Ch 12- Control of Microbial Growth Flashcards
Ionizing Radiation
Ionizes water to create hydroxyl radicals (ROS) that damage DNA
Ex. X-rays, gamma rays, electron beams
Nonionizing Radiation
Damages DNA by creating thymine dimers that inhibit DNA replication
Ex. UV, 260nm
Microwaves
Kill by heat
High-Efficiency Particulate Air Filters (HEPA Filters)
Remove microbes >0.3 um from air in clean rooms
Membrane Liquid Filters
Remove microbes >0.22 um from liquids. Used for heat-sensitive materials. Filters all microbes except viruses.
Use-dilution Test
Metal cylinders are dipped into test bacteria & dried
Cylinders are place in disinfectant for 10min at room temp
Cylinders are transferred to culture media to determine bacterial survival rate
Disk-diffusion Test
For chemical and antibiotics.
Evaluates efficacy of chemical agents
Filter paper disks are soaked in a chemical and place on inoculated bacteria plate
Look for zone of inhibition around disks
In-use Test
For disinfectant solution already in use
Evaluates microbial contamination of cleaning solutions
Alcohols (Chemical Disinfectant)
Denature proteins & dissolve phospholipids in bacteria, fungi, and enveloped viruses
Does nothing to endospores or non-enveloped viruses
Peroxygens
Oxidizing Agents
Ex. Hydrogen peroxide, Peracetic acid, Benzoyl, Ozone
Hydrogen Peroxide (H2O2)
Kills: bacteria, viruses, fungi, endospores on inanimate objects
(not for wounds; human catalase)
Peracetic Acid (peroxyactic acid/PAA)
Kills: endospores, viruses, fungi, bacteria
Plasma
Electrically Excited Gas, 4th state of matter.
Kills: bacteria, viruses, fungi, endospores
Heavy Metals (Chemical Disinfectant)
Denature proteins
Just as toxic to humans
Uses/Ex. silver nitrate is used to prevent ophthalmia neonatorum, Mercuric chloride prevents mildew in paint, copper sulfate in algicide, zinc chloride in mouthwash
Halogens (Chemical Disinfectant)
Iodine
Chlorine gas & hypochlorites
Bleach
Chloramine
Iodine
One of the oldest disinfectants Oxidizing agent (damage sulfur containing amino acids, nucleotides, fatty acids)
Tincture
Solution in aqueous alcohol
Iodophor
Combined with organic molecules (povidone-iodine like Betadine)
Chlorine Gas & hypochlorite
Reacts with water to form hypochlorous acid
Hypochlorous Acid
Strong oxidizing agent that damages sulfur-containing amino acids, nucleotides, and fatty acids
Bleach
Sodium hypochlorite
Chloramine
Chlorine + ammonia
Phenolics & bisphenols
Damage phospholipids of plasma membranes causing leakage
Bisbiguanides
Damage phospholipids of plasma membranes. Effective against Gram-pos. bacteria, yeast, enveloped viruses, some Gram-neg. bacteria
Ex. Chlorhexidine
Aldehydes (alkylating agents)
Very effective disinfectants. Inactivate proteins by cross-linking with some amino acid functional groups.
Kills: bacteria, viruses, fungi, endospores
Uses: specimen preservation
Ex. Formaldehyde (formalin), Glutaraldehyde (used in hospitals)
Chemical Sterilization
Uses sterilant to cause alkylation
Ex. Ethylene oxide
Alkylation
Replacing hydrogen atoms of a chemical group with a free radical
Requirements for Growth
- Oxygen
- pH
- Temperature
- Osmotic Pressure
- Carbon
Sepsis
Microbial contamination
Asepsis
The absence of significant contamination
Aseptic Techniques
Prevent the microbial contamination
Biocide (germicide)
Treatments that kill microbes
Bacteriostasis
Inhibiting microbes
Bacteriocide
Killing microbes
Biosafety Levels
1-4, provide standardized ways to communicate laboratory hazard levels, range from non-harmful to deadly and contagious.
BSL 1
Minimal Risk. Microbes are not known to cause disease in healthy people. (Ex. E. coli)
BSL 2
Moderate Risk. Microbes are generally indigenous and are associated with various diseases that can be treated if needed. (Ex. S. aureus)
BSL 3
Indigenous and/or exotic microbes that cause serious or potentially fatal diseases via respiratory transmission. (Ex. M. tuberculosis)
BSL 4
Highest level. Microbes are dangerous and exotic. High risk of aerosol transmission. Frequently fatal without proper treatment/vaccines (Ex. Ebola)
Sterilization
Destroying all microbial life
Disinfection
Destroying harmful microbes on inanimate objects
Antisepsis
Destroying harmful microorganisms on living tissue
Degermining
The mechanical removal of microbes from a limited area
Sanitation & Commercial Sterilization (Food Microbiology)
Sanitation - lowering microbial counts to a safe level
Commercial Sterilization - killing endospores
Rate of Microbial Death
Microbes die at a constant rate.
Effectiveness of treatment depends on: Type of microbe, number of microbes, environment, composition of item, time of exposure
Highly Resistant Microbes
- Endospore Formers (Ex. Bacillus)
- Mycobacterium Cell Wall (requires strong disinfectant)
- Pseudomonas (will grow in disinfectants; nosocomial)
- Non enveloped viruses (Ex. Polio)
- Protozoan Cysts & Oocysts (Ex. Giardia)
Microbial Control Agents
Kill microbes or inhibit microbial growth by: Alteration of membrane permeability, Damage/denature proteins, Damage nucleic acids.
Methods: Physical & Chemical
Major Methods of Microbial Control
- Heat or chemical sterilization
- Physical methods of Disinfection
- Chemical Methods of Disinfection
Physical Methods of Disinfection
- High Temperature
- Low Temperature
- Filtration
- High Pressure
- Desiccation
- Osmotic Pressure
- Radiation
Thermal Death Point (TDP)
Lowest temperature for all bacteria in a liquid culture to be killed in 10mins
(Variable-temp; Set-time)
Thermal Death Time (TDT)
Lowest time for all bacteria in a liquid culture to be killed at a particular temperature.
(Variable-time; Set-Temp)
Decimal Reduction Time (DRT/D-value)
The minutes to kill 90% of a population at a given temperature
(TDP & TDT are used to determine the D-value)
Pasteurization
Reduces spoilage microbes and pathogens for storages in a refrigerator.
Mild heating for a short time
High Temperature Short Time (HTST)
Common form of time to temperature ration used in pasteurization
Ultra High Temperature (UHT)
Used for sterilization that allows for room temperature storage.
Low Temperature (Physical Disinfection Method)
Has a bacteriostatic effect
Ex. refrigeration, deep-freezing, lyophilization
High Pressure (Pascalization)
Destroys microbe cells and denatures proteins without heat.
Desiccation
An absence of water (prevents metabolism)
Osmotic Pressure
Uses sugars or salts to create a hypertonic environment
