Microbe of the Week

1
Microbe of the Week

• Escherichia coli
• Common intestinal bacterium
• Most strains non-pathogenic

2
Escherichia coli
3
Escherichia coli

• Gram negative rod
• Divides in 20 minutes under optimal conditions
• Widely used in molecular biology

4
Escherichia coli

• Some strains produce exotoxins that cause
  intestinal damage
• Example E. coli 0157

5
Prokaryotes

• Functional Anatomy

6
Escherichia coli

• Ferments lactose to produce acid
• Indicator organism for fecal contamination of
  water or food

7
Prokaryotes

• Cell walls usually peptidoglycan, a complex
  polysaccharide
• Divide by binary fission
• No internal membrane-bound organelles
• Include bacteria and archaea (no peptidoglycan)
• Unicellular

8
TOPICS

• External structures
• Cell Envelope
• Internal Structures
• Cell Shapes, Arrangement, and Sizes
• Classification
• Archaea
• Biofilms

9
(No Transcript)
10
External Structures

• Flagella
• Pili and fimbriae
• Glycocalyx

11
Flagella

• Flagella (singlular flagellum)
• Composed of protein subunits
• Motility (chemotaxis)
• Varied arrangement
• Monotrichous - single flagellum
• Lophotrichous - small bunches
• Amphitrichous - both poles of the cell
• Peritrichous - randomly over cell surface

12
(No Transcript)
13
Flagella Structure
14
Chemotaxis
15
Proteus vulgaris Swarming(due to peritrichous
flagella)
16
Axial Filament of Spirochetes

• Spirochete bacteria have their flagella embedded
  in the membrane

17
Diagnostic Use of Flagella

• H antigen differs within a species and can be
  used to distinguish a serovar (serotype)
• Example E. coli O157H7 makes a potent toxin that
  causes gastroenteritis

18
Pili and Fimbriae

• Fimbriae are used for attachment

19
Pili and Fimbriae

• Pili are used for mating (conjugation)

20
Glycocalyx

• Polysaccharide or polypeptide coat that surrounds
  cells - also called extracellular polysaccharide
  (EPS)
• Made inside cell and secreted

21
Function of Glycocalyx

• Virulence factor (disease severity)
• avoid phagocytosis (being engulfed and killed by
  WBC)
• Attachment to surfaces
• Protection from drying, viruses
• Provide nutrients

22
Capsule

• Capsule organized and tightly attached to cell
  wall

23
Slime Layer (EPS)

• Slime layer unorganized, loosely attached to
  cell wall

24
Biofilms

• Biofilm a microbial community attached to a
  surface
• May be one or several organisms

25
Environmental Biofilms
26
Environmental Biofilms
27
Environmental Biofilms
28
Infectious Disease Biofilms
29
Infectious Disease Biofilms

• On implants

30
Some Medically Important Biofilms

• CDC estimate 65 of human bacterial infections
  are associated with biofilms in vivo
• Dental plaque
• Infectious kidney stones
• Endocarditis
• Catheters
• Cystic Fibrosis

31
Cell Envelope

• Cell Wall
• classification
• shape
• Cytoplasmic (plasma) membrane

32
Cell Wall

• Located just outside plasma membrane
• Functions
• maintains cell shape
• protects cell from rupturing when water pressure
  is higher inside cell
• anchors flagella
• Differentiated by Gram stain

33
Peptidoglycan (PG)

• Repeating disaccharide of N-acetylglucosamine
  (NAG) and n-acetylmuramic acid (NAM)
• Cross linked by polypeptides
• Penicillin blocks peptidoglycan cross-linking
• Lysozyme breaks peptidoglycan

34
(No Transcript)
35
(No Transcript)
36
Gram Positive Cell Wall

• Many layers of peptidoglycan
• Teichoic acid
• Regulate positive ion flow
• Protect wall from breakdown
• Antigen specificity of cells

37
(No Transcript)
38
Gram Negative Cell Wall

• Thin peptidoglycan, no teichoic acid
• Outer membrane (OM) contains lipopolysaccharide
  (LPS) endotoxin ( O antigen)
• Protects cell from penicillin, lysozyme
• Contains porins that form channels to allow
  passage of nutrients

39
LPS
40
(No Transcript)
41
Gram Positive and Negative Cell Walls
42
Cytoplasmic membrane

• Lipid bilayer
• Phoispholipids
• Proteins
• Functions
• Regulates transport
• Site of ATP synthesis

43
Atypical Cell Walls

• Acid-Fast Staining wall
• Mycobacteria (TB, leprosy)
• Very thick outer lipid layer - acid fast
• Slow nutrient exchange
• Slow growth

44
Atypical Cell Walls

• No cell wall
• Mycoplasma lack cell wall - pleiotropic

45
Damage to Cell Walls

• Digested by lysozyme
• Gram positive bacteria become protoplasts, lyse
  in distilled water by osmotic lysis
• Gram negative cells become spheroplasts

46
Damage to Cell WallsProtoplasts, Spheroplasts
47
To Be Continued

• Internal Structures
• Cell shapes and arrangements
• Classification
• Archaea