Control of Bacterial Growth Flashcards
Sterilization
the complete killing or removal of all living microbes, including the most resistant forms (bacterial spores)
Heating is the most common method used for killing microbes.
Decontamination
the treatment of objects or surfaces to make it safe to handle
Disinfection
The control directed against pathogens.
Usually refers to destruction of vegetative (Not spores) pathogens.
In practice, the term is most commonly used for using chemicals to treat inanimate surfaces or obects.
Antisepsis
Application to living tissues, generally body surfaces or cavities to kill bacteria or reduce bacterial load.
Sanitization
Intended to lower microbial load to minimize the disease transmission
Sepsis
Greek word for decay or putrid
Indicates bacterial contamination
Asepsis
The absence of bacterial contaminations.
Object or area are free of pahtogens
Aseptic Technique
Important in bacteriology to prevent contamination
Factors Affecting Microbial Death
- The number of microbes:
- larger populations take longer to kill
- Environmental Conditions:
- presence of organic matter often inhibits the action of the antimicrobial.
- Time of exposure:
- a minimum contact time is required for efficacy of most antiseptics and disinfectant
- Microbial Characterisitics:
- bacterial spores are the most resistant forms of bacteria and are generally affected by few biocides. Most Biocides tend to be more effective against Gram + than Gram - bacteria because there is less lipid in the cell membrane.
Alteration of memebrane Permeability
The cytoplasmic membrane located inside the bacterial cell wall is the target of many control agents. The membrane has selective permeability regulating the entry of nutrients and exit of products.
Damage to the cytoplasmic membrane caused cellular contents to leak and interferes with the growth of the cell.
Damage to Proteins
Altered (denaturation) or destruction of protein structures or their activites will interfere with growth of or kill the bacteria.
Chemicals or heat may disrupt bonding, which is the reason for altered structure or destruction of activities.
Damage to nucleic acids
Damage to RNA or DNA by heat, chemicals, or radiation is frequently lethal to the cells and cannot carry our normal metabolic functions.
Heat
Most common method for the control of microbial growth.
Kills bacteria by denaturing proteins.
Thermal Death Point
As the lowest temperature at which all microorganisms in a particular liquid suspension will be killed in 10 minutes.
Moist Heat
Kills microbes be denaturing protiens (coagulation), which is caused by breaking hydrogen bonds and loss of three dimensional structure of proteins.
Boiling
@100C
Kills vegetative bacterial cells, but not bacterial spores. Generally done for 5-10 mins.
NOT a method of sterilization.
Steam Under Pressure
Autoclave, or pressure cooker
Required to raise the temperature above 100C.
In an Autoclave, temperatire reacheds 121C becuase steam is applied under a pressure of 15psi, which is atmosphere above sea level pressure.
Higher the pressure, higher the temp.
@ 121C for 15 minutes evern bacterial spores are killed.
Perfect method for steriliziation.
Pasteurization
Uses precisely controlled hfeat to reduce microbial numbers in heat sensitive liquids (milk).
Does not kill all microorganisms; hence, it is not the same as sterilization.
Dry heat
NOT as effective as moist heat because moisture allows heat to penetrate better.
Kills by oxidation.
Dry sterilization is done by flaming. Incineration to sterilize contaminated materials or carcasses.
Hot-air sterilization: Done in an oven at a temperature of 170C maintanied for 2 hours will ensure sterilization.
Radiation
Microwaves, ultraviolet rays, x-rays, gamma rays, and electrons are all forms of electromagnetic radiation. Radiation that kills microorganisms is of two types:
Ionizing and nonionizing.
Ionizing Radiation
These have a wave length less than 1nm.
Gamma rays and X-rays have sufficient energy to produce ions and other reactive products from molecules with which radiation particles collide.
Creat electorns, hydroxyl radicals, and hydride radicals.
Nonionizing Radiation
Have wave lengths greater than 1nm.
Ultraviolet rays (220-300nm)
Damages the DNA of exposed bacteria by causing bonds to form between pyrimidine bases. Particularly Thymine.
Thymine dimers inhibid DNA replication.
Filter Sterilization
Involves the use of a filter with pores too small for the passage of microorganisms.
Used for sterilization of heat-sensitive liquids, like culture media.
Most common filter used is a membrane filter.
HEPA-filters can be used to remove airborne microbes.
Phenols and Phenolics
Phenol was the first chemical used to control surgical infections.
Derivatives of Phenol (pheolics) contain a molecule of phenol to reduce irritation and increase antibacterial activity.
Active in the presence of organic compounds and are stable for long periods of time.
Halogens
Iodine and Chlorine, alone ore as constituents of inorganic or organic compounds are effective antimicrobial agents.
Iodine: the oldest and most effective antiseptic.
Chlorine: a gas or in combination with other chemicals is also used widely.
Alcohols
Kill bacteria but not endospores.
Mode of action is protein denaturation, and the disruption of cytoplasmic membranes. Dissolve lipid components
Heavy metals and their compounds
Silver, Mercury, Copper, and Zinc have antibicrobial activity. Effective in small amounts.
Use is limited because of toxicity and corrosiveness,
Surface Active Compounds
Also called Surfactants
decrease surface tension among molecules of a liquid. Soaps and detergents.
Useful for mechanical removal of microbes by scrubbing.
Quanternary Ammonium Compounds
Cationic detergents are most widely used surface active agents.
Cleaning action is due to the positively charged milecules and mode of action is not known.
Ozone
Highly reactive form of oxygen that is fenerated by passin oxygen through high-voltage discharges. Often used to supplement chlorine in the disinfection of water.
Hydrogen Peroxide
Commonly used antiseptic.
Not good for open wounds because it is rapidly broken down to water and oxygen by catalase.
Peracetic Acids
Effective liquid sporicide and is considered as sterilant. Kills spores withing 30 minutes,
Useful in food processing and medical equipment.
Formaldehyde
Gas is an excellent disinfectant. Commonly available as formalin.
Used in preserving biological specimens and to inactivate bacteria or toxins in vaccines.
Glutaraldehyde is less irritating and more effective than formalydehyde.
Gaseous Sterilizers
Chemicals are used in a closed chamber to sterilize heast sensitive materials. Most commonly used chemical is ethylene oxide.
Toxic and flamable.
Effective against all microbes and spores, but requires period of several hours 4-18 of exposure.
