Chapter 8 Flashcards
antimicrobial agent
any physical or chemical agent that either kills microbes or inhibits their growth
Microbiocidial
antimicrobial agent that kils microorganisms, specifically it could be bacteriocidal, viricidial
Microbiostatic
antiomicrobial agent that inhibits the growth of microorganims
Sterile
something is sterile if its free of all viable microorganisms (removal or killing)
Sterilization
process of killing and or removing all microorganisms in a material or object, including any spores
disinfection
the process of decreasing the number of viable microorganisms on an inanimate object/surface to a level that presents a minimum possibility of disease transmission or contamination
antisepsis
disinfection of living tissues
sanitization
reduction of microbial population to levels deemed safe
death for microorganisms
inability to reproduce (loss of ability to reproduce)
Mechanisms of death: alter physical state of cytoplasm, inactivate enzymes, disrupt cell membrane
Conditions influencing effectiveness of antimicrobial agent activity
Population size=larger populations take longer to kill than smaller populations. Population composition=microorganisms differ markedly in their sensitivity to antimicrobial agents. Concentration or intensity of an antimicrobial agent. Duration of exposure. Local environment.
Methods of Controlling Growth
Heat-high temps, one most effective and widely used ways kill microbes.heat denatures proteins, nucleic acids and cell membrane.Moist heat - (steam or hot water) - more effective than dry heat to kill.Sub boiling temperatures (Pasteurization) – mild heating to kill vegetative microbes, but does not sterilize (does not kill spores); disinfection
Methods of controlling growth 2
) Boiling H2O - kill vegetative bacteria, many viruses and fungi; kills some spores (fungal);-doesn’t kill all endospores and some viruses; doesn’t strerilize (cause doesn’t kill all spores). Steam under pressure – heating water under pressure causes it to boil at higher temperatures than at normal atmospheric pressures
Moist Heat
Destroys viruses, fungi, and bacteria
Boiling will not destroy spores and does not sterilize
Degrades nucleic acids, denatures proteins, and disrupts membranes
Steam Sterilization
Carried out above 100oC which requires saturated steam under pressure
Uses an autoclave
Effective against all types of microorganisms (including spores!)
Quality control - includes strips with Geobacillus stearothermophilus
Dry Heat
cause oxidation of organic constituents of cell
not as effective as moist heat - use when want no moisture
1) Oven - need higher temps and longer exposure times – 160-180 oC for 2 – 3 hrs in drying ovens can sterilize
Used for materials that can’t get wet (ie, glassware) but can get hot
2) Incineration – fire; burn materials (medical wastes, animal corpses); sterilizes
Flame loops
Low Temperatures
primarily microbiostatic
Refrigeration - 4oC; for inhibiting microbial growth to extend shelf life; some slow growth by psychrotolerant mesophiles;doesn’t kill most vegetative cells or spores
Standard Freezing -20 oC – stops growth, but doesn’t kill all vegetative cells or spores; extends shelf life or foods or other products
Ultra-low temperature freezing - 80 oC; no microbial growth; more killing; but cells can survive if put into cryoprotectants (ie, glycerol); for very long term storage of cell lines, enzymes, viruses
Liquid Nitrogen- -196 oC; no growth; long term storage
Filtration
pass liquid or gas through screen-like subs w/pores small enough to retain microbes, but let gas or liquid pass thru-filter out bacteria, fungi (0.44 µM or 0.22 µM pore size)
used to sterilize heat sensitive liquids or gasses which cannot be autoclaved (ie, certain medias, enzymes, antibiotics
usually use cellulose or nitrocellulose membrane filters, aka membrane filters for liquids
other filters, sterilize air -> HEPA (high effiiciency particulate air)
Membrane filters
porous membranes with defined pore sizes that remove microorganisms primarily by physical screening
have replaced depth filters for the most part
Radiation
Ionizing Radiation
Gamma irradiation, X-irradiation and electron beams are known as ionizing radiation because they are high energy and cause the production of ions in water (ie, -OH) and other materials. Gamma irradiation, X-irradiation and electron beams can sterilize (at high doses) or disinfect at lower doses.
Ionizing radiation can damage and denature proteins and DNA
Ionizing radiation can penetrate packaging; used to sterilize sealed medical equipment, food, and other things that can’t get hot or wet (ie, autoclaved)
Radiation
Nonionizing Radiation
Ultraviolet radiation – is a type of non ionizing radiation – it is lower in energy so it does not produce ions; it can’t penetrate packaging and it can’t penetrate into spores; it does kill vegetative cells (260 nm damages DNA primarily)
Thus, it is best considered a type of disinfection; UV is useful in decontamination of surfaces
Cannot penetrate solid, opaque, or light-absorbing surfaces
Has been used for water treatment
Dessication
remove H2O from microorganisms: drying vegetative cells stops metabolic activity
used to preserve some foods, chemicalss
dry fruits, beef jerkey, bread, dry grains to preserve
diff. microbes can survive for diff times after dessication
ie, Neisseria gonorrhoeae die w/in min after dessication
-Mycobac.tuberculosis -viable for hours or even days
-endospores viable indefinitely
Lyophilization – (freeze-drying) – dry out material with vacuum at same time lowering the temperature below freezing – for foods, cell lines
High salt or sugar –hypertonic environment dessicates microorganisms
- jelly, jam, salted fish
Smoking (cooking) – heat, drying plus toxic combustion products
Phenolics
Derived from phenol (first disinfectant)
Commonly used as laboratory and hospital disinfectants
Act by denaturing proteins and disrupting cell membranes
Tuberculocidal, effective in presence of organic material, and long lasting
Disagreeable odor and can cause skin irritation
Triclosan is used in hand sanitizers
Alcohols
Among the most widely used disinfectants and antiseptics
methanol - not a good antimicrobial agent (toxic and not very bactericidal)
concentrations of 70%-90% ethanol - are effective against vegetative forms of microbes (prokaryotes and fungi);but doesn’t kill endospores, so doesn’t sterilize
-70% ethyl alcohol used as common skin antiseptic against bacteria and fungi
-bacteriocidal props of alcohols increase with increasing carbon chain, but beyond propyl alcohol, they not too H2O sol, so not used too much as disinfectants
-propyl and isopropyl alcohol (40 -80 % sol) are bactericidal for veg cells
How w alcohols work ? 1) denature proteins; 2) also lipid solvents, so damage lipids in CM and damages CM
Halogens
Any of five elements: fluorine, chlorine, bromine, iodine, and astatine
Important antimicrobial agents
