Microbiology exam 4

I will get an A

Chemotherapy

Use of chemicals to treat disease

Antimicrobial

Compound that kills or inhibits microorganisms

Antibiotic

Natural compound made by a microorganism that kills or inhibits other microorganisms

Synthetic antimicrobial

Antimicrobial made completely in the laboratory

Semisynthetic antimicrobial

Natural antimicrobial chemically modified in the laboratory

Selective toxicity

Ability of a drug to harm the pathogen more than the host

Magic bullet

Drug that targets a pathogen without harming the host

Paul Ehrlich

Scientist associated with the magic bullet concept

Alexander Fleming

Discovered penicillin in 1928

Penicillin

Antibiotic discovered by Alexander Fleming that targets bacterial cell wall synthesis

Dorothy Hodgkin

Helped determine chemical structures of natural products such as penicillin

Selman Waksman

Discovered important antibiotics from Streptomyces

Streptomyces

Soil actinomycete genus that produces many medically important antibiotics

Streptomycin

Antibiotic from Streptomyces that was important for treating tuberculosis

John Mueller and Jane Hinton

Developed Mueller-Hinton agar

Mueller-Hinton agar

Medium used for Kirby-Bauer disk diffusion testing

Spectrum of activity

Range of microbes affected by an antimicrobial

Narrow-spectrum antimicrobial

Drug that affects only a few specific types of bacteria

Broad-spectrum antimicrobial

Drug that affects many Gram-positive and Gram-negative bacteria

Narrow vs broad spectrum

Narrow affects few bacteria, broad affects many types

Broad-spectrum risk

Can disrupt normal microbiota and lead to superinfection

Superinfection

Secondary infection that occurs after normal microbiota are reduced

Bacteriostatic

Inhibits bacterial growth without directly killing bacteria

Bactericidal

Kills bacteria

Bacteriostatic vs bactericidal

Bacteriostatic inhibits growth, bactericidal kills cells

Synergism

Two drugs together work better than either drug alone

Antagonism

Two drugs together work less effectively than either drug alone

Synergism vs antagonism

Synergism increases drug effect, antagonism decreases drug effect

Kirby-Bauer test

Disk diffusion test used to determine antimicrobial susceptibility

Zone of inhibition

Clear area around an antimicrobial disk where bacteria did not grow

Large zone of inhibition

Bacteria are more likely susceptible to the drug

No zone of inhibition

Bacteria are likely resistant to the drug

Susceptible

Microbe is inhibited by the antimicrobial

Resistant

Microbe is not effectively inhibited by the antimicrobial

Cell wall synthesis inhibitors

Drugs that block peptidoglycan formation

Beta-lactams

Antimicrobials that inhibit peptide cross-linking in peptidoglycan

Penicillin mode of action

Blocks peptidoglycan cross-linking in bacterial cell walls

Vancomycin

Antimicrobial that inhibits cell wall synthesis

Bacitracin

Antimicrobial that blocks steps in peptidoglycan synthesis

Why cell wall drugs have selective toxicity

Humans do not have peptidoglycan cell walls

Cell membrane disruptors

Drugs that damage microbial membranes

Polymyxin B

Antimicrobial that disrupts Gram-negative outer/cell membranes

Daptomycin

Antimicrobial that disrupts bacterial cell membrane function

Protein synthesis inhibitors

Drugs that target bacterial ribosomes

Why ribosomes are antimicrobial targets

Bacterial 70S ribosomes differ from eukaryotic 80S ribosomes

Aminoglycosides

Protein synthesis inhibitors that bind the 30S ribosomal subunit

Streptomycin mode of action

Binds 30S ribosome and causes codon-anticodon mismatching

Tetracyclines

Prevent tRNA from associating with the ribosome

30S ribosome inhibitors

Aminoglycosides and tetracyclines

Metabolic pathway inhibitors

Drugs that block essential microbial metabolic reactions

Sulfamethoxazole

Broad-spectrum drug that blocks the folic acid synthesis pathway

Folic acid pathway

Metabolic target blocked by sulfa drugs

Why sulfa drugs have selective toxicity

Bacteria synthesize folic acid differently than humans

Isoniazid

Narrow-spectrum drug used against Mycobacterium

Isoniazid mode of action

Interferes with mycolic acid synthesis

Mycolic acids

Waxy cell wall components found in Mycobacterium

Nucleic acid synthesis inhibitors

Drugs that block DNA or RNA synthesis

Fluoroquinolones

Drugs that inhibit bacterial DNA gyrase/topoisomerase

Ciprofloxacin

Fluoroquinolone that inhibits DNA synthesis

DNA gyrase

Enzyme needed for bacterial chromosome replication

Rifampin

Drug that inhibits bacterial RNA polymerase

Rifampin mode of action

Blocks bacterial transcription

DNA vs RNA synthesis inhibitors

Fluoroquinolones inhibit DNA gyrase, rifampin inhibits RNA polymerase

Antifungal drugs

Drugs used to treat fungal infections

Miconazole

Imidazole antifungal used for fungal skin infections and yeast infections

Imidazoles

Antifungals that affect fungal sterol metabolism

Antiprotozoan drugs

Drugs used to treat protozoan infections such as malaria

Mefloquine

Antiprotozoan drug used against malaria

Antihelminthic drugs

Drugs used to treat parasitic worm infections

Ivermectin

Antihelminthic used for roundworm diseases such as river blindness

Main antimicrobial targets

Cell wall, cell membrane, ribosomes, metabolic pathways, DNA synthesis, and RNA synthesis

Cell wall vs membrane target

Cell wall drugs block peptidoglycan, membrane drugs disrupt membrane integrity

Antibiotic resistance

Ability of bacteria to survive antibiotic treatment

Persister cells

Bacterial cells that survive antibiotic exposure without necessarily being genetically resistant

Superbug

Bacterium resistant to many different antibiotics

Resistance genes can spread by

Horizontal gene transfer, plasmids, conjugation, and transduction

Antibiotic selective pressure

Antibiotic exposure favors bacteria with resistance traits

Selection and resistance

Antibiotics select for resistant bacteria already present or acquired

Resistance mechanism: drug destruction

Bacterial enzymes destroy or inactivate the antibiotic

Resistance mechanism: reduced uptake

Bacteria prevent the drug from reaching its target

Resistance mechanism: target alteration

Bacteria change the drug target so the drug binds poorly

Resistance mechanism: efflux pump

Bacteria pump the antibiotic out of the cell

Efflux pump

Transport protein that ejects antimicrobial drugs from the cell

Misuse of antibiotics

Practices that increase selection for resistant bacteria

Antibiotic misuse examples

Not finishing prescriptions, using old antibiotics, treating viral diseases, and using antibiotics in animal feed

Antibiotics and viral disease

Antibiotics do not treat viral infections

Not finishing antibiotics

Can leave harder-to-kill bacteria behind and select for resistance

Outdated antibiotics

May be weakened and can contribute to resistance selection

Antibiotics in animal feed

Can select for resistant bacteria in agriculture

Why new antibiotics are hard to develop

Discovery and testing are expensive, profits may be low, and resistance can develop

Last-resort antibiotics

Drugs saved for infections resistant to many other treatments

High-yield resistance idea

Antibiotics do not create resistance on purpose, they select for resistant cells

Broad-spectrum vs superinfection

Broad-spectrum drugs can reduce normal microbiota, superinfection is secondary infection after that disruption