Microbiology: Module 19

salvarsan

The first "magic bullet" drug, used as a treatment for syphilis, that was discovered in 1909 was _____

bactericidal

______ drugs kill their target bacteria.

tetracycline

antimicrobial drug that targets the ribosome

fungi

Imidazoles are effective against which type of microorganism?

Kirby-Bauer

The _____ disk diffusion test is used at a starting point for determining susceptibility

"magic bullet"

A drug that kills or inhibits a pathogen while causing little harm to the host.

Alexander Fleming in 1928.

Who discovered penicillin, and when?

antibiotics

Antimicrobial substances produced naturally by microorganisms that kill or inhibit bacteria.

semi-synthetic antimicrobials

Natural antibiotics that have been chemically modified to improve their effectiveness or properties.

Dorothy Hodgkin

Who is associated with determining the structure of penicillin?

Selman Waksman, produced by Streptomyces.

Who discovered streptomycin, and what organism produces it?

narrow-spectrum antimicrobial

An antimicrobial effective against only a small group of bacteria.

a broad-spectrum antimicrobial

An antimicrobial effective against many different types of bacteria, including Gram-positive and Gram-negative species.

superinfection

A secondary infection that occurs when broad-spectrum antibiotics eliminate normal microbiota, allowing resistant organisms to overgrow.

• Bacteriostatic: Stops bacterial growth.

• Bactericidal: Kills bacteria.

What is the difference between bacteriostatic and bactericidal drugs?

synergism

When two antimicrobial drugs work better together than either drug alone.

antagonism

When one antimicrobial drug reduces the effectiveness of another.

Kirby-Bauer disk diffusion test

Used to determine whether bacteria are susceptible, intermediate, or resistant to specific antibiotics.

Mueller-Hinton agar

What agar is used for the Kirby-Bauer test?

selective toxicity

The ability of an antimicrobial drug to harm the microorganism without causing significant harm to the host.

Because microorganisms have different structures and processes that drugs can specifically attack.

Why do different antimicrobial drugs have different targets?

• Cell wall synthesis

• Cell membrane

• Protein synthesis

• Nucleic acid synthesis

• Metabolic pathways

What are the five major targets of antibacterial drugs?

Human cells do not have peptidoglycan cell walls, making bacterial cell walls an ideal selective target.

Why are bacterial cell walls good drug targets?

Bacteria have 70S ribosomes, while humans have 80S ribosomes, allowing selective inhibition.

Why is protein synthesis a good target?

Some drugs specifically inhibit bacterial DNA replication or RNA synthesis without strongly affecting human cells.

Why can nucleic acid synthesis be targeted?

Some bacteria make their own folic acid, while humans obtain it from food, allowing drugs to selectively block bacterial metabolism.

Why are metabolic pathways targeted?

Drugs that treat fungal infections.

Example: Imidazoles such as miconazole, used for skin and yeast infections.

What are antifungal drugs? Give an example.

Drugs that treat protozoan infections.

Example: Quinolines such as mefloquine, used to treat malaria.

What are antiprotozoan drugs? Give an example.

Drugs that treat parasitic worm infections.

Example: Avermectins such as ivermectin, used to treat roundworm diseases like river blindness.

What are antihelminthic drugs? Give an example.

To recover unused penicillin because supplies were limited.

Why were patients' urine once filtered?

Mega-Plate experiment

A giant Petri dish used to observe bacteria evolving antibiotic resistance in real time.

Escherichia coli

Which bacterium was used in the Mega-Plate experiment?

Mutations allowed some bacteria to survive, reproduce, and spread into stronger antibiotic zones.

How did bacteria move into areas with higher antibiotic concentrations?

11 days.

How long did it take E. coli to evolve resistance to the highest antibiotic concentration?

Because they reproduce very rapidly (E. coli can divide about every 20 minutes).

Why can bacteria evolve resistance so quickly?

Sensitive bacteria die, while resistant mutants survive and reproduce.

How does natural selection lead to antibiotic resistance?

It selects for resistant bacteria that can spread to animals, crops, and humans.

How does antibiotic use in livestock contribute to resistance?

Overusing antibiotics promotes resistant bacteria and contributes to deaths from untreatable infections.

What warning did Alexander Fleming give about antibiotics?

Unnecessary use may promote antibiotic resistance and disrupt beneficial bacteria.

Why should antibacterial soaps and similar products not be overused?

persister cells

Dormant bacterial cells that survive antibiotic treatment without being genetically resistant.

superbugs

Bacteria that are resistant to multiple antibiotics, making infections difficult to treat.

horizontal gene transfer (HGT)

The movement of genes between bacteria without reproduction, allowing resistance genes to spread rapidly.

Transformation – uptake of free DNA.

Transduction – DNA transferred by bacteriophages.

Conjugation – DNA transferred through direct cell-to-cell contact (pilus).

What are the three methods of horizontal gene transfer?

• Enzymatically destroy or modify the drug.

• Prevent drug entry.

• Pump the drug out (efflux pumps).

• Alter the drug's target.

• Bypass the inhibited metabolic pathway.

What are the main mechanisms bacteria use to resist antibiotics?

selection of resistance

Antibiotics kill susceptible bacteria, allowing resistant bacteria to survive and become the dominant population.

Because resistance is increasing while few new antibiotics are being developed.

Why is antibiotic resistance becoming a greater long-term concern?

Cell wall synthesis

Penicillin’s mode of action

RNA synthesis

Rifampin’s mode of action

Protein synthesis

Streptomycin’s mode of action

On the right side of the plate

In the antibiotic resistance evolution experiment, the highest concentrations of antibiotic were found: