Terminology for Microbial
Control
0 Sterilization- removal or destruction of all forms of
microbial life
0 Commercial sterilization- subjects canned food to
only enough heat to destroy the endospores of
Clostridium botulinum
0 Disinfection- is the destruction of vegetative
pathogens on a surface, usually with chemicals
0 Spores and viruses are not necessarily destroyed
0 Antisepsis- is the chemical disinfection of living
tissue, such as skin or mucous membranes
Terminology for Microbial
Control
0 Asepsis- is the absence of pathogens on an object or area,
as in antiseptic surgery
0 Degerming (degermation)- is the removal of transient
microbes from the skin by mechanical cleansing or by
antiseptic
0 Sanitation- is the reduction of microbial populations on
objects to safe public health levels
0 A biocide or germicide- kills microorganisms
0 Fungicides kill fungi, virucides kill viruses
0 Suffix – cide means the killer of a specified microorganism
0 Suffix- stat used in this way indicates only that the substance
inhibits – for example bacteriostasis
Rate of Microbial Death
0 Bacterial populations killed by heat or chemicals tend to die at
constant rates—for example, 90% every 10 minutes. Plotted
logarithmically, these figures form straight descending lines.
Factors that influence effectiveness of an
antimicrobial treatment:
0 1. Number of microbes
0 -more cells, more time needed to kill all
0 2. Environmental influences
0 -organics often inhibit chemical agents (blood, feces,
vomit)
0 -temperature (disinfectants work better in warm
temperatures)
0 -pH (heat is more effective in an acid pH)
Factors that influence effectiveness of an
antimicrobial treatment:
0 3. Time of exposure
0 -Chemical antimicrobials require a certain amount of
exposure; same agent may need longer on resistant
organisms or spores
0 -with heat, lower temps require longer to kill
0 4. Microbial characteristics
0 -resistance genes, protective structures
0 (e.g.capsules) etc. can inhibit action
0 -bioflims prevent penetration
Type and Age of Microbe
0 Bacteria- susceptible to protein denaturing BUT
mycobacteria is not because of its hydrophobic coat
0 Growth cycles- physiologically young bacteria(early in
growth cycle) susceptible to heat
0 Endospores more resistant to heat the older they get
Properties of Materials:
0 Plastic and rubber- not heat tolerant
0 Cutting edges of surgical instruments- no moisture
or corrosive chemicals
0 Edges can become pitted due to rust and corrosion,
microbes can hide there
0 Fabrics- no chemical disinfection; some too fragile
Actions of Microbial Control
Agents
0 1. Alteration of membrane permeability
0 The plasma membrane controls the passage of nutrients
and wastes into and out of the cell.
0 Damage to the plasma membrane causes:
0 leakage of cellular contents
0 interferes with cell growth.
0 = Leak
lysis, death
Actions of Microbial Control
Agents
0 2. Damage to proteins and Nucleic Acids
0 Enzymes and other proteins are essential for cell function
0 Denatures proteins
0 Enzymes (no reactions)
0 Proteins necessary for bacteria metabolism
0 Hydrogen bonds are broken
0 Covalent bonds are also broken
0 3. Damage to nucleic acids
0 Prevent replication, transcription, or translation
Physical Methods of Microbial
Control
0 -to disinfect objects, food, and solutions common
methods:
0 -Temperature: kill or inhibit growth
0 Heat
0 Low Temps.
0 -Filtration: physical removal
0 -Desiccation: inhibit growth
0 -Osmotic pressure
0 -Radiation: kill
Methods involving Heat:
0 Heat: Common food preservation
0 Denatures protein (changes shape)
0 Thermal Death Point (TDP) = lowest temp at which all
microbes in liquid suspension will be killed in 10 min
0 Thermal Death Time (TDT)= minimal length of time for all
microbes in liquid suspension to be killed at given temp
0 *Both are different for different species due to microbial
variation in heat tolerance
0 Decimal Reduction Time (DRT) = Time in minutes in
which 90% of bacteria at a given temperature will be
killed
Methods involving Heat:
0 1. Moist heat will always kill faster than dry heat at
the same temperature
0 Kills microbes by coagulation of cell proteins
0 A. Boiling (100°C) kills vegetative forms of bacterial
pathogens, many viruses, and fungi within 10 minutes
0 Some mo’s and viruses are resistant
0 Endospores (up to 20 hrs.) and some viruses (30 minutes) survive
boiling for longer times.
Methods involving Heat:
0 B. Autoclaves
0 Moist Heat (steam) and pressure for sterilization
0 Achieves higher temps. than boiling
0 Preferred method (sealed chamber, air is exhausted, and
steam under pressure is injected) for all materials that
can withstand it
0 Kills all organisms and their endospores in about 15 - 20
minutes
0 An autoclave is shown in Figure 1.1 and 1.2
Autoclave
Figure 1.1
Figure 1.2
Autoclave tape
Methods involving Heat:
0 C. Pasteurization
0 Louis Pasteur
0 Mild Heating
0 Kills most pathogens
0 Kills bacteria that cause spoilage
0 Preserves taste in product
0 Lowers bacterial numbers
Methods involving Heat:
0 2. Dry Heat
0 Kills by burning to ashes or by oxidation
0 Flaming- we use this on loops in labs
0 Incineration- burning of contaminated paper
0 Hot air sterilization
0 Hot ovens
0 Mainly used for items not suitable for autoclaving
0 Oily substances, powders
0 Large amounts of glassware
Low Temperature
0 Lower temp inhibits growth, rapid
freezing limits moisture
(bacteriostatic)
0 Refrigerator temperatures (0° to
7°C) slow the metabolic rate of
microbes; however
0 Psychrotrophic species still
grow slowly.
0 Some organisms grow at
temperatures slightly below
freezing, but microbes at the
usual temperatures of freezer
compartments are completely
dormant.
Filtration
0 Liquids
0 Heat- sensitive materials
0 Small pores prevent passage of bacteria
0 High-efficiency particulate air filters
(HEPA)
0 Operating rooms
0 Special clean rooms
0 Masks
0 Used with solutions for: renal dialysis,
heart bypass machines, I.V.’s
0 Catch particles autoclaves miss
Desiccation
0 Microbes require water for growth, and adequately
dried (desiccated) foods will not support their
growth, therefore inhibiting growth
0 Absence of Water
0 Lyophilization- rapid freeze drying
0 Used for blood products , serum products, enzymes,
cultures
0 Avoids ice crystal formation; cells burst when water
expands
Osmotic Pressure
0 High salt or sugar concentrations cause water to leave
the cell; this is an example of osmosis.
0 Generally, molds and yeasts resist osmotic pressures
better than bacteria.
Radiation
0 Ionization Radiation
0 includes X rays, gamma rays, and high-energy electron
beams
0 very short wavelengths and high levels of energy
0 Penetrate deeply
0 Ionizes water to form hydroxyl radicals
0 These destroy cell components, especially DNA
0 Kills: vegetative cells, viruses, most endospores with
adequate exposure
0 Applications: food preservation, sterilization of
pharmaceuticals, medical supplies, mail
Radiation
0 Nonionizing radiation
0 Have a longer wavelength and less energy
0 Ultraviolet (UV) light is the common example
0 Causes the formation of thymine dimers, which interferes with DNA
replication and formation of mRNA.
0 UV lamps are used in hospitals and in food service
0 This method does not sterilize, but it does reduce bacterial growth
0 Penetrating power is very low, so any type of covering protects
microbes.
0 Sunlight has some weak antimicrobial effects (biocidal), but the
wavelengths of sunlight are too long to work well.
Types of Chemical Agents
0 1. Phenols and Phenolics
0 A. Phenol (carbolic acid)
0 Irritating to skin and mucous membranes
0 Bad odor
0 Rarely used today
0 B. Phenolics
0 Chemicals derived from phenol
0 Chemically altered to make it less irritating and more effective
0 Damages plama mbs., inactivates enzymes, denature proteins
0 Often used as disinfectants as they remain active in the presence
of organic matter
Types of Chemical Agents
0 C. Bisphenols
0 contain 2 phenolic groups connected by a bridge
0 Hexachlorophene
0 pHisoHex is an example
0 Prescription antibacterial lotion
0 Used in nurseries to control gram + bacteria
0 Skin bacteria: Staphylococcus and Streptococcus
0 Triclosan
0 Found in antibacterial soap
0 Effective against G+ and G- bacteria
Types of Chemical Agents
0 2. Biguanides
0 Chlorhexidine is an example
0 Hibiclens soap
0 Used on skin and mucous membranes
0 Similar to phenolics but less toxic
0 Disrupt plasma mb.
0 Broad spectrum
0 Effective against most vegetative bacteria and fungi, but not
against endospores and many viruses.
0 Damaging to eyes
Types of Chemical Agents
0 3. Halogens- Effective alone or in compounds
0 A. Iodine (I2)
0 One of the oldest and most effective
0 Very effective on: all bacteria, many endospores, fungi and some
viruses
0 Combines with amino acids in proteins and denatures proteins
0 Alters plasma mb.
0 Negative Aspects
0 Staining
0 Sometimes irritating to the skin
0 May trigger allergies
0 Applications
0 Skin disinfection, wound treatment, water treatment
Types of Chemical Agents
0 B. Chlorine (Cl2)
0 Action: forms hypochlorus acid with water → oxidizing agent,
denatures proteins
0 Broad spectrum: bacteria, fungi, some endospores, some viruses
0 Positive aspects: -effective against all vegetative cells including
Mycobacterium
0 -cost effective
0 Negative aspects: -action inhibited by organics
0 -can form carcinogenic compounds
0 Applications: water and sewage treatment, surface and instrument
disinfection
0 Sodium hypochlorite (NaClO): Is active ingredient of bleach
Types of Chemical Agents
0 C. Alcohols- frequently used for skin degerming
0 Kill bacteria, fungi, but not endospores or naked viruses.
0 Act by denaturing proteins and disrupting cell membranes.
0 Used to mechanically wipe microbes off skin before injections or blood
drawing, instrument disinfection
0 Not good for open wounds, because cause proteins to coagulate and leave bacteria
unharmed
0 Ethanol (ethyl alcohol): Optimum concentration is 70%.
0 Isopropanol: Rubbing alcohol
0 Better disinfectant than ethanol
0 Usual concentration is 90%
0 Also cheaper and less volatile.
Types of Chemical Agents
0 5. Heavy metals and their compounds
0 Oligodynamic action- Very tiny amounts are effective
0 Includes- silver, mercury, copper, zinc
0 Bind sulfur groups causing inactivation or denaturing of proteins
0 A. Silver:
0 1% silver nitrate used to protect infants against gonorrheal eye infections until recently.
0 B. Mercury
0 Organic mercury compounds like merthiolate and
0 mercurochrome are used to disinfect skin wounds.
0 C. Copper
0 Copper sulfate is used to kill algae in pools and fish tanks (fungicidal, algicidal)
0 D. Zinc
0 Used in mouthwashes
0 Superficial fungal and bacterial infections
Types of Chemical Agents
0 6. Surface-Acting Agents
0 Disrupt plasma membrane & denature proteins
0 Decrease surface tension
0 Include soaps and detergents
0 Washing with soap breaks up the oily film that covers skin and allows
microbes and dirt to be washed away
0 7. Quaternary Ammonium Compounds
0 Widely used surface active agents
0 Denature proteins & disrupt cell membranes
0 Cationic (positively charge) detergents
0 Effective against gram positive bacteria, less effective against gram-negative bacteria.
0 Also destroy fungi, amoebas, and enveloped viruses.
Types of Chemical Agents
0 8. Aldehydes
0 These can act very effectively against microbes
0 Inactivate proteins
0 Action: cross-link (thus inactivate) nucleic acids and proteins
0 High activity (sterilization)
0 biocidal including endospores
0 Positive aspects
0 achieves sterilization
0 Negative aspects
0 unstable
0 -toxic
0 -volatile with noxious fumes
0 Applications: specimen preservation (embalming), vaccine sterilization
Types of Chemical Agents
0 9. Gaseous Sterilizers
0 Chemicals that sterilize in a chamber similar to an autoclave.
0 Denature proteins, by replacing functional groups with alkyl
groups
0 A. Ethylene Oxide
0 Kills all microbes and endospores , but requires exposure of 4 to 18
hours.
0 Toxic and explosive in pure form.
0 Highly penetrating.
0 Most hospitals have ethylene oxide chambers to sterilize
mattresses and large equipment.
Types of Chemical Agents
0 10. Peroxygens
0 Oxidize cellular components
0 A. Hydrogen Peroxide
0 Common household antiseptic
0 Not good for open wounds because quickly broken down by catalase
present in human cells
0 used in deep wounds because it releases oxygen as it breaks down, which
makes conditions unfavorable for anaerobic bacteria
0 Effective in disinfection of inanimate objects (kills endospores)
0 Sporicidal at higher temperatures
0 Used by food industry and to disinfect contact lenses
Types of Chemical Agents
0 B. Benzoyl Peroxide
0 Main ingredient in many acne treatments
0 May be used in treating wound infections caused by
anaerobes
0 C. Peracetic Acid
0 One of the most effective liquid sporicides available
0 Sterilant :
0 Kills bacteria and fungi in less than 5 minutes
0 Kills endosporesand viruses within 30 minutes
0 Used widely in disinfection of food and medical
instrument because it does not leave toxic residues