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Microbiology > Ch 9: Controlling Microbial Growth in the Environment > Flashcards

Ch 9: Controlling Microbial Growth in the Environment Flashcards

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1
Q

How do antimicrobial agents work?

A

Alteration of cell walls and membranes:

  • -Cell wall - when damaged, cells burst because of osmotic effects
  • -Cytoplasmic (cell) membrane - when damaged, cellular contents leak out
  • -Non-enveloped viruses (aka “naked”) more tolerant of harsh conditions

Damage to proteins and nucleic acids (messing up enzyme means it cant reproduce)

  • -Protein function depends on 3-D shape
  • Extreme heat or certain chemicals denature proteins
  • -Chemicals, radiation, and heat can alter/destroy nucleic acids
  • Produce fatal mutants
  • Halt protein synthesis through action on RNA
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2
Q

Ideally, agents should be:

A

Inexpensive
Fast-acting
Stable during storage
Capable of controlling microbial growth while being harmless to humans, animals, and objects

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3
Q

What are some considerations when choosing site of a control method?

A

Consideration of the site to be treated:

  • Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects (heat labile means you can melt or be “messed up” by heat)
  • Microbial control based on site of medical procedure
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4
Q

What are some considerations when considering the susceptibility of a microorganism while choosing a control method?

A

Consideration of the relative susceptibility of microorganisms
-Germicides classified as high, intermediate, or low effectiveness:
–High—kill all pathogens, including endospores
–Intermediate—kill fungal spores, protozoan cysts, viruses, pathogenic bacteria
–Low—kill vegetative bacteria, fungi, protozoa, some viruses
(doesn’t care what it kills- too general)

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5
Q

Name most resistant to most susceptible microbes

A 
Prions
Bacterial endospores
Mycobacteria (acid fast)
Cysts of protozoa
Active-stage protozoa (trophozoites)
Most Gram-negative bacteria
Fungi
Nonenveloped viruses
Most Gram-positive bacteria
Enveloped viruses
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6
Q

What is sterilization?

A

completely destroys all forms of microbial life

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7
Q

What is commercial sterilization?

A

limited heat treatment, destroys pathogens but not all bacteria (like pasteurizing)

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8
Q

What is disinfection?

A

destroys vegetative cells on a surface;

reduces # of viable organisms in/on the material

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9
Q

What is a disinfectant?

A

chemical treatment used to disinfect inanimate objects

Cannot disinfect your skin , reduces # of living cells

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10
Q

What is antisepsis?

A

treatment of living skin or tissue to kill microorganisms

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11
Q

What is degerming?

A

physical removal of microbes (alcohol swab, soap)

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12
Q

What is sanitizing?

A

systematic cleansing of inanimate objects to reduce the microbial count to a safe level (for public health, used in restrooms, kitchens)

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13
Q

What does a bacteriocidal control do?

A

(-cidal, to kill) - kill all bacteria

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14
Q

What does a bacteriostatic control do?

A

(-static, to stop) halt (inhibit) the growth of bacteria for as long as the inhibitory substance is present - if inhibitor is removed, growth begins again (e.g. refridgerator)

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15
Q

What does an aseptic control do?

A

prevention of (or absence of) sepsis

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16
Q

What is sepsis?

A

bacterial contamination (decay, putrefaction)

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17
Q

Describe the microbial death curve

A

Killing in a population is not instantaneous. Death, like growth, occurs exponentially (if the log of the number of cells is plotted on the Y axis, then a straight line results)

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18
Q

Name six physical methods of control

A

Heat (moist & dry)

Filtration

Cold

Desiccation

Osmotic Pressure

Radiation

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19
Q

Describe effects of high temperatures

A

Effects of high temperatures

  • Denature proteins
  • Interfere with integrity of cytoplasmic membrane and cell wall
  • Disrupt structure and function of nucleic acids
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20
Q

What is TDP?

A

Thermal death point- Lowest TEMPERATURE that kills all cells in broth in 10 min

21
Q

What is TDT?

A

Thermal death time- Time to sterilize volume of liquid at set temperature

22
Q

Describe moist heat

  • Used for what?
  • How does it destroy microbes?
  • Why moist?
  • What methods are used?
A
  • Used to disinfect, sanitize, and sterilize
  • Denatures proteins and destroys cytoplasmic membranes
  • More effective than dry heat
  • Methods of microbial control using moist heat
  • -Boiling
  • -Autoclaving
  • -Pasteurization
  • -Ultrahigh-temperature sterilization
23
Q

Describe boiling (moist heat)

  • tyndallization
  • boiling time
  • endospores
A

Kills vegetative cells of bacteria and fungi, protozoan trophozoites, most viruses (not important)

Tyndallization: can be used with endospore-forming bacteria

Boiling time is critical
-Different elevations require different boiling times

Endospores, protozoan cysts, and some viruses can survive boiling

24
Q

Describe autoclaving (moist heat)

  • what is it
  • autoclave conditions
  • what endospore needs to be killed
  • conditions for death
A

Pressure applied to boiling water prevents steam from escaping

Boiling temperature increases as pressure increases

Autoclave conditions – Steam alone can reach 100oC, but under pressure (15 psi) can reach 121oC – kills Bacillus stearothermophilus endospores in 15 minutes at this temperature

To kill all microorganisms, all contents must be available for steam to reach all surfaces

25
Q

Describe pasterurization (moist heat)

  • what is it
  • what microbe is the target?
  • what is classical pasteurization?
  • what is flash pasteurization?
  • what is ultrahigh-temperature sterilization?
A

Pasteurization uses temperature below boiling to kill pathogens (Brucella melitensis) and reduces total microorganism count (doesn’t kill all, some harmless microorganisms survive), does not alter food taste - used for milk, ice cream, yogurt, and fruit juices

Classical Pasteurization - 63oC for 30 minute

Flash Pasteurization - now use high-temperature short-time 72oC for 15 seconds. Sometimes called High Temperature Short Time (HTST) Pasteurization

Ultrahigh-temperature sterilization

  • 140ºC for 1 sec, then rapid cooling
  • Treated liquids can be stored at room temperature
26
Q

Describe dry heat (fire)

  • what is it used for
  • how does it damage microbes
  • what techniques does it include
A

Used for materials that cannot be sterilized with moist heat, but requires higher temperatures for longer time than moist heat

Denatures proteins and oxidizes metabolic and structural chemicals

Aseptic techniques including flaming mouth of tubes, inoculating loops/needles - empty glassware can be sterilized in oven in 1-3 hours at 180oC

Incineration is ultimate means of sterilization (except some prions)

27
Q

Describe negative heat

  • what does it do
  • refrigerator temperatures
  • what does a refrigerator do
A

Refrigeration and freezing decreases microbial metabolism, growth, and reproduction
-Chemical reactions occur more slowly at low temperatures b/c liquid water not available (ice is not water, liquid water is needed for life)

Psychrophilic microbes can multiply in refrigerated foods home refrigerator is at 4-7oC, freezer at -10oC (commercial is -20oC) (7o is used on test for home refrigerator)

Refrigeration halts growth of most pathogens

Slow freezing more effective than quick freezing (not important)

28
Q

What is dessication?

A

Drying inhibits growth because of removal of water

29
Q

What is lyophilization (freeze drying)?

A

used for long-term preservation of microbial cultures

-Prevents formation of damaging ice crystals

30
Q

Describe osmotic pressure

What has a greater ability to survive in hypertonic environments?

A

High concentrations of salt or sugar in foods to inhibit growth

Cells in hypertonic solution of salt or sugar lose water

Fungi have greater ability than bacteria to survive hypertonic environments (not important)

31
Q

Describe non-ionizing radiation

  • what wavelengths
  • how does it affect cells
  • what is it suitable for disinfecting
A

Wavelengths greater than 1 nm (most lethal at wavelength of 260 nm)

Affects 3-D structure of proteins and nucleic acids

UV light causes pyrimidine dimers in DNA
(shatters DNA, knocks out A’s in DNA, causing two T’s next to each other to bond aka dimer)

UV light does not penetrate well, so it is most suitable for disinfecting air, transparent fluids, and surfaces of objects (but cannot expose skin) (messes up skin, but not organs)

32
Q

Describe ionizing radiation

  • wavelength
  • electron beams
  • gamma rays
  • advantage
A

Wavelengths shorter than 1 nm

Electron beams – effective at killing but do not penetrate well

Gamma rays – penetrate well but require hours to kill microbes (Gamma radiation from Cobalt-60)

Advantage - penetrates deep into objects

can be used to sterilize plastic objects, even foods

33
Q

Describe filtration and pore size

A

Filtration is a form of sterilization by physically removing bacteria from liquid or air

most bacterial filtration by .45 or .2 micron pore size

34
Q

Describe the 4 biosafety levels

A

Four levels of safety in labs dealing with pathogens
-Biosafety Level 1 (BSL-1)
Handling pathogens that do not cause disease in healthy humans (E. coli)
-Biosafety Level 2 (BSL-2)
Handling of moderately hazardous agents (hepatitis, flu, MRSA)
-Biosafety Level 3 (BSL-3)
Handling of microbes in safety cabinets (Tb, anthrax, yellow fever, Rocky Mountain spotted fever)
-Biosafety Level 4 (BSL-4)
Handling of microbes that cause severe or fatal disease (Ebola, small pox, Lassa virus, HIV)

35
Q

Describe phenol and phenolics

  • commonly used where
  • first used when
  • action of the chemical
  • advantage
  • disadvantage
A

Commonly used in health care settings, labs, and homes

Phenol was the first chemical used to control microorganisms by Joseph Lister in 1867; used as disinfectants and antiseptics (example, Lysol)

Action of chemical: denature proteins and disrupt lipid containing cell membranes

Advantage: Stable & persist for long periods, good surface disinfectants

Disadvantage Have disagreeable odor and possible side effects

36
Q

Describe Triclosan (one of three bisphenolics)

A

Two hexagons

One has Cl and OH, the other has two Cls, they are connected by one O bond

37
Q

What phenol is good for wounds? (maybe bonus?)

A

hexachlorophene

38
Q

Describe alcohols

  • What type of antimicrobial agent
  • What is the most effective concentration
  • Actions
  • More effective than what
A

both disinfectants and antiseptics

Ethanol and isopropanol used most (at 70-80% concentrations)

Actions: denature proteins, possibly dissolve membrane lipids and viral envelopes

More effective than soap in removing bacteria from hands (swabbing of skin with 70% ethanol prior to injection)

39
Q

Describe halogens

  • what are they
  • applications
  • Iodine used as
  • Chlorine used as
  • Action
A

Halogens are elements in the same group of the periodic table (fluorine, chlorine, bromine, iodine, etc.).

Widely used in numerous applications (Betadine*, iodine tablets, chlorine treatment, bleach, chloramines, and bromine disinfection)

Iodine often used in a tincture (alcohol solution)

Chlorine may be used as Cl2 gas or in solution with other chemicals

Action: damage cellular materials (through oxidation)

40
Q

What are peroxygens (oxidizing agents)

  • what are they and how do they work
  • what can they disinfect
  • what are they not useful for
  • what is peracetic acid effective for
A

High-level disinfectants and antiseptics that kill by oxidation of microbial enzymes (H2O –> H2O2 down)

Peroxides (hydrogen peroxide) can disinfect and sterilize surfaces
-Not useful for treating open wounds because of catalase* activity

Ozone treatment of drinking water (O2 –> O3)

Peracetic acid is effective sporocide used to sterilize equipment (super vinegar) (not important)

41
Q

Describe surface acting agents (surfactants)

  • soaps and detergents
  • quats
  • action
  • antibacterial agents –effective against G+
A

Soaps & detergents have hydrophilic and hydrophobic ends (good degerming/disinfecting agents but not antimicrobial)

Quats: Low-level disinfectants ideal for many medical and industrial applications

Action: mechanical removal of microbes by reducing surface tension of solvents

Some contain antibacterial agents such as triclocarban (effective against G+)

42
Q

Describe heavy metals

  • names of heavy metal ions
  • silver nitrate
  • thimerosal
  • copper
A

Heavy-metal ions (mercury - hat glue, silver, arsenic, zinc, copper) denature proteins and disrupt co-factor binding

1.0% silver nitrate rubbed in the eyes of newborns to prevent gonorrheal neonatal ophthalmic blindness caused by N. gonorrhoeae

Thimerosal (mercury compound) used to preserve vaccines

Copper controls algal growth (not important)

43
Q

Name and describe aldehydes

  • action
  • benefit
A

Formaldehyde is a preservative (cannot have on public campuses)

Glutaraldehyde disinfects and sterilizes

Formalin used in embalming and disinfection of rooms and instruments

Action: cross-link proteins, inactivate nucleic acids
Benefit: sporicidal
Disadvantage: aldehydes are highly reactive molecules and are toxic to humans

44
Q

Describe gaseous agents

  • useful for
  • e_____ oxide
  • advantages
  • disadvantages
A

Useful for sterilizing heat-sensitive objects (example: the disposable Petri dishes in the lab) (like a bacteria bug bomb)

Ethylene oxide reacts with cell proteins

Advantages: microbiocidal and sporicidal

Disadvantages:

- Can be hazardous to people 
- Often highly explosive
- Extremely poisonous
- Potentially carcinogenic
45
Q

Describe enzymes and antimicrobials

A

Human tears contain lysozyme
Digests peptidoglycan cell wall of bacteria
Lysozyme used to reduce the number of bacteria in cheese (not important)

Enzymes to control microbes in the environment
Prionzyme can remove prions on medical instruments

  Antimicrobials Antibiotics and synthetic chemicals typically used for treatment of disease Some used for antimicrobial control outside the body (not important)
46
Q

Describe evolution of resistant microbes

A

Little evidence that products containing antiseptic and disinfecting chemicals add to human or animal health

Use of such products promotes development of resistant microbes

47
Q

Describe chemical food preservatives

A

Usually organic acids like sodium benzoate, sorbic acid, calcium propionate

Action: keep food pH low to inhibit growth - these are biostatic and merely halt growth, they are microbiocides

48
Q

List least affective cleaner to most affective

A 
Soap and water
Aqueous zephiran 1:1000
Mixtures of 50% ethanol and 10% acetone
Tincture of Zephiran
70% ethanol and 30% water
1% iodine in 70% ethanol (tincture of iodine)

Microbiology (7 decks)

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