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Bacterial Morphology and Structure

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  1. Bacterial Morphology and Structure Xiao-Kui Guo PhD

  2. SIZE OF BACTERIA • Unit for measurement : Micron or micrometer,μm: 1μm=10-3mm • Size: Varies with kinds of bacteria, and also related to their age and external environment. • Cocci: sphere, 1μm • Bacilli: rods , 0.5-1 μm in width -3 μm in length • Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in width

  3. Structure of Bacteria Essential structures cell wall 细胞壁cell membrane 细胞膜Cytoplasm 细胞质nuclear material核质 Particular structures capsule 荚膜 flagella 鞭毛 pili 菌毛 spore芽胞

  4. Flagellum Nucleoid Cell membrane Cell wall Gram + Pili Gram - Granule Capsule Cell (inner) membrane Outer membrane Ribosomes Cell wall 1884: Christian Gram: First publication for the Gram stain method) Editor's note: I would like to testify that I have found the Gram method to be one of the best and for many cases the best method which I have ever used for staining Schizomycetes. Gram, C. 1884. Ueber die isolirte Farbung der Schizomyceten in SchnittÄund Trockenpraparaten. Fortschritte der Medicin, Vol. 2, pages 185-189.

  5. Cell wall • Situation: outmost portion. 15-30nm in thickness, 10%-25% of dry weight.

  6. Cell wall :Common peptidoglycan layer • A backbone of N-acetyl glucosamine and N-acetylmuramic acid: Both discovered in Gram positive and Gram negative bacteria. • A set of identical tetrapeptide side chain attached to N-acetyl-muramic acid: different components and binding modes in Gram positive and Gram negative bacteria. • A set of identical peptide cross bridges: only in Gram positive bacteria

  7. Special components of Gram positive cell wall Teichoic acid SPA / M POTEIN

  8. Special components of Gram negative cell wall

  9. Functions of Cell Wall • Maintaining the cell's characteristic shape- the rigid wall compensates for the flexibility of the phospholipid membrane and keeps the cell from assuming a spherical shape • Countering the effects of osmotic pressure • Providing attachment sites for bacteriophages • Providing a rigid platform for surface appendages- flagella, fimbriae, and pili all emanate from the wall and extend beyond it • Play an essential role in cell division • Be the sites of major antigenic determinantsof the cell surface。 • Resistance of Antibiotics

  10. Wall-less forms of Bacteria. • When bacteria are treated with 1) enzymes that are lytic for the cell wall e.g. lysozyme or 2) antibiotics that interfere with biosynthesis of peptidoglycan, wall-less bacteria are often produced. • Usually these treatments generate non-viable organisms. Wall-less bacteria that can not replicate are referred to as spheroplasts (when an outer membrane is present) or protoplasts (if an outer membrane is not present). • Occasionally wall-less bacteria that can replicate are generated by these treatments (L forms).

  11. Cell membrane • Site of biosynthesis of DNA, cell wall polymers and membrane lipids.Selective permeability and transport of solutes into cells • Electron transport and oxidative phosphorylation • Excretion of hydrolytic exoenzymes

  12. Mesosomes • Mesosomes are specialized structures formed by convoluted inveigh-nations of cytoplasmic membrane, and divided into septal and lateral mesosome.

  13. Cytoplasm • Composed largely of water, together with proteins, nucleic acid, lipids and small amount of sugars and salts • Ribosomes: numerous, 15-20nm in diameter with 70S; distributed throughout the cytoplasm; sensitive to streptomycin and erythromycin site of protein synthesis • Plasmids: extrachromosomal genetic elements • Inclusions: sources of stored energy, e,g volutin

  14. Plasmids are small,circular/line,extrachromosomal,double-stranded DNA molecules。They are capable of self-replication and contain genes that confer some properties,such as antibiotic resistance,virulence factors。Plasmids are not essential for cellular survival. Plasmid Inclusions of Bacteria • Inclusions are aggregates of various compounds that are normally involved in storing energy reserves or building blocks for the cell. Inclusions accumilate when a cell is grown in the presence of excess nutrients and they are often observed under laboratory conditions. granulose

  15. Nucleus • Lacking nuclear membrane, absence of nucleoli, hence known as nucleic material or nucleoid, one to several per bacterium.

  16. Attachment • Protection from phagocytic engulfment. • Resistance to drying. • Depot for waste products. • Reservoir for certain nutrients. • protection Capsules and slime layers • These are structures surrounding the outside of the cell envelope. They usually consist of polysaccharide; however, in certain bacilli they are composed of a polypeptide (polyglutamic acid). They are not essential to cell viability and some strains within a species will produce a capsule, whilst others do not. Capsules are often lost during in vitro culture.

  17. Some bacterial species are mobile and possess locomotory organelles - flagella. Flagella consist of a number of proteins including flagellin • The diameter of a flagellum is thin, 20 nm, and long with some having a length 10 times the diameter of cell. Due to their small diameter, flagella cannot be seen in the light microscope unless a special stain is applied. Bacteria can have one or more flagella arranged in clumps or spread all over the cell. Flagella Monotrichate/Amphitrichate/Lophotrichate/Peritrichate • Identification of Bacteria • Pathogenesis • Motility of bacteria

  18. Pili • Pili are hair-like projections of the cell , They are known to be receptors for certain bacterial viruses. Chemical nature is pilin • Classification and Function • Common pili or fimbriae: fine , rigid numerous, related to bacterial adhesion • Sex pili: longer and coarser, only 1-4, related to bacterial conjugation

  19. Endospores (spores) • Identification of Bacteria • Pathogenesis • Resistance • Dormant cell • Resistant to adverse conditions • - high temperatures • - organic solvents • Produced when starved • Contain calcium dipicolinate • DPA, Dipicolinic acid • Bacillus and Clostridium

  20. Methods Microscope • Light Microscope • Electron Microscope • Darkfield Microscope • Phase Contrast Microscope • Fluorescence Microscope • Cofocal Microscope) Staining Methods • Simple staining; • Differential staining ( Gram stain, Acid-fast stain), • Special staining( Negative stain, Spore stain, Flagella stain)