MICROBIOLOGY PPT LECTURE NOTES | Karya Tulis Ilmiah

Bacterial Morphology and Structure

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

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



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

Cell wall
 Situation:

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

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

Special components of
Gram positive cell wall
Teichoic acid

SPA / M POTEIN

pecial components of Gram
negative cell wall

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 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).

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

Mesosomes
•

Mesosomes 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 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

Plasmid

granulo
se

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
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

Inclusions of
Bacteria

Nucleus

 Lacking

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

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.

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/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

Endospores
(spores)





• Dormant cell
• Resistant to adverse
conditions
- high temperatures
- organic solvents

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
 Simple

staining;
 Differential staining ( Gram
stain, Acid-fast stain),
 Special staining( Negative stain,
Spore stain, Flagella stain)