Physical and Chemical Agents for Microbial Control

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Physical and Chemical Agents for Microbial Control
Chapter 11
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Control of microbes

• Physical and chemical methods to destroy or
  reduce microbes in a given area

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OVERVIEW
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Why do we want to control microbes?

• How do we do it?

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Relative resistance of microbes

• Least resistance
• most vegetative cells
• Fungal spores
• enveloped viruses
• Yeast
• Protozoan trophozoites

• Highest resistance
• Bacterial endospores
• Prions
• Moderate resistance
• Pseudomonas sp.
• Mycobacterium tuberculosis
• Staphylococcus aureus
• Protozoan cysts

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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

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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)

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Microbial death

• Permanent termination of an organisms vital
  processes
• microbiological definition
• Involves permanent loss of reproductive
  capability, even under optimum growth conditions

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Factors that influence microbial killing
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How antimicrobial agents work Cellular targets
of control (mode of action)

• Cell wall
• Cell membrane
• Cellular synthetic processes (DNA, RNA)
• Proteins

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Cell wall
mode of action

• Action
• Block synthesis
• Digestion
• Disrupt surface
• w/o cell wall, bacteria will lyse (especially
  gram positive remember?)
• Examples penicillin, detergents, alcohol

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mode of action
Surfactants disrupt
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Affect on synthesis (DNA, RNA)
mode of action

• 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

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mode of action
Heat, pH, heavy metals can alter proteins
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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?

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Types of Control I. Methods of Physical Control

• Heat
• Cold temperatures
• Desiccation
• Radiation
• Filtration

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1. Heat
Physical Control

• 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)

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Physical Control
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1. Heat moist heat
Physical Control

• 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
  non-spore-forming pathogens
• _______________ kills Salmonella, Listeria
  overall microbe count

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Physical Control
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Pasteurization

• Pasteurization heat ? kill potential agents of
  infection and spoilage without destroying the
  food flavor or value
• 63C66C for 30 minutes (batch method)
• 71.6C for 15 seconds (flash method)
• Not sterilization kills non-spore-forming
  pathogens and lowers overall microbe count does
  not kill endospores or many nonpathogenic
  microbes

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1. Heat dry heat
Physical Control

• Dry heat uses higher temperatures than moist
  heat, can also sterilize
• incineration 600-1200oC combusts dehydrates
  cells
• dry ovens 150-180oC- coagulate proteins

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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
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2. Cold temperatures
Physical Control

• _______________ slows the growth of microbes
• refrigeration 0-15oC freezing lt0oC
• used to ____________food, media and cultures

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3. Desiccation
Physical Control

• 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.
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4. Radiation
Physical Control

• _______________ radiation deep penetrating
  power, breaks DNA
• gamma rays, X-rays, cathode rays
• used to sterilize medical supplies food
  products
• _______________ radiation little penetrating
  power to sterilize air, water solid surfaces
• uv light creates thymine dimers, which interfere
  with replication

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Ionizing radiation
Physical Control
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Physical Control
Nonionizing radiation - UV
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UV treatment of wastewater
Physical Control
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Other waves
Physical Control

• Sound (high frequency)
• Can also be used to disrupt cells (vibrations) or
  generate heat
• Ultrasonic devices are used clean dental, medical
  instruments before sterilization

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5. Filtration
Physical Control

• physical removal of microbes by passing a gas or
  liquid through filter
• Pores of filter large enough for liquid but too
  small for microbe (lt1 µm)
• used to

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OVERVIEW
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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

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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

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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

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Levels of activity
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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

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Ways to express strength/concentration

• Dilution (1200 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

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Chemical control - categories

• Halogens
• Phenolics
• Chlorhexidine
• Alcohols
• Hydrogen peroxide
• Detergents soaps
• Heavy metals
• Aldehydes

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1. Halogens

• Ionic (halide) or nonionic
• Mostly _______________
• Germicidal and sporicidial with long exposure
• Affect protein structure (bonds)

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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

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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

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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.

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_______________
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3. _______________

• Hibiclens, Hibitane
• A surfactant protein denaturant with broad
  microbicidal properties
• Not sporicidal
• Used as skin _________ agents for preoperative
  scrubs, skin cleaning burns

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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

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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

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colonoscope
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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

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Figure 11.17
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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

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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)

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Gases aerosols

• _______________, propylene oxide,
  betapropiolactone chlorine dioxide
• Strong _______________ agents, sporicidal
  (sterilization)

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________________________ uses ethylene oxide
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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 _______________ )