2011.6.7 Microbe - Introduction

8/6/2019 2011.6.7 Microbe - Introduction

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Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Microbiology : Systematic study of MicroorganismsMicroorganisms : Bacteria, Fungi, Algae,Parasites,Viruses,Prions and Viroids

Basic branches

Bacteriology Study of Bacteria Virology Study of Viruses

Mycology Study of Fungi

Parasitology Study of parasites

Phycology Study of algae

Prions and Viroids .

Applied Branches

Medical Microbiology Study of microorganisms of medical importance Agriculural Microbiology Study of microorganisms in Agriculture

Food Microbiology Study of Microorganisms in Food

Environmental Microbiology Study of Microorganisms in Environment

Industrial Microbiology Study of Microorganisms applied in industries


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Medical Microbiology

Branches

Medical Bacteriology Study of Bacteria Medical Virology Study of Viruses

Medical Mycology Study of Fungi Medical Parasitology Study of parasites

Immunology Study of Immunity

Immunity : The resistance offered by host againstmicroorganisms or their parts or products


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Identification and Characterization of

Microbes

Cell shape or form is important fordistinguishing different bacteria: Three

Basic shapes:

1. Spherical2. Rod

3. Spiral shape

BACTERIAL MORPHOLOGY


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Identification and Characterization

Spherical shaped: Coccus Cocci

Short rods: Coccobacillus - Coccobacilli

Rods: Bacillus Bacilli

Curved rods: Vibrio vibrio

Spiral shaped: Spirillum spirilla

Branched bacteria: Actinomycete Actinomycetes

Irregular: Mycoplasma Mycoplasma


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Different Arrangements of Bacteria

y Cocci in Chains: Streptococci

y Cocci in clusters: Staphylococci

y

Cocci in pairs: Diplococciy Cocci in four: Tetrad

y Bacilli in pair: Diplobacilli

y Bacilli in chains: Streptobacilli


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Arrangements

Pairs: diplococci,diplobacilli

Clusters:staphylococci

Chains:streptococci,streptobacilli


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BACTERIA STRUCTURE

BACTERIAL CELL PARTS: Essential for Survival

Cell Wall

Cell membrane

Cytoplasm

Nucleoids

Mesosomes

Ribosomes


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BACTERIA STRUCTURE

BACTERIAL CELL PARTS: Non-Essential forSurvival

Flagellum

Pili

Capsule

Endospore

Intracellular Inclusions


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BACTERIAL CELL PARTS

1. Cell Wall

Cell wall: is the outermost component part.

The thickness of the cell wall ranges from 10-25 nm,

Cell wall is used:

To Protects bacteria against lysis

Allows them to grow over a wide range of osmotic pressures.

It gives Rigidity to bacterial cells, which determines theircharacteristic shape.

The main constituent of bacterial cell wall is a chemically

complex polymer known as peptidoglycan.


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Cell Wall

Christian Gram recognized 2 different types of bacteriabased on their staining reaction.

Gram-positive bacteria stain purple and have thicklayers of peptidoglycan combined with teichoic acid.

Gram-negative bacteria stain pink and have muchthinner layer of peptidoglycan covered with an outerlipid membrane.


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Gram Stain Mechanism1. Prepare a thin bacterial smear on glass slide.2. Fix the smear by dry heat

3. Flood the smear with Crystal Violet for 1 min.

4. Wash the slide with tap water

5. Flood the smear with Grams Iodine for 1 min.6. Wash with tap water

7. Decolorize the smear by alcohol for 20-30 sec.

8. Wash slide with water

9. Flood the smear with Safranin

10.Wash with Tap water

11. Air dry slide and Observe under 100X oil immersion


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Gram negativeGram negative Gram positiveGram positive

Heat/DryHeat/Dry

Crystal violet stainCrystal violet stain

IodineIodine FixFix

Safranin stainSafranin stain

AlcoholAlcohol dede-stainstain


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Gram Stain Mechanism

Crystal violet -iodine crystals give blue coloration tocell

Gram-positive Alcohol dehydrates peptidoglycan

CV-crystals do not leave

Gram-negative Alcohol dissolves outer membrane and leaves holes in

peptidoglycan

CV- washes out


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Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 4.13b, c


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Peptidoglycan

The peptidoglycan is a complex, interwoven networkthat

surrounds the entire cell and is composed of threeparts:

1. Sugar (glycan) backbone which is composed of alternating N-acetylmuramic acid andN-acetylglucosamine

2. A set of identical tetrapeptide side chains attachedto the N- acetylmuramic acid.

3. A set of identical peptide cross-bridges betweentwo tetrapeptides.


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Peptidoglycan

Polymer of disaccharide

N-acetylglucosamine (NAG) & N-acetylmuramicacid (NAM)

Linked by polypeptides

Figure 4.13a


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Gram-positive cell walls

Special Components of Gram-positive cell walls

Contain significant amount of teichoic andteichuronic acids, which account up to 50% of thedry weight of the cell wall.

Teichoic acids are negatively charged fibers whichprotrude at the outer surface of Gram +ves.

In addition to this some gram-positive walls containpolysaccharide molecules.


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Gram-Positive cell walls

Teichoic acids: two types

Lipoteichoic acid links to plasma membrane

Wall teichoic acid links to peptidoglycan

May regulate movement of cations

Figure 4.13b


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Gram-Negative Cell wall

Special components of Gram-Negative cell walls:

Gram-negative cell walls contain three componentsthat lie outside of the peptidoglycan layer:

Lipopolysaccharide (LPS)

Outer membrane

Lipoprotein

LPS - also known as endotoxin.

The endotoxin is responsible for many of thefeatures of disease, such as fever and shock(especially hypotension) caused by theseorganisms.


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Periplasmic space = space between inner andouter membrane.

Gram-negative bacteria only have degradativeenzymes located in this area.

Periplasmic enzymes act on the wide variety of

substrates which a GN bacterium encounters innature to convert them to molecules which aretransportable into the cell.


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Figure 4.13c


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Cell wall less forms in bacteria

L forms : cell wall less forms of bacteria that appearspontaneously or due to treatment with Penicillium.Common in many bacteria E.coli, Neisseria.

Penicillin inhibits peptide bridges in peptidoglycan.

Bacteria can revert back to cell wall forms.


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Cell wall less forms in bacteria

Lysozyme are enzymes that digest disaccharide inpeptidoglycan.

Protoplast : Spherical form of Gram Positive

bacterium when treated with lysozyme.Spheroplast : Spherical form of Gram Negative

bacterium when treated with lysozyme.

Mycoplasma: Natural cell wall less forms and they

have Sterols in plasma membrane

Protoplasts and spheroplasts are susceptible toosmotic lysis and are used for research.


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Cell wall of Acid-fast bacteria

Mycobacteria have an unusual cell wall,resulting in their inability to be Gram-stained.

These bacteria are said to be acid-fast,

They resist decolorization with acid-alcohol afterbeing stained with Crystal violet.

This is due to the high concentration of lipids,

called as mycolic acids, in the cell wall.


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Plasma Membrane

Figure 4.14a


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Plasma MembraneComponents ofPlasma membrane

Phospholipid bilayer

Peripheral proteins

Integral proteins

Transmembrane proteins

Figure 4.14b


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Plasma Membrane

Simple diffusion: Movement of a solute from an area ofhigh concentration to an area of low concentration.

Facilitated diffusion: Movement of solutes combinedwith a transporter protein in the membrane.

Movement Across Membranes


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Figure 4.17


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Osmosis Movement of water

across a selectivelypermeable membranefrom an area of high

water concentration to anarea of lower waterconcentration.

Osmotic pressure

The pressure needed tostop the movement ofwater across themembrane.

Figure 4.18a


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Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 4.18c-e



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Active transport of substances requires atransporter protein and ATP. Substances such as amino acids, organic acids and

inorganic ions combined with carrier proteins aretransported across membrane and released inside the

cell by this mechanism. Group translocation of substances requires a

transporter protein similar to active transport butthe nutrients being transported undergoes chemical

modification. Sugars and fatty acids are transported by this

mechanism.


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3. Cytoplasm

The cytoplasm is the cellular material outside thenucleus but enclosed by the cell membrane.

Consists of 70% water

~1000 different enzymes

Many ribosomes

It is site of the bacterium for all activities

It is controlled by the information carried in the DNAof the nucleus.


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CytoplasmCytoplasm Cell membrane

Cell Wall


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4. Nucleoid

Genetic material that controls all characteristics ofcell .

Centrally located cellular mass without a nuclearmembrane. Contains a single circular chromosome,in which DNA is located.


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5. Mesosome and Ribosomes

Mesosome =It is an invagination of the cytoplasmic

membrane, which forms septum during cell division.

Site for some respiratory enzymes.

More seen in Bacilli.

Ribosomes =site for protein synthesis. Bacteria

ribosomes are 70S in size with two subunits 50S and

30S.


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Ribosomes

Figure 4.19


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BACTERIAL CELL PARTS: Non Essential forSurvival1. Flagella: are long (3-20 ), whiplike appendages

that move the bacteria toward nutrients andother attractants, a process called chemo-taxis.

Made of chains of flagellin

Attached to a protein hook

Anchored to the wall and membrane

The system enables bacteria to detect changes

in concentration of certain chemicals and tomove either toward (positive chemotaxis) oraway (negative chemotaxis) from the substancedepending on its nature.


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Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 4.8


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Flagellar Arrangement in Bacteria:

Monotrichous bacteria that have a single polarflagellum.

Amphitrichous bacteria having flagella at bothends.

Lophotrichous A tuft of flagella in a single

location

Peritrichous bacteria flagella random

distributed all over cell surface.


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Flagella Arrangement

Figure 4.7


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Motile Cells

Figure 4.9


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2. Fimbriae or pili

Pili are straight rigid rod like appendages. shorter and thinner than flagella, composed ofa single protein pilin.

Function :

Facilitate adherence of bacteria to otherbacterial, red blood cells, or lining of theintestine.

Provide a site for attachment of bacteriophages(bacterial viruses).

Enable bacteria that have a sex pilus to transfergenetic material across a pilus bridge from oneto another by a process known as Conjugation


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3. Capsule Capsule is a thick gelatinous layer produced by the

plasma membrane secreted outside of the cell wall. It is polysaccharide that forms a protective outer

coat to the cell.

Can be detected by negative staining. Plays

important role in bacterial virulence.Function:

Protects bacteria from phagocytosis by white bloodcells inside the body.

Protects bacteria from external toxic substances &degradative enzymes.

Provides water molecules to bacteria in dryconditions.


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4. Endospores

Spore or endospore is a highly resistant,metabolically inactive forms of bacteria.

Endospores are also formed during unfavorabletemperature, pH and gaseous requirement.

Endospore formation is protective measure and notreproductive process.

The genetic material is enclosed in several proteincoats that are resistant to heat, drying, freezing,

toxic chemicals, and radiation. The process of Spore formation is - Sporulation

The process of outgrowth or vegetative growth is Germination


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Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 4.21a


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Copyright 2004 Pearson Education Inc publishing as Benjamin Cummings

5.Intracytoplasmic inclusions:

Granules: are intracellular inclusions that serve as a storagefor nutrients.

Bacteria store food in reserve form during favorable

conditions, when there is sufficient amount of nutrients &

utilized during unfavorable conditions.

Plasmids: are double stranded extrachromosomal DNA,

particles that carry important genes for antibiotic

resistance, toxin production, and carbohydratefermentation.

Plasmids number may vary from one to many.

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2011.6.7 Microbe - Introduction