Physical and Chemical Control of Microorganisms
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Transcript Physical and Chemical Control of Microorganisms
Physical and Chemical
Control of
Microorganisms
Controlling Microorganisms
Reduce or destroy undesirable microbes in a given area
Physical
Chemical
Mechanical
Relative Resistance of Microbes
Highest resistance
Moderate resistance
Bacterial endospores & prions
Pseudomonas sp.
Mycobacterium tuberculosis
Staphylococcus aureus
Protozoan cysts
Least resistance
most vegetative cells
fungal spores
enveloped viruses
yeast
protozoan trophozoites
Terms for Microbial Control
Sterile
Sterilization
destroy vegetative pathogens
not endospores
Sanitization
destroys all viable microbes
including viruses & endospores
Disinfection
Inanimate objects free of all life
cleansing technique that mechanically removes microbes
to safe levels
Degerming
removing organisms from an object’s surface
Terms for Microbial Control
Microbicidal agents
Causes microbial death
Bactericide
Sporocide
Fungicide
Viricide
Microbistasis
Prevents microbial growth
Bacteriostatic
Fungistatic
Factors That Affect Death Rate
1.
2.
3.
4.
5.
6.
Number of microbes
Nature of microbes in the population
Temperature & pH of environment
Concentration or dosage of agent
Mode of action of the agent
Presence of solvents, organic matter, or
inhibitors
Cellular Targets of Control
Mode of action of
antimicrobials:
Cell wall
Cell membrane
Cellular synthetic
processes (DNA, RNA)
Proteins
Practical Concerns for Microbial Control
Does the application require sterilization?
Is the item to be reused?
Can the item withstand heat, pressure, radiation,
or chemicals?
Is the method suitable?
Will the agent penetrate to the necessary extent?
Is the method cost- and labor-efficient & is it
safe?
Methods of Physical Control
1.
2.
3.
4.
Heat – Moist verse Dry
Cold temperatures
Desiccation
Radiation
1. Heat (Moist)
Moist heat – use of hot
water or steam
mode of action
denaturation of proteins
destruction of membranes
destruction of DNA
Sterilization
Steam under pressure
Autoclave
15psi/121oC/10-40 min
Steam must reach surface
of item being sterilized!
Autoclave Tape
1. Heat (Moist)
Intermittent sterilization
Disinfection
unpressurized steam
100oC 30-60 min for 3 days
spores, which are unaffected, germinate during
the intervening periods and are subsequently
destroyed
boiling at 100oC for 30 minutes
destroy non-spore-forming pathogens
Pasteurization
1. Heat (Moist)
Pasteurization
heat applied to kill potential agents of
infection and spoilage
without destroying the food flavor or value
63°C - 66°C for 30 minutes
71.6°C for 15 seconds
batch method
flash method
Not sterilization
kills non-spore-forming pathogens and lowers
overall microbe count
does not kill endospores or many nonpathogenic
microbes
1. Heat (Dry)
Dry heat - higher
temperatures than moist
heat
incineration
dry ovens
150-180oC
coagulate proteins
Bunsen burner
600-1200oC
combusts & dehydrates
cells
1870oC
Dehydrates cells and
removes water
Can also sterilize
Thermal Death Measurements
Thermal death time (TDT)
shortest length of time required to kill all
microbes at a specified temperature
Thermal death point (TDP)
lowest temperature required to kill all microbes
in a sample in 10 minutes
2. Cold Temperatures
Microbistatic
slows the growth of
microbes
refrigeration 0-15oC
freezing <0oC
used to preserve food,
media and cultures
3. Desiccation
gradual removal of water from cells
leads to metabolic inhibition
not effective microbial control
many cells retain ability to grow when water is
reintroduced
4. Radiation
1.
Ionizing radiation
2.
deep penetrating power breaks DNA
gamma rays, X-rays, cathode rays
used to sterilize medical supplies & food
products
Nonionizing radiation
little penetrating power to sterilize air, water &
solid surfaces
UV light creates thymine pyrmidines
interfere with replication
Chemical Agents in Microbial Control
Chemicals that sterilize
Chemicals that inhibit deterioration
Disinfectants, antiseptics, sterilants
Degermers, and preservatives
Desirable qualities of chemicals:
rapid action in low concentration
solubility in water or alcohol, stable
broad spectrum, low toxicity
penetrating
noncorrosive and nonstaining
affordable and readily available
Levels of Chemical Decontamination
High-level germicides
Intermediate-level
kill endospores
devices that are not heat sterilizable and intended to be
used in sterile environments (body tissue)
kill fungal spores (not endospores), tubercle bacillus, and
viruses
used to disinfect devices that will come in contact with
mucous membranes but are not invasive
Low-level
eliminate only vegetative bacteria, vegetative fungal cells,
and some viruses
clean surfaces that touch skin but not mucous membranes
Factors that Affect Germicidal
Activity of Chemicals
Nature of the material being treated
Degree of contamination
Time of exposure
Strength and chemical action of the
germicide
Dilutions
Volume of liquid chemical diluted in larger volume
of solvent (water)
Chemical Control Of Microbial Agents
1.
2.
3.
4.
5.
6.
7.
8.
9.
Halogens
Phenolics
Chlorhexidine
Alcohols
Hydrogen peroxide
Detergents & soaps
Heavy metals
Aldehydes
Gases and aerosols
1. Halogens
Chlorine
Cl2, hypochlorites (chlorine bleach), chloramines
Denaturation of proteins by disrupting disulfide bonds
Can be sporicidal
Iodine
I2, iodophors (betadine)
Denature proteins
Can be sporicidal
Milder medical & dental degerming agents, disinfectants,
ointments
2. Phenolics
Disrupt cell
membranes &
precipitating proteins
bactericidal, fungicidal,
virucidal, not sporicidal
Lysol
Triclosan
antibacterial additive
to soaps
3. Chlorhexidine
A surfactant & protein denaturant with
broad microbicidal properties
Not sporicidal
Used as skin degerming agents for
preoperative scrubs, skin cleaning &
burns
4. Alcohols
Ethyl, isopropyl in solutions of 50-90%
Act as surfactants
dissolve membrane lipids and coagulating
proteins of vegetative bacterial cells and fungi
Not sporicidal
Good for enveloped viruses
5. Hydrogen Peroxide
Weak (3%) to strong (35%)
Produce highly reactive hydroxyl-free
radicals that damage protein & DNA while
also decomposing to O2 gas
toxic to anaerobes
Strong solutions are sporicidal
in increasing concentrations
6. Detergents & Soaps
Ammonia compounds
act as surfactants
Soaps
alter membrane
permeability of some
bacteria & fungi
Not sporicidal
mechanically remove
soil and grease
containing microbes
Low concentrations
Only have microbistatic
effects
7. Heavy Metals
Solutions of silver &
mercury
kill vegetative cells in
low concentrations by
inactivating proteins
Oligodynamic action
Not sporicidal
8. Aldehydes
Glutaraldehyde & formaldehyde kill by
alkylating protein & DNA
glutaraldehyde in 2% solution (Cidex)
used as sterilant for heat sensitive
instruments
formaldehyde
disinfectant, preservative, toxicity limits use
9. Gases & Aerosols
Ethylene oxide, propylene oxide,
betapropiolactone & chlorine dioxide
Strong alkylating agents, sporicidal
Mechanical Control
Filtration
physical removal of
microbes
passing a gas or liquid
through filter
organisms above a certain
size trapped in the pores
used to sterilize heat
sensitive liquids & air in
hospital isolation units &
industrial clean rooms
Air can be filtered using a
high-efficiency particulate air
(HEPA) filter
Antimicrobial Therapy
Origins of Antimicrobial Drugs
Antibiotics
Common metabolic products of aerobic sporeforming bacteria & fungi
bacteria in genera Streptomyces & Bacillus
molds in genera Penicillium & Cephalosporium
Inhibiting other microbes in the same
habitat
antibiotic producers have less competition for
nutrients & space
Ideal Antimicrobial Drug…..
Selectively toxic to microbe
Not host cells
Microbicidal, not microbistatic
Soluble
Potent
No antimicrobial resistance
Remains active
Readily delivered to site of infection
Expense
Not allergen
Chemotherapy
Antimicrobial
Antibiotic
Produced by the natural
metabolic processes of
microorganisms
Can inhibit or destroy
other microorganisms
Semisynthetic
Control infection
Chemically modified drugs
in lab
Synthetic
Synthesized compounds in
lab
Chemotherapy
Narrow spectrum
Effective against limited microbial types
Target a specific cell component that is found only in
certain microbes
Broad spectrum
Effective against wide variety microbial types
Target cell components common to most pathogens
Selectively Toxic
Should kill or inhibit microbial cells without
simultaneously damaging host tissues
Complete selective toxicity
Difficult to achieve
Characteristics of the infectious agent become
more similar to the vertebrate host cell
More side effects are seen
Selective toxicity
toxic dose of a drug
therapeutic dose
The concentration causing harm to the host
the concentration eliminating pathogens in the host
Together, the toxic and therapeutic doses are used
to formulate the chemotherapeutic index
Targets of Antimicrobial Drugs
1.
2.
3.
4.
Inhibition of cell wall
synthesis
Inhibition of nucleic
acid synthesis,
structure or function
Inhibition of protein
synthesis
Disruption of cell
membrane structure
or function
1. Bacterial Cell Wall
Most bacterial cell walls
contain peptidoglycan
Penicillin and
cephalosporin block
synthesis of peptidoglycan
Penicillins do not penetrate
the outer membrane
Causes the cell wall to lyse
less effective against
gram-negative bacteria
Broad spectrum penicillins
and cephalosporins
cross the cell walls of
gram-negative bacteria
2. Inhibit Nucleic Acid Synthesis
May block synthesis of
nucleotides, inhibit
replication, or stop
transcription
sulfonamides and
trimethoprim
block enzymes required
for tetrahydrofolate
synthesis
needed for DNA & RNA
synthesis
3. Drugs that Block Protein Synthesis
Ribosomes
Aminoglycosides
(streptomycin,
gentamicin)
eukaryotes differ in size
and structure from
prokaryotes
insert on sites cause
misreading of mRNA
Tetracyclines
block attachment of
tRNA and stop further
synthesis
4. Disrupt Cell Membrane Function
Damaged membrane
These drugs have
specificity for a particular
microbial group
based on differences in
types of lipids in their cell
membranes
Polymyxins
dies from disruption in
metabolism or lysis
interact with phospholipids
cause leakage, particularly
in gram-negative bacteria
Amphotericin B and
nystatin
form complexes with
sterols on fungal
membranes
causes leakage
Drug Resistance
Microorganisms begin to tolerate an
amount of drug that would ordinarily be
inhibitory
due to genetic versatility or variation
intrinsic and acquired
Intrinsic verse Acquired
Intrinsic resistance
Microbe must be resistant to antibiotic that
they produce
Acquired resistance:
1. spontaneous mutations in critical
chromosomal genes
2. acquisition of new genes or sets of genes via
transfer from another species
originates from resistance factors (plasmids) encoded
with drug resistance, transposons
Mechanisms of Drug Resistance
Drug inactivation by
acquired enzymatic activity
penicillinases
Decreased permeability to
drug or increased
elimination of drug from
cell
acquired or mutation
Change in drug receptors
mutation or acquisition
Change in metabolic
patterns
mutation of original
enzyme
Antibiotic Resistance in Medical Community
Improper or excessive use of antibiotics
causes antibiotic resistance
Unnecessarily large antibiotic doses
Antibiotics are available over the counter in
developing countries
Allow resistant strains to overgrow susceptible ones
If resistant strains spread to other patients, a
superinfection occurs
allows for overuse and incorrect use
Antibiotic use is widespread in livestock feeds
can be transmitted to humans through meat
consumption
Side Effects of Drugs
5% of all persons
taking antimicrobials
will experience a
serious adverse
reaction to the drug
Toxicity to organs
Allergic responses
Suppression and
alteration of
microflora
Considerations in Selecting an
Antimicrobial Drug
1. Identify the microorganism causing the
infection
Specimens should be taken before
antimicrobials initiated
2. Test the microorganism’s susceptibility
(sensitivity) to various drugs in vitro
when indicated
(Next slide)
3. Overall medical condition of the patient
Testing for Drug Susceptibility
Essential for groups of
bacteria commonly showing
resistance
Kirby-Bauer disk diffusion test
Dilution tests
Minimum inhibitory
concentration (MIC)
In vitro activity of a drug is not
always correlated with in vivo
effect
smallest concentration of drug that
visibly inhibits growth
If therapy fails, a different drug,
combination of drugs, or different
administration must be considered
Best to chose a drug with
highest level of selectivity but
lowest level toxicity
What about viruses?!?!?
Do not destroy their target pathogen
Instead they inhibit their development
Inhibit virus before enters cell
Viral-associated proteins
Stop it from entering the cell
Stop it from reproducing
Prevent from exiting the cell