Lab 4: Acid Fast Stain and Bacterial Growth Factors

Flashcards covering topics from Lab 4 notes, including Acid Fast Stain, temperature requirements for bacterial growth, water activity and osmotic pressure, and aerotolerance classifications, as well as culture media types. These flashcards are in a question-and-answer format, designed to help students review key concepts for an exam.

What is the primary purpose of the acid-fast stain?

To detect the presence or absence of mycolic acids in the bacterial cell wall.

What are mycolic acids?

Waxy materials composed of fatty acids and fatty alcohols, found in the cell walls of certain bacteria.

Name two bacterial genera known for having mycolic acids in their cell walls.

Mycobacterium and Nocardia.

How do mycolic acids contribute to bacterial virulence?

They allow bacteria to survive in phagocytes and contribute to resistance to disinfectants and antimicrobial therapy.

What common infection does Mycobacterium tuberculosis cause?

Tuberculosis (TB).

What are re-emerging diseases?

Diseases that reappear after they have been on a significant decline.

Why is Mycobacterium tuberculosis becoming a health issue again?

Due to drug resistance to multiple antibiotics.

What is the typical treatment regimen for tuberculosis?

A combination of antibiotics taken for 6-12 months.

What trend has been observed in TB cases in the United States since 2021?

An increase in TB case counts and rates after nearly three decades of decline.

What factors are believed to contribute to the recent increase in TB cases in the U.S.?

Recovery from pandemic-related health care disruptions, increases in post-pandemic travel and migration, and outbreaks.

What is the primary dye used in the Kinyoun method of acid-fast staining?

Carbolfuchsin.

Why is carbolfuchsin effective as a primary stain in the acid-fast method?

It is lipid-soluble and contains phenol, which helps it penetrate the waxy cell wall of acid-fast bacteria, forming a fuchsia-pink complex.

What is the role of acid alcohol in the acid-fast stain?

It strips the stain from all non-acid-fast cells but does not penetrate the cell wall of acid-fast organisms.

How do acid-fast bacteria resist decolorization by acid alcohol?

Mycolic acids in their cell walls give lipids a higher affinity for carbolfuchsin, trapping the stain.

What is the counterstain used in the acid-fast method, and what color do non-acid-fast cells appear?

Methylene blue; non-acid-fast cells appear blue.

What color do acid-fast positive bacteria appear after completing the acid-fast stain?

Pink-red or fuchsia-pink.

What color do acid-fast negative bacteria appear after completing the acid-fast stain?

Blue.

What is the optimum temperature for bacterial growth?

The ideal temperature at which an organism grows best.

What does a spectrophotometer measure in a broth culture to indicate bacterial growth?

Turbidity (cloudiness) or absorbance of light, which correlates to the optical density.

Which classification of microbes grows best below 20°C?

Psychrophiles.

Which classification of microbes is adapted to temperatures between 15°C and 45°C, like the human body?

Mesophiles.

Which classification describes microbes that can survive at high temperatures (70°C or higher) for short periods, often relevant in pasteurization?

Thermoduric bacteria.

What type of microbes can function at cold temperatures but survive up to 35°C, often contributing to food spoilage under refrigeration?

Psychrotrophs.

Give an example of a mesophilic bacterium that commonly causes human infections.

Escherichia coli, Staphylococcus aureus, or Streptococcus pyogenes.

Why is water essential for bacterial cells?

It is used to maintain turgor pressure, pH, and metabolism.

What is osmosis?

The diffusion of water across a semi-permeable membrane, occurring due to different solute concentrations.

What effect does a hypotonic environment have on a bacterial cell?

Water will move into the cell, causing it to swell and increase turgor pressure, but the rigid cell wall prevents bursting.

What effect does a hypertonic environment have on a bacterial cell?

Water will leave the cell, causing the cell membrane to shrink away from the cell wall, a process called plasmolysis.

Which microbes are adapted to live and grow only in high salinity environments?

Halophiles (including moderate and extreme halophiles).

What is water activity, and what determines it?

It relates to the solute concentration in an environment, and solutes can include salts, sugars, amino acids, or other molecules.

What are Reactive Oxygen Species (ROS), and why are they a concern for microbes?

Toxic metabolites produced during aerobic cellular respiration that can damage cellular components like DNA.

Which microbes rely solely on oxygen as the final electron acceptor for cellular respiration?

Strict aerobe (or obligate aerobe).

Which microbes can use oxygen but do not require it and are capable of growing in its absence?

Facultative anaerobes.

Which microbes cannot grow in the presence of oxygen at all?

Strict anaerobes (or obligate anaerobes).

Why do facultative anaerobes generally grow better with oxygen than without?

Aerobic respiration, which uses oxygen, is a more efficient process for ATP production than anaerobic respiration or fermentation.

What is the purpose of general purpose media in microbiology?

To support the growth of many microorganisms that do not require special growth factors.

What is enrichment media, and when is it used?

Media containing special growth factors required by some microorganisms to grow, used to encourage the growth of specific organisms.

How does selective media function?

It inhibits the growth of some groups of microorganisms while selecting for the growth of others.

How does differential media function, and give an example?

It shows differences between microbial colonies based on their cultural characteristics; blood agar is an example that shows different patterns of hemolysis.