Bacterial Morphology and Structure Bacterial Morphology and Structure Xiao-Kui Guo PhD

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Transcript of Bacterial Morphology and Structure Bacterial Morphology and Structure Xiao-Kui Guo PhD

  • Bacterial Morphology and StructureXiao-Kui Guo PhD

    http://basic.shsmu.edu.cn/passw/micro2/index.asp

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

  • Structure of Bacteria

    Particular structures capsule flagella pili spore Essential structures cell wall cell membrane Cytoplasm nuclear material

  • Gram, C. 1884. Ueber die isolirte Farbung der Schizomyceten in Schnittund Trockenpraparaten. Fortschritte der Medicin, Vol. 2, pages 185-189. 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 ofthe best and for many cases the best method which I have ever used for staining Schizomycetes.

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

  • Cell wall :Common peptidoglycan layerA 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

  • NAM CH2OH H

    CH C=O H N LAla DGlu LLys GlyGlyGlyGlyGlyN DAla C=O

    O

    OH

    HNH

    H3C

    H

    O

    H

    O

    H

    O=C CH3

    O

    OH

    HNH

    H

    O=C CH3

    CH2OH

    H

    H

    H

    NAG

    NAM CH2OH H

    CH C=O H N LAla DGlu LLys GlyGlyGlyGlyGlyN DAla C=O

    O

    OH

    HNH

    H3C

    H

    O

    H

    O

    H

    O=C CH3

    O

    OH

    HNH

    CH2OH

    H

    H

    H

    NAG

    O=C CH3

    H

  • Special components of Gram positive cell wall Teichoic acid

    SPA / M POTEIN

  • Special components of Gram negative cell wall

  • Functions of Cell WallMaintaining 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 pressureProviding attachment sites for bacteriophagesProviding a rigid platform for surface appendages- flagella, fimbriae, and pili all emanate from the wall and extend beyond itPlay an essential role in cell divisionBe the sites of major antigenic determinants of the cell surfaceResistance of Antibiotics

  • 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).

  • Cell membraneSite of biosynthesis of DNA, cell wall polymers and membrane lipids. Selective permeability and transport of solutes into cellsElectron transport and oxidative phosphorylationExcretion of hydrolytic exoenzymes

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

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

  • PlasmidPlasmids are smallcircular/lineextrachromosomaldouble-stranded DNA moleculesThey are capable of self-replication and contain genes that confer some propertiessuch as antibiotic resistancevirulence factorsPlasmids are not essential for cellular survival. Inclusions of BacteriaInclusions 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

  • Nucleus

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

  • Capsules and slime layersThese 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.Attachment Protection from phagocytic engulfment. Resistance to drying. Depot for waste products. Reservoir for certain nutrients. protection

  • Flagella Monotrichate/Amphitrichate/Lophotrichate/Peritrichate Identification of BacteriaPathogenesisMotility of bacteriaSome bacterial species are mobile and possess locomotory organelles - flagella. Flagella consist of a number of proteins including flagellinThe 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.

  • PiliPili are hair-like projections of the cell , They are known to be receptors for certain bacterial viruses. Chemical nature is pilinClassification and FunctionCommon pili or fimbriae: fine , rigid numerous, related to bacterial adhesionSex pili: longer and coarser, only 1-4, related to bacterial conjugation

  • Endospores (spores)Dormant cell Resistant to adverse conditions - high temperatures- organic solventsProduced when starvedContain calcium dipicolinate DPA, Dipicolinic acidBacillus and ClostridiumIdentification of BacteriaPathogenesisResistance

  • Microscope Light MicroscopeElectron MicroscopeDarkfield MicroscopePhase Contrast MicroscopeFluorescence MicroscopeCofocal MicroscopeMethodsStaining MethodsSimple staining;Differential staining ( Gram stain, Acid-fast stain), Special staining( Negative stain, Spore stain, Flagella stain)