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Microbiology – Alcamo Lecture: Bacterial Structures

Microbiology – Alcamo Lecture: Bacterial Structures. -Not all bacteria have all structures. Shapes of Bacteria. 3 Different Shapes:. Bacilli. Rod shaped Most occur singly, but some form long chains called Streptobacilli Examples: Typhoid fever Anthrax Diptheria. Cocci.

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Microbiology – Alcamo Lecture: Bacterial Structures

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  1. Microbiology – Alcamo Lecture: Bacterial Structures -Not all bacteria have all structures

  2. Shapes of Bacteria • 3 Different Shapes:

  3. Bacilli • Rod shaped • Most occur singly, but some form long chains called Streptobacilli • Examples: • Typhoid fever • Anthrax • Diptheria

  4. Cocci • Usually sphere shaped but can be oval • Diplococci – cocci that remain in pairs • Examples – Gonorrhea, Menengitis • Streptococci – cocci in chains • Examples - Strep throat, Tooth decay • Staphylococcus – irregular grape-like cluster of cells • Examples – Food poisoning, staph skin infections

  5. Spiral Bacteria • Vibrios – curved rods - look like a comma • Example - Cholera • Spirilla – corkscrew shape with flagella • Example – Rat Bite fever • Spirochetes – corkscrew shape but no flagella • Example - syphilis

  6. Flagella • Used by some bacteria to achieve motion • Made of long rigid strands of protein called flagellin • Protein strands are permanently coiled • Permits the flagellum to rotate and propel the bacterium forward

  7. Flagella • Complicated structure: Filament attached to hook-like shaft which is inserted through cell wall and attached to cell membrane

  8. Flagella Monotrichous Lophotrichous Amphitrichous Peritrichous

  9. Axial Filament • Only spirochete • One flagella attached at both ends of flexible spiral MO • Motion effected by cell spinning around filament

  10. Pili • Look like short flagella but have nothing to do with motion • Very tiny protein “Hairs” that enable MO to stick to surfaces - like “Velcro”

  11. Pili • Pili aid in transfer of genetic material between bacteria • Pili anchor bacteria to surfaces like living tissue • Can enhance MO’s disease effect • Example - gonorrhea

  12. Capsule • Some bacteria secrete a layer of polysaccharides and proteins that stick to its surface • Sticky and gelatinous • Serves as a buffer between the bacteria and its environment • Protects bacteria against dehydration • Protects bacteria against host’s immune system

  13. Glycocalyx • Some bacteria produce a Slime Layer • Complex sugar, made inside cell wall secreted as liquid, polymerizes to jelly like substance • Cavities – S. mutans attaches itself to teeth by using the sugar a person eats – creates an acid that breaks down tooth enamel

  14. Cell Wall • All bacteria have a cell wall except mycoplasmas • Semi-rigid structure, protects, gives shape • Amount of chemical “Peptidoglycan” determines characteristics of cell wall • If a lot: Thick, G+ stain reaction, sensitive to penicillin and lysozyme in tears, saliva, mucous

  15. If small: thinner, G- stain reaction, not sensitive to penicillin or lysozyme • If MO is pathogenic, disease more difficult to cure

  16. Cell Membrane • Boundary layer of the cell inside of cell wall • Contains Cytoplasm, controls molecular traffic in and out of the cell • Triple layer structure, 60% proteins, 38% lipids (phospholipid bilayer), 2% sugars • Antimicrobials (detergents, alcohol, some antibiotics) dissolve cell membrane

  17. cell membrane animation

  18. Cytoplasm Gelatinous mass of proteins carbohydrates lipids nucleic acids salts ions water

  19. Important Structures in Cytoplasm • Ribosomes – protein synthesis • Inclusion Bodies – globules of starch or lipids – store nutrients • Bacterial Chromosome – closed loop of DNA without a membrane or proteins (nucleoid region) • Plasmids – smaller, separate molecules of DNA – few genes but do give bacteria drug resistance (R genes)

  20. Endospores • Some Gram + bacteria produce highly resistant structures - spores • Bacteria grow, mature and reproduce as vegetative cells • Then the bacterial chromosome replicates and the cell membrane grows in to seal off a developing spore • Next, thick layers of peptidoglycan form to protect the cell • Finally, the cell wall of the vegetative cell disintegrates and the spore is released

  21. Endospores • Very resistant to poor environmental conditions: • Extreme temperatures – boiling water • Chemicals – 70% alcohol • Spores have even been recovered alive from an Egyptian mummy’s intestines • Examples of spore formers – anthrax, botulism, tetanus

  22. “Sporulation” is spore formation - DNA + some cytoplasm wrapped in spore case formed by cell membrane • “Germination” occurs when good environmental conditions return – vegetative cell

  23. Kingdom Classification

  24. Archaeobacteria • Have existed on earth longer than any other living organism • They are different from eubacteria: • No peptidoglycan in cell wall • Different lipids in cell membrane • Different ribosomal RNA • Now archaeobacteria and eubacteria are classified as different kingdoms

  25. Archaeobacteria • 3 Types: • Methanogens – rods that live in anaerobic conditions and produce methane gas – common in marshes and the guts of cows and humans • Thermoacidophiles – resistance to acid and high temperatures – live in hot springs and ocean vents • Extreme Halophiles – thrive in high salt environments (Great Salt Lake)

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