Bacterial Morphology and Structure

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Bacterial Morphology and Structure

• Xiao-Kui Guo PhD
• http//basic.shsmu.edu.cn/passw/micro2/index.asp

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SIZE OF BACTERIA

• Unit for measurement Micron or
  micrometer,µm 1µm10-3mm
• 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 13 µm in length and 0.3-0.6 µm
  in width

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Structure of Bacteria
Essential structures cell wall ???cell
membrane ???Cytoplasm ???nuclear material ??

• Particular structures
• capsule ??
• flagella ??
• pili ??
• spore ??

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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.
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Cell wall

• Situation outmost portion. 15-30nm in thickness,
  10-25 of dry weight.

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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

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Special components of Gram positive cell wall

• Teichoic acid

SPA / M POTEIN
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Special components of Gram negative cell wall
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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 determinants of
  the cell surface?
• Resistance of Antibiotics

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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).

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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

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Mesosomes

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

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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

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Plasmid
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.
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
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Nucleus

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

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Capsules and slime layers

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

• 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.

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Flagella

• 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.

• Identification of Bacteria
• Pathogenesis
• Motility of bacteria

• Monotrichate/Amphitrichate/Lophotrichate/Peritrich
  ate

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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

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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

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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)