CONTROL OF MICROORGANISMS
CONTROL OF MICROBIAL GROWTH
control by:
1) physical or environmental factors
2) antimicrobial agents
terms used in microbial control
sterilization
cidal
static
disinfectant
antiseptic
sanitation
STERILIZATION
the killing or removal of viable organisms
Sterility indicates free from viable organisms
There are no degrees of sterility
CIDE
to kill
kills the organism that is named
e.g. Bactericidal, fungicidal, etc
STATIC
inactivation or inhibition, but not killing
prevent multiplication of the organism named
e.g. Fungistatic, bacteriostatic
DISENFECTANTS
used on inanimate objects, not living tissues
destroy harmful pathogens in their vegetative state.
can be achieved by physical and chemical antimicrobial procedures
Most are not sporicidal
ANTISEPTIC
an agent applied externally on living tissues to kill or inhibit the growth of organisms
Antiseptics are milder than disinfectants
SANITATION
the removal of organisms from a location by cleaning
does not imply sterilization
PHYSICAL CONTROL OF MICROBIAL GROWTH
Each microorganism species has a specific tolerance range for different environmental
factors
microbial populations can be controlled by modifying environmental conditions
1) filtration
2) high temperature
3) low temperature
4) desiccation
5) radiation
FILTRATION
Passage of liquid or gas through a screen-like material with pores small enough to retain
the microorganisms
filtered air in operating rooms, burn wards and research labs
many IV solutions are sterilized by filtration
High-efficiency particulate air (HEPA) filters
virus or small bacteria may pass through
Surgical face masks
impenetrable wraps, cans, plastic
surgical gloves, gowns
Neucleopore filters
HIGH TEMPERATURE
Temperature influences rates of chemical reactions (metabolic activity)
high temperatures kill microorganisms by denaturing their proteins (enzymes)
Denaturing proteins
HEAT
Thermal death time
The shortest time to kill a suspension of organisms at a specific temperature
Thermal death point (TDP)
The lowest temperature to kill a suspension of organisms in 10 minutes
most widely applicable, effective, economical and easily controlled agent for sterilization
Excessive heat destroys the quality of some foods
dairy products
milk can be sterilized by exposure to 141 degrees centigrade for 2 seconds
produces milk with an indefinite shelf life
MOIST HEAT
Acts by denaturation and coagulation of proteins
more penetrating and more effective than dry heat, also kills endospores
To kill:
Vegetative bacteria, yeast and mold
80º C for 5 -10 minutes
Mold spores
80º C for 30 minutes
Bacterial spores
121º C, 15 lbs/sq. in. pressure for at least 15 minutes
BOILING
Vegetative forms are killed in minutes
boil water at 100 degrees centigrade for 10 minutes will eliminate microorganisms from
water
unreliable sporicidally
STEAM
Steam at atmospheric pressure
Latent heat is released when steam condenses on a cold surface causing proteins
to coagulate
Steam under pressure
121º C is required to kill spores
To achieve this temperature steam must be placed under pressure of at least 15
lbs/sq. in. in an autoclave
PASTEURIZATION
kills vegetative forms while preserving the flavor of foods
holding or batch method
pasteurization is achieved at 62º C for 30 minutes
continuous flow method
pasteurization is achieved at 71.7º C for 15 sec
Prolongs shelf life and ensures safety of the food
pasteurization of milk eliminates
Brucella
Mycobacterium tuberculosis
CANNING
Food preservation method in which foods are heated and sealed in anaerobic conditions
commercial canning typically heats to 121degrees centigrade for 2.5 minutes
home canning exposure is usually 100 degrees centigrade for 10 minutes
DRY HEAT
Kills by oxidation effects
170º C for 2 hours
INCINERATION
Sterilizing inoculating loops
sterilize and dispose paper bags, cups and dressings
LOW TEMPERATURE
Refrigeration or freezing is used to extend shelf life but not indefinitely
freezing precludes microbial growth but does not kill most microorganisms
slows the metabolic rate so they cannot reproduce or synthesize toxins
ice formation can cause damage to certain foods (freezer burn)
slow freezing is most harmful to bacteria because of the formation of ice crystals which
disrupt the cellular and molecular structure
refrozen food products are more prone to microbial spoilage
permit invasion of the food by microorganisms normally restricted to the food surfaces
Refrigeration does not protect against all bacteria
DESICCATION
Removal of water
microbial growth is prevented by eliminating water or keeping surfaces dry
wood is painted to repel water and keep it dry
lack of water prevents microbial growth
may not accelerate death rates
Microorganisms can be preserved by drying
active dried yeast
freeze-drying (lypholization) is a common means of removing water
high vacuum, low temperature is used to allow water to go from the solid frozen
state directly to a gas
does not interrupt the cellular structures from expansion of ice crystals
Mycobacterium tuberculosis
able to withstand desiccation and remain ineffective
Treponema pallidum (syphilis)
extremely sensitive to drying
dies instantly when exposed to air or a dry surface
RADIATION
Acts to disrupt the function and reproduction of DNA
1) ionizing radiation
2) non-ionizing radiation
ionizing radiation is very high energy but not very good penetration
x-ray, gamma ray
plastics, latex, catheters
non-ionizing radiation are lower energy, low penetrating power
Ultraviolet, infrared, microwave
germicidal lamps, sterilize toxins, vaccines and drinking water
do not appear to kill microorganisms directly
absorption of radiation increases temperature which can kill microorganisms
CHEMICAL METHODS OF STERILIZATION
Chemical inhibitors which kill or prevent growth of microorganisms
agents are called disinfectants and germicides
not effective against metabolically dormant stages of microorganisms (endospores, virus)
classified according to application and spectrum of action
1) preservative
2) disinfectant
3) antiseptic
4) antibiotic
PRESERVATIVE
Prevent growth of microorganisms in food
must be FDA approved
some have been shown to be possible carcinogens
red dye #2
classification of preservatives
1) salt and sugar
2) acids
3) nitrates
SALT AND SUGAR
Reduces the amount of available water
alters the osmotic pressure
high salt levels are associated with high blood pressure
sucrose is effective in preserving fruits, candies, condensed milk
ACIDS
Lactic, acetic, propionic, citric, benzoic and sorbic acids
benzoates are used extensively as food preservatives
NITRATES
Added to cured meats to preserve the red meat color
also acts a growth inhibitor of microorganisms
can react with amines (in meat) forming carcinogenic nitrosamines
DISINFECTANT
Antimicrobial substances that kill microorganisms on inanimate objects
generally too harsh to be used on living tissues
may sterilize but will not kill endospores
critical factors of effectiveness
1) concentration
2) contact time
Effective disinfectants
highly germicidal
chemically stable
effective in the presence of organic compounds and metals
ability to penetrate crevices
inexpensive
aesthetic
kill spores
ANTISEPTIC
Kill or prevent growth of microorganisms on living tissues
may be toxic if ingested
Types of antiseptics
1) halogens
2) phenolics
3) detergents
4) alcohols
5) aldehydes
6) acids
7) ethylene oxide
8) hydrogen peroxide
9) ozone
10) dyes
11) heavy metals
HALOGENS
Widely used as disinfectants
chlorine, bromine, iodine
chlorine kills by disrupting membranes and inactivating enzymes
sodium hypochlorite (bleach)
drinking supplies are often chlorinated
prevent spread of cholera and typhoid fever
chlorine is used to disinfect swimming pools
water in air conditioning towers is often chlorinated
prevent Legionnaire’s disease
bromine is used in hot tubs and whirlpools
iodine is used as skin antiseptic and disinfectant
PHENOLICS
acts to disrupt plasma membranes, inactivate enzymes, denature proteins
used in disinfecting floors, walls
Carbolic acid
oldest disinfectant
Joseph Lister
1867 operating room
JOSEPH LISTER
Joseph Lister was British surgeon
discovered antiseptics in 1865
greatly reduced the number of deaths due to operating-room infections
before Lister’s discovery gangrene and other infections were thought to be caused by bad
air
Despite his efforts to keep surgical instruments and rooms clean, the mortality rate
remained close to 50 percent
Believing infection to be caused by airborne dust particles, Lister sprayed the air with
carbolic acid
a chemical that was being used to treat foul-smelling sewers
the germ theory of Louis Pasteur later became known to Lister
Pasteur’s experiments revealed that disease was caused by microbes brought in contact
with human tissue
Lister subsequently reduced surgical mortality to 15 percent by 1869
By applying carbolic acid to instruments and directly to wounds and dressings
Lister's discoveries in antisepsis met initial resistance
by the 1880s antiseptic practices had become widely accepted
PHENOLICS
creosols in carbolic acid are derivatives of coal tar
active ingredient in LYSOL
characteristic smell of hospitals
incorporated into telephone poles and railroad ties to prevent deterioration
Resorcinal is used in treating acne, ringworm, eczema, psoriasis, mouthwash, sore throat
fluids, vaginal deodorants
Hexachlorophene is widely used as a skin disinfectant
non-irritating, high residual action
pHisoHex
shown some evidence of causing neurological damage to developing fetus
surgical scrubs use iodine based soaps
DETERGENTS
Chemicals which contain a hydrophilic end and a hydrophobic end
one end is attracted to water and the other end is attracted to a non-polar organic
molecule
laundry detergents
Surfactants are attracted to the surface of the cell wall
they attach to the surface and weaken the cell wall tension
Surfactants inserting in the lipid layers
disrupt the membrane
create abnormal channels
Disruptions alter permeability and cause leakage both into and out of the cell
ALCOHOLS
Denatures proteins, disrupts membranes, dehydrates microbes
bacteria and virus are inactivated
methanol, ethanol, isopropanol
70% ethanol kills 90% of cutaneous bacteria in two minutes
ALDEHYDES
acts to disrupt metabolic pathways
Formaldehyde
Leaves a residue
must be rinsed after exposure
ACIDS
Acetic acid
often used in surgical dressings
used in burn therapy, vaginal douches
undecylenic acid
effective against fungus causing ringworm and athlete’s foot
Desenex
benzoic acid
Whitfield’s ointment
ETHYLENE OXIDE
Kills all microbes and spores
excellent penetrating ability
sterilize without heat
plastic-ware, mattress, nuts, spices
HYDROGEN PEROXIDE
H2O2
anaerobic bacteria are very susceptible
lack catylase which degrades peroxides
useful against soil-contaminated wounds, surgical implants, contact lens
leaves no residual toxicity after a few minutes
OZONE
Can be used to disinfect drinking water
advantage is that ozone leaves no residue
expensive
DYES
Useful in vaginal tract infections
crystal violet
HEAVY METALS
Copper sulfate
used as an algicide
mercury compounds
act as preservatives in serums and vaccines
mercuric chloride
disinfectant
silver nitrate
prevents transmission of gonococcus infections
zinc salts
anti-dandruff agents
calamine lotion
ANTIBIOTIC
Substances produced by microorganisms that inhibit or kill other microorganisms
used to treat infections inside the body
antimicrobic (synthesized) is now used often instead of antibiotic
used to treat disease in humans and animals
can act as inhibitors of:
cell wall synthesis
cell membrane
protein synthesis
metabolites (Antimetabolites)
INHIBITORS OF CELL WALL SYNTHESIS
Penicillins, cephalosporin, bacitracin,
INHIBITORS OF CELL MEMBRANE
Polyenes, Imidazole
INHIBITORS OF PROTEIN SYNTHESIS
Streptomycin, Tetracyclines, Erythromycin
INHIBITORS OF METABOLITES
Sulfonamides, sulfadiazine
INHIBITORS OF NUCLEIC ACIDS
Quinolones, Rifamycin
FACTORS IN SELECTING DRUGS
1) type of organism
2) Dosage depends on excretion rate, toxicity, age of the patient and underlying illness
Minimal Inhibitory Concentration (MIC ) of the drug
3) Rate of administration
depends on the route of drug absorption
Parenteral route is preferred for severely ill patients
the drug appears rapidly at the site of infection, and at a high concentration
DRUG COMBINATIONS
1) Indifference
When 2 drugs are combined the effect is no greater than either one alone
2) Synergism
Two drugs given together
the effect exceeds the combined activity of each drug given separately
3) In addition
The effect of combined drugs is equal to the sum effect of each drug separately
4) Antagonism
The combined effect of 2 drugs is less than each drug given separately
saliva inoculated pour plate
heavy metals create clear zones indicating growth inhibition
the slightly larger zone surrounding the amalgam reflects the synergistic effect of the two
metals (silver and mercury)
END CONTROL OF MICROOGRANISMS