lecture 3 bacterial ultra structure

8/6/2019 Lecture 3 Bacterial Ultra Structure

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BACTERIAL CELL

ULTRASTRUCTURES


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General Division:

I. External - Capsule- Fimbriae- Flagellum

II. Internal - Cell Wall- Cytoplasmic Membrane- Cytoplasm- Mesosome

- Nuclear Body- Ribosome- Plasmid- Inclusion Granule- Endospore


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BACTERIAL ULTRASTRUCTURE

A . Bacterial Surface Coating:= are extracellular polysaccharide polymers whichsurrounds the bacterial cell

Capsule= well-formed thick viscous jelly-like structure firmly

attached to the cell wall surrounding the cell= not readily removed.= easily visualized by negative staining using India

ink method


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Slime layer

= loose and irregularly arranged meshwork of fibrils totally detached from the cell but still surrounds the cell

= when present are more easily washed off


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Chemical Comp.:= water main component 98-99%= 1-2% of bacterial capsule are chemically

polysaccharide, Except capsule of:B. anthracis-polypeptide (D-glutamic acid)S. pyogenes-Hyaluronic acid

Function:= protection from phagocytosis= correlates with virulence= act as antigen (used in the identification)

and typing of capsulated bacteria= allows bacteria to adhere/attach to various

surfaces in its natural environment inorder to surviveDetection:

1. Negative staining (India Ink)2. Special staining (Capsular method)3. Serological (Quellung reaction)


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B. Appendages Flagellum & A xial filamentsFimbriae

FLAGELLUM:= long, thick, helical protein filament of uniform length

and diameter= commonly seen among free-swimming bacteria

= originates in cytoplasmic membrane= composed of 3 parts:1. Basal body anchors the flagellum to the

cell wall and plasma membrane

2. Hook attached to the basal body andconnects to the filament

3. Filament external to the cell and contains

the flagellar protein


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Chemical Comp.: protein monomer - Flagellin

Function - Motility organelle of many pathogenic bacteria

Detection:1. Darkfield / Phase contrast microscopy

(Wet mount / Unstained smear)2. Brightfield/Electron Microscopy using stained

specimen3. Serological use of specific antisera against

flagellar (H) antigen4. Swarming phenomenon5. Motility medium6. Hanging drop preparation


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T ypes and A rrangement of flagella in relation to thedistribution and number:

I. Monotrichous single polar flagellum at one end

II. Multitrichous more than one flagella


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Types: A ) Lophotrichous tuft of flagella at one polar end

B) A mphitrichous single flagellum or tulf of flagella at both polar end

C) Peritrichous flagella distributed all over thebody of the bacteria


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A xial Filaments= flagella-like sheathed filaments located in

the periplasmic space (between the inner)and outer membrane of the cell

= move by traveling helical wave on oppositedirection

= motility organelle of spirochete

Fimbriae / Pili / Microfibrils= short, straight, thin hair-like filaments usually

distributed around the body of bacteria.= originates in the cytoplasmic membrane= found virtually among all gram (-) bacteria but not in

gram (+) bacteria


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2 types according to function:

1. Common/ordinary for attachment or adherenceto mucosal surfaces of host cell duringcolonization and infection.

2. Sex pili responsible for attachment of donor andrecipient cell during bacterial conjugationwhereby genetic material (DN A ) from one cellis transferred to another (reproduction).

Chem. Comp. - Protein (Pilin)

Detection: Electron Microscopy


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Cell wall (Peptidoglycan, Murien, Mucopeptide / Glycopeptide)= complex, rigid, multilayered structure that protects the

protoplast and the underlying fragile plasmamembrane

= found in all pathogenic free-living bacteria except Mycoplasma (cell-walless bacteria)

Chemical Comp.:1. Protein (Mesodiaminopimelic acid,Isomers of D-glutamic)

acid and D-alanine

2. Polysaccharide(N-acetylmuramic acid and N-acetylglucosamine)= responsible for rigidity of cell wall

3. Lipids


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Function :1. Responsible for the characteristic shape of bacterium

2. Provides strong structural support necessary to keepbacterial cell from rupturing due to changes inthe environmental osmotic pressure

3. Contain somatic O antigen that can serologicallyidentify particular bacteria

4. Site of action of some antibiotics5. Determines differences in gram staining reaction

Detection :

1. Microscopy of smear prepared from specialstaining method.2. Electron microscopy.3. By chemical methods using lysozyme.


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COMPARISON OF GRAM POSITIVE AND GRAM NEGATIVE CELL WALL

Gram PositiveGram Positive Gram NegativeGram Negative

PeptidoglycanPeptidoglycan V

ery thick homogenous single layer V

ery thick homogenous single layerextensively crossedextensively crossed- -linked.linked.Constitute 50Constitute 50- -90% of the cell wall90% of the cell wall

material.material.(N A M, N A G, D(N A M, N A G, D--alanine)alanine)

Diaminophemilic acidDiaminophemilic acid

More complex layer composedMore complex layer composedof thin peptidoglycan with fewof thin peptidoglycan with fewcrossedcrossed--linked and an outerlinked and an outermembrane layer.membrane layer.

Constitute 5Constitute 5- -10% of the cell10% of the cellwall material.wall material.

A uxiliary A uxiliary compoundscompounds T eichoic acid (Polymer of ribitol and)T eichoic acid (Polymer of ribitol and)glycerol phosphateglycerol phosphate

Lipoteichoic acidLipoteichoic acidSurface proteinSurface protein

No teichoic acidNo teichoic acidOuter membrane contains:Outer membrane contains:

PhospholipidsPhospholipids--located in thelocated in theinner membraneinner membrane

LipoprotienLipoprotien connects OM toconnects OM tothe peptidoglycanthe peptidoglycan

LipopolysaccharideLipopolysaccharide(LPS/Endotoxin layer)(LPS/Endotoxin layer)

located in the outerlocated in the outerlayer of the OMlayer of the OM

-- contains the lipid A contains the lipid A

PenicillinPenicillin sensitivitysensitivity SensitiveSensitive Resistant Resistant

Response toResponse tolysozymelysozyme

Digest/Digest/ DegradeDegrade Resistant Resistant


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GramPositive

GramNegative


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Damage to the cell wall may result to:

= when a gram positive bacteria is exposed tolysosyme will degrade the peptidoglycanlayer resulting to complete removal of the cellwall producing a osmotically fragile wall-lessspherical body called Protoplast

= since all cell wall components is removed,therefore incapable of regeneration

Spheroplast = when a gram negative bacteria is exposed to

lysozyme it looses the peptidoglycan layerbut retain the outer membrane leaving aless fragile spherical body capable

of regenerating the cell wall.


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Protoplast: comprises the naked cytoplasmic membrane andits content

PERIPL A SM = space between the plasma inner membraneand the outer membrane layer

= readily observe among gram negative bacteria= consist of a gell-like substances which help

secure nutrients from the environment

CY T OPL A SMIC/PL A SM A /CELL MEMBR A NE:= thin elastic bilayered semi-permeable membrane

lying underneath the cell wall enclosing thecytoplasm of the cell.

Chemical Composition - Lipoprotein -(composed of phospholipids and protein molecules)


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Functions:1. Serve as selective permeability barrier

(transport of nutrient material in & out of cell)2. Site of electron transport and oxidative

phosphorylation of substances involve in thegeneration of chemical energy ( AT P)

3. Helps in the excretion of metabolic waste product

4. Site for excretion of enzyme involved in OMsynthesis, CW synthesis and in the secretionof extracytoplasmic & extracellular substances: A . Permease for active uptake of nutrient B. RespiratoryC. Polymerase that manufacture substances

of the cell wallD. Hydrolytic

Detection - Electron microscopy


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MESOSOME:= usually seen as an invagination of the membrane

associated cytoplasmic sac seen in Gram (+) cell= contains lamellar, tubular and vesicular structure= often associated with division septaChemical Composition - LipoproteinFunctions:

1. Site for the synthesis of cytochrome oxidase

and reductase enzyme2. Provide support for enzymes present in the cellmembrane

3. Responsible for compartmenting DN A duringcell division and sporulation

Detection - Electron microscopy

Cytoplasm = refers to everything that is enclosed by thecytoplasmic membrane

= site for most bacterial metabolism

= 80% is composed of water


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NUCLE A R BODY: (Nucleus / Nucleoid)= genetic material of bacteria= contains a single circular molecule of double

stranded DN A network which runs parallel to thelong axis of the cell

= found homogenous within the cytoplasm not enclosed in a nuclear membrane.

= constitute 2-3% of the cell weight.= no definite form and seen at all stages of growthcycle of the bacteria.

Chemical Composition DN A Function:

1. Controls the growth and metabolic activity of the bacteria

2. Responsible for hereditary characteristics of the cell.

Detection - Electron microscopy, Feulgin staining (+)


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PL A SMID/EPISOME:= extrachromosomal genetic material capable of

autonomous replication usually located nearthe chromatin body.

Chemical Composition DN A

Function:1. T ransfer of genetic material from one cell to anotherby conjugation ( T ransmissible Plasmid)

2. Carry genes for activities like:a) A ntibiotic resistance

b) T oxin productionc) Synthesis of enzymed) T olerance to toxic metals

Detection Feulgin staining (+), Electron microscopy


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RIBOSOME:= histone-like particles composed of ribosomal RN A

(rRN A ) and protein molecules found in thecytoplasm of the cell.= site of action for many antibiotics that inhibit protein

synthesis.= have a sedimentation coefficient of 70S and are

composed of 50 S and 30 S subunits containing16 S, 23 S and 5 S RN A respectively

= procaryotic ribosome - 70s= eucaryotic ribosome - 80s

Function Site of protein synthesis

Detection Feulgin staining (-), Electron microscopy


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INCLUSION / CY T OPL A SMIC GR A NULE:= large granules found anywhere in the cytoplasm= are accumulation of organic and inorganic substances

which serves as source of energy and nutrient supply to the organism

Kinds:1. Babes Ernst / Volutin / Metachromatic granules

Chemical Composition polymerizedmetaphosphate which can be used in thesynthesis of AT P

Function reserve energy supply

Demonstration simple staining / specialstaining ( A lbert s stain)


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2. Lipid granules

Chemical Composition polymer of beta-hydroxybutyric acid

Function reserve food supply.

3. Sulfur granules derived energy by oxidizing

sulfur and sulfur-containingcompounds.

Function reserve energy supply for sulfur-containing bacteria.

4. Glycogen granule polymer of glucose.

Function reserve food supply.


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ENDOSPORES:

= highly refractile body formed within vegetative

bacterial cells in response to adverse environmental

condition and due to deficient nutrient supply

= known as endospore, because it is formed inside thebacteria cell and is genetically controlled

= are metabolically inactive bacterial cell that are highly

resistant to desiccation, heat and various chemicalagents

= found in the cytoplasm of rod-shaped sporeforming

bacteria of the genus Bacillus & Clostridium


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= Composed of five parts:1. Core located at the center which is the spore

cytoplasm/protoplast.

- contains the nucleus and enzyme dipicolinic acid2. Spore wall enclosing the core.3. Cortex laminated structure surrounding the spore

wall4. Spore coat multilayered membrane enclosing the

cortex5. Exosporium the outermost covering of the spores

which give the spore a rigid appearance.


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= contains Calcium Dipicolinate which aids in heat resistance within the core by making the proteinand nucleic acid more resistant to denaturation

= germinate under favorable nutritional condition after

an activation process that involves damage to thespore coat

= helpful in identifying some specie of bacteria especiallythose sporeforming bacilli (Clostridium and Bacillus)


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Classification accdg. to:

A . Location - Central, Subterminal, T erminal

B. Shape - a) Ovoidb) Circular

C. Swollen/not swollen(swollen when the diameter is more than the of the)

bacterial cell, not swollen diameter the same asbacterial cell

Detection:1. Microscopy of stained smear

A ) Negative stainingB) Positive staining

2. Phase contrast microscopy

lecture 3 bacterial ultra structure

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