THE BASES FOR CLASSIFYING BACTERIABACTERIA

PROKARYOTIC CELL CHARACTERISTICS•Unicellular•Bacteria and Archaea•Different in chemical composition.•Differentiated by many factors including:•A. Morphology (shape)•B. Chemical composition (often detected by

staining reactions)•C. Nutritional requirements •D. Biochemical activities•E. Source of energy (sunlight or chemicals)

THE SIZE SHAPE AND ARRANGEMENT OF BACTERIAL CELLS•Range from 0.2 to 2.0 um in diameter.•2 to 8 um in length.•Few basic shapes:•A. Coccus (berries ) – spherical•B. Bacillus ( little staff) – rod-shaped•C. Spiral

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS• Cocci are usually round but can be oval, elongated or

flattened on one side.• Diplococci – remain in pairs after dividing.• Streptococci – divide and remain attached in

chainlike patterns.• Tetrads – divide in 2 planes and remain in groups of

4.• Sarcinae - divide in three planes and remain

attached in cubelike groups of eight.• Staphylococci – divide in multiple planes and form

grapelike structures.• Frequently helps in the identification of cocci.

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS•Bacilli divide only across their short axis.•Most bacilli are single rods.•Diplobacilli - appear as pairs after

division.•Streptobacilli – occur in chains.•Coccobacilli – oval and look so much like

cocci.•Others are like straws and others are like

cigars with tapered ends.

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS•“Bacillus has two meanings.•Refers to a bacterial shape.•Refers to a genus.•E.g. Bacillus anthracis•Bacillus often form long and twisted

chains of cells.

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS•Spiral bacteria have one or more twist

they are never straight.•Vibrio – curved rods.•Spirilla – have helical shape like a cork

screw and fairly rigid bodies with flagella.•Spirochetes – helical and flexible with

axial filaments.

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS• In addition to the three basic shapes:• Genus Stella – star shaped.• Genus Holoarcula – Halophilic Archaea with

rectangular, flat cells.• Some Genera are triangular.

• Most bacteria are• Monomorphic – maintain a single shape.• Environmental conditions could alter shape.• Some bacteria are • Pleomorphic – they have many shapes not just one.

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS

THE SIZE, SHAPE AND ARRANGEMENT OF BACTERIAL CELLS

THE STRUCTURES EXTERNAL TO THE CELL WALL• POSSIBLE STRUCTURES EXTERNAL TO

THE CELL WALL.• Glycocalyx – is a viscous, gelatinous polymer

that is external to the cell wall.• Composed of polysaccharide, polypeptide or

both.• Capsule – organized and firmly attached

glycocalyx.• Presence determined by staining.• Slime layer – unorganized and loosely attached

glycocalyx.

THE STRUCTURES EXTERNAL TO THE CELL WALL•POSSIBLE STRUCTURES EXTERNAL

TO THE CELL WALL.•Capsules – important in contributing to

bacterial virulence.•Protect the pathogenic bacteria from

phagocytosis.•Bacillus anthracis secretes a capsule of

D-glutamic acid.

THE STRUCTURES EXTERNAL TO THE CELL WALL•POSSIBLE STRUCTURES EXTERNAL TO

THE CELL WALL.•Extracellular Polysaccharide (EPS) •Glycocalyx made of sugars.•Enables bacterium to attach to various

surfaces in its natural environment.•E.g. rocks in fast moving streams, human

teeth, medical implants and etc.•Streptococcus mutans – attaches to teeth

and causes dental caries.

THE STRUCTURES EXTERNAL TO THE CELL WALL•POSSIBLE STRUCTURES EXTERNAL

TO THE CELL WALL.• Glycocalyx can be broken down and serve

as nutritional source.•Can protect the cell against dehydration.•Its viscosity may inhibit the movement of

nutrients out of the cell.

THE STRUCTURES EXTERNAL TO THE CELL WALL• POSSIBLE STRUCTURES EXTERNAL TO THE CELL

WALL.• Flagella – Long filamentous appendages that propel

bacteria.• Atrichous – Bacteria that lack flagella.• Bacteria that have flagella are:• A. Monotrichous – a single polar flagellum.• B. Amphitrichous – a tuft of flagella at each end of the

cell.• C. Lophotrichous – two or more flagella at one or both ends of the cell.• D. Peritrichous – flagella distributed over the entire cell.

THE STRUCTURES EXTERNAL TO THE CELL WALL•A flagellum has three basic parts.•Filament – the long outermost region.•Constant in diameter and contains the

globular protein flagellin.•Arranged as intertwining chains that form

a helix around a hollow core.•Hook – where filament is attached.•Basal body – Anchors the flagellum to

the cell wall and plasma membrane.

THE STRUCTURES EXTERNAL TO THE CELL WALL•Prokaryotic flagellum – semirigid,

helical structure that moves the cell by rotating the basal body.

•Either clockwise or counterclockwise along its axis.

•Movement due to rotation of the basal body.

•Flagellar rotation depends on continuous supply of energy.

THE STRUCTURES EXTERNAL TO THE CELL WALL

THE STRUCTURES EXTERNAL TO THE CELL WALL

THE STRUCTURES EXTERNAL TO THE CELL WALL•Motility – the ability of an organism to

move by itself.•Run – moves in one direction for a length

of time.•Tumble – random changes in direction.•Swarm – show rapid wavelike movement

across a solid culture medium.•E.g. Proteus

THE STRUTURES EXTERNAL TO THE CELL WALL

THE STRUCTURES EXTERNAL TO THE CELL WALL

THE STRUCTURES EXTERNAL TO THE CELL WALL•Motility enables bacteria to move toward

a favorable environment.•Taxis – the movement of a bacteria toward

or away from a particular stimulus.•Chemotaxis – chemicals like oxygen,

ribose and galactose.•Phototaxis – light.•Attractant – positive chemotactic signal.•Repellent - negative chemotactic signal.

THE STRUCTURES EXTERNAL TO THE CELL WALL•H antigen – flagellar protein useful for

distinguishing serovars.•Serovars – Variations within a species of

gram negative bacteria.•E.g.•E. coli. has at least 50 different H

antigens.•Serovar E. coli. o157:H7 are associated

with foodborne epidemics.

THE STRUCTURES EXTERNAL TO THE CELL WALL•AXIAL FILAMENTS•Anchored at one end of the spirochete.•Have a structure similar to flagella.•Filament rotation produces a movement

of the outer sheath.•Propels the bacteria in a spiral motion

(corkscrew motion).•E.g. Treponema pallidum – syphilis•Borrelia burgdorferi – Lyme disease

THE STRUCTURES EXTERNAL TO THE CELL WALL

THE STRUCTURES EXTERNAL TO THE CELL WALL

THE STRUCTURES EXTERNAL TO THE CELL WALL•FIMBRIAE AND PILI•Many gram negative bacteria contain

hairlike appendages.• Used for attachment and transfer of

DNA.•Consists of a protein called pilin arranged

helically around a central core.

THE STRUCTURES EXTERNAL TO THE CELL WALL•Fimbriae – can occur at the poles of the

bacterial cell.•Or evenly distributed over the entire cell

surface.•Number to few or several hundred per

cell.•Enable cell to attach to surfaces including

other cells.•E.g. Neisseria gonorrhoeae – colonizes

mucus membrane.

THE STRUCTURES EXTERNAL TO THE CELL WALL

THE STRUCTURES EXTERNAL TO THE CELL WALL•Pili – usually longer than fimbriae.•Number only to one or two per cell.•Conjugation – Transfer of DNA from one

bacterial cell to another.•Pili for these are called conjugation pili.

THE CELL WALL•Cell wall – a complex, semirigid structure

responsible for the shape of the cell.•Protects cell from adverse changes in the

outside environment.•Almost all prokaryotes have cell walls.•Major function is to prevent bacterial

cells from rupturing. •Maintain the shape of the bacterium.•Serve as point of anchorage for flagella.

THE CELL WALL•Clinical importance•Contributes to Pathogenecity•Site of action of some antibiotics.•Cell wall composition used to differentiate

major types of bacteria.

THE CELL WALL•COMPOSITION AND

CHARACTERISTICS•Peptidoglycan – Macromolecular

network that composes cell wall.•Peptidoglycan is also known as murein.•Present either alone or in combination

with other substances.•Peptidoglycan consists of a repeating

disaccharide unit attached by polypeptides.

•It forms a lattice that surrounds the entire cell.

THE CELL WALL•Disaccharide portion is made up of N-

acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

•NAM and NAG molecules are linked in rows of 10 to 65 sugars to form the carbohydrate backbone.

•Adjacent rows are linked by polypeptides.•The polypeptides could either be a

tetrapeptide side chain or peptide crossbridge.

THE CELL WALL•Penicillin interferes with the final linking

of the peptidoglycan rows by peptide crossbridges.

•The cell wall is greatly weakened and the cell undergoes lysis.

•Lysis – is the destruction of caused by rupture of the plasma membrane and the loss of cytoplasm.

GRAM POSITIVE CELL WALLS•Thick rigid structure of peptidoglycan

layers.•Gram-positive bacteria also contain

teichoic acids.•Teichoic acids primarily consist of alcohol

and phosphate.•Alcohol could be ribitol and glycerol.

GRAM POSITIVE CELL WALLS• Teichoic acids could be •A. Lipoteichoic acids – span the

peptidoglycan layer and is linked to plasma membrane.

•B. Wall teichoic acids – linked to the peptidoglycan layer.

•Teichoic acid may have a role in binding and regulating movement of cations and prevents extensive cell wall breakdown and lysis.

GRAM POSITIVE CELL WALLS•Teichoic acids provide much of the wall’s

antigenic specificity.•Makes it possible to identify bacteria.•Gram-positive cell walls covered with

polysaccharides allow them to be grouped to significant types.

GRAM NEGATIVES CELL WALLS•Cell wall consists of one or a very few layers

of peptidoglycan and an outer membrane.•Peptidoglycan is bonded to lipoproteins.•Lipoproteins are located in the outer

membrane and in the periplasm.•Periplasm contains a lot of degradative

enzymes and transports proteins.•Gram-negative having small amount of

peptidoglycan means they are more susceptible to mechanical breakage.

GRAM NEGATIVE CELL WALLS•Outer membrane of the gram-negative

cell consists of LPS, Lipoproteins, and phospholipids.

•Outer membrane specialized functions:•Strong negative charge evades

phagocytosis and complement.•Barriers against antibiotic, digestive

enzymes, detergents and etc.

GRAM NEGATIVE CELL WALLS• The gram-positive cell wall has porins.• Porins are protein channels.• It allows the entrance of molecules like

nucleotides, disaccharides, amino acids, vitamin B12 and iron.

• LPS has O polysaccharides that function as antigen and is important for distinguishing species of gram-negative bacterium.

• Lipid portion of LPS called lipid A is an endotoxin.• Endotoxin is toxic to bloodstream and GIT.• Causes fever and shock.

CELL WALLS

CELL WALL