Control of Microbial Growth Flashcards
why should microbial growth be controlled? (3)
- To prevent spread of pathogens and disease in hospitals, nursing homes, medical offices, homes, etc.
- To prevent food contamination and spoilage at home and elsewhere
- To prevent microbial degradation of materials in industry or in homes
what does sterile mean?
something is sterile if it is free of all viable microorganisms (by removal or killing)
what is sterilization?
process of killing and/or removing all microorganisms in a material or object, including any spores
what is 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 (99.99 %)
what are antisepsis? (3)
- disinfection of living tissues
- antiseptics usually are applied to surface of body, that prevents microorganisms from multiplying; it must not be caustic/toxic to tissues
- can work either by killing or inhibiting their growth or metabolism
What is sanitization/sanitizer? (2)
- reduction of microbial population to levels deemed safe (based on public health standards)
- a sanitizer is an agent that kills 99.99% of all microorganisms in contaminated area (mostly used on inanimate objects)
what is an antimicrobial agent?
- any physical or chemical agent that either kills microorganisms or inhibits their growth
- specifically, there are antibacterial, antiviral, antifungal, antiprotozoal
what does microbiocidal mean
- antimicrobial agent that kills microorganisms
- Specifically it could be bacteriocidal, viricidal, fungicidal
what does microbiostatic mean?
- antimicrobial agent that inhibits the growth of microorganisms
- specifically it could be bacteriostatic, viristatic, fungistatic
slides 6 and 7
take a look
death for microorganisms=………
inability to reproduce (loss of ability to reproduce)
different antimicrobial agents can act in different ways to kill or inhibit. List these different ways (5)
1.) alter physical state of cytoplasm –i.e., damage
2.) ribosomes (cells)
inactivate enzymes – destroy proteins (cells and viruses)
3.) disrupt cell membrane (CM) (cells)
-alter CM permeability
-lyse CM
-affect transport
4.) disrupt cell wall –> lysis (cells)
5.) destroy or damage DNA or damage DNA or RNA (cells and viruses)
are microorganisms killed instantly?
no
Population death usually occurs _____
exponentially
measure of agents killing efficiency is done by…
-decimal reduction time – time to kill 90%
-must be sure persister cells (viable but nonculturable (VBNC) condition) are dead
once they recover they may regain the ability to reproduce and cause infection
(slides 9-11)
what are some Conditions Influencing the Effectiveness of Antimicrobial Agent Activity? (5 things; describe them)
- ) 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
- usually higher concentrations or intensities kill more rapidly
- but relationship is not linear - ) Duration of exposure
- longer exposure –>more organisms killed - ) Local environment
- many factors (e.g., pH, viscosity, and concentration of organic matter) can profoundly impact effectiveness
- organisms in biofilms are physiologically altered and less susceptible to many antimicrobial agents
what are the physical methods for controlling microbial growth?
slides 16 and 17
describe moist heat (2)
-Destroys viruses, fungi, and bacteria
-Degrades nucleic acids, denatures proteins, and disrupts membranes
(chart on slide 18)
describe Steam Sterilization (4)
- 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
slides 20 and 21
too hard to make into a card but know this stuff
what is filtration?
what are filters normally made of?
- 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)
- usually use cellulose or nitrocellulose membrane filters, aka membrane filters for liquids
- other filters, sterilize air -> HEPA (high effiiciency particulate air)
why is filtration used?
-used to sterilize heat sensitive liquids or gasses which cannot be autoclaved (ie, certain medias, enzymes, antibiotics
what are membrane filters?
porous membranes with defined pore sizes that remove microorganisms primarily by physical screening
(slides 23-26)
what are some ways we filter the air? (3)
-Surgical masks
-Cotton plugs on culture vessels
-High-efficiency particulate air (HEPA) filters
(used in laminar flow biological safety cabinets)
describe ionizing radiation
-destroys bacterial endospores
-Gamma irradiation, X-irradiation and electron beams - high energy and cause the production of ions in water (ie, -OH) and other materials
-Ionizing radiation can sterilize (at high doses) or disinfect at lower doses
-damages 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)
(slides 28-30)
describe nonionizing radiation (4)
-Ultraviolet radiation – lower in energy, does not produce ions; can’t penetrate packaging, can’t penetrate into spores; it does kill vegetative cells (260 nm damages DNA primarily)
-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
(slides 32)
what is dessication?
remove H2O from microorganisms: drying vegetative cells stops metabolic activity
what are some examples of dessication?
1.) used to preserve some foods, chemicalss
2.)dry fruits, beef jerkey, bread, dry grains to preserve
2.) 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 indefinately
what is Lyophilization?
(freeze-drying) – dry out material with vacuum at same time lowering the temperature below freezing – for foods, cell lines
-form of dessication
what are 2 other forms of dessication not discussed already? describe them
- ) High salt or sugar –hypertonic environment dessicates microorganisms
ie: jelly, jam, salted fish - ) Smoking (cooking) – heat, drying plus toxic combustion products
slides 36-39
look over 36 for sure
describe phenolics (6)
-Derived from phenol (first disinfectant)
-Commonly used as laboratory and hospital disinfectants
-Denature proteins and disrupt cell membranes
-Effective in presence of organic material, and long lasting
-Disagreeable odor and can cause skin irritation
-Triclosan is used in hand sanitizers
(slide 40 for picture)
describe alcohols
(slides 41 and 42)
Halogens are any of these 5 elements
fluorine, chlorine, bromine, iodine, and astatine
**they are important antimicrobial agents
