Transcript Control of Microorganisms Physical and Mechanical

In order to control microorganisms,
you must either:
Kill them
Inhibit their growth
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When various cell structures become dysfunctional and the
entire cell sustains irreversible damage
If a cell can no longer reproduce under ideal environmental
conditions
Death begins when a certain threshold of microbicidal agent
is met, and continues in a logarithmic manner
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Figure 11.1
Alteration of cell walls and
membranes
 Cell wall maintains integrity of
cell
 When disrupted, cannot
prevent cell from bursting
due to osmotic effects
 Cytoplasmic membrane contains
cytoplasm and controls passage
of chemicals into and out of cell
 When damaged, cellular
contents leak out
 Viral envelope responsible for
attachment of virus to target
cell
 Damage to envelope
interrupts viral replication
 Nonenveloped viruses have
greater
tolerance of harsh
Action
of Antimicrobial
Agents
conditions
◦ Damage to proteins and nucleic
acids
 Protein function depends on
3-D shape
 Extreme heat or certain
chemicals denature
proteins
 Chemicals, radiation, and
heat can alter or destroy
nucleic acids
 Can produce fatal mutants
 Can halt protein synthesis
through action on RNA
Action of Antimicrobial A
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Binding to ribosomes
to stop translation
Bind irreversibly to
DNA preventing
transcription and
translation
Mutagenic agents
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Inexpensive
Fast-acting
Stable during storage
Capable of controlling all
microbial growth while being
harmless to humans,
animals, and objects
Ideally, agents should be
◦ Site to be treated
 Harsh chemicals and
extreme heat cannot be
used on humans, animals,
and fragile objects
 Method and level of
microbial control based on
site of medical procedure
Factors Affecting the
Efficacy of Antimicrobial
Methods
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The number of microorganisms
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The nature of the microorganisms in the population
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The temperature and pH of the environment
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The concentration of the agent
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The mechanism of action of the agent
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The presence of solvents, interfering organic matter, and
inhibitors
◦ Relative susceptibility of
microorganisms
 Effectiveness of germicides
classified as high,
intermediate, or low
 High-level kill all
pathogens, including
endospores
 Intermediate-level kill
fungal spores, protozoan
cysts, viruses, and
pathogenic bacteria
Factors Affecting
Efficacy
Low-level killthe
vegetative
bacteria, fungi,
protozoa,
of Antimicrobial
Methods
and some viruses
◦ Phenol coefficient
 Evaluating the efficacy of
disinfectants and
antiseptics by determining
an agent’s ability to
control microbes as a ratio
to that of phenol
 Greater than 1.0 indicates
that agent is more
effective than phenol
Methods
for replaced
Evaluating
 Has been
by
newer methods
Disinfectants
and
Antiseptics
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Heat as an Agent of
Microbial Control
◦ Generally, elevated
temperatures are
microbicidal and lower
temperatures are
microbistatic
◦ Can use moist heat or dry
heat
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Temperature and length of exposure must be
considered
Higher temperatures generally allow shorter exposure
times; lower temperatures generally require longer
exposure times
Thermal death time (TDT): the shortest length of time
required to kill all test microbes at a specified
temperature
Thermal death point (TDP): the lowest temperature
required to kill all microbes in a sample in 10 minutes
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Steam under pressure
◦ Pressure raises the
temperature of steam
◦ Autoclave is used
◦ Most efficient pressuretemperature combination
for sterilization: 15 psi
which yields 121°C
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Used to disinfect beverages
Heat is applied to liquids to kill
potential agents of infection and
spoilage, while retaining the
liquid’s flavor and food value
Special heat exchangers
– Flash method: expose to 71.6°C
for 15 seconds
– Batch method: expose to 63°C
to 66°C for 30 minutes
Does not kill endospores or
thermoduric microbes
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For disinfection and
not sterilization
Expose materials to
boiling water for 30
minutes
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Usually an electric oven
Coils radiate heat within an
enclosed compartment
Exposure to 150°C to 180°C
for 2 to 4 hours
Used for heat-resistant
items that do not sterilize
well with moist heat
effective against endotoxin
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Radiation: energy emitted
from atomic activities and
dispersed at high velocity
through matter or space
For microbial control:
◦ Gamma rays
◦ X rays
◦ Ultraviolet radiation
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Food products
Medical products
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Wavelength approximately
100 nm to 400 nm
Germicidal lamp: 254 nm
Not as penetrating as
ionizing radiation
Powerful tool for destroying
fungal cells and spores,
bacterial vegetative cells,
protozoa, and viruses
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Usually disinfection
rather than
sterilization
Hospital rooms,
operating rooms,
schools, food prep
areas, dental offices
Treat drinking water or
purify liquids
◦ Decrease microbial
metabolism, growth, and
reproduction
 Chemical reactions occur
slower at low
temperatures
 Liquid water not available
◦ Psychrophilic microbes can
multiply in refrigerated
foods
◦ Refrigeration halts growth of
most pathogens
◦ Slow freezing more effective
than quick freezing
◦ Organisms vary in
susceptibility to freezing
◦ Drying inhibits growth
due to removal of water;
only microbiostatic
◦ Lyophilization used for
long = term preservation
of microbial cultures
 Prevents formation of
damaging ice crystals
Dessication and
Lyophilization
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Osmotic Pressure
◦ High concentrations of salt or sugar in foods to
inhibit growth
◦ Cells in a hypertonic solution of salt or sugar lose
water; cell desiccates
◦ Fungi have greater ability than bacteria to survive
hypertonic environments
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Approximately 10,000 different antimicrobial
chemical agents are manufactured
Approximately 1,000 used routinely in health care
and the home
Occur in liquid, gaseous, or solid state
Tinctures: solutions dissolved in pure alcohol or
water-alcohol mixtures
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Effective for removing
microbes from air and liquids
Fluid strained through a filter
with openings large enough for
fluid but too small for
microorganisms
Filters are usually thin
membranes of cellulose
acetate, polycarbonate, and a
variety of plastic materials
Pore size can be controlled and
standardizes
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Prepare liquids that
can’t withstand heat
Can decontaminate
beverages without
altering their flavor
Water purification
Removing airborne
contaminants (HEPA
filters)
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