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CONTROL OF MICROORGANISMS BY PHYSICAL AND CHEMICAL AGENTS
I.
II.
Types of Control
A.
STERILIZATION:
Process by which all living organisms are destroyed or removed from an
object or habitat
B.
Disinfection:
Killing, inhibition or removal of microorganisms that may cause disease
Disinfectants:
Agents (chemical) used to carry out disinfection:
Not safe for use on skin or membrane surfaces:
Does not sterilize:
Viable spores may remain
Used on:
Dishes
Linens
Walls
Floors
Rest rooms
Laboratory benches
C.
Sanitization:
Closely related to disinfection:
Microbial population reduced to levels considered safe by public health
standards:
Sanitizers:
Used to clean dishes and utensils in restaurants
D.
Generalities
Microorganisms occur almost everywhere in the environment
Media is contaminated when it is made
Must be sterilized before use
Equipment must be sterilized before use
Sterile:
Complete absence of living organisms
Sterilization techniques
A.
Autoclave:
Used to sterilize media
Heat under pressure (15 lbs psi) to 121oC (247oF)
Heat to above the boiling point of water to kill any endospores that may be
present
Endospores are much more resistant to heat than vegetative cells
Autoclave is a giant pressure cooker:
Used to prepare canned foods at home and commercially
Food is heated and held under pressure to temperature high enough to kill
endospores
B.
Membrane Filtration
Used to sterilize media that can't be autoclaved
Heat may destroy essential ingredients or cause salts to precipitate out
Filter has holes too small for bacteria to get through
Allows the passage of liquids
Microorganisms trapped on the filter
C.
Hot Air Oven:
Used to sterilize:
Glassware
Hypodermic needles
Pipettes
Test tubes
Petri dishes etc.
Glassware heated at 170oC for at least 90 minutes
Temp. and time enough to kill endospores
D.
Gas Sterilization:
Used for solid materials that can't be heated:
Plastics such as:
Petri dishes
Flasks
Pipettes
Beakers
Surgical gloves
Placed in gas chamber and exposed to toxic gas (ethylene oxide) long
enough to kill all microorganisms present
Gas is removed
Allowed to air for 8 to 10 days
Gets rid of gas which is toxic to humans
E.
Radiation:
X rays and ultra violet are also used to sterilize plastics
F.
III.
Incineration:
Used to dispose of:
Contaminated disposable items
Lab animals
Flame microbiological loops
ANTIMICROBIAL AGENTS
A.
Chemicals used to kill or inhibit the growth of microorganisms
Synthetic or natural products
Cidal agents - kill
B.
Mode of action:
1. Bind tightly to cell structures -can't be removed by washing
2. Cause cell to lyse (bacteriolytic agents)
C.
Germicide
Cidal agent with broad application
a. disinfectants - kill bacteria - not safe for use on skin or
membrane surfaces
Used on:
Dishes
Linens
Walls
Floors
Rest rooms
Laboratory benches
b. Antiseptics - kill bacteria - safe for use on skin and membrane
surfaces
D.
Static agents
Do not kill - but inhibit bacterial growth
Many bind loosely to ribosomes -inhibit protein synthesis
Must be continuously present - if removed organism grows again
Used as food preservatives:
NaNO3 and NaNO2 used as preservatives in cured meats
Prevents growth of Clostridium botulinum
NaNO2 converted to nitrous acid and nitroso cpds. in stomach
(carcinogens)
E.
Antibiotics
Chemical product of biological origin - kills or inhibits microorganisms
Derived from microorganisms
Penicillium penicillin, griseofulvin
Streptomyces Streptomycin, tetracycline, erythromycin, chloramphenicol,
Bacillus
peptide antibiotics (bacitracin, polymyxin)
Penicillin - first antibiotic discovered
Discovered by Sir Alexander Fleming
Acts against actively growing cells
Prevents the synthesis of peptidoglycan
Most effective against Gram positive cells
Eukaryotic cells not affected - don't produce peptidoglycan
Effective against:
Streptococcus pyogenes
Streptococcus pneumoniae
Staphylococcus aureus
Neisseria gonorrhea
Treponema palladium
F.
Strep throat and Scarlet fever
Lobar pneumonia
Toxic shock syndrome
Gonorrhea
Syphilis
Bacterial resistance
Develops as the result of mutation or the acquisition of a resistance
plasmid
Multiple resistances - resistant to more than one antibiotic
Two Types of resistance
1.
Inherent
2.
Acquired