Transcript c. Basic Bacteriology

Basic Bacteriology
Bacteria
 Bacteria are single-celled organisms
 Contain no membrane bound nucleus
 Termed prokaryotes = pre nucleus
Pro = pre
 karyote = nucleus

 Do not contain any other organelles (such as ER or
Golgi or mitochondria)
 Cytoplasm is surrounded by a lipid membrane with is
surrounded by a rigid cell wall
 DNA bundled in a region called the nucleoid
The Bacterial Cell
Flagella
Ribosomes
Capsule
Cell wall
Plasma
membrane
Nucleoid region (DNA)
Pili
The Bacterial Cell
Nucleoid DNA
Bacterial Nomenclature
 Binomial naming system
 Two word naming system
 First word is genus name
 Always capitalized
 Escherichia
 Second word is species name
 Not capitalized
 coli
 When writing full name genus usually abbreviated
 E. coli
 Full name always italicized
 Or underlined
Bacterial Morphology
 Morphology classification by shape
 Morphology is often expressed in the binomial naming
system
 Ex. Bacillus subtillis, the word Bacillus means rod
 Ex. Streptococcus pyogenes, Streptococcus means a chain of
spheres
 Ex. Helicobacter pylori, helix shaped bacterium
 Many names of bacteria do not reference there shape such as E.
coli, Pseudomonas aeruginosa, or Burkholdaria cepacia.
Bacterial Morphology
Examples of Morphology
• Bacteria exhibit a variety
of shapes
• Coccus
• Spherical
• Bacillus
• Rod or cylinder
shaped
Examples of Morphology
• Other shapes
• Coccobacillus
• Short round rod
• Vibrio
• Curved rod
• Spirillum
• Spiral shaped
• Spirochete
• Helical shape
Bacterial Anatomy and Structures
 Cytoplasm- fluid that fills the cell where most reactions and
activities of the cell take place
 Cell Membrane- barrier between the internal cell fluid
(cytoplasm) and the exterior environment. It is selectively
permeable only allowing in selected comounds
 Cell Wall- rigid structure surrounding the cell membrane
that gives bacteria there shape. Stronger than the cell
membrane helps hold the cell together and maintain
structural integrity. The cell wall can be of varying degrees of
thickness depending on the type of bacteria
 Cell capsule- slime layer that protects bacteria and helps
bacteria to adhere to surfaces
Bacterial Anatomy and Structures
 Nucleoid region- location of the genetic material (DNA) in
the bacterial cell. Typically bacterial DNA is one large
circular DNA molecule that is packed together by
supercoiling.
 *Bacterial DNA should not be referred to as a chromosome
because it is not packed together using chromatin and does not
resemble the organization of DNA in eukaryotes. The alternate
name for bacterial DNA is genophore
 Plasmid- a small genetic element of circular DNA that is
separate and distinct from the nucleoid DNA. The plasmid is
typically thousands of times smaller than the nucleoid DNA
but often very important as it may carry genes for antibiotic
drug resistance
Bacterial Anatomy and Structures
 Flagella- long structure made of protein that propels the
bacteria when it spins.
 Pili- structure made of protein subunits that extend out of
the cell. Function for attachment to surfaces and gliding
motility.
 Inclusions- small structure used to store excess material
typically as nutrient reserve. Stored materials include
phosphates, polysaccharides, nitrogen, sulfur, proteins and
biopolymers
 Ribosome- a structure consisting of protein and rRNA. It
translates mRNA into a sequence of amino acids (proteins)
Size Distribution
Size in the Microbial World
 Tremendous range in size
 Smallest virus approximately 1/1,000,000th size of largest eukaryotic cell
Prokaryotic Cells
 Comparing Prokaryotic and Eukaryotic Cells
 Prokaryote comes from the Greek words for prenucleus.
 Eukaryote comes from the Greek words for true nucleus.
Prokaryote
Eukaryote
 One circular




chromosome, not in a
membrane
No histones
No organelles
Peptidoglycan cell walls
Binary fission
 Paired chromosomes, in




nuclear membrane
Histones
Organelles
Polysaccharide cell walls
Mitotic spindle
 Average size: 0.2 -1.0 µm  2 - 8 µm
 Basic shapes:
 Unusual shapes
 Star-shaped Stella
 Square Haloarcula
 Most bacteria are monomorphic
 A few are pleomorphic
Figure 4.5
Arrangements
 Pairs: diplococci,
diplobacilli
 Clusters: staphylococci
 Chains: streptococci,
streptobacilli
Glycocalyx
 Outside cell wall
 Usually sticky
 A capsule is neatly
organized
 A slime layer is
unorganized & loose
 Extracellular
polysaccharide allows cell
to attach
 Capsules prevent
phagocytosis
Figure 4.6a, b
Flagella
 Outside cell wall
 Made of chains of flagellin
 Attached to a protein hook
 Anchored to the wall and
membrane by the basal
body
Figure 4.8
Flagella Arrangement
Figure 4.7
Figure 4.8
Motile Cells
 Rotate flagella to run or tumble
 Move toward or away from stimuli (taxis)
 Flagella proteins are H antigens
(e.g., E. coli O157:H7)
Motile Cells
Figure 4.9
Axial Filaments
 Endoflagella
 In spirochetes
 Anchored at one end of a
cell
 Rotation causes cell to
move
Figure 4.10a
 Fimbriae allow
attachment
 Pili are used to transfer
DNA from one cell to
another
Figure 4.11
Cell Wall
 Prevents osmotic lysis
 Made of peptidoglycan (in bacteria)
Figure 4.6a, b
Peptidoglycan
 Polymer of disaccharide
N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)
 Linked by polypeptides
Figure 4.13a
Figure 4.13b, c
Gram-positive cell walls
negative cell walls
Gram-
 Thick peptidoglycan
 Teichoic acids
 In acid-fast cells,
contains mycolic acid
 Thin peptidoglycan
 No teichoic acids
 Outer membrane
Gram-Positive cell walls
 Teichoic acids:
 Lipoteichoic acid links to plasma membrane
 Wall teichoic acid links to peptidoglycan
 May regulate movement of cations
 Polysaccharides provide antigenic variation
Figure 4.13b
Gram-Negative Outer Membrane
 Lipopolysaccharides, lipoproteins, phospholipids.
 Forms the periplasm between the outer membrane and the plasma
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


membrane.
Protection from phagocytes, complement, antibiotics.
O polysaccharide antigen, e.g., E. coli O157:H7.
Lipid A is an endotoxin.
Porins (proteins) form channels through membrane
Gram-Negative Outer Membrane
Figure 4.13c
Gram Stain Mechanism
 Crystal violet-iodine crystals form in cell
 Gram-positive
 Alcohol dehydrates peptidoglycan
 CV-I crystals do not leave
 Gram-negative
 Alcohol dissolves outer membrane and leaves holes in peptidoglycan
 CV-I washes out
Atypical Cell Walls
 Mycoplasmas
 Lack cell walls
 Sterols in plasma membrane
 Archaea
 Wall-less, or
 Walls of pseudomurein (lack NAM and D amino acids)
Damage to Cell Walls
 Lysozyme digests disaccharide in peptidoglycan.
 Penicillin inhibits peptide bridges in peptidoglycan.
 Protoplast is a wall-less cell.
 Spheroplast is a wall-less Gram-positive cell.
 L forms are wall-less cells that swell into irregular shapes.
 Protoplasts and spheroplasts are susceptible to osmotic lysis.
Plasma Membrane
Figure 4.14a
Plasma Membrane
 Phospholipid bilayer
 Peripheral proteins
 Integral proteins
 Transmembrane proteins
Figure 4.14b
Fluid Mosaic Model
 Membrane is as viscous as olive
oil.
 Proteins move to function
 Phospholipids rotate and move
laterally
Figure 4.14b