Physical and chemical control of microorganisms
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Physical and Chemical Control of Microorganisms. I. Terms II. Factors which determine the effectiveness of control methods III. Methods of physical control IV. Chemical agents. Terms. 1) “ Control ” -- Limiting exposure to _______________________ agents

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Physical and Chemical Control of Microorganisms

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Physical and chemical control of microorganisms

Physical and Chemical Control of Microorganisms

  • I. Terms

  • II. Factors which determine the effectiveness of control methods

  • III. Methods of physical control

  • IV. Chemical agents


Terms

Terms

  • 1) “Control” -- Limiting exposure to _______________________ agents

    • Microorganisms are part of our environment

    • Infection can be controlled by limiting exposure to infectious agents

  • 2) _______________ -- Removal or destruction of all _________________ microorganisms. “sterile”

  • 3)Disinfection -- Removal or destruction of pathogens from ________________________ areas. “disinfectant”

  • 4) Antisepsis -- Removal or destruction of vegetative forms from _______ _____________. “antiseptic”

Note: Antiseptics and disinfectants do the same thing, but in different environments


Terms continued

Terms (continued)

  • 5) Sanitization -- any cleansing technique that mechanically removes microorganisms. Usually soaps


More terms

More terms

  • 7) “-static” means ‘to stand still’. Refers to an agent which prevents _______________ but doesn’t kill.

    • “Bacteriostatic” or “fungistatic” or “virustatic” agent

  • 6) “-cide” refers to ______________.

    • “Bacteriocide” kills bacteria, “fungicide” kills fungi, etc.


Factors which determine the effectiveness of a control method

Factors which determine the effectiveness of a control method

  • 1. The number of microorganisms

“Death curve”

107

106

# of ________ cells

105

104

Note log scale on y axis (each increment is 10X reduction in numbers)

103

102

101

100

4

5

6

7

8

3

2

1

Time (min.)


Physical and chemical control of microorganisms

107

106

105

  • Decimal reduction time (DRT) -- Time for a _____ reduction in population size. Here DRT = ______

  • If the goal is to reduce numbers to 102 then the size of the initial population will determine how long it will take, in this case, ____________ minutes.

104

103

102

101

100

4

5

6

7

8

3

2

1

Time (min.)


Factors which determine the effectiveness of a control method cont

Factors which determine the effectiveness of a control method (cont.)

Spore formers vs. non-spore formers

107

106

# of viable cells

__________________

105

104

103

Vege-tative cells

102

101

100

4

5

6

7

8

3

2

1

Time (min.)


Factors which determine effectiveness of a control agent cont

Factors which determine effectiveness of a control agent (cont.)

  • Temperature and _______ of the environment

  • ___________________ of the agent

  • Mode of action of the agent

    • Microbistatic vs. microbicidal

    • Cellular target

  • Presence of ________________ compounds or inhibitors of the control agent


Methods of physical control heat

Methods of Physical Control: Heat

  • _________ heat

    • Hot water, boiling water, steam

    • 60° - 135° C

    • Denatures proteins, nucleic acids

  • __________ heat

    • Ovens

    • 160° - >1000° C

    • Denatures, oxidizes

At lower temperatures, moist heat is __________ effective than dry heat


Moist heat methods

Moist heat methods

  • I. Boiling water -- ________ min. boiling kills all vegetative cells

  • II. Pasteurization -- Heating to temp. below boiling to kill specific pathogens and increase shelf-time

    • Batch method -- 63°-66° for 30 min.

    • ___________ method -- 71.6° for 15 sec.

      • Results in killing of most viruses and 97-99% reduction in veg. stages of bacteria and fungi

    • UHT (Ultra High Temp) -- 134° 1-2 ___________.

      • Milk can last up to 3 months unrefrigerated

    • Primary pathogen targets of pasteurization: ______________, Listeria, Mycobacterium, Campylobacter, Brucella


Moist heat methods cont

Moist heat methods (cont.)

  • III. Steam under pressure

    • Highest temp. of moist heat at sea level -- _________° C

    • If ____________ increased, higher temps. can be reached

    • Autoclaving

Commonly: _______° C at 15 PSI

________ min. at this temp. is very effective


Effects on cellular proteins

Effects on cellular proteins

Text, Fig. 11.4


Physical methods radiation

Physical methods: radiation


Physical methods radiation1

____________ -- knocks electrons off atoms --> ions

e.g. gamma rays, x-rays

Damages DNA and proteins by breaking bonds -- Fig. 11.8

Exposure hazard to humans

Penetrates ___________ and liquids

Used in fruits & vegetables, now meats

Non-ionizing -- excites atoms but doesn’t ionize

e.g. ____________, sunlight

Damages DNA by creating T-T dimers -- Fig. 11.8, 11.10

Relatively safe to use

Doesn’t penetrate solids or liquids well

______________ sterilization, water treatment

Physical methods: radiation


Physical and chemical control of microorganisms

Text, Fig. 11.8


Physical and chemical control of microorganisms

Text, Fig. 11.10


Other physical control methods

Sonication -- Disruption using ___________ waves

Filtration

Text, Fig. 11.13

Other physical control methods


Chemical control agents

Chemical control agents

  • I. Many kinds but most function by:

    • Disrupting __________________

    • Altering ________________ and/or nucleic acid structure

  • II. Effectiveness is determined by:

    • Concentration

    • Contact time


Major groups

Major groups

  • ________________

  • Phenol and its derivatives

  • Alcohols

  • Hydrogen peroxide

  • Detergents

  • Heavy ___________


Halogens

Halogens

  • Mainly _______________, also iodine and fluorine

  • Iodine “iodophors” most common iodine compound used in hospitals: Betadine, Povidone, etc. Less ____________ than free iodine due to slow release of free iodine.

  • 3 Chlorine forms:

    Cl2 (chlorine gas)

    OCl (hypochlorite -- common ‘bleach’)

    NH2Cl (chloramines)

  • In solution, these compounds combine with water to form hypochlorous acid (HOCl). This is the active form which destroys by ____________

  • Effective against: bacteria, fungi, spores, viruses

  • Limitations:

    • ineffective at _____________ pH

    • ______________: light and O2 cause breakdown


Phenols

p-cresol (lysol)

phenol

OH

OH

CH3

Hexachlorophene (phisohex)

OH

OH

Cl

CH2

Cl

Cl

Cl

Cl

Cl

Phenols

  • Phenolics affect protein function and/or disrupt membranes


Alcohols

Alcohols

  • Ethanol -- 70% to 95%

  • Isopropanol -- more microbicidal but also more __________

  • Destroy cell membranes, can coagulate proteins


Hydrogen peroxide h 2 o 2

Hydrogen peroxide (H2O2)

  • Forms _______________ free radicals (e.g. superoxides, hydroxyl radicals: see last lecture) which are toxic to all cells

  • Also breaks down to H2O and O2, therefore is strongly effective against _____________.


Detergents

Detergents

  • All solubilize membranes and disrupt proteins

Text, Fig. 11.3


Detergents cont

Detergents (cont.)

  • Two types: ___________ (charged) and non-ionic

    • Non-ionic and anionic detergents (like soaps) are not very microbicidal, although they may be very effective in sanitization.

    • _____________ detergents (like benzalkonium chloride) are the most effective ionic detergents.


Heavy metals

Heavy metals

  • Mainly only mercury and silver preparations are used now.

    • Merthiolate, mercurochrome, silver nitrate, etc.

  • Form ions which complex with cell components, stopping growth

  • Disadvantages:

    • _________________

    • _________________

    • Microbes can develop ___________________


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