crash course Flashcards
(28 cards)
What are the main differences between Gram-positive and Gram-negative bacteria?
Gram-positive: Thick peptidoglycan layer, teichoic acids, no outer membrane, stains purple.
Gram-negative: Thin peptidoglycan, outer membrane with LPS, stains pink.
What is the function of peptidoglycan in bacteria?
Provides structural integrity and resistance to osmotic pressure.
What is the major component of the Gram-negative outer membrane?
Lipopolysaccharide (LPS), containing Lipid A (toxic endotoxin), core polysaccharide, and O antigen.
What is the function of bacterial capsules?
Prevents phagocytosis and enhances virulence.
What is the role of pili (fimbriae) in bacteria?
Adhesion to surfaces and other cells (e.g., Neisseria gonorrhoeae).
What are bacterial endospores, and which bacteria produce them?
Dormant, resistant structures that survive harsh conditions.
Produced by Bacillus (e.g., B. anthracis) and Clostridium (e.g., C. tetani, C. difficile).
What are the four phases of bacterial growth?
Lag phase: Metabolic adaptation, no division.
Log (exponential) phase: Rapid division, most sensitive to antibiotics.
Stationary phase: Nutrients deplete, waste accumulates.
Death phase: Bacterial decline due to toxicity and starvation.
What are obligate aerobes and obligate anaerobes?
Obligate aerobes: Require oxygen (e.g., Mycobacterium tuberculosis).
Obligate anaerobes: Cannot survive in oxygen (e.g., Clostridium species).
What is the role of catalase, superoxide dismutase, and peroxidase in bacteria?
These enzymes detoxify reactive oxygen species (ROS) and allow survival in oxygen environments.
What are the three main mechanisms of horizontal gene transfer?
Transformation: Uptake of naked DNA.
Transduction: Bacteriophage-mediated transfer.
Conjugation: Direct transfer via sex pilus (F plasmid).
What is the difference between generalized and specialized transduction?
Generalized: Any bacterial DNA is transferred.
Specialized: Only specific bacterial genes near prophage are transferred.
What is the significance of transposons in bacterial genetics?
Mobile genetic elements that can insert into bacterial genomes, spreading antibiotic resistance.
What is the difference between endotoxins and exotoxins?
Endotoxin: LPS from Gram-negative bacteria; causes septic shock (e.g., Lipid A).
Exotoxin: Secreted proteins from both Gram-positive and Gram-negative bacteria.
Give examples of notable exotoxins and their effects.
Diphtheria toxin: Inhibits EF-2 (Corynebacterium diphtheriae).
Botulinum toxin: Blocks ACh release → flaccid paralysis (Clostridium botulinum).
Tetanus toxin: Inhibits GABA/glycine → spastic paralysis (Clostridium tetani).
Cholera toxin: Activates Gs → massive diarrhea (Vibrio cholerae).
What is quorum sensing in bacteria?
Bacterial communication system regulating gene expression based on population density.
How does the immune system respond to intracellular vs. extracellular bacteria?
Intracellular bacteria → Cell-mediated immunity (T cells, macrophages).
Extracellular bacteria → Humoral immunity (antibodies, complement).
What is molecular mimicry in bacterial infections?
Bacterial antigens resemble host proteins, leading to autoimmune reactions (e.g., Rheumatic fever from Streptococcus pyogenes).
What is the primary virulence factor of Streptococcus pneumoniae?
Polysaccharide capsule (prevents phagocytosis).
Which bacteria are obligate intracellular pathogens?
Rickettsia, Chlamydia, Mycobacterium leprae.
What differentiates Staphylococcus aureus from other Staphylococcus species?
Coagulase-positive (converts fibrinogen to fibrin).
What bacteria are associated with nosocomial (hospital-acquired) infections?
Pseudomonas aeruginosa (ventilators, burns).
Staphylococcus aureus (MRSA).
Clostridium difficile (C. diff colitis).
What is the causative agent of Lyme disease?
Borrelia burgdorferi, transmitted by Ixodes tick.
What are the three stages of syphilis?
Primary: Painless chancre.
Secondary: Rash on palms/soles, condylomata lata.
Tertiary: Neurosyphilis, gummas, aortitis.
What test differentiates Gram-positive cocci?
Catalase test:
Positive → Staphylococcus.
Negative → Streptococcus.
