67 terms

Microbiology Chapter 9

the destruction of all microbial life, Removes all viable microorganisms including viruses, Sterile, for inanimate objects, Sometimes chemicals called sterilants are used
destroys most microbial life, reducing contamination on inanimate surfaces, Physical process or chemical agent to destroy vegetative pathogens,toxins, does not kill endospores, 5% bleach
destroys most microbial life, reducing contamination on a living surface (ex. wash hands) applied directly to exposed body surfaces to destroy or inhibit vegetative pathogens (iodine)
the mechanical removal of most microbes from an animate or inanimate surface (ex. cleaning horse stalls), decreases the risk of infection or spoilage, Sanitation, Sanitizer, Sanitary, Degermation
Microbial Control Methods
physical agents, chemical agents, mechanical removal methods
Types of Physical Agents
heat, radiation
Types of Heat
dry: incineration (sterilization), dry oven (sterilization)
Types of Radiation
steam under pressure (sterilization), Boiling water, hot water, pasteurization (disinfection)
Types of Chemical agents
gases: (sterilization, or disinfection) liquid: animate (antisepsis), inanimate (disinfection or sterilization)
Types of Mechanical removal
filtration: air (decontamination), liquids (decontamination)
Contaminates that need to be controlled
bacterial vegetative cells and endospores, fungal hyphae and spores, yeasts, protozoan trophozoites and cysts , worms, viruses, prions
Primary Targets of Microbial Control
Microorganisms that can cause infection or spoilage that are constantly present in the external environment.
the growth of microorganisms in the blood and other tissues
any practice that prevents the entry of infectious agents into sterile tissues (gloves, mask, wash hands)
The agents Verses the Process
cide=to kill; stasis and static=to stand still
chemical that destroys bacteria (not endospores)
a chemical that can kill fungal spores, hyphae, and yeasts
a chemical that inactivates viruses
can destroy bacterial endospores
Germicide and Microbicide
chemical agents that microorganisms
prevent growth of bacteria
inhibit fungal growth
materials used to control microorganisms in the body, for example
any cleansing technique that mechanically removes microorganisms to reduce contamination to safe levels
compound such as soap or detergent that sanitizes
may not be free from microbes but are safe for normal use
reduces the numbers of microbes on the human skin (alcohol wipes)
Microbial death
when cell structures become dysfunctional and has irreversible damage, call no longer reproduce in good conditions, logarithmic manner
How Antimicrobial Agents work
blocks its synthesis, digest it, break down its surface( by osmotic shock), makes the cell membrane fragile and sled easily
Protein and Nucleic Acid Synthesis
binding to ribosomes to stop translation, bind irreversibly to DNA preventing transcription and transaction, mutagenic agents
Methods of physical control
heat as an agent of microbial control -generally elevated temperature are mi
Thermal Death Time (TDT)
the shortest length of time required to kill all test microbes are a specified temperature
Thermal Death Point (TDP)
the lowest temperature required to kill all microbes in a sample in 10 minutes
Steam Under Pressure
Pressure raises the temperature combination for sterilization: 15 psi which yields 121*C (will not kill prions)
Non-pressurized Steam
intermittent sterilization or tyndallization- expose to free flowing steam fro 30-60 minutes, incubate fro 23-24 hours, treat again; repeat for 3 days in a row
used to disinfect beverages to kill potential agents of infection and spoilage, two methods: flash method, batch method (does not kill endospores or thermoduric microbes)
Flash Method
expose to 71.6*C fro 15 seconds (does not kill endospores or thermoduric microbes)
Batch Method
expose to 63-66*C fro 30 minutes (does not kill endospores or thermoduric microbes)
Boiling Water
for disinfection and not sterilization, expose materials to boiling water for 30 minutes
Dry Heat: Hot Air and Incineration
reduces microbes to ashes and gas- bunsen burner, tabletop in fared incinerators
Dry Oven
exposure to oven at 150-180*C for 2-4 hours- used for resistant items that do not sterilize well with moist heat
The Effects of Cold and Desiccation
slows growth of cultures and microbes in food, does not kill most microbes; freezing can actually preserve cultures- two types: Desiccation, Lyophilization
dehydration of vegetative cells when directly exposed to normal room air
a combination of freezing and drying; used to preserve microorganisms and other cells in a viable state for many years
energy emitted from atomic activities and dispersed at high velocity. gamma rays, x rays, ultraviolet radiation
Ultraviolet Radiation
damages DNA and kills it, disinfection rather than sterilization, used for hospital rooms , schools, drinking water
Decontamination by Filtration: Techniques for Removing Microbes
removes microbes from air and liquid , fluid strained through a filter with openings large enough for fluid but too small fro microorganisms, filters are thin membranes of cellulose acetate, polycarbonate , and a variety of plastic materials
Applications of Filtration
liquids that cant withstand heat, can decontaminate beverages without altering their flavor, water purification, removing airborne contaminants (HEPA filters)
solutions dissolves in pure alcohol or water- alcohol mixtures
Choosing a Microbicidal Chemical
rapid action even in low concentrations, solubility in water or alcohol and long-term stability, broad-spectrum microbicidal action without being toxic to human and animal tissues, penetration of inanimate surfaces to sustain a cumulative or persistent action, resistance to becoming inactivated by organic matter, noncorrosive or nonstaining properties
Halogen Antimicrobial Chemicals
fluorine, bromine, chlorine, and iodine
Chlorine Compounds
liquid and gaseous chlorine, hypochlorites, chloramines: kills bacteria, endospores, fungi, and viruses (ex. household bleach)
Iodine Compounds
free iodine and iodophors: topical antiseptic, disinfectant
Phenol Coefficient
compares a chemical;s anti-microbic properties to those of phenol: high concentrations-cellular poisons, lower concentrations- inactivate certain critical enzyme and systems (denatures proteins)
Alcohols as Antimicrobial Agents
ethyl and isopropyl are suitable fro microbial control, does not destroy bacteria and spores at room temperature but can destroy resistant vegetative forms- more effective in inactivating enveloped viruses
Alcohol concentration 50-70%
dissolve membrane lipids, disrupt cell surface tension, and compromise membrane integrity
Alcohol concentration 50-90%
denatures proteins through coagulation; but higher concentration does not increase microbial activity
100% Absolute Alcohol
dehydrates cells and inhibits their growth
Hydrogen Peroxide and Related Germicides
germicidal effects are due to the direct and indirect actions of oxygen, oxygen forms hydroxyl free radicals which are highly toxic and reactive to the cells, bactericidal, virucidal, and fungicidal, in higher concentrations it is sporicidal
act as surfactants, anionic detergents have limited microbicidal power, cationic detergents are more effective because the positively charged end binds well with the predominantly negatively charged bacterial surface proteins (destroys membrane)
Heavy Metal Compounds
Hg, Ag,Au, Cu, As, Zn, only Hg and Ag still have significance as germicides, Oligodynamic action, bind onto functional groups of proteins and inactivating them, Drawbacks: can be very toxic to humans, can cause allergic reaction, large quantities of biological fluids and wastes neutralize their actions (pus), microbes develop resistance to them
Oligodynamic Action
having antimicrobial effects in exceedingly small amounts
Aldehydes as Germicides
-CHO functional group on the terminal carbon (gas), Glutaraldehyde and formaldehyde (formalin- aqueous solution)- most often used for microbial control
Dyes as Antimicrobial Agents
certain drugs used in chemotherapy, Two types: Anukube dyes, Yellow acridine dyes (limited applications because they stain and have a narrow spectrum of activity)
Aniline Dyes
crystal violet and malachite green- are very active against gram-positive species of bacteria and various fungi
Yellow Acridine Dyes
acriflavine and proflavine- sometimes used for antisepsis and wound treatment
Acids and Alkalis
very low or high pH can destroy or inhibit microbial cells, limited in applications due to their corrosive, caustic, and hazardous nature (preservatives ex. vinegar)