Microbiology: UV Damage, Osmolarity, Antiseptics, Antibiotics, Catalase, Negative Staining

What is UV radiation?

Ultraviolet (UV) radiation is electromagnetic radiation that can damage microorganisms.

What is the wavelength of UV radiation that specifically causes DNA damage?

260 nm

What type of DNA damage is caused by UV radiation?

Pyrimidine dimer, specifically thymine dimers.

How does UV radiation affect DNA replication?

UV causes thymine dimers, distorting the DNA helix and disrupting replication.

What is a mutation?

A change in the base sequence of DNA that may potentially be passed to offspring.

How does UV radiation eventually kill microorganisms?

It causes DNA damage leading to distorted DNA, preventing successful replication and causing cell death.

What is osmosis?

Movement of water across a selectively permeable membrane from an area of lower solute concentration to higher solute concentration.

What is the difference between osmosis and diffusion?

Osmosis refers to the movement of water, while diffusion refers to the movement of solutes/molecules.

What happens to a cell in an isotonic solution?

The cell neither swells nor shrinks; there is no net water movement.

What occurs in a hypotonic solution?

Water moves into the cell, which can lead to cell lysis (bursting).

What is the effect of a hypertonic solution on a cell?

Water leaves the cell, causing it to shrink (plasmolysis).

Why does salt preserve food?

High salt concentration creates a hypertonic environment, causing microorganisms to lose water and inhibiting their growth.

What is a halophile?

A microorganism adapted to salty environments.

What is the difference between a halotolerant organism and an obligate halophile?

Halotolerant organisms can grow under saline conditions but do not require salt, while obligate halophiles require salt to grow.

What is an antiseptic?

An antimicrobial chemical used on living tissue.

What is a disinfectant?

An antimicrobial chemical used on nonliving surfaces/objects.

What is the main difference between antiseptics and disinfectants?

Antiseptics are used on living tissue, while disinfectants are used on nonliving surfaces.

What is an antibiotic?

A substance used to inhibit or kill bacteria.

Why are antibiotics ineffective against viral infections?

Antibiotics target specific bacterial structures or processes that viruses do not have.

What is one target of antibiotics in bacteria?

Cell wall synthesis, which can lead to bacterial death if disrupted.

How do antibiotics affect bacterial ribosomes?

Some antibiotics interfere with protein synthesis, disrupting bacterial growth and function.

What is the outcome of disrupted cell wall synthesis in bacteria?

The cell wall weakens, which can lead to cell lysis and bacterial death.

What is the relationship between UV exposure time and microbial death?

Increasing UV exposure generally increases microbial death due to more accumulated DNA damage.

What are the three types of tonicity?

Isotonic, hypotonic, and hypertonic.

What happens to a cell in a hypotonic solution?

The cell swells and may burst due to water influx.

What is the effect of a hypertonic solution on microbial cells?

Microbial cells lose water and shrink, leading to plasmolysis.

What do some antibiotics interfere with in bacteria?

Nucleic-acid synthesis or processes required for replication/transcription.

What is selective toxicity?

An antimicrobial agent can harm microorganisms while causing relatively less harm to the host.

Why can antibiotics selectively target bacteria?

Because bacteria have structures/processes that human cells either don't have or have in sufficiently different forms.

What are the two types of antibiotic action?

Bactericidal (kills bacteria) and bacteriostatic (stops/inhibits bacterial growth).

What is antibiotic resistance?

A bacterium's ability to survive exposure to an antibiotic that would normally inhibit or kill susceptible bacteria.

How can bacteria acquire antibiotic resistance?

Through mutations or acquisition of resistance genes via transformation, transduction, or conjugation.

What is one mechanism by which bacteria resist antibiotics?

Destroying or modifying the antibiotic.

What is the Kirby-Bauer test used for?

To determine bacterial susceptibility to antibiotics.

What indicates greater susceptibility in the Kirby-Bauer test?

A larger zone of inhibition around the antibiotic disk.

What does MIC stand for?

Minimum Inhibitory Concentration.

What is the role of catalase?

To break down hydrogen peroxide (H₂O₂) into water and oxygen.

What is the catalase reaction?

2 H₂O₂ → 2 H₂O + O₂.

What does bubbling indicate in a catalase test?

The presence of catalase (catalase positive).

What is negative staining?

A technique where the background is stained while the cells remain relatively unstained.

What is the purpose of using nigrosin in negative staining?

Nigrosin is an acidic stain that does not enter the cell due to charge repulsion.

What does a negative stain reveal about cells?

Cells appear clear/light against a dark background.

Why is heat-fixing not used in negative staining?

It can dislodge the capsule and change cell size.

What are capsules composed of?

Polysaccharides or polypeptides.

What is the significance of observing cell morphology?

It helps in determining shape, size, and arrangement of bacterial cells.

What does the term 'bactericidal' mean?

Refers to antibiotics that kill bacteria.

What does the term 'bacteriostatic' mean?

Refers to antibiotics that inhibit bacterial growth.

What is the zone of inhibition?

The area where bacterial growth is prevented around an antimicrobial.

What is one way bacteria can reduce drug entry?

By altering their cell membrane to prevent antibiotic entry.

What is an efflux pump?

A mechanism used by bacteria to pump out antibiotics, reducing their effectiveness.

What is the purpose of negative staining in observing capsules?

It allows visualization of the capsule as a clear area surrounding the cell.

What does a catalase-negative result indicate?

Little or no bubbling, meaning the organism lacks detectable catalase.

What is the difference between an antibiotic and an antiseptic?

An antibiotic is used to treat bacterial infections, while an antiseptic is used on living tissue.

What is the difference between an antibiotic and a disinfectant?

An antibiotic treats bacterial infections, while a disinfectant is used on nonliving surfaces.