1. Chapter 23, 24, 26 Lecture Outline
Human Microflora, Nonspecific and Specific Host Defenses, and Immunizations

2. Human Microbiota Humans colonized by many microbes Normal flora
Bacteria, archaea, fungi, protzoa, and viruses
Normal flora
“Commensal” (mutualistic) organisms
Resident
Transient
Microbe populations change constantly
Vary with type of tissue, condition
pH, moisture, other microbes present
Intestinal flora varies with nutrient uptake
Can cause disease if reach abnormal location or if epithelial defense is impaired

3. Distribution of Microbiota
Gram+
Gram-
Gram+
Gram- Gram+
Gram-
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

4. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Body Site
Lead Bacteria
Skin
Staphylococcus spec.
Nose/pharynx
Neisseria, viridans streptococci
Stomach
Sparsely populated
Small intestine
Bifidobacterium spec., Clostridium spec.
Large intestine
Bacteroides spec., E. coli
Vagina
Lactobacillus spec.
Urethra
Mycobacterium spec.
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

5. Human Microbiota: Skin
Skin is difficult to colonize
Dry, salty, acidic, protective oils
Gram+ tolerate salt and dry environment well
1012 microbes in moist areas
Scalp, ears, armpits, genital and anal areas
Disease involvement:
Propionibacterium acnes degrades skin oil
Free fatty acid induce inflammation
Inflamed sebaceous glands
Causes acne
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

6. Human Microflora: Nose, Mouth
Nasopharynx and Oropharynx
Many Gram+
Staphylococcus species
Streptococcus species
Also Gram-
Neisseria spec.
Fusobacterium spec.
Disease involvement:
Viridans streptococci
can enter bloodstream and cause endocarditis
Streptococcus mutans
Can form biofilm around teeth
Plaque
Cause of gum disease
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

7. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Viridans Streptococci
S. mutans
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

8. Human Microbiota: Stomach
Very high acidity
Few microbes survive
Disease involvement
Helicobacter pylori
Survive at pH 1
Burrow into protective mucous
Cause of ulcers, cancer
Loss of acidity = achlorhydria
Caused by malnourishment
Allows pathogen growth
Example: Vibrio cholerae survive
Pass through stomach
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

9. Human Microbiota: Intestine
Vast majority of human microbiota
cells/ cm3
Feces consists primarily of bacteria
Disease development
Urinary tract infection
Sepsis
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

10. Human Genitourinary Microbiota
Kidney and bladder are sterile
Urethra and vagina are populated
Vagina
Acidic secretions prevent pathogens
Lactobacillus acidophilus in vagina
Composition is influenced by hormonal cycle
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

11. Important Contributions of Human Microbiota to Human Health
Production of antimicrobials hampers colonization by pathogenic microbes
Degradation of nutrients
Vitamin production
Modulation of immune system
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

12. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Probiotics
Oral uptake of microbes to the benefit of human health
Gram-positive bacteria
Must be able to survive stomach and small intestine
Lactobacillus
Bifidobacterium
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

13. Risks of Microbiota Opportunistic pathogens
Surface breach allows bacterial entry
Immunocompromised hosts
E.g., Bacteroides fragilis
E.g., Clostridium difficile
Gas gangrene caused by Bacteroides after intestinal surgery
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

14. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Host Defenses
General mechanism
Innate Immunity
Adaptive immunity
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

15. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
General Host Defenses
Physical barriers to infection
Skin
Keratin
Dead skin cells, washing, remove attached cells
Mucous
Trap, destroy pathogens
Mucous layers slough off, removed
Cilia remove microbes from lungs
Chemical barriers to infection
Acidic pH: stomach, skin, vagina
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

16. Overview of the Immune System
Innate immunity
Widely present in nature
Natural immunity
Defense system functional at birth
Preformed or available within hours after infection
Pattern recognition
Adaptive immunity
In higher vertebrates
Acquired
Available within days
Specificity
Memory
Proliferation and clonal expansion

17. Key Molecules of Our Immune System
Antimicrobial peptides and polypeptides
Natural peptide antibiotics
Make pores in microbial membranes
Lysozyme
Peptidoglycan hydrolase
Can make membrane pores too
Complement
Makes pores in microbial membranes
Enhances phagocytosis
Alerts the host
Antibodies
Neutralize
Block
Enhance phagocytosis
Innate Immunity
Adaptive Immunity
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

18. Key Cells of Our Immune System
Epithelial cells
Leukocytes
White blood cells
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

19. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Epithelial Cells
Innate immune system
Line all body surfaces
Equipped with receptors that recognize microbial products (Toll-like receptors, TLRs)
LPS
Peptidoglycan
Produce antimicrobial peptides
Produce cytokines that alert the host
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

20. Epithelial Cell Defense
Microbial Products
(LPS, PG, etc)
TLR
Antimicrobial Peptides
TLR: Toll-like receptor (pattern recognition)
LPS: lipopolysaccharide
PG: peptidoglycan
Cytokines

21. Leukocytes Neutrophils and monocytes Basophils and eosinophils
Engulf and destroy bacteria and fungi
Monocytes are immature cells that eventually differentiate into macrophages and dendritic cells
Basophils and eosinophils
Release toxins to poison parasites
Natural killer cells
Eliminate virus infected cells
Lymphocytes
T cells: modulate specific immune response (T helper cells) and kill infected host cells (cytotoxic T cells)
B cells: produce antibodies to bind foreign antigens
Innate
Immunity
granules with toxin
Adaptive
Immunity

22. Main Steps of Phagocytosis
Adhesion
Engulfment (ingestion)
Phagosome formation
Phagolysosome formation
Killing
Digestion
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

23. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

24. Acute Inflammatory Response
Initial lesion
Microbial specific structures activate epithelial cells and attract nearby phagocytes
Cytokines from epithelial cells and local phagoctes make capillaries permeable and
attract neutrophils
Phagocytes engulf microbes.
Microbes are killed, wound heals, and return to normal.
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

25. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Fever
Pyrogens induce temperature rise
Exogenous pyrogens
LPS
Cause release of endogenous pyrogens
Endogenous pyrogens
Cytokines
Signal brain to raise temperature
High temperature stresses invading microbes
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

26. Innate Defense by Interferon
Type 1 interferons produced by infected host cells
Cells with viral or bacterial pathogens
Secrete small interferon proteins
Nearby cells respond to interferons
Causes recipient cells to resist virus
Synthesizes ds RNA endonuclease
Makes proteins to prevent protein translation from viral RNA
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

27. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Adaptive Immunity
Humoral immunity
Mediated by antibodies
Involves B cells that respond to specific antigens and produce specific antibodies
Cellular immunity
Involves T cells
Special subtypes
T helper cells control antibody production, activate innate immune cells
Cytotoxic T cells (killer cells) directly kill infected host cells
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

28. Immunological Memory Mediated by Lymphocytes
Specific antigen recognition +
Memory m m m m
Clonal proliferation m m m
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

29. Basic Structure of Antibodies (Immunoglobulins)
Made by B lymphocytes
2 light chains
2 heavy chains
Connected by disulfide bridges
Antigen binding region
Amino acids in this region are highly variable
Each B cell makes a unique antibody
Effector region
Interact with host cells
Amino acids in this region are highly constant
5 different classes (M, G, A,E,D)
B cell can switch Ig classes

30. Antibody Isotypes have Different Functions
IgM—First antibody in immune response
Forms pentamer, agglutinates
IgG—Primary circulating antibody in blood
Coats antigen, eases engulfment by phagocytes (opsonization)
IgA—Secreted across mucosa
IgE—bound by mast cells and basophils and plays role in allergic responses
IgD—on surface of B cells and maturation marker
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

31. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Antibody Response
Primary antigen exposure
Disease or vaccination
Antibodies appear in serum after several days
B cells that bind antigen make antibodies
IgM, then switch to IgG—Isotype switching
B cells change to memory cells
Secondary exposure to antigen
Pathogen or booster dose
Antibodies appear in blood within hours
Mostly IgG antibodies
Some new IgM are also formed
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

32. Natural and Artificial Immunity
Course of natural infection
Antigen is in its natural form
Toxin (active)
Microbe (replicative)
Artificial
Vaccination and immunizations
Antigen is modified
Inactivated
Ex: Toxoid
Attenuated
Live vaccine but unable to cause the disease
Never give to pregnant and immunocompromised individuals
Ex: BCG vaccine
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

33. Active and Passive Immunizations
Antigen (active, inactivated or attenuated) is introduced into host
Natural infection
Vaccination
Host mounts immune response
Antibodies
T cell mediated immunity
Long-term protection
Host must be immunocompetent
Passive
Functional specific immune mediators are introduced into the host
Antibodies
Ex: maternal antibody transfer in utero
Host does not mount an immune response
No long-term protection
For immediate protection
Host can be immunocompromised
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

34. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Vaccines
Most vaccines administered in childhood
Most administered as multiple booster doses
Except influenza—new vaccine every year
Herd immunity
Protects from person-to-person transmission
If 70% of community is immune
Vaccinated or recovered from disease
Remaining individuals protected
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.