Chapter 11

Physical and
Chemical Agents
for Microbial
Control
Control of microbes
Physical and chemical
methods to destroy or reduce
microbes in a given area
OVERVIEW

3
Why do we want to control
microbes?

How do we do it?
Relative resistance of microbes
Least resistance
Highest resistance
– Bacterial endospores
– Prions

Moderate resistance
–...
Methods that kill microbes
_______________ – a process that destroys all
viable microbes, including viruses & endospores
–...
Methods that reduce numbers
_______________– any cleansing technique that
mechanically removes microbes and reduces
number...
8
Microbial death
Permanent termination of an organism’s
vital processes
microbiological definition:
Involves permanent loss...
Factors that influence microbial killing

10
How antimicrobial agents work:
Cellular targets of control
(mode of action)
1. Cell wall
2. Cell membrane
3. Cellular synt...
mode of action

Cell wall
Action:
– Block synthesis
– Digestion
– Disrupt surface

w/o cell wall, bacteria will lyse (espe...
Surfactants disrupt

mode of action
mode of action

Affect on synthesis (DNA, RNA)
Proteins – have many functions in the cell!
Antimicrobials can block: DNA s...
mode of action

Heat, pH, heavy metals can alter proteins
Practical concerns
Does the application require sterilization?
Is the item to be reused? (time, $$)
Can the item withstand...
Types of Control:
I. Methods of Physical Control
1. Heat
2. Cold temperatures
3. Desiccation
4. Radiation
5. Filtration
Physical Control

1. Heat
Moist vs. dry
Moist heat = lower temp and shorter time
Causes coagulation/denaturation of
protei...
Physical Control
Physical Control

1. Heat – moist heat
Moist heat uses hot water or steam
sterilization
 _______________ 15 psi/121oC/10-...
Physical Control
Pasteurization
Pasteurization – heat  kill
potential agents of infection and
spoilage without destroying the
food flavor ...
Physical Control

1. Heat – dry heat
Dry heat uses higher
temperatures than moist
heat, can also sterilize
incineration – ...
Thermal death

Physical Control

Thermal death time (TDT) – shortest
length of time required to kill all test
microbes at ...
Physical Control

2. Cold temperatures
_______________– slows the growth of
microbes
refrigeration 0-15oC & freezing <0oC
...
Physical Control

3. Desiccation
gradual removal of water from cells, leads
to metabolic inhibition
not effective microbia...
Physical Control

4. Radiation
1. _______________ radiation – deep

penetrating power, breaks DNA
– gamma rays, X-rays, ca...
Ionizing radiation

Physical Control
Nonionizing radiation - UV

Physical Control
UV treatment of wastewater

Physical Control
Physical Control

Other “waves”
Sound (high frequency)
Can also be used to disrupt cells
(vibrations) or generate heat
Ult...
5. Filtration
physical removal of
microbes by passing a
gas or liquid through
filter
Pores of filter large
enough for liqu...
OVERVIEW

33
Types of Control:
II. Methods of Chemical Control
Categories:
•
Halogens
•
Phenolics
•
Chlorhexidine
•
Alcohols
•
Hydrogen...
Chemical antimicrobials
10,000 manufactured today
About 1,000 routinely used
Society is obsessed with “killing germs” –
to...
Qualities of chemical antimicrobials
Rapid action, even in low concentration
Water/alcohol soluble, stabile
Broad spectrum...
Levels of activity
Factors that affect activity
Type of microorganism being treated
Material being treated
Amt of contamination
Exposure time...
Ways to express
strength/concentration
Dilution (1:200 is one part chemical in 200
parts dilutant such as water)
ppm – par...
Chemical control - categories
1.
2.
3.
4.
5.
6.
7.
8.

Halogens
Phenolics
Chlorhexidine
Alcohols
Hydrogen peroxide
Deterge...
1. Halogens
Ionic (halide) or nonionic
Mostly _______________
Germicidal and sporicidial with long
exposure
Affect protein...
1. Halogens
Chlorine – Cl2, hypochlorites (chlorine
bleach - OCl), chloramines
– In water – release hypochlorous acid (HOC...
1. Halogens
Iodine - I2, iodophors (betadine)
– Denature proteins – similar to Chlorine but not
affected by organic matter...
44
2. Phenolics
Phenol ring (aromatic carbon ring) +
groups
Disrupt cell membranes & precipitate
(denature) proteins; bacteri...
_______________
3. _______________
Hibiclens, Hibitane
A surfactant & protein
denaturant with broad
microbicidal properties
Not sporicidal...
4. Alcohols
Ethyl, isopropyl in solutions of 50-90%
(water needed for protein coagulation)

Act as surfactants dissolving ...
5. Hydrogen peroxide
Weak (3%) to strong (25%)
_______________ agent (steals electrons)
Produce highly reactive hydroxyl f...
colonoscope
52
6. Detergents & soaps
________ compounds that work as
_______________
Quaternary ammonia cpds (__________)
act as surfacta...
Figure 11.17

55
56
7. Heavy metals
Solutions of silver & mercury kill
vegetative cells in low concentrations by
inactivating proteins
Metalli...
59
8. Aldehydes
Glutaraldehyde & formaldehyde kill by
alkylating protein & DNA (-CHO is reducing
group)
_______________ = H o...
Gases & aerosols
_______________, propylene oxide,
betapropiolactone & chlorine dioxide
Strong _______________ agents,
spo...
________________________ –

uses ethylene oxide
65
Miscellaneous antimicrobials
Dyes – crystal violet, acriflavine
Acids, bases (alkalies) – destroy but some
are corrosive a...
steriliz
steriliz
steriliz
steriliz
steriliz
Upcoming SlideShare
Loading in …5
×

steriliz

730 views
584 views

Published on

sterliz

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
730
On SlideShare
0
From Embeds
0
Number of Embeds
8
Actions
Shares
0
Downloads
29
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

steriliz

  1. 1. Chapter 11 Physical and Chemical Agents for Microbial Control
  2. 2. Control of microbes Physical and chemical methods to destroy or reduce microbes in a given area
  3. 3. OVERVIEW 3
  4. 4. Why do we want to control microbes? How do we do it?
  5. 5. Relative resistance of microbes Least resistance Highest resistance – Bacterial endospores – Prions Moderate resistance – Pseudomonas sp. – Mycobacterium tuberculosis – Staphylococcus aureus – Protozoan cysts – – – – – most vegetative cells Fungal spores enveloped viruses Yeast Protozoan trophozoites
  6. 6. Methods that kill microbes _______________ – a process that destroys all viable microbes, including viruses & endospores – Heat, sterilants _______________– a process to destroy vegetative pathogens, not endospores – disinfectants or germicides – chemical - kills pathogenic microorganisms – _____________________ – destroy/inhibit vegetative pathogens on exposed body surfaces – Sepsis – infection/growth in body – Asepsis – preventing entry of pathogens and infection
  7. 7. Methods that reduce numbers _______________– any cleansing technique that mechanically removes microbes and reduces numbers to safe levels – _______________– reduces the number of microbes on skin ___________________________ – controls numbers by preventing growth (multipication)
  8. 8. 8
  9. 9. Microbial death Permanent termination of an organism’s vital processes microbiological definition: Involves permanent loss of reproductive capability, even under optimum growth conditions
  10. 10. Factors that influence microbial killing 10
  11. 11. How antimicrobial agents work: Cellular targets of control (mode of action) 1. Cell wall 2. Cell membrane 3. Cellular synthetic processes (DNA, RNA) 4. Proteins
  12. 12. mode of action Cell wall Action: – Block synthesis – Digestion – Disrupt surface w/o cell wall, bacteria will lyse (especially gram positive… remember?) Examples: penicillin, detergents, alcohol
  13. 13. Surfactants disrupt mode of action
  14. 14. mode of action Affect on synthesis (DNA, RNA) Proteins – have many functions in the cell! Antimicrobials can block: DNA synthesis (master code), transcription, translation  Mutagens (radiation = permanent inactivation of DNA)  Antimicrobial therapy (drugs)  Chemicals – some destroy nucleic acids
  15. 15. mode of action Heat, pH, heavy metals can alter proteins
  16. 16. Practical concerns Does the application require sterilization? Is the item to be reused? (time, $$) Can the item withstand heat, pressure, radiation, or chemicals? Is the method suitable? Will the agent penetrate to the necessary extent? Is the method cost- and labor-efficient & is it safe?
  17. 17. Types of Control: I. Methods of Physical Control 1. Heat 2. Cold temperatures 3. Desiccation 4. Radiation 5. Filtration
  18. 18. Physical Control 1. Heat Moist vs. dry Moist heat = lower temp and shorter time Causes coagulation/denaturation of protein Dry heat = higher temp/longer time Dehydrates cell, removes water, denatures proteins, oxidation (burning)
  19. 19. Physical Control
  20. 20. Physical Control 1. Heat – moist heat Moist heat uses hot water or steam sterilization  _______________ 15 psi/121oC/10-40min (steam under pressure)  intermittent sterilization – 100oC 30-60 min for 3 days (unpressurized steam) disinfection  Boiling at 100oC for 30 minutes to destroy nonspore-forming pathogens  _______________ kills Salmonella, Listeria & overall microbe count
  21. 21. Physical Control
  22. 22. Pasteurization Pasteurization – heat  kill potential agents of infection and spoilage without destroying the food flavor or value 63°C–66°C for 30 minutes (batch method) 71.6°C for 15 seconds (flash method) Not sterilization – kills non-sporeforming pathogens and lowers overall microbe count; does not kill endospores or many nonpathogenic microbes 22
  23. 23. Physical Control 1. Heat – dry heat Dry heat uses higher temperatures than moist heat, can also sterilize incineration – 600-1200oC combusts & dehydrates cells dry ovens – 150-180oCcoagulate proteins
  24. 24. Thermal death Physical Control Thermal death time (TDT) – shortest length of time required to kill all test microbes at a specified temperature Thermal death point (TDP) – lowest temperature required to kill all microbes in a sample in 10 minutes
  25. 25. Physical Control 2. Cold temperatures _______________– slows the growth of microbes refrigeration 0-15oC & freezing <0oC used to ____________food, media and cultures
  26. 26. Physical Control 3. Desiccation gradual removal of water from cells, leads to metabolic inhibition not effective microbial control – many cells retain ability to grow when water is reintroduced _______________ = freeze-drying Note: cold and dessication ARE NOT good methods of disinfection or sterilization.
  27. 27. Physical Control 4. Radiation 1. _______________ radiation – deep penetrating power, breaks DNA – gamma rays, X-rays, cathode rays – used to sterilize medical supplies & food products 1. _______________ radiation – little penetrating power to sterilize air, water & solid surfaces – uv light creates thymine dimers, which interfere with replication
  28. 28. Ionizing radiation Physical Control
  29. 29. Nonionizing radiation - UV Physical Control
  30. 30. UV treatment of wastewater Physical Control
  31. 31. Physical Control Other “waves” Sound (high frequency) Can also be used to disrupt cells (vibrations) or generate heat Ultrasonic devices are used clean dental, medical instruments before sterilization
  32. 32. 5. Filtration physical removal of microbes by passing a gas or liquid through filter Pores of filter large enough for liquid but too small for microbe (<1 μm) used to Physical Control
  33. 33. OVERVIEW 33
  34. 34. Types of Control: II. Methods of Chemical Control Categories: • Halogens • Phenolics • Chlorhexidine • Alcohols • Hydrogen peroxide • Detergents & soaps • Heavy metals • Aldehydes Uses: •Disinfectants •antiseptics •sterilants •degermers •preservatives
  35. 35. Chemical antimicrobials 10,000 manufactured today About 1,000 routinely used Society is obsessed with “killing germs” – to the point of being excessive Result: widespread overuse  resistance of pathogens, death of natural flora
  36. 36. Qualities of chemical antimicrobials Rapid action, even in low concentration Water/alcohol soluble, stabile Broad spectrum w/o being toxic Penetration, sustained action Resitance to inactivation Noncorrosive, nonstaining Sanitizing and deodorizing Inexpensive and available
  37. 37. Levels of activity
  38. 38. Factors that affect activity Type of microorganism being treated Material being treated Amt of contamination Exposure time Strength/action of germicide  Appendix C shows procedures for testing effectiveness
  39. 39. Ways to express strength/concentration Dilution (1:200 is one part chemical in 200 parts dilutant such as water) ppm – parts per million Percent – 70% alcohol, or mg/ml _______________ solutions – have water as the solvent _______________– are dissolved in alcohol
  40. 40. Chemical control - categories 1. 2. 3. 4. 5. 6. 7. 8. Halogens Phenolics Chlorhexidine Alcohols Hydrogen peroxide Detergents & soaps Heavy metals Aldehydes
  41. 41. 1. Halogens Ionic (halide) or nonionic Mostly _______________ Germicidal and sporicidial with long exposure Affect protein structure (bonds)
  42. 42. 1. Halogens Chlorine – Cl2, hypochlorites (chlorine bleach - OCl), chloramines – In water – release hypochlorous acid (HOCl) – Denaturation of proteins by disrupting disulfide bonds – Can be sporicidal – 0.6-1 ppm Cl2 to clean water – Bleach – sanitization/disinfection
  43. 43. 1. Halogens Iodine - I2, iodophors (betadine) – Denature proteins – similar to Chlorine but not affected by organic matter or pH – Broad spectrum microbicide, can be sporicidal – Milder medical & dental degerming agents, disinfectants, ointments, topical antiseptic – Betadine (iodophor) = iodine + neutral polymer; allows for slow release and increased penetration – used as antiseptic
  44. 44. 44
  45. 45. 2. Phenolics Phenol ring (aromatic carbon ring) + groups Disrupt cell membranes & precipitate (denature) proteins; bactericidal, fungicidal, virucidal, not sporicidal – _______________ – ____________antibacterial additive to soaps – Mouthwash! (thymol) – Can be VERY toxic! Not typically used as antiseptics.
  46. 46. _______________
  47. 47. 3. _______________ Hibiclens, Hibitane A surfactant & protein denaturant with broad microbicidal properties Not sporicidal Used as skin _________ agents for preoperative scrubs, skin cleaning & burns
  48. 48. 4. Alcohols Ethyl, isopropyl in solutions of 50-90% (water needed for protein coagulation) Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi _______________ Isopropanol = rubbing alcohol, but vapors can be toxic
  49. 49. 5. Hydrogen peroxide Weak (3%) to strong (25%) _______________ agent (steals electrons) Produce highly reactive hydroxyl free radicals that damage protein & DNA while also decomposing to O2 gas (bubbles) toxic to _______________ , overwhelms catalase in aerobes Strong solutions are sporicidal
  50. 50. colonoscope
  51. 51. 52
  52. 52. 6. Detergents & soaps ________ compounds that work as _______________ Quaternary ammonia cpds (__________) act as surfactants that alter membrane permeability of some bacteria & fungi – Not sporicidal, ineffective against TB, hepatitis, pseudomonas Soaps- mechanically remove soil and grease containing microbes
  53. 53. Figure 11.17 55
  54. 54. 56
  55. 55. 7. Heavy metals Solutions of silver & mercury kill vegetative cells in low concentrations by inactivating proteins Metallic salts Oligodynamic action Not sporicidal _________ to humans – Not used on broken skin
  56. 56. 59
  57. 57. 8. Aldehydes Glutaraldehyde & formaldehyde kill by alkylating protein & DNA (-CHO is reducing group) _______________ = H on AA is replaced by the aldehyde (and crosslinked) _______________ in 2% solution (Cidex) used as sterilant for heat sensitive instruments _______________ - disinfectant, preservative, toxicity limits use (formalin is aqueous solution)
  58. 58. Gases & aerosols _______________, propylene oxide, betapropiolactone & chlorine dioxide Strong _______________ agents, sporicidal (sterilization)
  59. 59. ________________________ – uses ethylene oxide
  60. 60. 65
  61. 61. Miscellaneous antimicrobials Dyes – crystal violet, acriflavine Acids, bases (alkalies) – destroy but some are corrosive and hazardous – Pickling – acetic acid – Sauerkraut, olives – lactic acid – Benzoic, sorbic acid – in lots of processed foods (preservatives = _______________ )

×