Lecture 29 and 30 Flashcards
What caused the two dips in the human population?
- Black plague
- Spanish flue (Influenza) affected young people
What was the major cause of death before vaccines and antibiotics?
- A simple cut
- Tooth decay
- Surgery was the last resort
- Parents had to have many children
- Childhood infections
Sterilization
-The process by which all living cells, spores and viruses are destroyed on an object
Disinfection
- The killing or removal of disease-producing organisms from inanimate surfaces
- Pathogens are killed-other microbes may survive
Antisepsis
- Removing pathogens from the surface of living things-skin
- not as toxic as disinfectants
Sanitation
-Reduction of the microbial population to safe levels
Why don’t all members of the targe population succumb instantly?
-Genetics differences, mutations,
duration of exposure
-different growth phases
Cells that are treated with antimicrobials die at what rate?
- They die at an exponential rate
- Exposure to microbes to lethal chemicals does not cause instantaneous death
- The efficiency of an antimicrobial is measured as a decimal reduction time (D-VALUE)
What is the D-value?
- It is the length of time it takes an agent or condition to kills 90% of the population
- Influenced by
1. duration of exposure
2. population size
3. concentration of antimicrobial agent
What are the five physical agents that kill microbes?
- High temperature and pressure
- Pasteurization
- Cold temperatures
- Filtration
- Irradiation
High temperature and pressure
- Moist heat is a more effective killing agent than dry heat
- An autoclave combines moist heat (steam) with high pressure to effectively kill even endospores
Pasteurization
- Louis Pasteur who wanted to save french wine
- Involves heating a food to a specific temperature for a short time to kill Coxiella burnetii the most heat resistant non-spore forming bacterium known.
- Low t/long time-63 for 30min
- Ultra high temperature-134 for 1-2s
Cold temperature
- Most pathogens grow poorly at 4-8C
- refrigeration is an effective way to preserve food
Filtration
- What do you do if your solution is sensitive to heat?
- Filtration
Filtration through 0.2micron pore size filters is effective at removing most cellular microbes
-Doesn’t remove viruses
-Biological safety cabinets use air filtration to protect the worker from bacterial contamination
Irradiation
- Bombardment of food with high energy eletromagnetic radiation
- UV, GAMMA, X-RAY, ELECTRON BEAMS
- It needs to expose microbes to radiation at a dose of that is millions of times higher than typical exposure for a chest x ray
- because the target cell is so smaller
- we need high conc. of irradiation
What about chemical agents?
- Lister introduced the use of phenol as a disinfectant
- phenol can be pretty toxic so it is no longer used
- used as a great benchmark for an effective disinfectant
- Phenol coefficient test
- Higher the number the more effective the disinfectant
- Formalin even though it got a low score it needs a longer exposure time to work
Commercial disinfectants
- Cause damage to proteins, lipids and DNA
- include ethanol, chlorine, iodine and surfactants
- Aldehydes such as formaldehyde are effective.
- Items that cannot be sterilized using liquids or heat may be sterilized using a gas such as ETHYLENE OXIDE or betaproteolactone
- good penetrance and very effective.
Copper
- An antimicrobial metal
- Copper ions are toxic to bacteria
- Incorporating copper into easily contaminated surfaces (doorknobs, beds, handrails) is an effective measure against microbial contamination.
- Fresher water
Biofilms
- Provide resistance against chemical disinfectants
- Extracellular matrix proteins and polysaccharides bind disinfectant, slowing penetration into the biofilm
- This allows time for viable cells inside the biofilm to activate stress response systems
- Mixed species biofilms containing resistant microbes may act as shields for less resistant biofilm members.
What is an antibiotic, who discovered it?
- A compound that kills or inhibits the growth of microorganisms
- produced by a microbial species
- Synthetic agents
- Duchesne, Fleming, Florey, Chain.
How are antibiotic made?
- They are natural products
- Produced by other microbes (bacteria or fungi)
- Particularly in soil
- Probably used to establish territory
- Present in much lower concentrations than are used in medicine.
Main properties of antibiotics
- Selective toxicity
- Must not affect humans or animals
- Should target microbial physiology
- Specific bacterial property which humans don’t have - Broad vs Narrow Spectrum
- The range of species of bacteria affected
- Broad-spectrum is effective against many species
- Narrow spectrum is effective against a few/single species
The problem with A is that they have a lot of off-targets.
What is the difference between bactericidal and bacteriostatic?
- Bactericidal
- Kills the target bacteria - Bacteriostatic
- Inhibits growth, immune system clears the infection
- slows their growth so the immune system can attack them.
What is Minimum Inhibitory Concentration?
- MIC
- the lowest concentration of the antibiotic that will prevent the growth of the organism
- The measure of the relative effectiveness of different antibiotics
- What does will be effective
- Consider achievable concentration in tissues
- Must reach a bright point in a lawn and then it is effective.
What are the mechanisms of action?
-Classic Targets
1. Cell wall synthesis
2. Peptidoglycan
-Nucleic acid synthesis
-DNA AND RNA SYNTHESIS
-Protein synthesis
Metabolism
-Cell membrane
Target: Cell wall synthesis
- Example (Penicillin B-lactam)
- Chemical structure of penicillin resembles the D-ALA-D-Ala component of peptidoglycan (the part that interacts with the penicillin-binding proteins)
- Penicillin-binding proteins bind to penicillin instead of peptidoglycan
- Stops peptidoglycan synthesis
- Penicillin also activates autolysin
Gram negative vs gram positive
- Gram negative thin peptidoglycan wall and an outer membrane
- insensitive to b-lactam
-Gram positive-most effective
Target: Cell Wall synthesis (Vancomycin)
- Glycopeptidde antibiotic that binds to D-Ala-D-Ala
- Prevents the action of the transglycosylases and transpeptidases
- Stops peptidoglycan synthesis
TARGET: DNA Synthesis
-Quinolones
- They bind and inhibit gyrase
- Gyrase functions to relieve the strain on the DNA as it is being unwound by helicase during replication
- Quinolones bind to gyrase and stabilize the complex
Target: RNA Synthesis
- Rifampin
- Binds RNA polymerase to prevent transcription
- Obstructs the exit opening of the RNA polymerase
Target: Protein synthesis
-Streptomycin
- Binds 30S ribosomal subunit
- Interferes with translation by causing misreading of the mRNA resulting in misfolded proteins
- Changes the shape of the ribosomal subunit
Tetracycline
- Also binds the 30S ribosomal subunit
- Prevents attachment of the trna molecules to the mRNA complex stopping translation
What is resistance?
-The ability of microorganisms to resist the effects of antimicrobial agents (one or more) that they were originally sensitive to
Why does resistance happen?
-Antibiotics have been overused and misused
-selective pressure for resistance
-Resistance can occur by:
DNA mutations
Acquiring new genes through horizontal gene transfer
-Conjugation, transformation and transduction
Mechanism 1: Alter the Target
-This strategy involves modifying the target so it no longer binds to or is recognized by the antibiotic
- Vancomycin Resistance in Enterococcus faecium (VRE)
- VRE has genes that produced D-ALA-D-LAC instead of D-ALA-D-ALA
Mechanism 2: Destroy the Antibiotic
- Before it gets into the cell or it causes damage to the cell
- Resistance to B-Lactam antibiotics
- B0lactamase producing E.coli
- The B-lactamase enzyme cleaves the B-lactam ring
Mechanism 3: Modify the Antibiotic
- Modify the antibiotic so it is no longer functional
- Example:
- Streptomycin resistance in Pseudomonas aeuruginosa
- Aminoglycoside phosphotransferase modifies streptomycin so that it cannot bind to the target (30S ribosomal subunit)
- Translation proceeds as usual
- Acetyltransferases and adenyltransferases
Mechanism 4: Pump Antibiotics out of the cell
- Efflux pumps/multidrug exporter
- Functions in the extrusion of substances toxic to the cell
- Multidrug resistance conferred by a proteinaceous pump that spans the cell wall
3 components:
- Inner membrane pump protein
- Accessory protein
- Outer membrane channel
Example: MexXY OprM efflux pump conferring aminoglycoside resistance in Pseudomonas aeruginosa
