Biology 9: Living vs Dead Cells

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Questions and Answers

Which type of microscopy allows the differentiation between living and dead cells based on membrane integrity?

Electron Microscopy

Confocal Microscopy

Fluorescence Microscopy (correct)

Phase Contrast Microscopy

What color do dead cells appear when stained with propidium iodide in a combination with Syto 9?

Blue

Red (correct)

Green

Yellow

What is the process by which most bacteria reproduce?

Mitosis

Budding

Binary fission (correct)

Meiosis

In flow cytometry, what property is primarily used to sort and separate cells?

Fluorescence intensity Signup and view all the answers

What indicates that viable cells can replicate when performing a viable count?

Formation of colonies Signup and view all the answers

During bacterial growth, what happens as the nucleoid expands?

DNA replication nears completion Signup and view all the answers

What measurement indicates a culture's cell count based on density using a spectrophotometer?

Optical density Signup and view all the answers

What differentiates symmetrical binary fission from asymmetrical binary fission in bacteria?

Equal or unequal division of cytoplasm Signup and view all the answers

What is the primary role of the catalase enzyme in bacterial cells?

Breaking down hydrogen peroxide to prevent cellular damage Signup and view all the answers

How does the catalase test help in distinguishing between different bacterial families?

By identifying the ability to synthesize catalase Signup and view all the answers

What role does quorum sensing play in the development of biofilms?

It coordinates individual bacteria's response to environmental stimuli Signup and view all the answers

In the context of cystic fibrosis, what impact do biofilms have on respiratory infections?

They enhance the resistance of bacteria to treatment efforts Signup and view all the answers

What factor primarily contributed to the mortality of the two women with cystic fibrosis in the historical case described?

Insufficient antibiotic coverage for Pseudomonas aeruginosa Signup and view all the answers

What type of environment do thermophiles thrive in?

High temperatures Signup and view all the answers

Which of the following microorganisms is classified as a facultative anaerobe?

All of the above Signup and view all the answers

What is a defining characteristic of strict anaerobes?

Generate energy through fermentation only Signup and view all the answers

Which type of microorganism survives in environments with lower oxygen concentrations?

Microaerophiles Signup and view all the answers

Which of the following statements about catalase is true?

Catalyzes the breakdown of hydrogen peroxide into oxygen and water Signup and view all the answers

What is the typical pH level of the environment where most pathogens thrive?

Slightly alkaline to neutral Signup and view all the answers

What characterizes aerotolerant anaerobes?

Prefer anaerobic conditions but tolerate oxygen Signup and view all the answers

Which of the following best describes strict aerobes?

Use oxygen as a terminal electron acceptor in respiration Signup and view all the answers

Which environmental condition do halophiles specifically thrive in?

High salt concentrations Signup and view all the answers

Which of these bacteria is known for rarely being pathogenic due to the extreme conditions they thrive in?

Thermophiles Signup and view all the answers

What is the primary product of nitrogen fixation performed by certain bacteria?

Ammonium ions (NH4+) Signup and view all the answers

Which process involves the transformation of ammonia to nitrate?

Nitrification Signup and view all the answers

In the context of urinary tract infections, what does the presence of nitrites in urine usually indicate?

Presence of E. coli bacteria Signup and view all the answers

Which statement best explains the role of nitrifying bacteria in the nitrogen cycle?

They oxidize ammonia to generate energy. Signup and view all the answers

What happens during denitrification in the nitrogen cycle?

Nitrates are reduced to nitrogen gas. Signup and view all the answers

When E. coli reduces nitrate in urine, what is the main intermediate compound formed?

Nitrites (NO2-) Signup and view all the answers

Why is nitrogen fixation considered crucial for biosynthesis?

It converts non-usable nitrogen into a usable form. Signup and view all the answers

In the diagnosis of UTIs, what factor is crucial for determining the need for treatment?

The amount of colonies forming units (CFU) found. Signup and view all the answers

What is the purpose of the nitrite test when analyzing urine for UTIs?

To indicate the metabolites of nitrite reductase. Signup and view all the answers

What type of bacteria participates in forming a symbiotic relationship for nitrogen fixation?

Nitrogen-fixing bacteria. Signup and view all the answers

What defines a hyperthermophile in terms of temperature tolerance?

Growth above 80°C Signup and view all the answers

Which type of microbe would best survive in a highly acidic environment?

Acidophiles Signup and view all the answers

What is a primary characteristic of psychrophiles regarding temperature?

Optimum growth temperature is usually around 15°C Signup and view all the answers

What adaptation allows thermophiles to withstand high temperatures?

Proteins that fold more tightly to prevent denaturation Signup and view all the answers

Which category of extremophile requires high salt concentrations to thrive?

Halophiles Signup and view all the answers

What is the optimal temperature range for mesophiles?

20°C to 40°C Signup and view all the answers

Which characteristic is NOT associated with strict anaerobes?

Require oxygen for survival Signup and view all the answers

Which group of microorganisms is primarily responsible for growth at extreme pressures?

Barophiles Signup and view all the answers

What is a defining feature of normophiles (mesophiles)?

Optimal growth around 37°C, human body temperature Signup and view all the answers

How do psychrophiles maintain cell integrity at low temperatures?

Their proteins are more flexible, requiring less energy Signup and view all the answers

Study Notes

Distinguishing Living from Dead Cells

Detroff Hausser Counting Chamber allows counting microorganisms directly with a microscope, but visual identification does not confirm liveliness.
Fluorescence Microscopy distinguishes living from dead cells using dyes:
- Propidium Iodide stains dead cells red by penetrating only energized membranes.
- Syto 9 stains both live and dead cells green.
- Combined application results in living cells appearing green and dead cells appearing red, yellow, or orange.

Flow Cytometry

FACS (Fluorescence-Activated Cell Sorting) counts and separates cells based on fluorescence.
Cells flow single-file past a laser for counting and fluorescence intensity measurement, allowing for separation.
Useful for differentiating bacterial cells with varying fluorescent protein synthesis capabilities.

Viable Counts

Viable Cells replicate and form colonies (e.g., 100 colonies from 100 ml of 10³ dilution corresponds to 1000 cells/ml).
Optical Density measures turbidity in liquid cultures via spectrophotometer, indicating cell density.

Bacterial Growth

Standard growth through binary fission; one parent cell divides to produce two offspring.
Growth cycle includes nucleoid expansion as DNA replicates.
Bacteria utilize nitrogen in various transformations: nitrogen fixation (N₂ to NH₄⁺), nitrification (NH₃ to NO₃⁻), and denitrification (NO₃⁻ to N₂).

Nitrogen Cycle and UTIs

Nitrate Reduction: Some bacteria (e.g., E. coli) convert nitrates (NO₃⁻) in urine to nitrites (NO₂⁻), indicating potential infections.
Presence of nitrite in urine suggests UTI but requires confirmation since other causes may exist.

Nitrite Test in UTIs

Sensitivity and Specificity of nitrite tests varies—sensitivity at 25% and specificity at 94%-100%.
A positive nitrite result usually indicates bacterial presence, especially if lacking in normal urine.

Treatment Considerations

Infections typically warrant treatment to prevent complications, particularly for asymptomatic bacteriuria or in pregnant patients.
Potential risk of sepsis and preterm birth linked to untreated infections.

Extremophiles

Extremophiles thrive in harsh conditions; classified by temperature, pH, salinity, and pressure.
Thermophiles grow at high temperatures (>55°C), while psychrophiles thrive at low temperatures (as low as -10°C).
Bacteria employ unique proteins to function under extreme conditions.

Oxygen Utilization

Strict Aerobes require oxygen for growth and metabolize reactive oxygen species (ROS).
Strict Anaerobes cannot use oxygen and are often harmed by ROS.
Facultative Anaerobes can grow with or without oxygen, while Microaerophiles prefer lower oxygen environments.

Catalase Test

Detects the presence of catalase, an enzyme that decomposes hydrogen peroxide into water and oxygen.
Catalase-positive bacteria form bubbles upon exposure to hydrogen peroxide; key for differentiating bacterial types.

Biofilms and Quorum Sensing

Biofilms consist of masses of bacteria adhering to surfaces, offering resistance to treatment.
Quorum Sensing enables communication and coordinated behavior among bacteria in biofilms.
Biofilms pose significant challenges in infections, such as in cystic fibrosis-related respiratory illnesses.

Case History Insight

Cystic fibrosis is linked to compromised chloride transport, leading to severe respiratory conditions.
The persistence of Pseudomonas aeruginosa in infected patients demonstrates the challenges in treating biofilm-associated infections.

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Description

This quiz explores the methods of distinguishing living from dead cells using various microscopy techniques. It covers fluorescence microscopy principles, the role of dyes like propidium iodide and Syto 9, and their interactions with cellular membranes. Test your knowledge on these important concepts in microbiology!