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Questions and Answers
What type of bacteria can only grow in the presence of oxygen?
Which type of bacteria can survive in both the presence and absence of oxygen but prefers to grow with oxygen?
What is the temperature range preferred by thermophiles?
What is the process called that involves the diffusion of water across a membrane?
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Which of the following statements about anaerobic respiration is true?
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What do obligate anaerobes require for growth?
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What is the net yield of ATP molecules from aerobic respiration?
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What is the main characteristic of hyperthermophiles?
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What causes gram-negative bacteria to lose their purple stain when treated with alcohol?
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Which of the following statements is true regarding gram-positive bacteria?
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What is the primary function of peptidoglycan in bacterial cells?
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What is the role of endotoxin in gram-negative bacteria?
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Where is the periplasmic space located in gram-negative bacteria?
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How do lysozymes kill bacteria?
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What is the purpose of transpeptidase in bacterial cells?
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Why do gram-positive bacteria remain purple during the Gram stain process?
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What is the term for the time it takes for a bacterial population to double in number?
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During which phase of the bacterial growth cycle does rapid cell division occur?
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Which of the following factors does NOT influence bacterial growth?
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What happens during the stationary phase of bacterial growth?
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What type of bacteria can grow at temperature ranges between –5°C and 15°C?
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Which nutrient source is essential for bacterial growth in terms of energy?
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Which of these drugs act during the logarithmic phase of bacterial growth?
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Which statement about the death phase of bacterial growth is true?
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What is the primary function of the B subunit in exotoxins?
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Which of the following is NOT considered a portal of entry for bacteria into the body?
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In which stage of infectious disease do characteristic features of a disease occur?
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What type of disease can result from vertical transmission?
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What typically occurs during the recovery period of infectious disease?
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What role do plasmids play in bacterial cells?
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What is a primary function of capsules in bacteria?
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Which bacterial structures are responsible for attachment to human cells?
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What characteristic do spores possess?
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How do transposons contribute to bacterial resistance?
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What defines normal flora in the human body?
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What is the main function of the glycocalyx in bacteria?
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What happens to spores when nutrients are restored?
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Study Notes
Bacteria Growth and Reproduction
- Bacteria reproduce through binary fission, where one cell splits into two.
- The generation time (time for a population to double) varies greatly, from 20 minutes for Escherichia coli to over 24 hours for Mycobacterium tuberculosis.
- Bacterial growth has four phases:
- Lag phase: Metabolic activity without cell division.
- Log (exponential) phase: Rapid cell division, where β-lactam drugs like penicillin are most effective.
- Stationary phase: Growth slows due to nutrient depletion or toxic buildup, resulting in a stable state.
- Death phase: Number of viable bacteria declines.
Factors Influencing Bacterial Growth
Physical Requirements
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Temperature:
- Psychrophiles: Grow in cold environments (-5°C to 15°C).
- Mesophiles: Grow at moderate temperatures (20°C to 40°C), common in soil and the body.
- Thermophiles: Grow in hot environments (45°C to 70°C).
- Hyperthermophiles: Grow in extremely hot environments (70°C to 110°C).
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Oxygen requirements:
- Obligate aerobes: Require oxygen for growth, using aerobic respiration.
- Microaerophiles: Require low oxygen concentrations (2%-10%) for growth, inhibited by higher levels.
- Obligate anaerobes: Can only grow in the absence of oxygen, using anaerobic respiration or fermentation.
- Aerotolerant anaerobes: Can tolerate oxygen but don't use it for energy, using only fermentation.
- Facultative anaerobes: Grow with or without oxygen, using aerobic respiration in oxygen-rich environments and fermentation or anaerobic respiration otherwise.
- pH: Optimal pH varies for different bacteria.
- Osmosis: Movement of water across a membrane from areas of higher water concentration (lower solute) to areas of lower water concentration (higher solute).
Nutritional Requirements
- Energy source: Required for metabolism.
- Carbon source: Needed for building organic molecules.
- Nitrogen source: Used for synthesizing proteins and nucleic acids.
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Minerals:
- Sulfur: Used for amino acids and proteins.
- Phosphorus: Used for nucleic acids and ATP production.
- Potassium, magnesium, and calcium: Involved in enzyme activity and cell structure.
- Iron: Used for electron transport chains and enzymes.
- Trace elements: Required in minute amounts.
- Water: Essential for all metabolic processes.
- Growth factors: Specific organic compounds bacteria can't synthesize themselves.
Respiration
- Aerobic respiration: Glucose catabolism in the presence of oxygen, producing 38 ATP molecules. Oxygen is the final electron acceptor.
- Anaerobic respiration: Occurs in the absence of oxygen. Final electron acceptor is an organic molecule like nitrate, sulfate, or CO2. Produces less ATP than aerobic respiration.
Bacterial Cell Structure
- Gram-negative bacteria: Have a thin peptidoglycan layer covered by an outer lipid-containing membrane.
- Gram-positive bacteria: Have a thick peptidoglycan layer but no outer membrane.
- Gram stain: Differentiates bacteria based on their cell wall composition, where gram-positive bacteria stain purple and gram-negative bacteria stain pink, due to differences in their ability to retain the stain.
Peptidoglycan
- Found only in bacterial cell walls.
- A network surrounding the bacteria.
- Provides structure and rigidity.
- Target of penicillin and cephalosporins antibiotics.
- Composed of a sugar backbone and peptide side chains, cross-linked by transpeptidase.
Outer membrane of gram-negative bacteria
- Contains lipopolysaccharide (LPS or endotoxin), which is a major inducer of septic shock.
- LPS consists of:
- Lipid A: Induces fever and hypotension in septic shock.
- Polysaccharide (O Antigen): Used for laboratory identification.
- Periplasmic space: Area between the inner and outer membrane of gram-negative bacteria, containing β-lactamases, which break down β-lactam antibiotics.
Cytoplasmic membrane
- Located beneath the peptidoglycan, a phospholipid bilayer without sterols.
- Regulates transport of nutrients into the cell.
- Involved in secretion of toxins.
Acid-fast bacteria
- Mycobacteria: Resist decolorization with acid-alcohol after carbolfuscin staining due to high lipid content in their cell wall.
- Gram stain doesn't work, but Ziehl Neilson (ZN) stain can be used.
Bacterial DNA
- Bacterial genome: A single circular DNA molecule located in the nucleoid, carrying genetic information.
- Plasmids: Extrachromosomal circular DNA molecules, encoding exotoxins, enzymes, and antibiotic resistance.
- Transposons (Jumping genes): Small DNA segments that move between chromosomal and plasmid DNA, sometimes carrying antibiotic-resistance genes.
Structures External to Cell Wall
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Capsules: Polysaccharide (exception: polypeptide in anthrax bacillus).
- Antiphagocytic: Protect bacteria from phagocytosis, preventing their engulfment by neutrophils.
- Antigenic: Used for vaccines, like pneumococcal vaccine.
- Target for identification: Antisera against capsular polysaccharides are used for specific identification.
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Glycocalyx: Polysaccharide "slime layer" secreted by some bacteria.
- Adherence to cells: Helps bacteria attach to surfaces like human cells, catheters, or prosthetic devices.
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Pili: Filamentous protein structures extending from the cell surface.
- Adherence to cells: Mediates attachment to host cells.
- Conjugation: Sex pili facilitate bacterial conjugation.
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Spores: Highly heat-resistant, metabolically inactive structures formed by some gram-positive bacteria, especially Bacillus and Clostridium.
- Survive harsh conditions: Survive for long periods, even in the soil.
- Resistant to disinfectants: Boiling doesn't kill them.
- Germination: Form active bacteria when conditions become favorable, causing disease.
Normal Flora and Bacterial Pathogenesis
- Normal flora (commensals): Organisms that live permanently on our bodies.
- Commensals: Benefit from the host without causing harm.
- Adherence: Bacteria attaching to mucous membranes, usually using pili.
- Colonization: Growth of bacteria at the site of adherence.
- Disease symptoms: Caused by toxin production or invasion and inflammation.
- Host responses: Both nonspecific (natural defenses) and specific (immune) responses.
- Progression and resolution: Disease course can lead to recovery, chronic carrier state, or latent infections.
Determinants of Bacterial Pathogenesis
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Transmission:
- Vertical transmission: From mother to offspring through placenta, birth canal, or breast milk.
- Horizontal transmission: From person to person.
- Zoonoses: Diseases transmitted from animals to humans.
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Portals of entry:
- Respiratory tract
- Gastrointestinal tract
- Skin
- Genital tract
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Toxin production:
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Exotoxins: Proteins released by bacteria.
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A-B subunit structure:
- A (active) subunit: Possesses the toxic activity.
- B (binding) subunit: Binds exotoxin to specific receptors on host cells.
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A-B subunit structure:
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Exotoxins: Proteins released by bacteria.
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Typical stages of infectious disease:
- Incubation period: Time between exposure and symptom onset.
- Prodrome period: Time with nonspecific symptoms.
- Specific-illness period: Time with characteristic disease symptoms.
- Recovery period: Time for symptoms to resolve and health restoration.
- Chronic carrier state: Individuals carry the pathogen after recovery.
- Latent infections: Subclinical infection with no or minor symptoms.
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Description
Test your knowledge on the processes of bacterial growth and reproduction! This quiz covers key concepts such as binary fission, generation time, and the different phases of growth. Understand the physical requirements necessary for the thriving of various bacterial types.
