Download Control of Growth

Control of Growth
Lister
• “ Saved more lives by introduction of his
system than all the wars of the 19th
century together had sacrificed”
• Revolutionized surgery
Definitions
• Sterilization
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Disinfection
Cide vs stasis
Sepsis
Asepsis
Rate of Microbial Death
• Factors that influence effectiveness
– # of microbes
– Presence of organic material interferes with
action of disinfectant
– Temperature
– Time of exposure
– Characteristic of organism
Potential Risk of Infection
• Critical items-direct contact with body tissues
• Semi critical- contact with mucous membranes
but do not penetrate body tissue
• Non critical-contact with intact skin
Actions of Agents
• Damage to membrane-leakage
• Damage to proteins & nucleic acids
– Enzymes
– Nucleic acids -lethal
Daily Life
• Soaps and detergents
• Hand cleansing
Physical Methods of Control
• Heat
– Denatures enzymes
• Moist heat coagulates proteins
– Boiling kills vegetative forms of pathogens
Autoclave
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Uses temperature above boiling water
Steam under pressure
Preferred method unless material is damaged
Higher the pressure, higher the temperature
Need direct contact with steam
All air is evacuated from chamber
15 psi at 121 C for 15 mins
Autoclave
• Prions- protein only
– 134 C for 18 mins
– Soak in 1N NaOH for 1 hour
• Flash sterilization-at 134 C for 3min
– Used for individual instruments
• Packaging
• Use of indicators
– Biological indicators-endospores
Physical Methods of Control
• Pasteurization for heat sensitive products
– Mild heating to kill pathogens
• Dry heat
– Kills by oxidation
– Flaming or hot air
Filtration
• Passage of liquid through screen device
• Pores small enough to retain microbes
• Sterilize heat sensitive materials
• Negative-uses vacuum
• Positive uses pressure
• HEPA hoods & TB rooms
High Pressure
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Can alter structure of proteins
Kill vegetative forms
Endospores relatively resistant
Osmotic pressure reduces availability of
water
Radiation
• Ionizing radiation-less than 1nm
– Gamma rays-cobalt or electron beams
– X rays
• Principle-ionization of water
Radiation
• Nonionizng radiation
– UV light
– Causes pyrimidine dimers
• T-T, T-C
Chemicals
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Considered pesticides
Regulated by EPA
Sterilants-sterilize in 6-10 hrs
High level disinfection do not kill all endospores
• Intermediate level kill bacteria and some viruses
• Low level – general purpose
Microbial Characteristics
• Gram negatives more resistant
– External layer of lipopolysaccharide
– Porins –holes in cell wall, selective
• Mycobacterium-lipids in cell wall
• Viruses without a lipid layer more resistant
Antimicrobial Chemotherapy
History
• Paul Ehrlich- magic bullets
• Chemotherapeutic agent
• Antimicrobial
• Antibiotic
• Synthetic drugs produced in lab
History
• Sulfa drugs- wide spread use in 1935
• Fleming-penicillin in 1928
• Waksman- bacteria from soil- Streptomyces
griseus-streptomycin
Selective Toxicity
• Harm microbe without causing significant
damage to host
• Penicillin
• Streptomycin to tx TB
Drug Administration
• Effective concentration of abx to site of infectionroute
• Topical-infection at body surface
– Athlete’s feet
• Systemic-IV fastest but need hospitalization
• IM intra muscular- peak levels in BS within 15
mins
Drug Administration
• PO- enters GI then into BS
– Painless, but slower and not as effective
– Only fraction enters BS
– Must follow directions
– Great for outpts
Drug Distribution
• Barriers to fast distribution: cell membrane &
proteins
– Prevent entry or bind drug
• CM of cells around BS can prevent free passage
into tissues from blood vessels
Drug Distribution
• Drug binding proteins
• Penicillin: about 65% reversible bound to
albumin
• Race between distribution of drug and
elimination
Elimination of Drugs
• Converted metabolically to another
compound: liver
• Excreted
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Penicillin excreted rapidly via kidneys
Within 90 minutes, most in urine
Take regularly and often or
Resistance can develop
Drug Resistance
• Natural or acquired resistance
• Species lacks target: penicillin attacks
peptidoglycan in cell wall
• Many can’t enter gram negative cell wall
Spectrum of Activity
• Range of microbes the agent acts against
• Broad –gram positive & negative
• Narrow –small number of microbes
• Prevents destruction of normal flora
Acquired Resistance
• Broad spectrum antibiotic changes normal
flora:
• Mutations and genetic exchange among
bacteria
• Antibiotics favor resistant strains but do
not cause genetic changes
Mechanisms
• Alteration of target of drug action
• Alteration of membrane permeability
• Efflux or pumps out the drug
Mechanism
• Development of enzymes: most common
– Destroy or inactivate drug
– B-lactamase-several
Genetics
• Mutations on chromosome
• Develop gradually over years of antibiotic
usage
• Need higher & higher concentrations of
drug
• Eventually becomes useless
Plasmid Borne Genes
• Occurs almost immediate via genetic
recombination
• R plasmids or factors
• Penicillin resistance from beta- lactamase
is an example
Slowing Use of Antibiotics
• 3/4 of all hospital pts receive several courses of
abxs-over kill
• 50 million of 150 million outpatient antibiotics are
unneeded
• Maintain high levels in body long enough to kill
all pathogens
Slow Resistance
• Limit use of antibiotics in animals
• Transmission of drug resistant organisms
from animals to humans
• Some countries drugs sold over the
counter
Drug Dosage
• Depends upon route of administration,
drug distribution, drug elimination
• Effective concentration depends upon
susceptibility of organism to drug
• Kirby-Bauer method
– MIC: minimum inhibitory concentration
– Microbial sensitivities
Kirby Bauer Method
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Disk diffusion method-standardized
Agent spread over MH plate
Disks impregnated with antibiotic
Agent diffuse out, lower MW faster
Zones of inhibition-clear areas around disk
Standardized for S, R I
Targets of Antimicrobial Drugs
• Bactericidal-kills
• Bacteriostatic-inhibits growth
– Phagocytosis & antibodies kill organisms
• Inhibition of cell wall synthesis
Cell Membrane
• Membrane of bacteria & fungi differ somewhat
from animal cell membranes
– Some selective toxicity but not ideal
Inhibition of Protein Synthesis
• Selective toxicity depends upon difference
between ribosomes
• Bacteria-70S (30S & 50S) & animals -80S
– Human 40S & 60S but mitochondria have 70S
– Side effects do occur
Inhibition of Nucleic Acid Synthesis
• Rifampin binds to bacterial RNA
polymerase
– inhibits RNA synthesis- TB
– Colors urine and contacts orange