Introduction-bacterial structure-031012

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Introduction to

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Microbiology

Diffinition

Microbiology is the science that study of microorganisms Microorganisms

:

-Small organisms that cannot be seen by unaided eye (Microscope needed)

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•

Prions

•

Viruses

•

Bacteria

•

Fungi

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Prions

 Infectious protein

 No DNA or RNA

 Normal cellular form of protein vs. pathological form

Pathological form found in neural

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Transmissible agent causing scrapie, a

degenerative central nervous system disease of sheep

The cellular form of the protein (PrPc) encoded by the host’s chromosomal DNA There are

additional prion diseases of importance. Kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker disease, and fatal familial insomnia affect humans. Bovine spongiform

encephalopathy (BSE)

A common feature of all of these diseases is the conversion of a host-encoded sialo-glycoprotein to a protease-resistant form as a

consequence of infection .

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Viruses

• _{DNA or RNA}

• _{Shell of protein (capsid) surrounding nucleic}

acid

• Classification on basis of nucleic acid

• DNA viruses: eg Herpes simplex virus (HSV)

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What is

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Bacteria

•

Unicellular, prokaryotes

•

DNA and RNA

•

No mitochondria

•

Rigid cell wall containing

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Mycoplasma genitalium 0.4 µm

Haemophilus influenza 1.0 µm

Staphylococcus aureus 0.9 µm

Escherichia coli 1.5µm

Bacillus megaterium 4 µm

RBC 8 µm

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Bacterial

Structure in

Relationship to

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Essential components of a bacterial cell

• Chromosome • Ribosomes • Cytoplasmic

proteins

• Cytoplasmic membrane • Cell wall

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Schematic Drawing of a typical bacterial cell

Anatomical Regions of a Bacterium

I. Appendages: Flagellum, Pilus

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Bacterial Anatomy

There three architectural regions of a bacterium

appendages (proteins attached to the cell surface) in the form of flagella and fimbriae cell envelope consisting of a capsule,

outer membrane (in Gram-negative

bacteria), cell wall and plasma membrane cytoplasmic region contains the cell

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Cell Walls

• Cell wall is a

structure that

completely surrounds

the cell protoplast.

• (Almost) all bacteria

have a cell wall.

• (Mycoplasma??)

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Cell Walls

Why study bacterial cell walls?

• They are essential structures in bacteria. • They are made of chemical components

found nowhere else in nature.

• They may cause symptoms of disease in animals.

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Profile of the bacterial cell envelope

• Gram-positive cell wall is thick homogeneous monolayer

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Chemical nature of bacterial cell walls

Peptidoglycan is made up of • 2 amino sugars

N-acetyl-glucosamine = G N- acetylmuramic acid = M

• 4 amino acids

L-alanine = L-ala

D-glutamic acid = D-glu

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Cell (cytoplasmic) membrane

• Completely encloses the bacterial cell

protoplast

• Composed of 60% protein and 40% phospholipid

• Arranged as a bilayer

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Membrane structure and assembly

• The proteins associate with both sides of the membrane, or may imbed in the membrane, or pass through the membrane.

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The cytoplasmic membrane of

E. coli

Functions

• permeability barrier • transport

• electron transport and energy generation

• coordination of nuclear

replication and cell division • specialized enzymatic

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Functions of the membrane during

expression of virulence

Functions

• permeability barrier (to antibiotics or host defensins) • transport of nutrients

• export of toxic substances • sensing the environment

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Bacterial Surface Appendages

• Flagella -

organelles for swimming

motility

• Pili (or fimbriae) - for attachment or adherence to surfaces; sex

pilus used during some genetic

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Salmonella enterica, like most enteric bacteria, is capable of swimming movement by

means of flagella.

Flagella

Flagella are long whiplike filaments composed of

protein that originate in the cell membrane.

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Detecting Motility in Bacteria

• ´Flagellar stain detects the presence and

distribution of flagella under microscope

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Detecting Motility in Bacteria

• Or by inoculation of the bacteria into motility

test medium

Staphylococcus epidermidis Non motile

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How Flagella Work

• Filament is rotated by a protein “motor” in the cell membrane

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Ecological Advantages to Swimming

1. Survival: escape predatory protozoa and white blood cells (phagocytes)

2. Swim towards nutrients or away from harmful substances (chemotaxis)

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Pili or Fimbriae

Pili (also called

fimbriae) are short hair-like structures composed of protein on the cell surface.

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Functions of Pili and Fimbriae

• Attachment to a

surface or substrate

Shigella dysenteriae uses its fimbriae to attach to the intestine and then produces a toxin that causes diarrhea.

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Functions of Pili and Fimbriae

• Resistance to Phagocytic engulfment

Phagocytosis of streptococci by a macrophage

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Functions of Pili and Fimbriae

• A special type of pilus called the sex pilus

is used in mating between bacteria

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Bacterial Cell Envelope

• Capsules - for adherence, resistance to

engulfment, storage • Cell wall - protection

against lysis or rupture of the cell • Cytoplasmic

membrane -

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Capsules

• Capsules are composed of polysaccharides

(occasionally polypeptides) deposited outside the cell wall.

Using special staining techniques, some capsules can be demonstrated as a halo surrounding the bacterial cells.

Bacterial cell

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Functions of Capsules

• Protection against phagotrophic

engulfment

• Mediate adherence to surfaces

• Protection against drying

• Reserve of nutrients

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Functions of Capsules

• Biofilms for protection and metabolic

communication among microbes

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Endospores are produced as intracellular structures within the cytoplasm of certain bacteria, most notably Bacillus and Clostridium species.

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Properties of Endospores

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Properties of Endospores

• Several unique

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Properties of Endospores

• Highly resistant to heat (boiling), acids, bases, dyes ( don’t stain) irradiation, disinfectants,

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Endospore formation is NOT a mechanism of reproduction. Rather it is a mechanism for survival in deleterious environments. During the process of spore formation, one vegetative cell develops into one endospore.

The sequential steps of endospore formation in a Bacillus species. The process of endospore formation takes about six hours. Eventually the mature endospore is released from its “mother cell” as a free spore

Free endospore

Vegetative cell Endospore

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Under favorable nutritional and environmental conditions, an endospore germinates into a vegetative cell.

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Medically-important

Endospore-forming Bacteria

• Bacillus anthracis causes anthrax

• Bacillus cereus causes food poisoning • _{Clostridium tetani}_{causes tetanus}

• _{Clostridium botulinum}_{causes botulism} • Clostridium perfringens causes food

poisoning and gas gangrene

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Bacterial Genetics

DNA is circular, Haploid circular chromosome (<1 - >13 Megabases) Advantages of 1N DNA over 2N DNA

More efficient; grows quicker

Mutations allow adaptation to environment quicker