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Cyclic amide functional group which binds to enzymes that cross-link NAM subunits, preventing cross-linkage of NAM subunits, weakening bacterial cell wall & lysing the cell
Beta-lactam ring
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How does inhibition of cell wall synthesis affect bacterial growth?
Prevents bacteria from increasing amt of peptidoglycan but no effect on existing pep layer (so works only on growing cells)
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Example of antibiotic that inhibits synthesis of cell wall
Penicillin, Vancomycin
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Part of antibiotic that is changed when bacteria become resistant
Beta-lactam ring
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Why can taking drugs that inhibit bacterial protein synthesis be harmful to humans too?
The location of protein synthesis is the ribosome, and the size of ribosomes within the mitochondria of proks and euks differ in size, but according to endosymbiotic theory, human mitochondria originated from bacteria. So both the bacterial AND human ribosomes of the mitochondria will be targeted.
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Killing all life forms, including endospores
Sterilization
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Avoiding contamination by technique
Aseptic
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Harsh method of microbial control which is for object use only
Disinfection
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Mild method of microbial control which can be used on skin; bacteria are not killed, just slowed
Antisepsis
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Killing all harmful life forms, not all life forms
Pasteurization
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Form of drug chemicals for all diseases in general, like Rx for heart probs, not only microbial related
Chemotherapeutics
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Suffix -stasis/-static
stopping growth
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Suffix -cide/-cidal
Killing
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Actions of antimicrobial agents (2)
- Alteration of cell wall and cell membrane
- Damage proteins and nucleic acids
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How damaging cell wall/mem kills microbes (3)
- Cell wall integrity damaged and can't prevent bursting due to osmotic effects
- Cytoplasmic membrane cannot control passage of chemicals in/out of cell
- Damage to viral envelope so can't attach
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How damaging proteins/nucleic acids kills microbes
- Extreme heat or chemicals denature protein by altering 3-D shape, so protein is no longer functional
- Chemicals, radiation, heat can produce fatal mutants; also affects RNA
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Controlling microbes by removing water; microbiostatic
Desiccation
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Effects of high temp on microbe
- Denaturation of proteins
- Damage cytoplasmic mem and cell wall
- Damage structure & function of nucleic acids
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Lowest temp that kills all cells in broth in 10 min
Thermal death point
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Time to sterilize volume of liquid at set temp
Thermal death time
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Methods of microbial control using moist heat (4)
- Boiling
- Autoclaving
- Pasteurization
- Ultrahigh-temp sterilization
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Method which kills vegetative cells of bacteria and fungi, protozoan tophozoites, & most viruses w/in 10 min
Boiling
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Method which applies pressure to boiling water which prevents steam from escaping
Autoclaving
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Alternative method which denatures proteins and oxidizes metabolic and structural chemicals, but requires higher temp for longer time than moist heat
Dry heat
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Method of long term preservation of microbial cultures which prevents formation of damaging ice crystals
Lyophilization
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Method of adding salt or sugar to inhibit growth; water in cell is drawn out & cell desiccates; fungi can survive it better than bacteria
Osmotic pressure
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Ionizing vs Non-Ionizing Raditation
-Denatures DNA; used for meats, fresh fruits & veggies
-Causes thymimn dimer by UV light; used for disinfecting air, transparent fluids, object surfaces
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Effects of chemical methods of microbial control varies with: (7)
and is more effective against: (2)
- Temp
- Length of exposure
- Amt of organic matter
- pH
- Concentration
- Age of chemical
- _
- Enveloped viruses
- Vegetative cells of bacteria, fungi, protozoa
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Major categories of chemical control
- Phenols
- Alcohols
- Halogens-algaecide used in pools: bromide or copper
- Oxidizing agents
- Surfactants
- Heavy metals
- Gaseous agents
- Antimicrobics
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What enzyme neutralizes hydrogen peroxide?
Catalase
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Why are oxidizing agents a good way to control microbes?
Oxygen kills proteins; microbial enzymes are oxidized
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Examples of oxidizing agents
Hydrogen peroxide disinfectant & ozone treatment of drinking water (kills cysts)
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Chemical method of control which dislodges bacteria from hands; reduce surface tension of solvents to make them more effective at dissolving solutes
Surfactants
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Chemical method of control which is colorless, tasteless, harmless to humans, and antimicrobial & used in medical settings
Quats = quaternary ammonia compound
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How are heavy metals antimicrobial?
Metal ions alter 3-D shape of protein so no longer functions
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What is used on babies to prevent blindness caused by N. gonorrhoeae?
1% silver nitrate
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What metal inhibits algal growth by interfering w/chlorophyll, so it's used in fish & water storage tanks?
Copper
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3 basic principles of antimicrobial therapy
- 1. Selective toxicity
- 2. Reach site of infection at inhibitory concentrations
- 3. Penetrate & bind to target
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Exploiting differences in structure & metabolism of pathogens and host cells
Selective toxicity
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5 modes of action of antimicrobials- what is inhibited or damaged in microbial cell
- 1. Synthesis of cell wall
- 2. Synthesis of proteins
- 3. Synthesis of nucleic acids
- 4. Damage cell membrane
- 5. Structural Analogues
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Example of disruption of cytoplasmic membrane
Amphotericin B (polyene) attaches to ergosterol in fungal membranes which makes the cell wall leaky
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Drug which disrupts cytoplasmic membranes of Gram-negatives; toxic to human kidneys so given as last resort
Polymyxin
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Drug which binds to particular enzyme involved in a bacterial metoblic pathway
Trimethoprim
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2 drugs which target viral metabolism
Amantadine & rimantadine
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Example of a structural analog- Growth factor analog structurally related to PABA which inhibits microbial growth by inhibiting folate synthesis
Sulfanilamide
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Why are drugs that inhibit bacterial nucleic acid synthesis toxic to human cells also?
Only slight differences b/w prok & euk DNA
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_____ and _____ (2 drugs) act against prok DNA gyrase
Quinolones, fluoroquinolones
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Drug binds to and inhibits action of RNA polymerase during transcription
Rifampin
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General term for drugs that prevent attachment by peptide in viruses
attachment antagonists
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What are the 2 general HIV drugs used
- Reverse Transcriptase Inhibitors: prevents RT enzyme from turning RNA into DNA; ex: AZT
- Protease Inhibitors: protease cuts DNA, so this is inhibited
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Lowest concentration of a substance that inhibits growth of a test organism
Minimum inhibitory concentration (MIC)
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Test which uses antibiotic-impregnated wafers to test whether particular bacteria are susceptible to specific antibiotics
Kirby-Bauer
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3 main categories of side effects
- Toxicity
- Allergies
- Disruption of normal microbiota
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Organs that are especially susceptible to toxicity
- Liver: maintains amt of chemicals in body & removes them
- Kidneys: excrete these chemicals
- Also, nerves
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Resistance by bacteria is acquired 2 ways:
- New mutations of genes
- Exchange of R-plamids
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Multiple resistance is caused by:
exchange of R-plasmids
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Bacteria that are resistant to many drugs
Superbugs
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When bacteria is resistant to one drug, as well as all other drugs that are in the same family
Cross resistance
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Spread of resistant bacteria throughout the community, outside of hospital setting
Community transfer
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2 diseases that are most problematic b/c of microbial resistance
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When 2 drugs work in combination & complement each other
Synergism
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Ways to reduce resistant microbes (2)
- Maintain intake of drug long enough for microbe to be killed off completely, not just until symptoms go away
- Limit use of antimicrobials
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Cellular mechanisms of antibacterial resistance (3)
- Altered target: target site or enzyme become altered
- Altered uptake: can increase impermeability of cell wall by losing porins, or by pumping drugs out of cell (efflux)
- Drug inactivation: producing enzymes which inactivate antibacterial
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2 major types of antifungals
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Antifungal which inhibits cell mem synthesis by blocking biosynthesis of ergosterol
Azoles
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Antifungal which affects function of cell membrane by binding to sterols in it, which causes leakage of cellular compenents & cell death
Polyenes (Amphotericin B)
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Who produces antibiotics in nature (antagonism)
(3)
- Streptomyces: bacteria
- Bacillus: bacteria
- Penicillium: fungi
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