MICROBIOLOGY PPT LECTURE NOTES | Karya Tulis Ilmiah

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Bacterial Morphology and Structure

Xiao-Kui Guo PhD

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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

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Structure of Bacteria

Particular structures

capsule 荚膜

flagella 鞭毛 pili 菌毛

spore 芽胞

Essential structures

cell wall

cell wall 细胞壁细胞壁

cell membrane

cell membrane 细胞膜细胞膜

Cytoplasm

Cytoplasm 细胞质细胞质

nuclear material

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Gram +

Gram

-Cell wall

Cell (inner) membrane Outer membrane Ribosomes Granule Cell wall Nucleoid Cell membrane Capsule Flagellum Pili

Gram, C. 1884. Ueber die isolirte

Farbung der Schizomyceten in

SchnittÄund Trockenpraparaten.

Fortschritte der Medicin

Fortschritte der Medicin, Vol. 2, pages , Vol. 2, pages 185-189.

185-189.

1884:

1884: Christian GramChristian Gram: First publication for the Gram stain method) : 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

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.

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Cell wall

 Situation:

outmost portion. 15-30nm in

thickness, 10%-25% of dry

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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.

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Special components of

Gram positive cell wall

Teichoic acid

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Special components of Gram Special components of Gram

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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 。

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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

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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

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Mesosomes

• Mesosomes are specialized structures

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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

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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.

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Nucleus

 Lacking nuclear

membrane, absence of nucleoli, hence known as nucleic

material or nucleoid, one to several per

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Capsules and slime layers

 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.

 Attachment

 Protection from phagocytic engulfment.

 Resistance to drying.  Depot for waste products.  Reservoir for certain

nutrients.

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Flagella

Monotrichate/Amphitrichate/Lophotrichate/Peritrichate

 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}

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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

a. Common pili or fimbriae: fine , rigid numerous,

related to bacterial adhesion

b. Sex pili: longer and coarser, only 1-4, related to

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Endospores

(spores)

• _{Dormant cell}_{Dormant cell}

• Resistant to adverse _{Resistant to adverse}

conditions

conditions

- high temperatures

- organic solvents

• _{Produced when starved}_{Produced when starved}

• _{Contain calcium dipicolinate}_{Contain calcium dipicolinate}

DPA, DPA, DDipicolinic acidipicolinic acid

• _Bacillus_Bacillus_and_and_Clostridium_Clostridium

 Identification of

Bacteria

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Microscope

 Light Microscope

 Electron Microscope

 Darkfield Microscope

 Phase Contrast Microscope

 Fluorescence Microscope

 Cofocal Microscope ）

Methods

Staining Methods

 Simple staining;

 Differential staining ( Gram

stain, Acid-fast stain),

 Special staining( Negative stain,