general considerations in microbial control
-desired level of cleanliness
-relative resistance of microbial forms
-factors that influence the action of antimicrobial agents
Levels of cleanliness
-Sterilization
-Disinfection
-Antisepsis
-Decontamination
Sterilization
the destruction of all microbial life
Disinfection
destroys most microbial life, reducing contamination on inanimate surfaces
Antisepsis
destroys most microbial life, reducing contamination on a living surface
Decontamination
the mechanical removal of most microbes from an animate or inanimate surface
Primary targets of microbial control
-are the microorganisms that can cause infection or spoilage that are constantly present in the external environment
these microorganisms show varying resistance to forms of control
-highest resistance
-moderate " "
-lowest "
Highest resistance
-prions & bacterial endospores
Moderate resistance
-protozoan cysts, some fungal spores, naked viruses, & some hearty bacteria (M. tuberculosis, S. aureus, & Pseudomonas sp.)
Lowest resistance
-most vegetative bacterial cells, most fungal spores & hyphae, enveloped viruses, yeasts, & protozoan trophozoites
Methods of microbial control
-sterilization
-disinfection
-antisepsis
-sanitization
-degermation
sterilization
-removes all viable microorganisms including viruses & spores
-usually reserved for inanimate objects
-mostly performed with heat but chemicals can also be used
disinfection
-the use of physical process or chemical agent (disinfectant) to destroy vegetative pathogens & most viruses
-does not destroy bacterial endospores & some viruses
-usually used only on inanimate objects
-also removes toxins
antisepsis
-antiseptics applied directly to exposed body surfaces to destroy or inhibit vegetative pathogens
sanitization
-any cleansing technique that mechanically removes microorganisms to reduce contamination to safe levels
-examples include washing dishes or clothes
degermation
-reduces the number of microbes on the human skin
-works by removing oils & microbes on the outer layer of skin through physical or chemical means or both (hand washing & surgical scrubbing; swabbing with an alcohol wipe)
agents of microbial control
-cide: to kill (doesn't necessarily result in sterilization)
-stasis or -static: to stand still <slow down/inhibit>
bactericide
-chemical that destroys bacteria (not endospores)
fungicide
-a chemical that can kill fungal spores, hyphae, & yeasts
virucide
-a chemical that inactivates viruses
sporicide
-can destroy bacterial endospores
germicide or microbicide
-chemical agents that kill a variety of microorganisms
bacteristatic
-prevent the growth of bacteria
fungistatic
-inhibit fungal growth
microbistatic
-materials used to control microorganisms in the body (ex. antiseptics)
Microbial death
-when various cell structures become dysfunctional & the entire cell sustains irreversible damages, or...
-if a cell can no longer reproduce under ideal environmental conditions
factors that influence the action of antimicrobial agents
-the NUMBER of microorganisms
-the NATURE of the microorganisms in the population
-the TEMPERATURE and pH of the environment
-the CONCENTRATION of the agent
-the MODE OF ACTION of the agent
-the PRESENCE OF solvents, interfering organic matter, & inhibito
MODES of ACTION of antimicrobial agents
-affect the cell wall
-affect the cell membrane
-affect protein synthesis
-affect protein function
affect the cell wall
-block its synthesis, digest it, or break down its surface
-the cell becomes fragile and is lysed easily
-ex. Penicillin, cephalosporins, vancomycin, detergents, & alcohol
affect the cell membrane
-disrupt the normal transport of materials in/out of the cell
-ex. surfactants : detergents that essentially open holes in the membrane
affect protein synthesis
-disruption of DNA transcription or replication
(ex. ciproflaxacin, sulfonamides, & radiation-gamma, UV, & X)
-disruption of translation in the ribosomes (ex. streptomycin, tetracycline, chloramphenicol, & erythromycin)
affect protein function
-generally work by altering the protein's natural structure (conformation)
-denaturation
-coagulation
denaturation
involves the breaking of bonds within the protein to disrupt its conformation
coagulation
aggregation of proteins resulting in a non-functioning mass
method of physical control- HEAT as an agent of microbial control
-generally elevated temperatures are microbicidal & lower temperatures are microbistatic
-moist heat control
-dry heat (incineration & hot air)
common methods of MOIST HEAT CONTROL
-steam under pressure (steam sterilization)
-non-pressurized steam
-pasteurization (hot water)
-boiling water
steam under pressure
-steam can only reach 100 degrees under normal pressure; increasing the pressure allows for higher temps and better microbe killing
-destroys vegetative cells, spores, and viruses
-AUTOCLAVE
-effective at sterilizing heat-resistant materials (glassware, c
Autoclave
the commercial device used for steam-heat sterilization
-similar in function to a pressure cooker
-average settings are 15psi, 121 degrees, 15minutes
Non-pressurized Steam
-sometimes referred to as intermittent sterilization
-expose to free-flowing stream for 30-60 minutes, incubate for 23-24 hours, treat again; repeat for 3 days in a row
-destroys vegetative cells & viruses but not spores
-most often used to sterilize heat
Pasteurization (hot water)
-technique in which heat is applied to liquids to kill potential agents of infection & spoilage while maintaining the flavor & food value
-does not sterilize the liquid as spores, thermoduric, & thermophilic orgs still remain
-3 methods: flash, batch, & u
flash pasteurization
71.6 degrees C. for 15 sec
common in Europe & Asia
batch pasteurization
63-66 degrees C. for 30 minutes
traditional method used in the U.S.
Utrahigh-temperature (UHT) pasteurization
134 degrees C. for 1-2 sec
Boiling water
-for disinfection & not sterilization
-expose materials to boiling water for 30 min (10 min will kill all non-spore-forming pathogens & most viruses)
-used by many to decontaminate suspect drinking water
-recontamination after removal form water is the bi
DRY HEAT control
-incineration
-dry oven (hot air)
Incineration
-ignites & reduces microbes to ashes & gas
-common practice in microbiology lab- flaming the loop
-hospitals often use incineration to eliminate their infectious waste materials
Dry oven (hot air)
-electric coils radiate heat within an enclosed compartment
-sterilization occurs at 150-180 degrees C for 2-4 hours
-used for heat-resistant items that do not sterilize well with moist air (some glassware, powders, oils, & metallic instruments)
method of physical control- the effects of COLD & DESICCATION
-cold treatment
-dessication
cold treatment
-refrigeration & freezing
-designed to slow microbial growth
-common in food processing & storage
-not considered a viable method of sterilization or disinfection
desiccation
-drying
-inhibits growth by removing water
-inhibits the spread of most pathogens but not all of them
-Lyophilization: mixture of freezing and drying (used to preserve microbes and other cells for long periods of time)
-not considered a viable method of s
method of physical control- RADIATION as a microbial control agent
-energy emitted from atomic activities and dispersed at high velocity through matter or space
-2 categories: ionizing & non-ionizing
Ionizing radiation
-excites the electrons to the point that they are ejected from the molecule entirely causing the formation of ions (DNA is most sensitive)
-also causes lethal chemical changes in organelles & the production of toxins
-used in the sterilization of commerci
Non-ionizing Radiation
-excites electrons causing them to jump orbitals but don't leave the molecule (leads to abnormal linkages & bonds within molecules; DNA again is very susceptible... thymine dimers are a common result)
-UV rays are the primary example
-> excellent for disi
decontamination by FILTRATION
-effective for removing microbes from air & liquids
-fluid strained through a filter with openings large enough for fluid but too small for microorganisms
-pore size can be controlled and standardized (can be small enough to trap viruses)
-applications of
applications of filtration
-prepare liquids that can't withstand heat (serum & other blood products, vaccines, IV fluids, & enzymes)
-can decontaminate beverages without altering their flavor
-water purification
-removing airborne contaminants (HEPA filters)
SOUND WAVES -method of physical control
-used high frequency sound waves to disrupt cell structure
-sonicator: water-filled chamber through which the sound waves become vibrations that can disrupt cell structure
-gram-negative bacteria are most susceptible
-often used to clean debris from instr
Osmotic Pressure (salt concentration)- physical control
-involves the use of salt to create a hypertonic environment
-results in water leaving the cell, inhibiting cellular processes
GERMICIDAL categories according to CHEMICAL groups
-halogens
-phenol & its derivatives
- alcohols
-oxidizing agents
-chemicals with surface action (surfactants): detergents
-heavy metal compounds
-aldehydes as germicides
-gaseous sterilants & disinfectants
Halogens
-fluorine, bromine, chlorine, & iodine
-they generally disrupt microbial enzyme function
-effective against vegetative cells and some spores
-ex. household bleach (chlorine) & Betadine (iodine)
Phenol & its Derivatives
-effective against vegetative cells but not spores
-they denature proteins and disrupt cell membranes
-often have a nasty odor & some side effects
-ex. orthophenylphenol (active ingredient in Lysol), hexylresorcinol (used in some throat lozenges), and hex
Alcohols
-effective against vegetative cells but not spores (more effective in inactivating enveloped viruses than non enveloped viruses)
-isopropanol & ethanol are most commonly used in 70-95% mixtures
-work by denaturing proteins & disrupting cell walls & membra
Oxidizing agents
-bactericidal, virucidal, & fungicidal; sporicidal in higher concentrations (especially effective against anaerobic organisms; also used to treat drinking water & to eliminate spores on open surfaces)
-work by oxidizing enzymes thus shutting down the micr
Chemicals with surface action (surfactants): Detergents
-generally work well against vegetative cells but not spores
-work by disrupting the cell membrane structure
-ex. soaps, detergents, & mouthwash
Heavy Metal compounds
-mercury, silver, gold, copper, arsenic, & zinc have all been used
-most are no longer used...
-> copper is still used to control algae growth in water
-> copper, zinc, & mercury are used to control fungal growth in paint
->silver nitrate is sometimes use
Aldehydes as germicides
-work by denaturing proteins & inactivating nucleic acids
-> glutaraldehyde is used for cleaning lensed instruments & some respiratory equipment
-> formaldehyde is used in vapor form to sterilize laboratories that have become contaminated
-> both are effe
Gaseous sterilants & disinfectants
-ethylene oxide gas
-> effective against all microbes, including endospores & viruses
-> works by reacting with proteins
-> useful in sterilizing fabrics (ex. mattresses & pillows) & implantable devices (ex. pacemakers & artificial hips), as well as any h