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 , μm in width -3 μm in length
Spiral bacteria: 1~3 μm in length and 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. 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 +
Gram -
Cell wall
Cell (inner) membrane
Outer membrane
Ribosomes
Granule
Nucleoid
Cell membrane
Capsule
Flagellum
Pili
Gram, C Ueber die isolirte Farbung der Schizomyceten in SchnittÄund Trockenpraparaten. Fortschritte der Medicin, Vol. 2, pages

5. Cell wall
Situation: outmost portion nm 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

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

9. Special components of Gram negative cell wall

10. 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

11. 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).

12. 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

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

14. 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

15. Inclusions of Bacteria
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

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

17. 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.

18. Flagella Identification of Bacteria Pathogenesis Motility of bacteria
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

19. 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

20. Endospores (spores) Dormant cell Resistant to adverse conditions
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

21. Methods Simple staining;
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)