the control of microbial growth
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7. The Control of Microbial Growth. The Control of Microbial Growth. Sepsis refers to microbial contamination. Asepsis is the absence of significant contamination. Aseptic surgery techniques prevent microbial contamination of wounds. Terminology. - PowerPoint PPT PresentationTRANSCRIPT
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
M I C R O B I O L O G Ya n i n t r o d u c t i o n
ninth edition TORTORA FUNKE CASE
7The Control of
Microbial Growth
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Control of Microbial Growth
Sepsis refers to microbial contamination.
Asepsis is the absence of significant contamination.
Aseptic surgery techniques prevent microbial
contamination of wounds.
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Terminology
Sterilization: Removal of all microbial life
Commercial sterilization: Killing Clostridium
botulinum endospores
Disinfection: Removal of pathogens
Antisepsis: Removal of pathogens from living tissue
Degerming: Removal of microbes from a limited area
Sanitization: Lower microbial counts on eating utensils
Biocide/Germicide: Kills microbes
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Bacterial populations die at a constant logarithmic rate.
Figure 7.1a
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Effectiveness of Antimicrobial Treatment
Depends on: Number of microbes Environment (organic
matter, temperature, biofilms)
Time of exposure Microbial
characteristics
Figure 7.1b
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Actions of Microbial Control Agents
Alternation of membrane permeability
Damage to proteins
Damage to nucleic acids
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Physical Methods of Microbial Control
Heat Thermal death point (TDP): Lowest temperature at
which all cells in a culture are killed in 10 min.
Thermal death time (TDT): Time to kill all cells in a
culture
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Heat
Moist heat
denatures
proteins
Autoclave:
Steam under
pressure
Figure 7.2
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 7.3
Steam Sterilization
Steam must contact
item’s surface.
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Physical Methods of Microbial Control
Pasteurization reduces spoilage organisms and
pathogens
Equivalent treatments
63°C (145.4°F) for 30 min
High temperature, short time: 72°C for 15 sec
Ultra high temperature: 140°C (284°F) for <1 sec
Thermoduric organisms survive
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Hot-air Autoclave
Equivalent treatments 170˚C, 2 hr 121˚C, 15 min
Physical Methods of Microbial Control
Dry heat sterilization kills by oxidation Flaming
Incineration
Hot-air sterilization
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Physical Methods of Microbial Control
Low temperature inhibits microbial growth Refrigeration
Deep freezing
Lyophilization
Desiccation prevents metabolism
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Physical Methods of Microbial Control
Radiation damages DNA Ionizing radiation (X rays, gamma rays, electron
beams) – damages many molecules
Nonionizing radiation (UV) – damages DNA
(Microwaves kill by heat; not especially antimicrobial)
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 7.5
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Chemical Methods of Microbial Control
Evaluating a disinfectant Use-dilution test
1. Metal rings dipped in test bacteria are dried.
2. Dried cultures are placed in disinfectant for 10
min at 20°C.
3. Rings are transferred to culture media to
determine whether bacteria survived treatment.
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Chemical Methods of Microbial Control
Evaluating a disinfectant
Disk-diffusion method
Figure 7.6
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Types of Disinfectants
Phenol Phenolics: Lysol
Bisphenols:
Hexacholorphene,
Triclosan
Disrupt plasma
membranes
Figure 7.7
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Types of Disinfectants
Halogens: Iodine, chlorine
Oxidizing agents
Bleach is hypochlorous acid (HOCl)
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Types of Disinfectants
Alcohols: Ethanol,
isopropanol
Denature proteins,
dissolve lipids
Table 7.6
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Types of Disinfectants
Heavy metals: Ag, Hg, and Cu
Oligodynamic action
Denature proteins
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Soap Degerming
Quarternary ammonium compounds “Quats”Cationic detergents
Bactericidal, Denature proteins, disrupt plasma membrane
Types of Disinfectants
Surface-active agents or surfactants
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 7.10
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Types of Disinfectants
Chemical food preservatives Organic acids
Inhibit metabolism
Sorbic acid, benzoic acid, and calcium propionate
Control molds and bacteria in foods and
cosmetics
Antibiotics. Nisin and natamycin prevent spoilage
of cheese
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Types of Disinfectants
Aldehydes Inactivate proteins by cross-linking with functional
groups (–NH2, –OH, –COOH, –SH)
Glutaraldehyde and formaldehyde
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Types of Disinfectants
Peroxygens Oxidizing agents
O3, H2O2, peracetic acid
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Microbial Characteristics and Microbial Control
Figure 7.11
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Microbial Characteristics and Microbial Control
Table 7.7
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 7.8 (1 of 4)
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 7.8 (2 of 4)
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 7.8 (3 of 4)