Module 7: Control of Microorganisms Flashcards
Methods of Microbial Control
- Sterilization
- Disinfection
- Decontamination (sanitization)
- Antisepsis (degermation)
Sterilization
- destroys or removes all viable microorganisms
- generally reserved for inanimate objects (surgical instruments, syringes, etc..)
Disinfection
- physical process or chemical agent used to destroy vegetative pathogens, but no bacterial endospores
- removes harmful products of microorganisms from material
- normally used on inanimate objects
Decontamination (sanitization)
- cleansing technique which mechanically removes microorganisms to reduce contamination to safe levels
Antisepsis
- form of decontamination but on living tissues
- reduces the number of microbes on human skin
- involves scrubbing the skin or immersing in chemical
cide
- “to kill” an antimicrobial agent aimed at destroying a certain group of microorganisms
Bactericide
- kills bacteria (except for those in endospore stage)
Fungicide
kills fungal spores, hyphae, and yeasts
Virucide
- kills viruses
Sporicide
- kills bacterial endospores
static
“to stand still”, denotes a condition in which microbes are temporarily prevented from multiplying but are not killed
Germicide/Microbicide
- kills or prevents the growth of microorganisms
Asepsis
any practice that prevents the entry of infectious agents into sterile tissues and thus prevents infection
Antiseptics
chemicals applied directly to exposed body surfaces, wounds and surgical incisions to destroy or inhibit vegetative pathogens
What is microbial death?
the permanent loss of reproductive capability, even under optimal growth conditions
What are the 6 factors that affect death rate?
- number of microorganisms
- nature of the microorganisms in the population
- temperature and pH of environment
- concentration of agent
- mode of action of agent
- presence of solvent, interfering organic matter and inhibitors
Mode of Action
- an antimicrobial agent’s adverse effect on cells
- 4 general categories: cell wall, cytoplasmic membrane, cellular synthesis processes, proteins
Modes of Action - Cell Wall
- block synthesis
- digest
Modes of Action - Cytoplasmic Membrane
- cell loses ability to retain important substances
- poisonous substances are let in
Modes of Action - Cellular Synthesis
- interrupts synthesis of proteins required in growth and metabolism -> preventing replication
- can introduce mutations
Modes of Action - Proteins
- disrupt/denature proteins
- loss of protein function = arrest in metabolism
Physical Methods of Control
- heat (dry and moist)
- cold & dessication
- radiation
- filtration
Moist Heath Methods
- occurs in the form of hot water, boiling water, or steam
- coagulation and denaturation of proteins
Dry Heat Methods
- refers to hot air or an open flame
- dehydrates cells and denatures proteins
Moist Heath Methods - Boiling Water
- will NOT kill all resistant cells - disinfect only
- 30 min at 100 degrees celsius
- items can easily be re-contaminated
Moist Heath Methods - Autoclave
- generation of steam under pressure to destroy microbial life
- at 15 psi above normal water boils at 121 degrees celsius
- sterile
Moist Heat Methods - Pasteurization
- heat applied to liquids to oil potential agents of infection and spoilage
- retains the liquids flavour and food value
- not sterile
Dry Heat Methods - Incineration
- reduces microbes and other substances to ashes and gas
- limited to metal and heat-resistant glass materials
- sterile
Dry Heat Methods - Hot-Air Oven
- electric coils radiate heat in an enclosed compartment
- ensures thorough heating of objects and destruction of endospores
- sterile
Cold and Desiccation
- cold treatment: only slows activity and growth of microbes (microbistatic)
- desiccation: vegetative cells exposed to room air gradually become dehydrated
- chilling, freezing, or desiccation can NOT be considered as methods of disinfection or sterilization
Filtration
- removes microbes from liquid and air
- useful for preparing liquids that cannot withstand heat
- cannot remove toxins that can cause disease
- high-efficenicy particular air (HEPA) filters
- can have pore size small enough to remove viruses and get sterilization
Chemical Agents Desirable Qualities
- rapid action even in low concentration
- broad-spectrum without toxicity to human and animal tissues
- penetration of inanimate surfaces to sustain persistent action
- non-corrosive or non-staining
- affordable and readily available
Factors that affect microbicidal activity of chemicals
- nature of microorganisms
- nature of the material being treated
- the degree of contamination
- strength + chemical action of germicide
Chemical Methods - Chlorine
- can kill endospores and all other microbes
- in solution, combined with water -> release hypochlorous acid -> denatures enzymes
- capable of sterilization
Chemical Methods - Halogens (Iodine)
- can kill endospores and all other microbes
- penetrates cells of microorganisms and interferes with metabolic function
- interferes with hydrogen and disulphide bonding of proteins
- capable of sterilization
Chemical Methods - Hydrogen Peroxide
- can kill endospores and all other microbes
- oxygen forms free radicals which are highly toxic and reactive to cells
- capable of sterilization
Chemical Methods - Aldehydes
- can kill endospores and all other microbes
- glutaraldehyde - disrupts activity of enzymes and proteins
- formaldehyde - dissolves in water -> formalin, attaches to nucleic acids and amino acids
- capable of sterilization
Chemical Methods - Ethylene Oxide
- blocks DNA replication + enzymatic action
- capable of sterilization
Chemical Methods - Phenol
- high concentrations: disrupt cell walls, membranes, and proteins
- low concentrations: inactivate certain critical enzyme systems
Chemical Methods - Chlorhexidine
- targets cell membrane causing loss of permeability
- denaturation of proteins
- low toxicity and rapid action
Chemical Methods - Alcohol
- concentration of 50% or higher dissolve membrane lipids, disrupt cell surface tension and compromise membrane integrity
- rate of evaporation decreases effectiveness
Chemical Methods - Detergents
disrupts cytoplasmic membranes -> loses selective permeability, causing cell death
