Bio Lab quiz 4

What are antibiotics?

Chemicals produced naturally by living organisms, such as soil bacteria and fungi, that kill or inhibit other microorganisms.

Are antibiotics living organisms?

No. Antibiotics are substances, not living organisms.

Who is credited with discovering penicillin, and when?

Alexander Fleming in 1928.

What is selective toxicity?

When antibiotics kill or inhibit bacteria while leaving eukaryotic host cells unharmed.

Why are antibiotics selectively toxic?

They target structures or processes unique to prokaryotic cells or sufficiently different from those of eukaryotic cells.

What is antibiotic resistance?

The ability of bacteria to survive or grow in the presence of an antibiotic that would normally inhibit or kill them.

What is antibiotic susceptibility?

The ability of an antibiotic to inhibit or kill a particular bacterium.

How do bacteria develop antibiotic resistance through natural selection?

Random mutations create variation; antibiotics select for resistant bacteria, which survive, reproduce, and pass on resistance genes.

What is variation in antibiotic resistance evolution?

Genetic differences among bacteria, including random mutations that may help some survive antibiotic exposure.

What is the selection pressure in antibiotic resistance?

The presence of an antibiotic that favors bacteria able to survive its effects.

What does fitness mean in the context of antibiotic resistance?

The ability to survive, grow, reproduce, and pass on genes in the presence of antibiotics.

How does a beneficial resistance mutation affect a bacterial population over time?

Bacteria with the mutation reproduce more successfully, making the resistance trait more common.

Does an individual bacterium develop a useful mutation because it needs to survive?

No. Mutations occur randomly; natural selection favors mutations that improve survival in a particular environment.

What happens to a mutation that does not improve survival in a particular environment?

It may have a neutral or negative effect and may not become more common in the population.

What is evolution by natural selection?

A change in the frequency of inherited traits in a population over generations because some individuals reproduce more successfully than others.

What are antibiotic resistance mechanisms?

Evolved strategies that allow bacteria to disable or evade the effects of antibiotics.

What are aminoglycoside antibiotics?

A group of antibiotics that bind to bacterial ribosomes and prevent protein synthesis.

Why does inhibiting protein synthesis harm bacteria?

Proteins are required for normal cellular structure and function, so disrupting their production prevents bacteria from functioning properly.

What is the central dogma of molecular biology?

Genetic information flows from DNA to RNA to protein.

What are transferases?

Enzymes that modify antibiotics by transferring chemical groups onto them.

How can transferases cause aminoglycoside resistance?

They chemically modify aminoglycosides, preventing the antibiotics from binding effectively to bacterial ribosomes.

What is acetyltransferase?

A transferase enzyme that attaches an acetyl group to a molecule.

How does acetyltransferase confer aminoglycoside resistance?

It attaches an acetyl group to an aminoglycoside, altering the antibiotic so it can no longer bind effectively to the ribosome.

What happens when an aminoglycoside binds to a susceptible bacterium's ribosome?

It blocks protein synthesis, inhibiting bacterial function.

What happens when a transferase modifies an aminoglycoside?

The antibiotic's structure changes, preventing effective ribosome binding and allowing protein synthesis to continue.

What is a plasmid?

A small, circular DNA molecule in bacteria that replicates independently of chromosomal DNA.

How can bacteria acquire plasmids?

They can acquire plasmids from their environment or receive plasmids introduced in a research laboratory.

What is the role of a plasmid carrying a transferase gene?

It provides genetic instructions for producing an enzyme that modifies certain antibiotics.

How does a transformed E. coli strain differ from the wild-type strain in this experiment?

The transformed strain contains an added plasmid carrying a gene for an acetyltransferase.

Would a transferase gene be expected to provide resistance to every antibiotic?

No. It modifies specific antibiotics; antibiotics with different mechanisms may remain effective.

What is the Kirby-Bauer test?

A laboratory test that assesses bacterial susceptibility to antibiotics using antibiotic-impregnated paper discs on an agar plate.

How is the Kirby-Bauer test performed in principle?

Bacteria are spread across an agar plate, antibiotic discs are placed on the surface, and bacterial growth is assessed after incubation.

What is a zone of inhibition?

The clear area around an antibiotic disc where bacterial growth is inhibited.

What does a zone of inhibition indicate?

It indicates inhibition of bacterial growth, but its size must be interpreted using the appropriate antibiotic-specific standards.

How do you determine whether a bacterium is resistant or susceptible in the Kirby-Bauer test?

Compare the measured zone of inhibition with the established interpretive criteria for that antibiotic.

Does a larger zone of inhibition always prove that one antibiotic is more effective than another?

No. Interpretation depends on the antibiotic-specific standards and testing conditions.

What is the purpose of a control disc in the Kirby-Bauer test?

To provide a comparison showing bacterial growth without an antibiotic.

What is gentamicin?

An aminoglycoside antibiotic.

What is streptomycin?

An aminoglycoside antibiotic.

What is netilmicin?

An aminoglycoside antibiotic.

What is ciprofloxacin?

A non-aminoglycoside antibiotic.

What is tetracycline?

A non-aminoglycoside antibiotic.

What is trimethoprim?

A non-aminoglycoside antibiotic.

Why can aminoglycoside resistance differ from resistance to other antibiotic classes?

The transferase in this experiment modifies certain aminoglycosides, whereas other antibiotic classes have different structures and targets.

What are potential consequences of increasing antibiotic resistance?

Higher healthcare costs, increased mortality, and fewer effective treatment options.

Why is understanding antibiotic resistance important in agriculture?

Animals can develop bacterial infections, and resistance can affect animal health and food security.

How can studying antibiotic resistance help scientists understand ecosystems?

It reveals how natural selection and interactions among bacteria, fungi, and other organisms shape microbial communities.