viruses
-Used for cold sterilization of: Antibiotics, lab/ medical supplies, pasteurized foods

Question 19

1) Describe how low temperatures can be antimicrobial
2) How does time affect the efficacy of low temperatures?

Answer 19

1) Refrigerator is bacteriostatic
2) Slow freezing is more toxic than fast (flash) freezing; time can matter

Question 20

1) How is high pressure antimicrobial?
2) How is dessication antimicrobial? Does resistance vary?

Answer 20

1) It bursts cells (French press)
2) It’s freeze-drying (lyophilization); resistance varies between organisms

Question 21

1) How is osmotic pressure antimicrobial?
2) What is most resistant?

Answer 21

1) Creates a hypertonic environment to make H2O exit cells
2) Molds and yeast are most resistant

Question 22

How are chemical control agents used?

Answer 22

Disinfection and antisepsis, food safety and treatment of disease

Question 23

List the ideal properties of chemical control agents (antimicrobial chemicals)

Answer 23

1) Have broad spectrum activity
2) Toxic to microbes, not to people
3) Stable for storage
4) Odorless
5) Soluble in water
6) Low surface tension (get in cracks)
7) Inexpensive

Question 24

Name the different groups of antimicrobial chemicals (6)

Answer 24

1) Aldehydes
2) Halogens
3) Alcohols
4) Quaternary ammonium compounds
5) Phenolics
6) Heavy metals

Question 25

Name the different methods of physical control of microbes

Answer 25

1) Heat
2) Filtration
3) Radiation
4) Low temperatures
5) High pressure
6) Desiccation (freeze-drying)
7) Osmotic pressure (hypertonic)

Question 26

1) What do aldehydes inactivate?
2) Do aldehydes kill spores?
3) Give 2 examples of aldehydes

Answer 26

1) Inactivate proteins/nucleic acids
2) Sporicidal
3) Glutaraldehyde, formaldehyde

Question 27

Name and describe the two antimicrobial halogens

Answer 27

1) Iodine: skin antiseptic
-Oxidizes/iodinates
-Betadine
2) Chlorine: water disinfectant
-Oxidizes cellular enzymes (carcinogenic byproducts)
-Halazone

Question 28

1) What can alcohols kill?
2) What are alcohols widely used for?
3) Give an example of an antimicrobial alcohol
4) What does alcohol denature? Is it membrane active?

Answer 28

1) Bactericidal and fungicidal
2) Widely used disinfectant & antiseptic
3) 60-80% ethanol
4) Denatures protein, membrane active

Question 29

1) What are quaternary ammonium compounds?
2) What do they disrupt and denature?
3) What are they used for?

Answer 29

1) Broad spectrum detergents/disinfectants
2) Disrupt membranes/denature proteins
3) Decontamination

Question 30

1) What are phenolics?
2) Give 2 examples of antimicrobial phenolics
3) What do phenolics denature?

Answer 30

1) Lister’s antiseptic / disinfectant
2) Triclosan, Lysol
3) Denature proteins

Question 31

1) Name 4 antimicrobial heavy metals
2) What do they inactivate?

Answer 31

1) Mercury, silver, copper, zinc
2) Inactivate/precipitate proteins

Question 32

Describe the diversity of biocides

Answer 32

1) Broad variation of effect between different biocides
2) Each requires a different concentration

Question 33

Describe triclosan:
1) What was it?
2) What was it designed to do and what was it marketed as?
3) What question did this raise?

Answer 33

1) Was a phenolic antiseptic that was very popular in the 1990s
2) Wasn’t designed to make the product safer, was designed to stop bacterial degradation of plastics, but was marketed as a product that makes bacteria die as soon as they land on substances cleaned with it.
3) Are we encouraging antibiotic resistance by making things too clean? (looks like we’re fine so far)

Question 34

1) What are antibiotics?
2) What are the two potential roles of antibiotics in nature?

Answer 34

1) A type of antimicrobial compound
2)
-Could be a kind of “germ warfare”
-Could be used as signaling molecules

Question 35

What are the 6 characteristics of antibiotics?

Answer 35

1) Low molecular weight compounds
2) Kill or inhibit growth of bacteria (cidal or static)
3) Can be ingested or injected with minimal side effects
4) Low toxicity but can be allergenic
5) In contrast to disinfectants/ antiseptics, antibiotics generally interfere with a specific bacterial enzyme or process (e.g. cell wall inhibitors)
6) Naturally occurring: produced by soil bacteria or fungi

Question 36

Are all antibiotics natural? If not, what categories are there?

Answer 36

No; there are natural, semisynthetic, and synthetic antibiotics

Question 37

1) What are broad spectrum antibiotics and how long have they been around?
2) Why are broad spectrum antibiotics used so often?

Answer 37

1) Antibiotics active against many different types of bacteria
2) Physicians often have to treat empirically (in emergencies); bacterial infections often have nonspecific symptoms and it takes time to isolate and identify the bacterium responsible

Question 38

What does it take to be a good antibiotic? (2 things)

Answer 38

1) Few or no side effects: principle of differential toxicity
2) Broad spectrum

Question 39

What are the two major problems with ‘good’ antibiotics?

Answer 39

1) Broad-spectrum antibiotics not only attack the bacterium causing the infection but also your “normal” flora
2) Use of Broad-spectrum antibiotics can select for resistant members of the normal flora that are capable of causing serious infections (e.g. hospital-acquired infections)

Question 40

In what 4 places can antibiotics be active? (inhibit the cell)

Answer 40

1) Cell wall structure (peptidoglycan and membrane)
2) Protein synthesis (30S and 50S)
3) Nucleic acid synthesis (DNA replication and RNA synthesis)
4) Antimetabolites (unique cytosolic precursor pathways)

Question 41

What are the common themes of nosocomial pathogens (pathogens originating from a hospital)? (5)

Answer 41

1) Ability to survive in the environment (hardiness)
2) Resistance to antibiotics (70% of HAIs)
3) Ubiquitous in the environment and in our bodies
4) Commonality in sites of infection (catheters, surgical sites, and central line sites)
5) Ability to form biofilms

Question 42

What 3 newer technologies have been used to prevent nosocomial infections?

Answer 42

1) Non-flammable alcohol vapor in carbon dioxide (NAV-CO2) or vaporized hydrogen peroxide allows for droplets to spread everywhere
2) X-Static fabrics: Silver mixed with cotton used for soft-surface antimicrobial protection; an ionic shield
3) UroShield: A type of catheter that emits surface acoustic waves to interfere with biofilm formation

Question 43

1) What is the best way to prevent nosocomial infections?
2) Besides recent technologies, what other ways can nosocomial infections be prevented?

Answer 43

1) Handwashing
2) Killer lights (UV lights); programs of surveillance, prevention, and control; overall breaking the chain of infection