Controlling Microbial Growth in the Environment
Chemical Methods of Microbial Control Surfactants
"Surface active" chemicals• Reduce surface tension of solvents• Soaps and detergents • Soaps have hydrophilic and hydrophobic ends • Good degerming agents but not antimicrobial • Detergents are positively charged organic surfactants • Quaternary ammonium compounds (Quats) • Low-level disinfectants • Ideal for many medical and industrial applications
Lyophilization at
-196oC for a few minutes while drying Inhibits metabolism Long-term storage of bacterial cultures and drugs
Refrigeration at
0-7oC Inhibits metabolism Preservation of food
Hot Air for
1 hours at 160oC or 1 hours at 171oC Denatures proteins, destroys membranes, oxidizes metabolic compounds Sterilization of water-sensitive materials such as powders, oils, and metals
Incineration for
1 second at >1,000oC Oxidizes everything Sterilization of inoculating loops, flammable contaminated medical waste and diseased carcasses
Ultra-High-Temperature Sterilization for
1-3 seconds at 140oC Denature proteins and destroys membranes Sterilization of dairy product
Boiling for
10 minutes at 100oC Denatures proteins and destroys membranes Disinfection of baby bottles and sanitization of restaurant cookware and tableware
Autoclaving (pressure cooker) for
15 minutes, 121oC, 15 PSI Denatures proteins and destroys membranes Sterilization of medical and laboratory equipment that can tolerate heat and moisture. Pressure cookers used for sterilization of canned foods
Pasteurization for
15 seconds, 72oC Denature proteins and destroys membranes Destruction of all pathogens and most microbes in dairy products, fruit juices, beer and wine
Freezing at
< 0 degrees C - Inhibits metabolism Long-term preservation of foods, drugs and bacterial culture
Which of the following types of radiation is more widely used as an antimicrobial technique? a) Electron beams b) Visible light waves c) Radio waves d) Microwaves
A = Electron beams
Which of the following statements is FALSE concerning antiviral drugs? a) Macrolide drugs block attachment sites on the host cell wall and prevent viruses from entering. b) Drugs that neutralize the acidity of phagolysosomes prevent viral uncoating c) Nucleotide analog can be used to stop microbial replication. d) Drugs containing protease inhibitors retard viral growth by blocking the production of essential viral proteins.
A = Macrolide drugs block attachment sites on the host cell wall and prevent viruses from entering..
In practical terms in everyday use, which of the following statements provides the definition of sterilization a) Sterilization eliminates organisms and their spores or endospores. b) Sterilization eliminates harmful microorganisms and viruses. c) Sterilization eliminates prions d) Sterilization eliminates hyperthermophiles.
A = Sterilization eliminates organisms and their spores or endospores.
Which of the following disinfectants acts against cell membranes? a) phenol b) peracetic acid c) silver nitrate d) glutaraldehyde
A = phenol
Which class of surfactant is most soluble in water? a) quaternary ammonium compounds b) alcohols c) soaps d) peracetic acids
A = quaternary ammonium compounds
Which of the following is an example of sanitization? a) A surgeon washes her hands before surgery. b) A nurse prepares an injection site with an alcohol swab. c) An autoclave is used to prepare nutrient agar. d) Heat is used to kill potential pathogens in apple juice. e) A public toilet is treated with disinfectants.
A public toilet is treated with disinfectants.
Antimicrobial (antibiotics, semisynthetics and synthetics)
Act against cell walls, cell membranes, protein synthesis, DNA replication and transcriptions Intermediate to low. Disinfectants and treatment of infectious disease
Quinolones and fluoroquinolones
Act against prokaryotic DNA gyrase
Sterility Indicators Incubation
After autoclaving, flexible vial is squeezed to break ampule and release medium onto spore strip
Antiviral agents can target unique aspects of viral metabolism
Amantadine, rimantadine, and weak organic bases prevent viral uncoating
Drugs that act against protein synthesis include
Aminoglycosides
Inhibition of Metabolic Pathway
Anti-metabolic agents can be effective when metabolic processes of pathogen and host differ • Quinolones interfere with the metabolism of malaria parasites • Heavy metals inactivate enzymes • Agents that disrupt tubulin polymerization and glucose uptake by many protozoa and parasitic worms • Drugs block activation of viruses • Metabolic antagonists
Antimicrobials
Antibiotics, semisynthetic, and synthetic chemicals • Typically used for treatment of disease • Some used for antimicrobial control outside the body
Enzymes cont.
Antimicrobial enzymes act against microorganisms • Human tears contain lysozyme • Digests peptidoglycan cell wall of bacteria • Enzymes to control microbes in the environment • Lysozyme used to reduce the number of bacteria in cheese • Prionzyme can remove prions on medical instruments
Synthetics
Antimicrobials that are completely synthesized in a lab
Azidothymidine (AXT), Lamivudine, and Efavirenz:
Antiretroviral drugs. • AZT inhibits viral reverse transcriptase • Efavirenz inhibits viral reverse transcriptase • Lamivudine nucleoside analog reverse transcriptase inhibitor
Prevention of Virus Attachment
Attachment antagonists block viral attachment or receptor proteins • CCR5 antagonist block the CCR5 coreceptor on CD4+ cells blocking HIV attachment • New area of antimicrobial drug development
Disruption of Cytoplasmic Membranes
Azoles and allylamines inhibit ergosterol synthesis • Polymyxin disrupts cytoplasmic membranes of Gram-negatives • Toxic to human kidneys • Some anti-parasitic drugs act against cytoplasmic membranes
Which of the following substances or processes kills microorganisms on laboratory surfaces? a) antiseptics b) disinfectants c) degermers d) pasteurization
B = disinfectants
Which of the following chemicals is active against bacterial endospores? a) copper ions b) ethylene oxide c) ethanol d) triclosan
B = ethylene oxide
The endospores of which organism are used as a biological indicator of sterilization?
Bacillus stearothermophilus
Mechanisms of Antimicrobial Action Inhibition of Cell Wall Synthesis
Bacteria have weakened cell walls and eventually lyse
Search for new antibiotics, semisynthetics, and synthetics
Bacteriocins • Design drugs complementary to the shape of microbial proteins to inhibit them
Biosafety Levels - Four levels of safety
Biosafety Level 1 (BSL-1) Biosafety Level 2 (BSL-2) Biosafety Level 3 (BSL-3) Biosafety Level 4 (BSL-4)
Fusion Inhibitors:
Block the HIV envelope from merging with the host CD4+ cell membrane thereby preventing HIV entry into the cell.
Bacitracin
Blocks secretion of NAG and NAM from cytoplasm
Methods of microbial control using moist heat
Boiling • Autoclaving • Pasteurization • High temperature short time (HTST) • Ultrahigh-temperature sterilization • Heating to 135oC for 1-2 sec
Which of the following substances would most effectively inhibit anaerobes? a) phenol b) ethanol c) hydrogen peroxide d) silver e) water
C = Hydrogen Peroxide
A sample of E. coli has been subjected to heat for a specific time, and 90% of the cells have been destroyed. Which of the following terms best describes this event? a) thermal death point b) thermal death time c) decimal reduction time d) none of the above
C = decimal reduction time
Which of the following substances is least toxic to humans? a) carbolic acid b) glutaraldehyde c) hydrogen peroxide d) formalin
C = hydrogen peroxide
CCR5 Antagonists (CCR5s):
CCR5 antagonist block CCR5 coreceptor on the surface of CD4+ cells preventing HIV from entering the cell.
Sterility Indicators
Cap that allows steam to penetrate Flexible plastic vial Nutrient medium containing pH color indicator Endospore strip
Toxicity
Cause of many adverse reactions poorly understood • Drugs may be toxic to kidneys, liver, or nerves • Consideration needed when prescribing drugs to pregnant women
An antimicrobial that inhibits cell wall synthesis will result in
Cells become more susceptible to osmotic pressure
Semisynthetics
Chemically altered antibiotics that are more effective than naturally occurring ones
Antimicrobial agents are drugs that treat microbial infections
Commonly called antibiotics • Examples include penicillin, amoxicillin, ciprofloxacin, azithromycin
Chemical Methods of Microbial Control Aldehydes
Compounds containing terminal -CHO groups • Cross-link functional groups to denature proteins and inactivate nucleic acids • Glutaraldehyde disinfects and sterilizes • Formalin used in embalming and disinfection of rooms and instruments
Develop in hospitals and nursing homes
Constant use of drugs eliminates sensitive bacteria and selects for resistant bacteria
Most common agents prevent
Cross-linkage of NAM subunits
Which of the following items functions most like an autoclave? a) A boiling pan b) An incinerator c) A microwave oven d) A pressure cooker
D = A pressure cooker
Which of the following statements is true concerning the selection of an antimicrobial agent? a) An ideal antimicrobial agent is stable during storage. b) An ideal antimicrobial agent is fast acting. c) Ideal microbial agents do not exist. d) All of the above
D = All of the above
An antimicrobial agent that __________will have the most lasting germicidal effect a) inhibits enzymatic activity b) damages cytoplasmic membranes c) damages cell walls d) damages DNA e) destroys metabolites
D = Damages DNA
Which of the following disinfectants contains alcohol? a) an iodophor b) a quat c) formalin d) a tincture of bromine
D = a tincture of bromine
Which of the following adjectives best describes a surgical procedure that is free of microbial contaminants? a) disinfected b) sanitized c) degermed d) aseptic
D = aseptic
Which antimicrobial chemical has been used to sterilize spacecraft? a) phenol b) alcohol c) heavy metal d) ethylene oxide
D = ethylene oxide
Which of the following substances would most effectively inhibit anaerobes? a) phenol b) silver c) ethanol d) hydrogen peroxide
D = hydrogen peroxide
Which of the following best describes the disinfecting of cafeteria plates? a) pasteurization b) antisepsis c) sterilization d) sanitization
D=Sanitization
Surfactants (soaps and detergints)
Decrease surface tension of water and disrupts cell membranes Low. Soaps: degerming Detergents: antiseptic
Aldehydes (glutaraldehyde/formaldehyd
Denature proteins High Disinfectant and embalming fluid
Enzymes
Denature proteins High Removal of prions on medical instruments
Gaseous agents (ethylene oxide, propylene oxide, and beta-propiolactone)
Denature proteins High Sterilization of heat and water sensitive objects
Heavy Metals (arsenic, zinc, mercury, silver, copper, etc)
Denature proteins Low Fungistats in paints silver nitrate cream: surgical dressings, burn creams and catheters; algicide in water reservoirs, swimming pools and aquariums
Oxidizing agent
Denature proteins by oxidation High Disinfectants, antiseptics for deep wounds, water purification and sterilizations of food-processing and medical equipment
Effects of high temperatures
Denature proteins • Interfere with integrity of cytoplasmic membrane and cell wall • Disrupt structure and function of nucleic acids
Phenolics
Denature proteins; disrupts cell membranes Intermediate to low Disinfectants and antiseptics
Phenol (carbolic acid)
Denature proteins; disrupts cell membranes,Intermediate to low, original surgical antiseptic, now replaced with odorous and injurious phenolics
The preservation of beef jerky from microbial growth relies on which method of microbial control?
Desiccation
Heat can increase the efficacy of antimicrobial agents.
Destabilizing proteins and nucleic acids • Driving antimicrobial agents into and through cells walls, membranes, endospores and cysts
Diffusion and dilution tests that expose pathogens to antimicrobials are designed to
Determine which drug is most effective and determine the amount of a drug to use against a particular pathogen.
Boiling time is critical
Different elevations require different boiling times because as elevation increases the boiling temperature of water decreases
Efficacy
Diffusion susceptibility test • Minimum inhibitory concentration test • Minimum bactericidal concentration test
Selman Waksman (1888-1973)
Discovered 20 antibiotics including streptomycin which was isolated from Streptomyces griseus
Alexander Fleming (1818-1955
Discovered benzylpenicillin (Penicillin G) released from the mold Penicillium notatum
Gerhard Domagk (1895-1964)
Discovered sulfonamidochrysoidine (Prontosil), the first commercially available broad spectrum antibiotic
Isoniazid and ethambutol
Disrupt mycolic acid formation in mycobacterial species
Biosafety Level 3 includes
Double sets of entry doors
Desiccation and Lyophilization
Drying inhibits growth because of removal of water • Lyophilization can also be used for long-term preservation of microbial cultures • Prevents formation of damaging ice crystals
Which is an example of sanitization? a) A surgeon washes her hands before surgery. b) A nurse prepares an injection site with an alcohol swab c) Heat is used to kill potential pathogens in apple juice. d) An autoclave is used to prepare nutrient agar. e) A public toilet is treated with disinfectant.
E = A public toilet is treated with disinfectant
Which of the following statements is true of disinfectants? a) They are effective in destroying endospores. b) They are only effective for short periods of time (seconds to minutes). c) They are used on living tissue. d) They are used for sterilization. e) They are used on inanimate surfaces.
E = They are used on inanimate surfaces.
Which of the following substances would most effectively inhibit anaerobes? a) Silver b) water c) ethanol d) phenol e) hydrogen peroxide
E = hydrogen peroxide
Which of the following is bacteriostatic? a) filtration b) heating in an oven at 171 degrees C for an hour c) flash pasturization d) autoclaving e) freezing below 0 degrees c
E= Freezing below 0 degrees c
Physical Methods of Microbial Control Heat-Related Methods
Effects of high temperatures Thermal death point Thermal death time
Seventy percent alcohol is effective against
Enveloped viruses
Chemotherapeutic agents are drugs that act against disease
Example include insulin, ibuprofen, anticancer drugs
Drugs are chemicals that affect physiology in any manner
Examples include caffeine, alcohol, and tobacco
Osmotic Pressure can
Exposure to hypertonic solutions Inhibits metabolism Preservation of food
Protein function depends on 3-D shape
Extreme heat or certain chemicals denature proteins causing them to lose function
Filtration can
Filter retains microbes (0.2 µm) Physically separates microbes from air and liquids Sterilization of air and heat-sensitive materials. Used in the manufacture of many medicines.
Multiple drug resistant microbes __________
Frequently develop in hospitals
Beta-lactams are most prominent in this group
Functional groups are beta-lactam rings • Beta-lactams bind to enzymes that cross-link NAM subunits
Most susceptible to Antimicrobial agents
Fungi Noneveloped viruses Most gram positive bacteria Enveloped viruses
Broad-spectrum synthetic antimicrobial were discovered by ___________.
Gerhard Domagk
Penicillin's are less effective in the treatment of
Gram-negative bacteria because the outer membrane of Gram-negative bacteria prevents uptake of beta-lactam antibiotics
Biosafety Level 3 (BSL-3)
Handling of microbes in safety cabinets
Handling of microbes in safety cabinets
Handling of microbes that cause severe or fatal disease
Biosafety Level 2 (BSL-2
Handling of moderately hazardous agents
Biosafety Level 1 (BSL-1)
Handling pathogens that do not cause disease in healthy humans
Chemical Methods of Microbial Control Heavy Metals
Heavy-metal ions denature proteins • Low-level bacteriostatic and fungistatic agents • 1% silver nitrate to prevent blindness caused by N. gonorrhoeae • Thimerosal used to preserve vaccines • Copper controls algal growth
Why are sulfonamides effective.
Humans and microbes use PABA differently in their metabolism.
Amphotericin B attaches to ergosterol in fungal membranes
Humans somewhat susceptible because cholesterol similar to ergosterol • Bacteria lack sterols; not susceptible
Hydroxide ions
Hydroxide ions denature other molecules (DNA)
An Etest Combines Elements of Kirby-Bauer and MIC tests also
Identifies the minimal inhibitory concentration. Can be use to quickly determine susceptibility and estimate the MIC for a bacteria
Antiviral Drugs and their Mechanisms of Action
Idoxuridine and Trifluridine Vidarabine acyclovir and Ganciclovir: P Ribavirin Oseltamivir (Tamiflu) Amantadine and Rimantadine: Azidothymidine (AXT), Lamivudine, and Efavirenz: Biological Response Modifiers:
A company that measures an antimicrobial cleaner for kitchen counters claims that its product is effective when used in a 50% water solution. By what means might scientist best verify this statement?
In use test
The Selection of Microbial Control Methods
Inexpensive • Fast-acting • Stable during storage • Selective: Capable of controlling microbial growth, harmless to humans, animals, and objects
Mechanisms of Antimicrobial Action Inhibition of Nucleic Acid Synthesis cont
Inhibitors of RNA polymerase during transcription • Reverse transcriptase inhibitors • Act against an enzyme HIV uses in its replication cycle • Do not harm people because humans lack reverse transcriptase
Amantadine and Rimantadine:
Inhibits viral Uncoating
Integrase Strand Transfer Inhibitor (INSTI)
Integrase strand transfer inhibitors block the HIV enzyme integrase, thus blocking the integration of the HIV DNA into host cell DNA.
Vancomycin and cycloserine
Interfere with bridges that link NAM subunits in many Gram-positives
Biological Response Modifiers:
Interferons, Interleukins, Hematopoietic growth factors.
Chemical Methods of Microbial Control Phenol and Phenolics
Intermediate- to low-level disinfectants • Denature proteins and disrupt cell membranes • Effective in presence of organic matter • Remain active for prolonged time • Commonly used in health care settings, labs, and homes • Have disagreeable odor and possible side effects
Chemical Methods of Microbial Control Halogens
Intermediate-level antimicrobial chemicals • Includes fluorine (F), chlorine (Cl), Bromine (Br), iodine (I) and astatine (At) • Believed to damage enzymes via oxidation or by denaturation • Widely used in numerous applications • Iodine tablets, iodophores, chlorine treatment, bleach, chloramines, and bromine disinfection
Chemical Methods of Microbial Control Alcohols
Intermediate-level disinfectants • Denature proteins and disrupt cytoplasmic membranes • More effective than soap in removing bacteria from hands • Swabbing of skin with 70% ethanol prior to injection
Nonionizing radiation (ultraviolet light with
Irradiation with 260 nm wavelength radiation Formation of thymine dimers, inhibits DNA transcription and replication Disinfection and sterilization of surfaces and of transparent fluids and gasses.
Broad-spectrum effective against many organisms
Killing of normal flora reduces microbial antagonism
Maintain high concentration of drug in patient for sufficient time
Kills all sensitive cells and inhibits others so immune system can destroy. • Remember the MIC and MIB examples
Boiling
Kills vegetative cells of bacteria and fungi, protozoan trophozoites, most viruses Boiling time is critical Endospores, protozoan cysts, and some viruses can survive boiling
Methicillin-Resistant Staphylococcus aureus
MRSA
Which of the following statements is false concerning antiviral drugs?
Macrolide drugs block attachment sites on the host cell wall and prevent viruses from entering.
Paul Ehrlich (1854-1915)
Magic bullets", compounds that selectively targeted a disease-causing organism to which a toxin could be attached for selective delivery of the toxin to the disease causing organism. • Arsphenamine (Salvarsan) the first effective medicinal treatment for syphilis, thereby initiating and also naming the concept of chemotherapy. Unfortunately arsenic based compounds have a high level of toxicity
Retarding Resistance
Maintain high concentration of drug in patient for sufficient time Use antimicrobials only when necessary • Develop new variations of existing drug. Search for new antibiotics, semisynthetics, and synthetics
Multiple Resistance and Cross Resistance
Many pathogens acquire resistance to more than one antibiotic • Common when R-plasmids exchanged • Develop in hospitals and nursing home Superbugs • Cross resistance
Narrow-spectrum effective against few organisms
May allow for secondary or superinfections to develop
Disruption of normal microbiota
May result in secondary infections • Overgrowth of normal flora causes superinfections • Of great concern for hospitalized patients • Clostridium difficile colitis (c diff) is a severe super infection where the normal microbiota is replace by Clostridium difficile often as a result of disruption of the normal intestinal microbiota by antibiotic treatment. C diff is a growing problem and results in approximately 30,000 deaths per year.
Use-dilution Test
Metal cylinders dipped into broth cultures of bacteria • Contaminated cylinder immersed into dilution ofdisinfectant • Cylinders removed, washed, and placed into tube of medium • Most effective agents prevent growth at highest dilution • Current standard test in the U.S. • New standard procedure being developed
Gaseous Agents
Microbicidal and sporicidal gases used in closed chambers to sterilize items • Denature proteins and DNA by cross-linking functional groups • Used in hospitals and dental offices • Disadvantages • Can be hazardous to people • Often highly explosive • Extremely poisonous • Potentially carcinogeni
Semisynthetic derivatives of beta-lactam are
More stable in acidic environments • More readily absorbed • Less susceptible to deactivation Active against a broader spectrum of bacteria
Most resistant to antimicrobial agents
Most Gram negative Bacteria Prions Bacterial Endospores Mycobateria Cysts of protzoa Active-state protozoa (trophozoites)
Resistance by bacteria acquired in two ways
Mutations of chromosomal genes • Acquisition of R-plasmids via transformation, transduction, and conjugation
Sites of Action of HIV Inhibitors Non-nucleoside Reverse Transcriptase Inhibitors (NNRTIs):
NNRTIs bind to and block HIV reverse transcriptase. HIV uses reverse transcriptase to convert its RNA into DNA (reverse transcription. Blocking reverse transcriptase prevents HIV from replicating.
Nucleoside Reverse Transcriptase Inhibitors (NRTI):
NRTIs bind to and block HIV reverse transcriptase. HIV uses reverse transcriptase to convert its RNA into DNA (reverse transcription. Blocking reverse transcriptase prevents HIV from replicatin
Spectrum of Action
Narrow-spectrum effective against few organisms • • Broad-spectrum effective against many organisms
Idoxuridine and Trifluridine:
Nucleoside analogues that inhibit viral DNA replication. Triflurdine is the agent of choice for treatment of herpesvirus keratitis but has significant toxic side effects
Osmotic Pressure
Osmotic pressure high concentrations of salt or sugar in foods can inhibit growth bacterial growth • Cells in hypertonic solutions of salt or sugar lose water adversely affecting protein & membrane structure & function • bacteria have a wide range of tolerance to osmotic pressure with halophiles tolerating & even requiring extreme salt conditions of >9%. Most pathogenic bacteria can only tolerate an osmotic pressure equivalent to that of the human body (0.9%) and are thus can be effectivelycontrolled by high salt. • The drying and salting of food has long been an effective method of food preservation • Fungi have greater ability than bacteria to survive hypertonic environments
Protease Inhibitor (PI)
PI's block HIV protease. By blocking protease, PIs prevent new (immature) HIV from becoming mature viruses that can infect other CD4+ cells.
Which of the following is most closely associated with a beta lactam ring a) Penicillin b) vancomycin c) bacitracin d) isoniazid
Penicillin
Chemical Methods of Microbial Control Oxidizing Agents
Peroxides, ozone, and peracetic acid • Kill by oxidation of microbial enzymes • High-level disinfectants and antiseptics • Hydrogen peroxide can disinfect and sterilize surfaces • Not useful for treating open wounds because of catalase activity • Ozone treatment of drinking water • Peracetic acid is effective sporocide used to sterilize equipment
Autoclaving
Pressure applied to boiling water prevents steam from escaping • Boiling temperature increases as pressure increases • Autoclave conditions - 121oC, 15 psi, 15 m
Halogens (iodine, chlorine, bromine, and fluorine)
Presumably denature proteins Intermediate Disinfectants, antiseptics and water purification
Inhibition of Cell Wall Synthesis Summary
Prevent bacteria from increasing amount of peptidoglycan • Have no effect on existing peptidoglycan layer • Effective only for growing cells
Mechanisms of Resistance
Produce enzyme that destroys or deactivates drug • Slow or prevent entry of drug into the cell • Alter target of drug so it binds less effectively • Alter their metabolic chemistry • Pump antimicrobial drug out of the cell before it can act • Biofilms retard drug diffusion and slow metabolic rate
Chemicals, radiation, and heat can alter/destroy nucleic acid
Produce fatal mutants •Melt DNA and RNA •Halt cell replication through disruption of critical DNA replication functions •Halt protein synthesis through action on RNA or ribosomes
Inhibition of Protein Synthesis
Prokaryotic ribosomes are 70S (30S and 50S) • Eukaryotic ribosomes are 80S (40S and 60S) • Because of structural differences in ribosomes of prokaryotic and eukaryotic ribosome, drugs have been identified that can selectively target prokaryotic ribosomes and selectively inhibit translation in prokaryotic pathogenic organisms • Mitochondria in eukaryotic organisms 70S ribosomes which are similar to prokaryotic ribosomes, thus there is the potential for cross reactivity of some drugs which target prokaryotic ribosomes.
Antimicrobial agents that damage nucleic acids also effect
Protein synthesis
Antimicrobial Agents Damage To
Proteins And Nucleic Acids
Vidarabine acyclovir and Ganciclovir:
Purine nucleoside analogues. General inhibitors of viral DNA synthesis.
Therapeutic Range:
Range of concentrations at which the antimicrobial is both effective and nontoxic.
Sterility Indicators red
Red medium means spores were killed; autoclaved objects are sterile.
Cross resistance is _____________
Resistance to one antimicrobial agent because of its similarity to another antimicrobial agent.
Ionizing radiation (electron beams, gamma rays and x-rays) at
Second to hours of exposure depending upon wavelength of radiation destroys DNA. Sterilization of medical and laboratory equipment and preservation of food
Develop new variations of existing drug
Second-generation drugs • Third-generation drugs
The key to successful chemotherapy is
Selective toxicity
Mechanisms of Antimicrobial Action Inhibition of Cell Wall Synthesis
Semisynthetic derivatives of beta-lactam Overcome resistance of beta-lactamase producing bacteria
Inhibition of Nucleic Acid Synthesis
Several drugs block DNA replication or mRNA transcription this class of drugs is poorly selective and often affect both eukaryotic and prokaryotic cells. Not normally used to treat infections • Used in research and perhaps to slow cancer cell replication
Disruption of Cytoplasmic Membranes
Some drugs form channels through cytoplasmic membrane and damage its integrity • Amphotericin B attaches to ergosterol in fungal membranes
Resistance to Antimicrobial Drugs Development of Antibiotic Resistance
Some pathogens are naturally resistant • Resistance by bacteria acquired in two ways
The Etest measures ________________.
Suceptability of a bacteria to an antibiotic and estimates the Minimum Inhibitory Concentration
Methods For Evaluating Disinfectants And Antiseptics In-Use Test
Swabs taken from objects before and after application of disinfectant or antiseptic • Swabs inoculated into growth medium and incubated • Medium monitored for growth • Accurate determination of proper strength and application procedure for each situation
Use antimicrobial agents in combination
Synergism vs. antagonism • Remember HIV example of combination therapy
An Etest Combines Elements of Kirby-Bauer and MIC tests
Test antibiotic is on the stick as a gradient from high concentration at the top to low concentration at the bottom.
In a Kirby - Bauer Susceptibility test, the presence of a zone of inhibition around disks containing antimicrobial agents indicates
That the microbe does not grow in the presence of the agents.
Selective toxicity,
The ability to kill bacteria without harming the host
The microbial death rate is used to measure ____________
The efficiency of a detergent The efficiency of an antiseptic The efficiency of sanitization techniques
The Microbial Death Rate is used to measure
The efficiency of sanitization techniques. The efficiency of an autoclave The efficiency of a detergent The efficiency of an antiseptic.
Therapeutic Index:
The mathematic comparison of the minimal dose of drug for efficacy/minimal toxic dose of drug.
Pharmacodynamics:
The study of the biochemical and physical effects of drugs on the body or microorganisms and the mechanisms of drug actions; and the relationship between drug concentration and effect
Thermal death point
Thermal death point
The hydrophobic nature of amphotericin B allows it to insert into the plasma membrane adjacent to ergosterol.
This results in the formation of a pore which allows the contents of the cytoplasm to leak out
Thermal death time
Time to sterilize volume of liquid at set temperature
Clinical Considerations in Prescribing Antimicrobial Drugs Safety and Side Effects
Toxicity Allergies Disruption of normal microbiota
Medications administered intravenously can provide much higher and continuous effective drug concentrations than other delivery methods.
True
Dry Heat-Related Methods
Used for materials that cannot be sterilized with moist heat • Denatures proteins and oxidizes metabolic and structural chemicals • Requires higher temperatures for longer time than moist heat • 160oC for 2 hours or 170oC for 1 hour • Incineration is ultimate means of sterilization
Physical Methods of Microbial Control Moist Heat-Related Methods
Used to disinfect, sanitize, and sterilize • Denatures proteins and destroys cytoplasmic membranes • More effective than dry heat
PABA is ____________
Used to synthesize folic acid
Mechanisms of Antimicrobial Action Inhibition of Cell Wall Synthesis
Vancomycin and cycloserine Bacitracin Isoniazid and ethambutol
Desiccation conditions
Varies with amount of water removed Inhibits metabolism Preservation of food
Ribavirin Oseltamivir (Tamiflu):
Viral prodrugs that inhibit viral RNA replication.
Nonionizing Radiation
Wavelengths greater than 1 nm • Excites electrons, causing them to make new covalent bonds • Affects 3-D structure of proteins and nucleic acids • UV light causes pyrimidine dimers in DNA • UV light does not penetrate well • Suitable for disinfecting air, transparent fluids, and surfaces of objects
Ionizing Radiation
Wavelengths shorter than 1 nm • Ejects electrons from atoms to create ions • Ions disrupt hydrogen bonding, oxidize double covalent bonds, and create hydroxide ions • Electron beams • Gamma rays
Sterility Indicators yellow
Yellow medium means spores are viable; autoclaved objects are not sterile.
Protease inhibitors interfere with
an enzyme HIV needs in its replication cycle
If administered together bacteriostatic drugs would act _________ with penicillin.
antagonistically
Some bacteria develop resistance to groups of drugs because the drugs are all structurally similar to each other; this is a phenomenon as ____________.
cross resistance
Which of the following statements is true of disinfectants? a) They are effective in destroying endospores b) They are used on Living tissue C) They are only effective for short periods of time. (sec to min) d) They are use on inanimate surfaces e) They are used for sterilization
d=They are used on inanimate surfaces.
An antimicrobial agent that ________ will have the most lasting germicidal effect.
damages DNA
Refrigeration and Freezing
decrease microbial metabolism, growth, and reproduction • Chemical reactions occur slowly at low temp• Liquid water not available below freezing • Psychrophilic microbes can multiply in refrigerated foods• Refrigeration halts growth of most pathogens cause they're mesophilic organisms • Organisms vary in susceptibility to freezing• Note that under special conditions (liquid nitrogen -196oC), freezing can be a suitable method for long-term viable storage of prokaryotic and eukaryotic cells
Physical removal of microbes without killing them is
degermining
Physical removal of microbes without killing them is ______________.
degermining
Electron beams
effective at killing but do not penetrate well
Seventy-percent alcohol is effective against _______.
enveloped viruses
By understanding the length of time the drug remains at efficacious levels we can
estimate the frequency of dosing to achieve a balance of maintaining the efficacious concentration in the blood and preventing accumulation of drug that could reach toxic levels
Which of the following is bacteriostatic? a) filtration b) autoclaving c) heating in an oven at 171°C for an hour flash pasteurization d) freezing below 0°C
freezing below 0°C
Germicides classified as
high, intermediate, or low effectiveness
High
kill all pathogens, including endospores
Intermediate
kill fungal spores, protozoan cysts, viruses, pathogenic bacteria
Low
kill vegetative bacteria, fungi, protozoa, some viruse
An Etest Combines Elements of Kirby-Bauer and MIC tests The Zone of Inhibition is
largest at the top where the highest concentration of antibiotic is and get smaller as the concentration decreases.
Gamma rays
penetrate well but require hours to kill microbes
Which of the following is most closely associated with a beta-lactam ring?
penicillin
Most drugs that inhibit the synthesis of the cell wall act by ____________.
preventing the cross-linkage of NAM subunits
Antimicrobial agents that damage nucleic acids also affect ________.
protein synthesis
The therapeutic range of an antimicrobial is the _________.
range of concentrations at which the antimicrobial is both effective and non-toxic
Treatment with antibiotic provides
selective pressure for the newly resistant bacteria to become dominant in the population.
Bacterial DNA replication requires the enzyme gyrase, but eukaryotic replication does not. Ciprofloxacin (Cipro) inhibits gyrase activity. This is an example of _____.
selective toxicity
The Microbial Death Rate is used to measure ________________.
the efficiency of an antiseptic the efficiency of a detergent the efficiency of an autoclav
Pharmacokinetics:
the science to ascertain the fate of a drug from the time it is administered to the time it is eliminated from the body.
Routes of Administration
topical application of drug for external infections • Oral route requires no needles and can be self-administered • Intramuscular administration delivers drug via needle into muscle • Intravenous administration delivers drug directly to bloodstream • Know how antimicrobial agent will be distributed to infected tissues
By understanding the concentration of drug in the blood
we can estimate the dose needed to reach a inhibitory concentration.
Nucleotide or nucleoside analogs
• Interfere with function of nucleic acids • Distort shapes of nucleic acid molecules and prevent further replication, transcription, or translation • Most often used against viruses • Effective against rapidly dividing cancer cells