Practice Questions: Physiology of Bacteria
Physiology of Bacteria - Comprehensive Practice Questions
Subject: Microbiology for Nursing Exams
Chapter: Physiology of Bacteria
Total Questions: 45
Difficulty Level: Mixed (Foundation to Advanced)
Type 1: Direct Factual Questions
Q1: What is the primary function of bacterial capsule?
(a) Energy production
(b) Protection from phagocytosis
(c) Protein synthesis
(d) DNA replication
Ans: (b)
Explanation: The bacterial capsule is a polysaccharide layer that protects bacteria from phagocytosis by host immune cells. It acts as a virulence factor, preventing white blood cells from engulfing the bacteria. Capsules do not participate in energy production, protein synthesis, or DNA replication, which occur in other cellular structures.
Q2: Which bacterial structure is primarily responsible for motility?
(a) Pili
(b) Flagella
(c) Capsule
(d) Cell wall
Ans: (b)
Explanation: Flagella are long, whip-like appendages that enable bacterial motility through rotation. Pili are used for attachment and conjugation, not movement. The capsule provides protection, and the cell wall maintains structural integrity. Flagellar movement is powered by the proton motive force.
Q3: Which phase of bacterial growth is characterized by rapid cell division?
(a) Lag phase
(b) Log phase
(c) Stationary phase
(d) Decline phase
Ans: (b)
Explanation: The log phase (exponential phase) is characterized by rapid cell division at a constant rate. During the lag phase, bacteria adapt to new environment without dividing. The stationary phase has equal rates of growth and death. The decline phase shows more death than growth.
Q4: The bacterial chromosome is typically composed of:
(a) Linear double-stranded DNA
(b) Circular double-stranded DNA
(c) Single-stranded RNA
(d) Linear single-stranded DNA
Ans: (b)
Explanation: Bacterial chromosomes consist of circular double-stranded DNA located in the nucleoid region. Unlike eukaryotes, bacteria lack a membrane-bound nucleus. The circular nature allows for continuous replication. Plasmids are also circular but are extrachromosomal genetic elements.
Q5: Which organelle is absent in bacterial cells?
(a) Ribosomes
(b) Mitochondria
(c) Cell membrane
(d) Nucleoid
Ans: (b)
Explanation: Bacteria lack mitochondria and other membrane-bound organelles. Energy production occurs at the cell membrane. Bacteria possess 70S ribosomes (smaller than eukaryotic 80S), a cell membrane, and a nucleoid region containing genetic material. This is a key difference between prokaryotic and eukaryotic cells.
Q6: What is the function of bacterial plasmids?
(a) Essential for cell survival
(b) Carry antibiotic resistance genes
(c) Primary site of protein synthesis
(d) Main chromosomal DNA storage
Ans: (b)
Explanation: Plasmids are extrachromosomal circular DNA molecules that often carry antibiotic resistance genes. They are not essential for bacterial survival but provide selective advantages. Plasmids can be transferred between bacteria through conjugation, spreading resistance. The main chromosome, not plasmids, contains essential survival genes.
Q7: Which type of bacterial respiration produces the most ATP?
(a) Aerobic respiration
(b) Anaerobic respiration
(c) Fermentation
(d) Photophosphorylation
Ans: (a)
Explanation: Aerobic respiration produces approximately 38 ATP molecules per glucose molecule, the highest yield. Anaerobic respiration produces less ATP than aerobic. Fermentation produces only 2 ATP per glucose. Aerobic respiration uses oxygen as the final electron acceptor, maximizing energy extraction.
Q8: The bacterial cell wall of Gram-positive bacteria is primarily composed of:
(a) Lipopolysaccharide
(b) Peptidoglycan
(c) Cellulose
(d) Chitin
Ans: (b)
Explanation: Gram-positive bacteria have a thick peptidoglycan layer (20-80 nm) that retains crystal violet stain. Lipopolysaccharide (LPS) is found in Gram-negative outer membranes. Cellulose is found in plants, and chitin in fungi. The thick peptidoglycan provides structural support and is the target of antibiotics like penicillin.
Type 2: Clinical Scenario / Case-Based Questions
Q9: A patient develops septic shock with high fever, hypotension, and disseminated intravascular coagulation. Blood culture shows Gram-negative bacteria. Which bacterial component is most likely responsible for these symptoms?
(a) Peptidoglycan
(b) Flagella
(c) Lipopolysaccharide (endotoxin)
(d) Capsule
Ans: (c)
Explanation: Lipopolysaccharide (LPS or endotoxin) from the outer membrane of Gram-negative bacteria triggers massive cytokine release, causing septic shock, fever, and DIC. The lipid A component is responsible for toxicity. Peptidoglycan, flagella, and capsules do not cause these severe systemic inflammatory responses.
Q10: A laboratory culture of bacteria shows no growth for 6 hours, followed by rapid increase in colony count. Which growth phase was observed initially?
(a) Stationary phase
(b) Lag phase
(c) Log phase
(d) Decline phase
Ans: (b)
Explanation: The lag phase shows no visible growth as bacteria adapt to new culture conditions, synthesize enzymes, and repair damage. This adaptation period can last several hours. After adaptation, bacteria enter the log phase with rapid division. This pattern is typical when transferring bacteria to fresh medium.
Q11: A wound infection culture grows bacteria that form endospores when nutrients are depleted. Which characteristic makes these bacteria difficult to eliminate?
(a) Rapid multiplication rate
(b) High resistance to heat and disinfectants
(c) Production of exotoxins
(d) Presence of flagella
Ans: (b)
Explanation: Bacterial endospores (formed by Bacillus and Clostridium species) are highly resistant to heat, radiation, desiccation, and chemical disinfectants. They have thick protective coats with dipicolinic acid and low water content. Autoclaving (121°C, 15 minutes) is required for sterilization. This makes spore-forming bacteria challenging in healthcare settings.
Q12: A patient with tuberculosis is prescribed multiple antibiotics. The prolonged treatment is necessary because Mycobacterium tuberculosis:
(a) Grows very slowly
(b) Has no cell wall
(c) Forms biofilms rapidly
(d) Lacks ribosomes
Ans: (a)
Explanation: Mycobacterium tuberculosis has an extremely slow generation time (12-24 hours) due to its complex mycolic acid-rich cell wall. Slow growth means fewer bacteria are in active division, making antibiotics less effective. Multi-drug therapy for 6-9 months is required. The organism does have a cell wall, ribosomes, and slow biofilm formation.
Q13: A stool sample from a patient with food poisoning shows bacteria that survived stomach acid. What bacterial adaptation likely enabled this?
(a) Spore formation
(b) Acid tolerance response
(c) Capsule production
(d) Flagellar movement
Ans: (b)
Explanation: Many enteric pathogens possess acid tolerance response (ATR) mechanisms, including proton pumps and acid-shock proteins that maintain internal pH. Species like E. coli and Salmonella can survive pH 2-3 in gastric acid. Spores also resist acid but are formed by limited species. Capsules and flagella don't provide acid protection.
Type 3: Bacterial Metabolism and Nutrition Questions
Q14: Which type of bacteria can synthesize all required organic compounds from CO₂?
(a) Chemoheterotrophs
(b) Photoautotrophs
(c) Chemoautotrophs
(d) Photoheterotrophs
Ans: (b)
Explanation: Photoautotrophs use light energy and fix CO₂ as their carbon source (e.g., cyanobacteria). Chemoautotrophs also use CO₂ but derive energy from chemical reactions. Heterotrophs require organic carbon compounds. The prefix "auto" indicates self-feeding through CO₂ fixation; "photo" indicates light energy use.
Q15: Bacteria that require oxygen for growth but at lower concentrations than atmospheric are called:
(a) Obligate aerobes
(b) Obligate anaerobes
(c) Microaerophiles
(d) Facultative anaerobes
Ans: (c)
Explanation: Microaerophiles require oxygen but at 2-10% concentration (atmospheric = 21%). High oxygen levels are toxic to them. Campylobacter is an example. Obligate aerobes require normal oxygen levels. Facultative anaerobes can grow with or without oxygen. Obligate anaerobes are killed by oxygen.
Q16: Which bacterial enzyme is essential for survival in the presence of oxygen by neutralizing hydrogen peroxide?
(a) Oxidase
(b) Catalase
(c) Coagulase
(d) Urease
Ans: (b)
Explanation: Catalase breaks down toxic hydrogen peroxide (H₂O₂) into water and oxygen:
2H₂O₂ → 2H₂O + O₂
This is essential for aerobic and facultative anaerobic bacteria. The catalase test (bubbling with H₂O₂) differentiates Staphylococcus (positive) from Streptococcus (negative). Oxidase, coagulase, and urease serve different functions.
Q17: Which metabolic pathway do bacteria use during fermentation to regenerate NAD⁺?
(a) Krebs cycle
(b) Electron transport chain
(c) Reduction of pyruvate
(d) Calvin cycle
Ans: (c)
Explanation: During fermentation, bacteria regenerate NAD⁺ by reducing pyruvate to lactate (lactic acid fermentation) or ethanol (alcoholic fermentation). This allows glycolysis to continue producing ATP. The Krebs cycle and electron transport chain require oxygen. The Calvin cycle is for carbon fixation in autotrophs.
Q18: Nitrogen fixation in bacteria converts atmospheric nitrogen to:
(a) Nitrate
(b) Nitrite
(c) Ammonia
(d) Nitrogen dioxide
Ans: (c)
Explanation: Nitrogen-fixing bacteria (e.g., Rhizobium, Azotobacter) convert atmospheric N₂ to ammonia (NH₃) using the enzyme nitrogenase. This process requires significant ATP and occurs in anaerobic conditions. Ammonia can then be assimilated into amino acids. Nitrate and nitrite formation occur during nitrification by other bacteria.
Type 4: Bacterial Genetics and Reproduction Questions
Q19: What is the primary method of reproduction in bacteria?
(a) Mitosis
(b) Meiosis
(c) Binary fission
(d) Budding
Ans: (c)
Explanation: Bacteria reproduce asexually through binary fission, where one cell divides into two identical daughter cells after DNA replication. This process involves chromosome replication, cell elongation, septum formation, and cell separation. Mitosis and meiosis occur in eukaryotes. Some bacteria like Streptomyces may use budding, but it's not the primary method.
Q20: Which mechanism of genetic recombination requires direct cell-to-cell contact?
(a) Transformation
(b) Transduction
(c) Conjugation
(d) Mutation
Ans: (c)
Explanation: Conjugation requires direct contact between donor and recipient cells through a pilus (sex pilus). DNA (usually plasmid) is transferred from F⁺ (donor) to F⁻ (recipient) cell. Transformation involves uptake of free DNA from the environment. Transduction uses bacteriophages as vectors. Mutation is not recombination.
Q21: Which process involves transfer of bacterial DNA via a bacteriophage?
(a) Conjugation
(b) Transformation
(c) Transduction
(d) Translation
Ans: (c)
Explanation: Transduction is the transfer of bacterial DNA from one bacterium to another via a bacteriophage (bacterial virus). In generalized transduction, any bacterial DNA can be transferred. In specialized transduction, specific genes near prophage integration sites are transferred. This is an important mechanism of horizontal gene transfer.
Q22: The F (fertility) plasmid in bacteria codes for:
(a) Antibiotic resistance
(b) Endospore formation
(c) Sex pilus formation
(d) Capsule synthesis
Ans: (c)
Explanation: The F plasmid carries genes for sex pilus formation, enabling conjugation. Cells with F plasmid (F⁺) act as donors; those without (F⁻) are recipients. The pilus creates a bridge for DNA transfer. R plasmids carry antibiotic resistance. F plasmids don't code for endospores or capsules.
Q23: What is the typical generation time for rapidly growing bacteria like E. coli under optimal conditions?
(a) 5-10 minutes
(b) 20-30 minutes
(c) 2-3 hours
(d) 12-24 hours
Ans: (b)
Explanation: E. coli and other rapidly growing bacteria have a generation time of approximately 20-30 minutes under optimal conditions. Generation time is the time required for a bacterial population to double. This can vary: Mycobacterium tuberculosis takes 12-24 hours. Understanding generation time is crucial for culture timing and antibiotic therapy.
Type 5: Bacterial Structure and Function Questions
Q24: Which bacterial structure is composed of protein and aids in attachment to host cells?
(a) Flagella
(b) Fimbriae (pili)
(c) Spores
(d) Ribosomes
Ans: (b)
Explanation: Fimbriae (common pili) are short, hair-like protein appendages that enable bacteria to attach to host tissues and surfaces. They are important virulence factors in infections (e.g., UTIs caused by E. coli). Flagella provide motility, not attachment. Sex pili are involved in conjugation, different from common pili.
Q25: The periplasmic space in Gram-negative bacteria contains:
(a) Ribosomes
(b) DNA
(c) Hydrolytic enzymes
(d) Mitochondria
Ans: (c)
Explanation: The periplasmic space (between inner membrane and peptidoglycan layer) in Gram-negative bacteria contains hydrolytic enzymes (including β-lactamases), binding proteins, and chemoreceptors. This space facilitates nutrient processing and antibiotic resistance. DNA and ribosomes are in the cytoplasm. Bacteria lack mitochondria.
Q26: Which component is unique to Gram-negative bacterial cell walls?
(a) Thick peptidoglycan layer
(b) Teichoic acids
(c) Outer membrane with LPS
(d) Mycolic acids
Ans: (c)
Explanation: Gram-negative bacteria possess an outer membrane containing lipopolysaccharide (LPS), making them resistant to lysozyme and certain antibiotics. Thick peptidoglycan and teichoic acids are found in Gram-positive bacteria. Mycolic acids are characteristic of Mycobacterium species. The outer membrane is a key structural and clinical difference.
Q27: Bacterial ribosomes are of which type?
(a) 40S
(b) 60S
(c) 70S
(d) 80S
Ans: (c)
Explanation: Bacterial ribosomes are 70S, composed of 30S and 50S subunits. This differs from eukaryotic 80S ribosomes (40S + 60S subunits). This structural difference allows selective targeting by antibiotics like aminoglycosides (bind 30S) and macrolides (bind 50S) without affecting human ribosomes. S = Svedberg units of sedimentation.
Q28: The glycocalyx in bacteria functions primarily in:
(a) Protein synthesis
(b) Adherence and biofilm formation
(c) DNA replication
(d) Energy production
Ans: (b)
Explanation: The glycocalyx (loose polysaccharide layer outside cell wall) facilitates adherence to surfaces and biofilm formation. When tightly organized, it's called a capsule; when loose, a slime layer. Biofilms increase antibiotic resistance and protect from host defenses. It's not involved in protein synthesis, DNA replication, or energy production.
Type 6: Bacterial Enzymes and Virulence Factors
Q29: Which bacterial enzyme breaks down fibrin clots, aiding in spread of infection?
(a) Coagulase
(b) Streptokinase
(c) Hyaluronidase
(d) Catalase
Ans: (b)
Explanation: Streptokinase (produced by Streptococcus species) dissolves fibrin clots by activating plasminogen to plasmin, promoting bacterial spread through tissues. Coagulase (from Staphylococcus aureus) clots plasma. Hyaluronidase breaks down hyaluronic acid in connective tissue. Streptokinase is also used therapeutically as a thrombolytic agent.
Q30: Hyaluronidase enzyme produced by bacteria is called "spreading factor" because it:
(a) Forms protective capsules
(b) Degrades connective tissue allowing bacterial spread
(c) Prevents phagocytosis
(d) Produces toxins
Ans: (b)
Explanation: Hyaluronidase breaks down hyaluronic acid in connective tissue, acting as a "spreading factor" that allows bacteria to penetrate tissues more easily. Produced by Streptococcus, Staphylococcus, and Clostridium species. This enzyme facilitates deep tissue invasion and abscess formation. It doesn't form capsules or directly prevent phagocytosis.
Q31: Which bacterial enzyme differentiates Staphylococcus aureus from other staphylococci?
(a) Catalase
(b) Oxidase
(c) Coagulase
(d) Urease
Ans: (c)
Explanation: Coagulase is the key differentiating enzyme: Staphylococcus aureus is coagulase-positive, while other staphylococci (coagulase-negative staphylococci or CoNS) are negative. Coagulase converts fibrinogen to fibrin, forming a protective clot around bacteria. All staphylococci are catalase-positive, so catalase doesn't differentiate species. The slide coagulase test is rapid; tube test is confirmatory.
Q32: Bacterial exotoxins differ from endotoxins in that exotoxins are:
(a) Heat-stable lipopolysaccharides
(b) Part of the cell wall
(c) Heat-labile proteins secreted by bacteria
(d) Released only when bacteria die
Ans: (c)
Explanation: Exotoxins are heat-labile proteins actively secreted by living bacteria, highly toxic even in small amounts, and can be converted to toxoids for vaccines. Endotoxins are heat-stable lipopolysaccharides (LPS) from Gram-negative cell walls, released when bacteria die. Exotoxins are more specific in action; endotoxins cause generalized inflammation.
Type 7: Oxygen Requirements and Culture Conditions
Q33: Which of the following bacteria would grow only at the bottom of a thioglycolate broth tube?
(a) Obligate aerobes
(b) Obligate anaerobes
(c) Facultative anaerobes
(d) Microaerophiles
Ans: (b)
Explanation: Obligate anaerobes grow only at the bottom of the tube where oxygen concentration is lowest. Thioglycolate broth has an oxygen gradient: high at top, low at bottom. Obligate aerobes grow at the top, facultative anaerobes throughout (preferring top), and microaerophiles grow in a band below the top surface.
Q34: Bacteria that cannot tolerate oxygen because they lack superoxide dismutase and catalase are:
(a) Facultative anaerobes
(b) Aerotolerant anaerobes
(c) Obligate anaerobes
(d) Microaerophiles
Ans: (c)
Explanation: Obligate anaerobes lack superoxide dismutase (SOD) and catalase, enzymes that neutralize toxic oxygen metabolites (superoxide radicals and hydrogen peroxide). Exposure to oxygen is lethal. Examples include Clostridium species. Aerotolerant anaerobes lack these enzymes but tolerate oxygen. Other groups possess protective enzymes.
Q35: What is the optimal pH range for growth of most pathogenic bacteria?
(a) 3.0 - 4.0
(b) 5.0 - 6.0
(c) 7.0 - 7.5
(d) 9.0 - 10.0
Ans: (c)
Explanation: Most pathogenic bacteria are neutrophiles, growing best at pH 7.0-7.5 (neutral), similar to human body pH. Acidophiles prefer pH < 5.5,="">alkaliphiles prefer pH > 8.5. Some pathogens like Helicobacter pylori tolerate acidic environments using urease. Culture media are usually buffered to maintain physiological pH.
Q36: The optimal temperature for most human pathogenic bacteria is:
(a) 10-15°C
(b) 20-25°C
(c) 37°C
(d) 45-50°C
Ans: (c)
Explanation: Human pathogens are mesophiles with optimal growth at 37°C (normal body temperature). Psychrophiles prefer < 15°c,="">thermophiles prefer > 45°C. Incubators are set at 37°C for clinical specimens. Some pathogens like Yersinia can grow at lower temperatures, and Campylobacter prefers 42°C.
Type 8: Bacterial Spores and Survival Mechanisms
Q37: Which component in bacterial endospores contributes to heat resistance?
(a) High water content
(b) Dipicolinic acid and calcium
(c) Flagella proteins
(d) Lipopolysaccharide
Ans: (b)
Explanation: Dipicolinic acid (DPA) complexed with calcium in the spore core contributes significantly to heat resistance. Spores also have low water content, thick protective coats (keratin-like), and specialized proteins. This allows survival at temperatures that kill vegetative cells. Autoclaving (121°C, 15 psi, 15 minutes) is required to kill spores.
Q38: Under which condition do bacteria form endospores?
(a) Optimal nutrient availability
(b) Nutrient depletion or adverse conditions
(c) Presence of antibiotics only
(d) Low temperature exposure
Ans: (b)
Explanation: Bacteria form endospores as a survival mechanism when facing nutrient depletion, desiccation, extreme temperature, or other adverse conditions. Sporulation is an energy-intensive process, occurring only when necessary. When conditions improve, spores germinate back to vegetative cells. Only certain Gram-positive bacteria (Bacillus, Clostridium) form endospores.
Q39: Which bacteria are capable of endospore formation?
(a) All Gram-positive bacteria
(b) All Gram-negative bacteria
(c) Only certain Gram-positive genera like Bacillus and Clostridium
(d) All aerobic bacteria
Ans: (c)
Explanation: Only certain Gram-positive genera, primarily Bacillus (aerobic) and Clostridium (anaerobic), form endospores. Not all Gram-positive bacteria have this capability. Gram-negative bacteria do not form endospores. Clinically important spore-formers include B. anthracis, C. tetani, C. botulinum, and C. difficile.
Q40: What position of endospore in Clostridium tetani gives it a characteristic "drumstick" appearance?
(a) Central
(b) Subterminal
(c) Terminal
(d) Lateral
Ans: (c)
Explanation: Clostridium tetani has a terminal (end) spore that bulges, creating a characteristic "drumstick" or "tennis racket" appearance. Spore position aids identification: central (e.g., B. anthracis), subterminal (e.g., C. botulinum), or terminal. The spore is usually wider than the bacterial cell, causing the bulge.
Type 9: Application and Integration Questions
Q41: A bacterial culture shows growth throughout a thioglycolate tube but grows better at the top. These bacteria are classified as:
(a) Obligate aerobes
(b) Obligate anaerobes
(c) Facultative anaerobes
(d) Microaerophiles
Ans: (c)
Explanation: Facultative anaerobes can grow with or without oxygen but grow better in the presence of oxygen (at the top). They grow throughout the tube with maximum growth near the surface. Examples include E. coli and Staphylococcus species. This versatility makes them successful pathogens in various body sites.
Q42: Which process would be most effective in destroying bacterial endospores in surgical instruments?
(a) Boiling at 100°C for 10 minutes
(b) 70% alcohol for 5 minutes
(c) Autoclaving at 121°C for 15 minutes
(d) UV radiation for 30 minutes
Ans: (c)
Explanation: Autoclaving (steam under pressure) at 121°C, 15 psi for 15 minutes is the gold standard for killing endospores. Boiling kills vegetative cells but not spores. Alcohol is ineffective against spores. UV radiation has poor penetration. For prions, autoclaving at 134°C for 18 minutes or chemical treatment is required.
Q43: A biofilm-forming bacteria is difficult to eradicate because biofilms:
(a) Increase bacterial mutation rate
(b) Provide physical barrier and resistance to antimicrobials
(c) Enhance bacterial motility
(d) Increase bacterial generation time
Ans: (b)
Explanation: Biofilms are structured communities of bacteria embedded in a self-produced extracellular polymeric substance (EPS) that provides a physical barrier, reducing antimicrobial penetration. Biofilm bacteria show altered metabolism and increased resistance. Common on catheters and implants. They don't increase motility or mutation rate significantly.
Q44: Bacteria growing in biofilms are approximately how many times more resistant to antibiotics compared to planktonic (free-floating) bacteria?
(a) 2-5 times
(b) 10-100 times
(c) 100-1000 times
(d) No significant difference
Ans: (c)
Explanation: Bacteria in biofilms can be 100-1000 times more resistant to antibiotics than planktonic cells. Resistance mechanisms include reduced penetration, altered microenvironment, slow growth of deep bacteria, and expression of resistance genes. This is clinically significant in chronic infections and device-related infections. Biofilm disruption may be necessary for treatment success.
Q45: Which bacterial characteristic would make an organism most suitable for use as a biological indicator in sterilization monitoring?
(a) Rapid growth rate
(b) High endospore resistance
(c) Capsule formation
(d) Antibiotic resistance
Ans: (b)
Explanation: Biological indicators for sterilization use highly resistant endospores. Bacillus stearothermophilus (now Geobacillus stearothermophilus) is used for steam sterilization monitoring; Bacillus subtilis for dry heat and ethylene oxide. If these resistant spores are killed, the sterilization process is validated as effective. Growth rate, capsules, and antibiotic resistance are irrelevant for this purpose.
Quick Revision Summary
Bacterial Structure Key Points
- Capsule: Polysaccharide layer, prevents phagocytosis, major virulence factor
- Cell wall: Gram-positive = thick peptidoglycan (20-80 nm); Gram-negative = thin peptidoglycan + outer membrane with LPS
- Flagella: Protein structures for motility, powered by proton motive force
- Pili/Fimbriae: Adherence to surfaces; sex pili for conjugation
- Ribosomes: 70S (30S + 50S subunits) - target for antibiotics
- Chromosome: Circular double-stranded DNA in nucleoid region
- Plasmids: Extrachromosomal DNA, carry resistance genes, transferable
Bacterial Growth and Metabolism
- Binary fission: Primary reproduction method, one cell → two identical cells
- Generation time: E. coli = 20-30 min; M. tuberculosis = 12-24 hours
- Growth phases: Lag (adaptation) → Log/Exponential (rapid division) → Stationary (growth = death) → Decline (death > growth)
- Oxygen requirements: Obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, aerotolerant anaerobes
- Nutritional types: Photoautotrophs (light + CO₂), chemoautotrophs (chemicals + CO₂), heterotrophs (organic carbon)
- Optimal conditions for pathogens: 37°C, pH 7.0-7.5
Genetic Mechanisms
- Conjugation: Direct cell contact via sex pilus, plasmid transfer
- Transformation: Uptake of free DNA from environment
- Transduction: DNA transfer via bacteriophage (virus)
- Mnemonic - CTT: Conjugation (Touch), Transformation (Take up), Transduction (Transport via virus)
Bacterial Enzymes and Virulence
- Catalase: Breaks down H₂O₂ → H₂O + O₂ (test: Staph positive, Strep negative)
- Coagulase: S. aureus positive (converts fibrinogen → fibrin)
- Streptokinase: Dissolves fibrin clots, promotes spread
- Hyaluronidase: "Spreading factor" - breaks down connective tissue
- Superoxide dismutase: Neutralizes superoxide radicals (O₂⁻)
Endospores
- Forming genera: Bacillus (aerobic), Clostridium (anaerobic)
- Heat resistance factors: Dipicolinic acid + calcium, low water content, thick coats
- Sterilization requirement: Autoclaving at 121°C, 15 psi, 15 minutes
- Spore positions: Central (B. anthracis), subterminal (C. botulinum), terminal (C. tetani - "drumstick")
- Formation trigger: Nutrient depletion, adverse conditions
Toxins
- Exotoxins: Heat-labile proteins, secreted by living cells, highly toxic, can be toxoided
- Endotoxins: Heat-stable LPS, released when Gram-negative bacteria die, causes fever/shock
Biofilms
- Structure: Bacteria in extracellular polymeric substance (EPS)
- Resistance: 100-1000× more resistant to antibiotics than planktonic cells
- Clinical significance: Catheter infections, chronic wounds, implant infections
Culture and Laboratory
- Thioglycolate broth: Oxygen gradient test - obligate aerobes (top), obligate anaerobes (bottom), facultative (throughout, better at top), microaerophiles (band below surface)
- Biological indicators: G. stearothermophilus for steam sterilization, B. subtilis for dry heat/EtO
Important Mnemonics
- Genetic transfer (CTT): Conjugation (Touch), Transformation (Take up DNA), Transduction (Transferred by virus)
- Oxygen detox enzymes (CSCP): Catalase, Superoxide dismutase, Catalase, Peroxidase
- Growth phases (LLSD): Lag, Log, Stationary, Decline
