What are the shapes of bacteria?
- Cocci (spherical)
- Rods (bacilli)
- Vibrios (comma-shaped)
- Spirilla (rigid spirals)
- Spirochetes (flexible spirals)
- Filamentous bacteria
- Pleomorphic forms (variable shapes)
Cocci can occur in pairs (diplococci), chains (e.g., Streptococcus), clusters (e.g., Staphylococcus), tetrads, or cubical packets.
Define biofilm.
A structured community of microorganisms encased in a self-produced extracellular polymeric substance (EPS)
Biofilms provide structural stability, protection from antibiotics, and allow bacteria to share resources.
Distinguish Gram-positive from Gram-negative bacteria based on cell wall structure.
- Gram-positive: Thick peptidoglycan layer, teichoic acids, stains purple, no outer membrane
- Gram-negative: Thin peptidoglycan layer, outer membrane with LPS, stains pink/red, more antibiotic resistant
Gram-positive bacteria retain crystal violet stain, while Gram-negative bacteria do not.
How do environmental factors affect bacterial growth?
- Temperature: Psychrophiles, mesophiles, thermophiles, hyperthermophiles
- Oxygen requirements: Obligate aerobes, facultative anaerobes, obligate anaerobes, microaerophiles, aerotolerant anaerobes
- pH: Neutrophiles, acidophiles, alkaliphiles
- Water availability: High solute concentrations inhibit growth
Different bacteria thrive in specific environmental conditions.
Fusobacterium nucleatum illustrates how bacterial features explain pathogenicity. Name some characteristics.
- Gram-negative
- Obligate anaerobe
- Spindle-shaped morphology
- Adhesion ability
- Lack of motility/spores
These characteristics help predict where bacteria live in the body and how they cause disease.
Explain how horizontal gene transfer enables rapid bacterial evolution.
Allows bacteria to acquire large segments of DNA in a single event, conferring new capabilities
Example: Pathogenic E. coli O157:H7 acquired nearly 900,000 additional base pairs through HGT.
Compare the four mechanisms of gene acquisition in bacteria.
- Natural competence (transformation)
- Conjugation
- Generalized transduction
- Lysogeny (specialized transduction)
Each mechanism contributes to genetic diversity and adaptation.
What role do bacteriophages play in bacterial pathogenesis?
- Carry genes encoding toxins or virulence factors
- Transform harmless bacteria into pathogens
Example: V. cholerae acquires cholera toxin genes via phage.
Describe how genomic islands and pathogenicity islands contribute to virulence.
- Genomic islands: Large DNA blocks acquired via HGT
- Pathogenicity islands: Specific genomic islands containing virulence genes
Example: LEE pathogenicity island in E. coli O157:H7 encodes proteins for attaching to gut.
What are the steps of bacterial infection establishment?
- Adhesion
- Colonization
- Invasion
Each step is crucial for successful infection and persistence.
What are some immune evasion strategies used by bacteria?
- Avoiding phagocytosis
- Surviving inside phagocytes
- Avoiding antibody recognition
Strategies include capsules, complement interference, and antigenic variation.
What are exotoxins?
Toxic proteins secreted by bacteria into their environment
Examples include botulinum toxin and cholera toxin.
What are endotoxins?
Structural components of the bacterial cell, specifically lipopolysaccharides (LPS) in Gram-negative bacteria
Released when bacteria die, triggering strong immune responses.
What are effectors in bacterial pathogenesis?
Molecules delivered by bacteria into host cells to manipulate them
Example: Salmonella effectors rearranging the host cytoskeleton.
Classify exotoxins by structure and mechanism.
- A-B toxins
- Membrane-damaging toxins
- Superantigens
Each type has a unique mechanism of action affecting host cells.
What is the mechanism of cholera A-B toxin?
B subunit binds to GM1 ganglioside receptors, A subunit activates adenylate cyclase, leading to increased cAMP and chloride secretion
This results in watery diarrhea characteristic of cholera.
Compare botulinum toxin and tetanus toxin.
- Botulinum: Prevents acetylcholine release, flaccid paralysis
- Tetanus: Prevents release of inhibitory neurotransmitters, spastic paralysis
Both are neurotoxins from Clostridium species.
What is the mechanism of cAMP in cholera?
Opens chloride channels → massive chloride & water secretion into the intestine → watery diarrhea
This mechanism is characteristic of cholera infection.
What is the source of Botulinum Toxin?
Clostridium botulinum
Botulinum toxin is associated with foodborne illness and can also be caused by wound contamination.
What is the target tissue for Tetanus Toxin?
Central nervous system inhibitory interneurons
Tetanus toxin affects the nervous system, leading to muscle rigidity.
What clinical effect does Botulinum Toxin cause?
- Muscle weakness
- Paralysis
- Respiratory failure
Botulinum toxin leads to severe muscle impairment due to its action at the neuromuscular junction.
What clinical effect does Tetanus Toxin cause?
- Muscle rigidity
- Lockjaw
- Spastic paralysis
Tetanus toxin prevents the release of inhibitory neurotransmitters, resulting in spastic paralysis.
How is Botulinum Toxin transmitted?
Foodborne, wound contamination
This transmission route highlights the importance of food safety and wound care.
How is Tetanus Toxin transmitted?
Wound contamination
Tetanus can occur when spores enter the body through cuts or wounds.
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Unit 1- Microbes and Humanity: Historical Impact and Modern Understanding30
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Unit 2- Microbial Diversity and Pathogenesis34
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Unit 3- Acellular Pathogens: Viruses & Prions31
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Unit 4- Bacterial Pathogens26
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Unit 5- Eukaryotic Pathogens16
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Unit 6- Immunity55
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Unit 7- Diagnostics14
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Unit 8- Stopping Microbial Growth26
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Unit 9- Antimicrobial Resistance12
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Unit 10- Epidemiology22
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Unit 11- Microbiome14
