Transcript Bacterial Morphology and Structure

Bacterial Morphology and Structure
Xiao-Kui Guo PhD
http://basic.shsmu.edu.cn/passw/micro2/index.asp
SIZE OF BACTERIA
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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.
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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
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
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.
Flagellum
Cell membrane Nucleoid
Cell wall
Gram +
Pili
Gram Granule
Capsule
Cell (inner) membrane Outer membrane
Ribosomes
Cell wall
Gram, C. 1884. Ueber die isolirte Farbung
der Schizomyceten in SchnittÄund
Trockenpraparaten. Fortschritte der
Medicin, Vol. 2, pages 185-189.
Cell wall
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Situation:
outmost portion.
15-30nm in
thickness, 10%25% of dry
weight.
Cell wall :Common peptidoglycan layer
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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
Special components of
Gram positive cell wall
Teichoic acid
SPA / M POTEIN
Special components of
Gram negative cell wall
Functions of Cell Wall
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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 appendagesflagella, 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
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
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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
Mesosomes
•
Mesosomes are specialized structures
formed by convoluted inveigh-nations of
cytoplasmic membrane, and divided into
septal and lateral mesosome.
Cytoplasm
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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
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Plasmids: extrachromosomal
genetic elements
 Inclusions: sources of stored
energy, e,g volutin
Plasmid
Plasmids are small，circular/line，
extrachromosomal，double-stranded DNA
molecules。They are capable of selfreplication and contain genes that confer
some properties，such as antibiotic
resistance，virulence factors。Plasmids are
not essential for cellular survival.
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granulose
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.
Inclusions of
Bacteria
Nucleus
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Lacking nuclear
membrane, absence
of nucleoli, hence
known as nucleic
material or nucleoid,
one to several per
bacterium.
Capsules and slime layers
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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.
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.
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Identification
of Bacteria
Pathogenesis
Motility of
bacteria
Monotrichate/Amphitrichate/Lophotrichate/Peritrichate
Flagella
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
a. Common pili or fimbriae: fine , rigid numerous,
related to bacterial adhesion
b. Sex pili: longer and coarser, only 1-4, related to
bacterial conjugation
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Endospores
(spores)
• Dormant cell
• Resistant to adverse
conditions
- high temperatures
- organic solvents
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Identification of
Bacteria
 Pathogenesis
 Resistance
• Produced when starved
• Contain calcium dipicolinate
DPA, Dipicolinic acid
• Bacillus and Clostridium
Methods
Microscope
 Light Microscope
 Electron Microscope
 Darkfield Microscope
 Phase Contrast Microscope
 Fluorescence Microscope
 Cofocal Microscope）
Staining Methods
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Simple staining;
 Differential staining ( Gram
stain, Acid-fast stain),
 Special staining( Negative stain,
Spore stain, Flagella stain)