CONTROL OF MICROBIAL GROWTH
ACTIONS OF MICROBIAL CONTROL AGENTS

Growth – an orderly increase in the quantity of cells


STERILIZATION – killing or removing microorganisms in a
material or an object
Alteration of membrane permeability
o Cellular contents leak
Damage to proteins – functional CHONS
Damage to nucleic acids – genetic information
COMMERCIAL STERILIZATION – Heat treatment destroys
endospores of Clostridium botulinum
PHYSICAL METHODS OF MICROBIAL
CONTROL
DISINFECTION – reducing the number of pathogens to the
point they can no longer cause a disease (vegetative &
nonendospore forming organisms)
A. HEAT
-
DISINFECTANT – applied to INANIMATE objects
ANTISEPTIC – living tissues (antisepsis)

DEGERMING – mechanical removal of most microbes in a
limited area (swab)

SANITIZATION – use of chemical agent to food-handling
equipment to meet public health standards and minimize
chances of disease transmission

SEPSIS – Indicates bacterial contamination
Kills microorganisms by denaturing their
enzymes and other proteins
Heat resistance varies widely among
microbes
Thermal Death Point (TDP) – Lowest temperature
at which all of the microbes in a liquid suspension
will be killed in 10 minutes
Thermal Death Time (TDT) – Minimal length of
time in which all bacteria will be killed at a given
temperature
Decimal Reduction Time (DRT) – Time in minutes at
which 90% of bacteria at a given temperature will
be killed. Used in canning industry.
ASEPSIS – absence of contamination by unwanted organism
ASEPTIC TECHNIQUE – lab techniques used to minimize
contamination
BACTERIOSTATIC AGENT – agent that inhibit the growth of
bacteria, but does not necessarily kill them. Example is
Refrigeration.
GERMICIDE – an agent that kills certain microbes


Bactericide, fungicide, sporicide
Virucide – inactivates viruses
FACTORS INFLUENCE THE EFFECTIVENESS
OF ANTIMICROBIAL TREATMENT
1.
2.
3.
4.
Number of Microbes
Types of Microbes
Environmental Influences
 Organic material (blood, feces, saliva) tends
to inhibit antimicrobials
Time of Exposure
 Chemical antimicrobials & radiation
treatments are more effective at longer
times
 Longer exposure compensates for lower
temperatures
1.
MOIST HEAT
o BOILING
Heat to up to 100 °C or more
Kills vegetative forms of bacteria, most
viruses, fungi and spores within 10 mins to
20 mins
Endospores and some viruses are not easily
destroyed
o
AUTOCLAVE
Chamber which is filled with hot steam
under pressure
Reliable sterilization Mtd :All organisms and
endospores are killed within 15 minutes
1210C at 15 psi for 15 minutes
KILIT AMPULES – biological indication used
to test the efficiency of autoclaves using
Bacillus stearothermophilus. (+)Growth :
turbid, changes from purple to yellow
o PASTEURIZATION
reduces microbes responsible for spoilage
of beverages
a. CLASSIC METHOD
650C for 30 min; used in foods w/o
changing taste
b. HIGH TEMPERATURE TO SHORT TIME
720C for 15 seconds; FLASH
PASTEURIZATION
Quick heating and immediate cooking
c. ULTRA HIGH TEMPERATURE METHOD
1400C for 3 seconds
-
2.
milk can be stored for 2 months at room
temperature without affecting the flavor
o FRACTIONAL
Alternate heating: kills vegetative cells
Incubation: spores germinate
Heating: kills remaining cells
a. Tyndallisation
Fractional/Intermittent/Discontinuous
sterilization
Arnolds sterilizer
100°C for 30 minutes for 3 consecutive
days
b. Inspissation
For culture medium
Principle: thickening through
evaporation
75-80°C for 2 hours for 3 consecutive
days
DRY HEAT
Kills by oxidation effects
Denaturing proteins
o DIRECT FLAMING (simple)
o INCINERATION
(300-4000C) ; common method in treating
infectious waste and infected lab animals
prevent communicable diseases
o HOT AIR STERILIZATION/ HOT AIR OVEN
Require 2 hours at 170°C for sterilization
Dry heat transfers heat less effectively to a cool
body than moist heat because moist heat
involves the use of water which enables the
heat to penetrate faster and better
B. FILTRATION
-
o
o
Removal of microbes by passage of a liquid
or gas through a screen-like material with
small pores
Used to sterilize heat sensitive materials like
vaccines, enzymes, antibiotics, and some
culture medis.
HIGH EFFICIENCY PARTICULATE AIR FILTERS
(HEPA)
- Remove bacteria from air
MEMBRANE FILTERS
- 0.22 and 0.45 Pores / 0.01um pores
- Different pore size
C. LOW TEMPERATURE
o
o
Effect depends on microbe
REFRIGERATION
0 TO 70C
Reduces metabolic rate of most microbes
so they cannot reproduce or produce
toxins
MICROBIOSTATIC
FREEZING
Below 00C
FLASH FREEZING
o Does not kill most microbes
SLOW FREEZING
o More harmful because ice crystals
disrupt cell structure
D. DESSICATION
-
-
E. OSMOTIC PRESSURE
-
-
2.
DEPTH FILTERS
Consists of fibrous granular material
Ex. asbestos
MEMBRANE FILTERS
Different pore size
Increased concentrations of salt & sugar in
substances can increase osmotic pressure
LYOPHILIZATION
o As water leaves the cell, plasma
membrane shrinks away from cell wall.
Cell may not die but usually stops
growing
o Used to preserve bacterial cultures
o Can also kill by (1) change in protein (2)
decrease chemical reaction
Staphylococci spp – on skin are fairly
resistant to high osmotic pressure
Plasmolysis – water will leave the plasma
F. RADIATION
-
TYPES OF FILTERS
1.
Without water, microbes cannot grow or
reproduce, but some may remain viable for
years
Destroy bacteria by disrupting metabolism
-
-
IONIZING RADIATION
o Gamma rays, Xrays, electron beams
o Dislodge electrons from atoms and
form ions
o Cause mutations in DNA and produce
peroxides
o Sterilize pharmaceuticals and
disposable medical supplies
DISADVANTAGES OF IONIZING RADIATION
o Penetrates human tissue
o May cause genetic mutation
NON-IONIZING RADIATION
o More than 1nm
o
-
-
Damages DNA by producing thymine
dimers, which cause mutations
o Used to disinfect ORs, nurseries,
cafeterieas
FREE RADICALS
o Results when radiation goes inside the
cell
o Produce intracellular degradation
o Damages DNA of the cell
DISADVANTAGES OF NON-IONIZING
RADIATION
o Doesn’t penetrate paper, cloth
-
-
Active ingredient of bleach
Act by denaturing proteins and disrupting
cell membranes
Kill bacteria, fungi but not endospores or
naked viruses
Used mechanically wipe microbes off skin
before injections or blood drawing
Not good for open wounds, because it can
cause proteins to coagulate
ETHANOL – drinking alcohol; optimum concentration (20%)
ISOPROPANOL – rubbing, better, cheaper, and less volatile
D. HEAVY METALS
o
o
o
B. HALOGENS
SODIUM HYPOCHLORITE (NaOCl)
More stable than iodine in pure forms
Combination of iodine and natural polymer
(Detergent)
-
o
o
Destroys bacteria by OXIDATION
Effective alone or in compounds
o IODINE
Inhibits protein synthesis
 TINCTURE OF IODINE
 IODOPHORE (betadine, isodine)
-betadine must be in contact for 1-2
mins
o CHLORINE
Recommended by CDC for blood spills
When mixed with water forms
HYDROCHLOROUS ACID
To disinfect drinking water, pools and
sewage
Easily inactivated by organic materials
-
C. ALCOHOLS
A. PHENOLS & PHENOLICS
-
Ideal contact time : 3mins ; 10-30mins
(MYCOBACTERIA)
IODOFORM
CHEMICAL METHODS OF MICROBIAL
CONTROL
-disrupts plasma membrane
o PHENOLS
Rarely used today because it is a skin
irritant and has strong odor
Irritates skin
o PHENOLICS
Chemical derivatives of phenol
Stable, persist for long times after applied
and remain active in the presence of
organic compounds
Cresols : LYSOL
Biphenols : EFFECTIVE AGAINST GRAM (+)
Triclosan : LOTION/ HANDWASH
-
Denatures enzymes and proteins
SILVER
1% AgNO3
MERCURY
Merthiolate, mercurochrome
COPPER
Copper sulfate (shampoo)
SELENIUM
ZINC
Zinc chloride, zinc oxide (lotion)
E. QUATERNARY NH4 COMPOUNDS (QUATS)
- surface active agents; cationic detergents
- also destroy fungi, amoebas, and enveloped viruses
- best against Gram (+) than Gram (-)
- ex: ZEPHIRAN
- ADVANTAGES
- strong antimicrobial action, colorless,
odorless, stable, and nontoxic
-DISADVANTAGES
- organic matter interferes with
effectiveness. Neutralized by soaps and anionic
detergents
F. ALDEHYDES
o
Inactivates proteins
FORMALDEHYDE GAS
Excellent disinfectant
o
FORMALIN (37% aqueous solution)
Irritates mucous membranes, strong odor
GLUTARALDEHYDE
Less irritating, more effective than
formaldehyde
Commonly used to disinfect hospital
instruments
Sterilizing agent for PSEUDOMONAS
2% Glutaraldehyde
o GERMICIDAL in 2mins
o SPORICIDAL in 3-10 mins
o Also effective against HIV and HPV
G. GASEOUS STERILIZERS
-
Denature proteins; by replacing functional
groups with alkyl groups
ETHYLENE OXIDE
o Kills all microbes & endospores
o Toxic and explosive in pure form
o Exposure time (4-18hrs)
H. PEROXYGENS (OXIDIZING AGENTS)
o
o
o
o
-
Oxidize cellular components of treated
microbes
Disrupt membranes and proteins
OZONE
Highly reactive for Oxygen
Used along with chlorine to disinfect water
More effective killing agent than chlorine but
less stable and more expensive
HYDROGEN PEROXIDE
Used as an antiseptic
Effective in disinfection of inanimate objects
Sporicidal at higher temperatures
BLEACH SOLUTION
BENZOYL PEROXIDE
Used in Acne medications (Stap aureus)
PERACETIC ACID
Effective liquid sporocide
Sterilant
Does not leave toxic residues