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Topic 5: Control of Microbial Growth
Terms in this set (48)
The reduction in the number of microbes
Known as the "father of aseptic surgery." Began using diluted phenol to treat surgical wounds, instruments and dressings. This reduced the incidences of infection and deaths.
Cells capable of growing and obtaining nutrients.
Removal or destruction of ALL living microorganisms.
A sterilizing agent
Destruction of vegetative cells, but not necessarily spores, on NON-LIVING surfaces or substances
Agent (physical or chemical) that is used for disinfection.
Destruction of vegetative cells but not necessarily spores, on LIVING tissue
Agent (almost always chemical) that is used for antisepsis.
Mechanical removal of microbes from a limited area -- ex. around an injection site
Treatment to lower microbial levels on eating and drinking utensils to safe public health levels
A treatment that kills microorganisms (but not necessarily endospores)
Kills vegetative bacteria
Treatment that inhibits the growth and multiplication of vegetative bacteria
Boiling water (moist heat)
Kills vegetative cells of bacteria, many viruses, fungi, and fungal spores within 10 minutes. Time is critical. Not always reliable: endospores and some viruses can survive.
Autoclave (moist heat)
Preferred method of sterilization. Uses steam under pressure (higher pressure = higher temp). Operated at 121 degrees Celsius at 15 lbs/in squared in pressure. Exposure time: normally 15 minutes. Kills all microbes but NOT PRIONS.
Pasteurization (moist heat)
Mild heat treatment. Not sterilization. Kills pathogens and spoilage microbes. Thermo-tolerant microbes survive.
Hot-air sterilization (dry heat)
170 degrees Celsius for 2 hours. For glassware.
Direct flaming (dry heat)
Flaming transfer loops
Incineration of infectious materials (dry heat)
Contaminated dressings, infected animal carcasses.
Used to physically remove bacteria from heat-labile solutions (ex. antibiotic solutions).
Used to deliver sterile air to hoods, aseptic transfer or packing rooms, operating rooms, and rooms with burn patients. Removes almost all AIRBORNE microbes larger than 0.3 micrometers in diameter.
0-7 degrees Celsius; inhibits growth WITHOUT killing (bacteriostatic). Reduces metabolic rate so cannot reproduce or synthesize toxins. Psychotrophs grow slowly.
Dessication or drying
Absence of water; microbes cannot grow but can remain viable. Viruses and endospores can resist this. VERY important in health-care -- infectious microbes might be harboured in dried organic matter (ex. mucus, urine, blood, pus, etc.)
High osmotic pressure (hypertonicity)
Water is lost from the cell and the cytoplasm shrinks (plasmolysis); high sugar and salt used to preserve food. Yeasts and molds are most resistant to these conditions than bacteria.
Germicidal. Exert effects by ionizing water and causing the formation of hydroxyl radicals (OH-) that damage cellular components, esp. DNA. Used in low levels for treating food and high levels for sterilizing plastic syringes, surgical gloves, suture materials, catheters.
Non-ionizing radiation (UV radiation)
Germicidal, cause mutations in DNA. Used for killing microbes on surfaces and in air because it has no penetrating power. Damages skin and eyes.
Metal or glass cylinders dipped into standardized cultures of test bacteria, then dried briefly. Placed into a solution of disinfectant (different concentrations) for 10 min at 20 degrees C. Cylinders then transferred to growth media. Effectiveness of disinfectant based on growth.
Filter paper disk is soaked with a disinfectant. Disk is then placed onto an agar plate that was previously inoculated with a test organism. If disinfectant is effective, will see a zone of clearing around the disk after incubation: inhibition of growth/cell death. Larger zone = greater effectiveness.
Germicide, used as an alcoholic solution called tincture of iodine or as an iodophor (ex. betadine). Good antiseptic on skin, wounds, disinfects water, equipment used for brewing and winemaking. Inhibits protein synthesis, disrupts membranes.
Forms hypochlorus acid in water which inactivates enzymes. Highly effective germicide. Used for water disinfection. Ex. sodium hypochloride (NaOCl) -- bleach
Ethanol and isopropranol
Used as disinfectants, antiseptics. Denature proteins, disrupt membranes, dissolve lipids. Kill bacteria, fungi but not endospores and nonenveloped viruses. Recommended optimal concentration is 70% v/v
Heavy metals (silver, copper, zinc)
Active in very small amounts (oligodynamic action). Cause denaturation of cellular proteins.
Soap (& detergents)
Decrease surface tension among molecules of a liquid. Not effective as antiseptics; aid in mechanical removal of microbes through scrubbing -- break the oily film on skin into tiny droplets (called emulsification). Good degerming agents.
Quats (Quaternary Ammonium Compounds)
Cationic detergents. Used as antiseptic for skin, disinfectant for instruments, utensils, surfaces. Ex. Zephiran, Cepacol. Less active against gram - bacteria. Do NOT kill endospores, Mycobacterium or Pseudomonas. Organic matter interfered with activity.
Denature and inactivate protein. Ex. Glutaraldehyde: effective sterilizing agent. Used to disinfect hospital instruments.
Gas, used as a chemical sterilant. Disrupts the structure of proteins. Application requires a closed chamber (toxic). Kills all microbes and endospores but requires lengthy exposure period (4-18h)
Cause transmissible spongiform encephalopathies (TSE's). Hard to get rid of -- resistant to heat, freezing, drying, chemicals, and radiation.
Consumption of tainted beef (esp. nerve tissue) believed to be linked to the appearance of the disease. First described in UK in 1996. Believed to be caused by same agent that causes BSE in cattle.
Chronic wasting disease (CWD)
Deer, elk, moose
Bovine spongiform encephalopathy (BSE)
i.e. mad cow disease -- cattle
Classic and variant CJD
Compounds/things that are active in very small amounts (ex. heavy metals -- silver, copper, zinc)
Shrinking of the cytoplasm due to hypertonic solutions
Recommended textbook explanations
Campbell Biology (AP Edition)
Cain, Jackson, Minorsky, Reece, Urry, Wasserman
Fundamentals of Biochemistry
Charlotte W. Pratt, Donald Voet, Judith G. Voet
Biocalculus: Calculus for the Life Sciences
Modern Biology: Student Edition
Janet L. Hopson, Postlethwait
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