2. CONTROL OF MICROORGANISMS Flashcards
→ complete removal or destruction of all forms of life, including bacterial spores
→chemical or physical methods
Sterilization
→process that eliminates a defined scope of
microorganisms
→process of killing or removing microorganisms in inanimate surfaces thru the use of chemical agents
Disinfection
→free of life of every kind
Sterile
→destroys pathogenic organisms, but not necessary all microorganisms or spores
→most are chemical substances
Disinfection
→having the property of inhibiting bacterial growth or multiplication
Bacteriostatic
→having the property of killing or destroying bacteria
→precipitates bacterial protein (H2SO4, HCl
Bactericidal
→chemical substance used to kill infection producing microorganisms on surface but too toxic to be applied directly on tissues
Germicide or Disinfectant
→characterized by the presence of pathogenic
microbes in living tissue
Septic
→characterized by the absence of pathogenic
microbes
Aseptic
→chemical substance which opposes sepsis or putrefaction either by killing microorganism or preventing their growth
→applied topically to living tissues
Antiseptic
Examples of Antiseptic
Phisohex, Hexachlorophene, Tincture of Iodine/Povidone Alcohol (Iodophore)
→time in minutes to reduce the bacterial population or spores by 90% at a specified temperature
Decimal Reduction Time (DRT/D/D)
Factors That Influence the Degree of Killing Microorganisms
a. Types of organisms
b. Number of organisms
c. Concentration of disinfecting agent
d. Presence of organic material
e. Nature of surface to be disinfected
f. Contact time
g. Temperature
h. pH
i. Biofilms
j. Compatibility of disinfectants and sterilants
Types of ORGANISMS!
✓Bacterial spores→ resistant
✓Acid-Fast Bacilli
✓Nonenveloped viruses
✓Vegetative bacteria
✓Enveloped viruses
→ most resistant to the actions of heat, chemicals, and radiation
→naked pieces of protein without nucleic acid
Prions
degenerative diseases of the nervous system (transmissible spongiform encephalopathy—mad cow disease)
Creutzfeldt-Jakob disease
blood, mucus, and pus
organic materials
at least 1 to 2 minutes to kill microorganisms
Alcohol and Iodine preparations (Betadine)
Most Resistant → Least Resistant organisms
Prions → Bacterial spores → Mycobacteria → Nonlipid viruses → Fungi → Bacteria → Lipid viruses
PHYSICAL METHODS
Heat
Low/Cold Temperature
Desiccation and Lyophilization
Filtration
Radiation
→most common method used for the elimination of microorganisms
→most reliable and universally applicable method of sterilization
Heat
→kills microorganisms rapidly than dry heat
→Lethal effect is attributed to DENATURATION and COAGULATION of protein and DEGRADATION of nucleic acid
Moist Heat
→fastest and simplest physical method of sterilization
→sterilization method of choice for heat-stable objects
Moist Heat
→ surgical instruments, needles, hypodermic syringes, rubber stoppers
→kills all vegetative organism but not all spores or viruses
Boiling
Boiling (Temperature and Time)
→100°C for 15-30 minutes (20 minutes minimum)
→ Sterilize biohazardous trash and heat-stable objects
→ all microorganisms (except for prions) and their endospores are destroyed within approximately 15 minutes of exposure
Autoclaving
→ chamber which is filled with hot Steam Under Pressure
Autoclave
Two common sterilization temperatures:
121°C (250°F), 15 psi for 15 minutes→ media, liquids, and instruments
132°C (270°F), 15 psi for 30-60 minutes→ infectious medical waste
BIOLOGIC INDICATOR: (Autoclaving)
Geobacillus stearothermophilus (B. stearothermophilus) incubated at 56°C
most commonly used steam sterilizer in the
microbiology laboratory
Gravity Displacement Type
Sterilizing heat-sensitive culture media containing carbohydrates
Flowing Steam
→Destroys vegetative cells and spores after three consecutive days
FRACTIONAL/INTERMITTENT STERILIZATION/ TYNDALLIZATION
Materials are exposed for 30 minutes for 3 successive days -
✓Day 1: Vegetative cells
✓Day 2: Sporulated cells
✓Day 3: Remaining cells
Instrument for flowing steam
Arnold Sterilizer
Flowing Steam (Temperature and Time)
100°C for 30 minutes
Principle: thickening through evaporation
Inspissation
Sterilize high protein containing media that
cannot withstand high temperature
Inspissation
Example of Inspissation:
LJ, Loeffler’s and Dorset egg medium
Inspissation (Temp. and Time)
→70-80°C for 2 hours for 3 consecutive days
→partially sterilizing organic solutions by heat without altering their chemical properties
→used to sterilize milk, dairy products, and alcoholic beverages
Pasteurization/Partial Sterilization
→eliminates food-borne pathogen and organisms responsible for food spoilage
→cannot eliminate bacterial endospores
Pasteurization/Partial Sterilization
3 types of Pasteurization
- Low Temperature Holding (LTH)/Batch Method
- High Temperature Short-Time(HTST)/Flash Pasteurization
- Ultra-high Temperature
→destroys milk-borne pathogens
→63°C for 30 minute
- Low Temperature Holding (LTH)/Batch Method
→72°C for 15 seconds
→quick heating and immediate cooling
- High Temperature Short-Time(HTST)/Flash Pasteurization
→140°C for 3 seconds
→Cooled very quickly in a vacuum chamber
- Ultra-high Temperature
Advantage of Ultra-high temperature Pasteurization
milk can be stored at RT for 2 months without affecting its flavor
→requires longer exposure times (1.5 to 3 hours) and higher temperatures than moist heat (160° to 180°C)
→does not require water
→sterilization of glasswares, oil products or powders
Dry Heat
Lethal Effects of Dry Heat
Protein denaturation, oxidative damage
and toxic effects of elevated levels of
electrolytes
FLAMING OR DIRECT HEATING
Flaming with a Bunsen Burner
Burning with a Bunsen Burner
→flaming mouth of culture tubes or slides
Flaming with a Bunsen Burner
wireloops, forceps and straight wire
Burning with a Bunsen Burner
→most widely used type of dry heat
→used for glasswares, certain metals and oils
→2 hours for 160-180°C kill organisms including all spore formers
Hot Air Oven
Hot Air Oven (QC)
Bacillus subtilis var. niger (Bacillus atrophaeus) at 35-37°C
→Principle: Burning of materials into ashes at 300-400°C
→most common method of treating infectious waste and infected laboratory animals
→destruction of sputum cups, garbage and used dressing
Incineration
considered as HAZARDOUS MATERIAL in Incineration
870-980°C
→burning dead human bodies control the spread of communicable disease
Cremation