chapter 7 the control of microbial growth terminology sepsis refers to microbial contamination....
TRANSCRIPT
Chapter 7The Control of Microbial Growth
TERMINOLOGY
• Sepsis refers to microbial contamination.
• Asepsis is the absence of significant contamination.
• Sterilization: Removal of all microbial life
• Commercial Sterilization:
• Disinfection: Killing of vegetative microbes on nonliving objects
•Antisepsis: Killing of vegetative microbes in/on living tissue
•Degerming: Removal of microbes from a limited area
•Biocide/Germicide: Kills microbes
• Bacteriostasis: Inhibits, does not kill microbes
• Factors influencing death rate are:
• Number of microbes
• Environmental influences (ie. Organic substances, biofilms, temperature, pH)
• Biofilms:
• Time of exposure
• Microbial characteristics
• [antimicrobial agent]
Microbe Death by Antimicrobial Agents
• Alteration of membrane permeability
• Lipids and proteins are altered
• Intracellular substances leak out of cell
• Damage to proteins
• Denaturation of enzymes, etc.
• Loose their structure and function
• Damage to nucleic acids
• Damaged DNA and RNA prevents production of vital proteins
Actions of Microbial Control Agents
• Heat denatures proteins
• Boiling water• (May not kill
spores)
• Autoclave: generates very high pressure and temperature via steam
• Steam must contact surface to kill microbes
Moist Heat
Figure 7.2
• Pasteurization reduces spoilage organisms and pathogens via heating
• Thermoduric (i.e. thermophiles) organisms survive
• Pasteurization treatments
• High-temperature short-time (HTST): 72°C for 15s
• Ultra-high-temperature (UHT): 140°C for 3s
Pasteurization
• Dry Heat Sterilization:
• Direct flaming
• Incineration
• Hot-air sterilization
Dry Heat
Hot-air Autoclave
Equivalent treatments 170˚C, 2 hr 121˚C, 15 min
• Filtration removes microbes
• Low temperature inhibits microbial growth:
• Refrigeration
• Deep freezing
• Desiccation prevents metabolism
• Hypertonicity causes plasmolysis
Other Physical Methods of Microbial Control
• Radiation damages DNA and other organic molecules
• Ionizing radiation (X rays, gamma rays, electron beams)
• Nonionizing radiation (UV)
• Microwaves kill by heat; not especially antimicrobial
Other Physical Methods of Microbial Control
• Evaluating a disinfectant
• Use-dilution test
• 1. Stainless steel cylinders are inoculated with Staphylococcus aureus, Salmonella choleraesuis, Pseudomonas aeruginosa
• 2. Cylinders are dried in an incubator
• 3. Cylinders are placed in test disinfectant
• 4. Cylinders are incubated in broth media
Chemical Methods of Microbial Control
Types of Disinfectants/Antiseptics
Figure 7.7
• Phenol
• Phenolics: Modified phenol
• reduced irritation, enhanced antibacterial action
• ie. Lysol
• Bisphenols:
• Hexachlorophene
• Triclosan (2nd link)
• Found in many household items
• Chlorhexidine
• surgical hand scrub
• preoperative patient scrub
• Halogens:
• Iodine: skin disinfectant; water treatment
• Chlorine (ie. Bleach): water, sewage treatment; swimming pools; restaurants, etc.
Types of Disinfectants/Antiseptics
Types of Disinfectants/Antiseptics
Table 7.6
• Alcohols: Ethanol, isopropanol
• May not be appropriate for wound cleaning
• May “seal in” microbes
• Alcohol-based handrubs
• Heavy Metals: ie. Ag, Cu
• Silver compounds: impregnated dressings; burn creams; catheters
• Copper sulfate: kills green algae in reservoirs, pools, ponds
Types of Disinfectants/Antiseptics
• Chemical Food Preservatives
• Organic Acids - Inhibit metabolism
• Sorbic acid, benzoic acid, calcium propionate
• Control molds and bacteria in foods and cosmetics
• Nitrite prevents endospore germination in meats
• Antibiotics. Nisin and natamycin prevent spoilage of cheese
Types of Disinfectants
• Aldehydes:
• Glutaraldehyde:
• sterilizes*
• hospital instrument disinfection
• used for embalming
Types of Disinfectants
• Gaseous Sterilants
• Ethylene oxide:
• Peroxygens
• Ozone = O3: ie. water treament
• Hydrogen peroxide = H2O2: ie. Food packaging; NOT good for open wounds
Types of Disinfectants
• Surface-Active Agents or Surfactants
Types of Disinfectants/Antiseptics
Soap Degerming
Cationic detergents:
Quaternary ammonium compounds = “Quats”
ie. Pseudomonads can grow in Quat solutions; can Norovirus?