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  1. 1. <ul><li>Bacterial Cell Structures & Functions </li></ul>
  2. 2. Bacterial Cell Structure
  3. 3. Bacterial Cell Structure <ul><li>Surface layers -Cell wall, cell membrane, capsule </li></ul><ul><li>Appendages - Flagella, pili or fimbriae </li></ul><ul><li>Cytoplasm - Nuclear material, ribosome, mesosome, inclusions etc. </li></ul><ul><li>Special structure - Endospore </li></ul>
  4. 4. Cell envelope <ul><li>Various layers-Collectively cell envelope </li></ul><ul><li>Gram positive- plasma memebrane, cell wall sometimes capsule </li></ul><ul><li>Gram negative- plasma memebrane, cell wall , outer membrane sometimes capsule </li></ul><ul><li>Plasma membrane in gram negative bacteria is sometimes called inner membrane </li></ul><ul><li>Space between inner membrane and outer membrane is called Periplasmic space. </li></ul>
  5. 6. <ul><li>Bacterial Cell Wall: </li></ul><ul><li>10-25nm in thickness, Neg 10-15nm, Pos 20-25nm </li></ul><ul><li>Functions </li></ul><ul><li>Accounts shape of the cells </li></ul><ul><li>Provides protection of the cells against Osmotic damage </li></ul><ul><li>Confers rigidity </li></ul><ul><li>Takes part in cell division </li></ul><ul><li>Target site for antibiotic </li></ul><ul><li>Carries bacterial antigens- virulence & immunity </li></ul>
  6. 7. <ul><li>General structure : </li></ul><ul><li>Chemically made up of Peptidoglycan. </li></ul><ul><li>It is made by two hexose sugars </li></ul><ul><li> N- acetylglucosamine [NAG] and </li></ul><ul><li> N- acetylmuramic acid [NAM] </li></ul><ul><li>in alternating chains interconnected by tri, tetra or penta pedtide chains. </li></ul>
  7. 8. <ul><li>Gram positive cell walls : </li></ul><ul><li>a. Peptidoglycan-Thicker in gram positive </li></ul><ul><li>b.Polysachharides –Teichoic acids- polymer of glycerol and ribitol phosphates </li></ul><ul><li>Some gram positive bacteria eg Mycobacteria contain lipid- Mycolic acids </li></ul>
  8. 9. Gram negative cell walls <ul><li>Complex structure </li></ul><ul><li>A. Lipoprotein layer- connects the peptidoglycan to outer membrane. </li></ul><ul><li>B. Outer membrane- Outer membrane proteins-target site for antibiotics. </li></ul><ul><li>C. Lipopolysachharides- This layer consists of lipid A to which is attached a polysachharide . </li></ul><ul><li>D. Periplasmic space- Inner and outer membrane. </li></ul><ul><li>E. Peptidoglycan </li></ul>
  9. 11. Cytoplasmic membrane <ul><li>5-10nm thick, elastic semipermeable layer which lies beneath cell wall </li></ul><ul><li>Chemically consists of phospholipids and protein molecules </li></ul><ul><li>Acts as osmotic barrier </li></ul><ul><li>Consists of enzymes permease, oxidase and polymerase </li></ul><ul><li>Contains enzymes of tricarboxylic acid cycle and enzyme necessary for cell wall synthesis. </li></ul><ul><li>Bacterial electron transport system </li></ul>
  10. 12. Cytoplasm <ul><li>Organic and inorganic solutes, water </li></ul><ul><li>Lacks mitochondria and endoplasmic reticulum etc </li></ul><ul><li>Contains ribosomes, mesosomes, vacuoles and inclusions. </li></ul>
  11. 13. Ribosomes <ul><li>Centre of protein synthesis </li></ul><ul><li>Composed of ribosomal RNA and robosomal proteins </li></ul><ul><li>Two subunits 50s and 30s - 70s </li></ul><ul><li>Mesosomes </li></ul><ul><li>Centre for respiratory enzymes </li></ul><ul><li>Septal and lateral </li></ul><ul><li>Septal attached to bacterial chromosome involved in DNA segregation and formation of cross wall during binary fission. </li></ul>
  12. 14. Inclusions <ul><li>Sources of stored energy. </li></ul><ul><li>May be present as polymetaphosphate,lipids and polysachharides and granules of sulphur. </li></ul><ul><li>Nucleus </li></ul><ul><li>No nuclear membrane and nucleolus. </li></ul><ul><li>Dna doesn’t contain any basic proteins. </li></ul><ul><li>Genomic DNA is double stranded in the form of circle. </li></ul>
  13. 15. Plasmids <ul><li>Small circular covalently closed double stranded DNA molecules found in cytoplasm. </li></ul><ul><li>Not essential for life , confer on certain properties like drug resistance and toxigenecity. </li></ul><ul><li>Can be transmitted from one bacteria to another by conjugation or by bacteriophage. </li></ul>
  14. 16. CAPSULE AND SLIME LAYER <ul><li>Amorphous viscid bacterial secretion surrounding the bacteria </li></ul><ul><li>Loose undemarcated secretion-slime layer </li></ul><ul><li>Sharply defined structure – capsule </li></ul><ul><li>Very thin- microcapsules </li></ul><ul><li>Protects bacteria against phagocytes,adherence promote virulence, reservoir of food, </li></ul><ul><li>Demonstrated by negative staining and capsule swelling reaction [ Quellung reaction]. </li></ul>
  15. 17. Flagella <ul><li>Cytoplasmic appendages protruding through cell wall. </li></ul><ul><li>Thread or hair like structure- protein flagellin </li></ul><ul><li>Organ of locomotion </li></ul><ul><li>All motile bacteria except spirochaetes </li></ul><ul><li>Parts: </li></ul><ul><li>Basal body: Embedded in cell envelope & consists of small,central rod surrounded by a series of rings </li></ul><ul><li>Hook :Connects basal body with the filaments </li></ul><ul><li>Filament or shaft: </li></ul><ul><li>External to cell surface </li></ul><ul><li>Composed of protein molecule flagellin </li></ul>
  16. 18. Organ of bacterial locomotion
  17. 19. <ul><li>Structure </li></ul><ul><li>Gram negative- 2 pair of rings- </li></ul><ul><li>M -Plasma membrane </li></ul><ul><li>S -periplasmic space </li></ul><ul><li>P- peptidoglycan </li></ul><ul><li>L- lps </li></ul><ul><li>Gram positive- 1 pair- </li></ul><ul><li>M- Plasma membrane </li></ul><ul><li>S - peptidoglycan </li></ul>
  18. 20. Structure of the flagellum
  19. 21. <ul><li>Parts: </li></ul><ul><li>Basal body : Embedded in cell envelope & consists of small , central rod surrounded by a series of rings </li></ul><ul><li>Hook :Connects basal body with the filaments </li></ul><ul><li>Filament or shaft : </li></ul><ul><li>External to cell surface </li></ul><ul><li>Composed of protein molecule - flagellin </li></ul>
  20. 22. <ul><li>Arrangements/Types </li></ul>
  21. 23. <ul><li>Demonstration: </li></ul><ul><li>Electron microscopy </li></ul><ul><li>Silver impregnation methods </li></ul><ul><li>Dark field microscopy </li></ul><ul><li>Special stains eg Leifsons stain </li></ul>
  22. 24. Fimbriae <ul><li>Hair like appendages projecting from cell surface as straight filaments. </li></ul><ul><li>Also called pili </li></ul><ul><li>0.1-1um length and 10nm thick </li></ul><ul><li>Gram negative bacteria </li></ul><ul><li>Protein pilin </li></ul><ul><li>Best seen in liquid cultures </li></ul><ul><li>Antigenic </li></ul>
  23. 25. <ul><li>E. coli fimbriae </li></ul>
  24. 26. <ul><li>Types </li></ul><ul><li>Common pili- Adhesion to host cells </li></ul><ul><li>Sex pili or F fertility pili- </li></ul><ul><li>Found on male or donor or + strains help in attachment to female or recipient or – strains through conjugation tubes and aid in gene transfer. </li></ul><ul><li>Functions </li></ul><ul><li>Adhesion, Transfer of genetic materials </li></ul><ul><li>Demonstration </li></ul><ul><li>Electron microscopy, Haemagglutination </li></ul>
  25. 27. Bacterial spores <ul><li>Highly resistant resting stages formed in unfavourable condition </li></ul><ul><li>Formed inside the cells so called endospores </li></ul><ul><li>Each form one spore, which on germination form a single vegetative cell </li></ul><ul><li>Non metabolising and non reproducing </li></ul><ul><li>Highly resistant to heat, UV radiation, mechanical disruption, chemical disinfectants etc </li></ul>
  26. 28. <ul><li>Structure </li></ul><ul><li>The core of the fully developed spore has homogenous protoplasm, containing chromosome, enzymes of glycolysis and protein synthesis. </li></ul><ul><li>Core is surrounded by spore walls or inner membrane. </li></ul><ul><li>Outside this spore wall is thick layer the cortex enclosed by outer membrane . </li></ul><ul><li>Spore coat surrounds this spore wall. </li></ul><ul><li>Some bacteria has additional loose outer covering Exosporium. </li></ul>
  27. 30. <ul><li>Demonstration </li></ul><ul><li>Gram stain- unstained. </li></ul><ul><li>AFB stain- 0.25-0.5% H2So4- Red colour. </li></ul><ul><li>Use </li></ul><ul><li>Spores of bacillus stearothermophilus are employed as indicator of proper sterilisation. </li></ul>