Fundamentals IIScribe: Nathan Krauss
Friday, October 23, 2009Proof: Hillary Carney
Microbial Pathogenesis Part IPage1 of 7
Note: Dr. Briles’ lecture has been updated on Blackboard since Friday’s lecture.
I. Microbial Pathogenesis
a) Interaction between pathogen and host.
b) Understand concepts, not details.
II. No Label
a) Whether a pathogen is able to cause symptoms (disease) is dependent on the interaction of the pathogen with the host.
b) This interaction is called Microbial Pathogenesis.
c) Without disease symptoms, we don’t know we are sick.
1. Definition of sick is “having symptoms”.
2. Many microorganisms live in us that do not cause symptoms, and we do not worry about them.
III. Microbial Pathogenesis- 2 sides
a) Immunity of host
1. Innate- Turned on within minutes or hours of pathogen arrival. Will not live long enough for adaptive without this.
i. Protects from things not too serious, like dirt in a cut. Gets rid of 99.9%
2. Adaptive- necessary for evolved pathogens that live in people
i. works well
b) Microbe has mechanisms to evade immune response
IV. Understanding Microbial Pathogenesis leads to:
a)New anti-microbial drugs (antibiotics)- old set is exhausted with resistance.
b) New and improved vaccines
1. As we learn more about disease process we make vaccines to block disease process.
c) Use of cytokines to stimulate innate immunity
1. Coordinate immune response. Can be given to patients as useful tools and will be used alot in the future.
d) Better supportive therapy
1. Understanding disease helps us do things to keep patient alive so body can take care of disease.
e) New preventive measures
V. Disease symptoms
a) Generally are the result of inflammation caused by host response to pathogen.
1. soar throat is usually result of inflammation. Same with finger.
b) Can be caused by toxins of the pathogen that damage the host
1. Diptheria- constricts area so patient can’t breathe
c) Can be caused by chronic infection that leads to erosion and destruction of host tissue and sometimes whole organisms.
1. Hepatitis causes loss of liver function completely
d) What is the importance of disease symptoms?
1. Importance of symptoms is to identify what is wrong with patient, or to know when to go to the doctor.
VI. Antibiotics
a) Originally from natural products(selected in nature from the competition between microbes).
1. First shown in penicillin.
2. Can put streak of penicillin on bacteria and they will not grow where penicillin fungi grows.
3. Fungi make this to kill competing bacteria.
4. Microbes are competing all the time, everywhere.
5. Need new generation of antibiotics because bacteria are getting resistance.
b) Antibiotics block essential microbial-specific functions.(DNA replication, protein synthesis, cell wall synthesis etc.)
c) Antibiotic resistance is the result of mutations and gene exchange, which lead to new variants of the original pathogen.
1. Resistant genes can be spread.
2. Bacteria take DNA in mating from own species, but can get from other species.
3. There is much movement of virulence factors and antimicrobial resistance passed from one to another.
4. Pathogen can pick up resistance from gut flora.
5. This is why physicians are encouraged not to use antibiotics unless absolutely necessary.
d) Future antibiotics will exploit new targets identified by studies of microbial pathogenesis.
VII. In vivo studies are conducted by
a) Administering of drugs, cytokines, antibodies or gene product that targets specific bacterial or host processes.
1. This will knock them out, replace them, or augment them.
b) Genetic knock-out mutants in:
1. The host (effector molecules or receptors)
i. Numbers of genetic knockouts for mice is in several hundreds.
2. The pathogen (virulence factors)
i. In animal model can find out if virulence factor does what we thought.
ii. Very powerful experiments.
iii. Numbers of mutants is way up in 10’s of thousands of different pathogens.
VIII. Classification of Microbes (with respect to human health)
a) In lab portion of course, we talk about gram negative, positive, fungi, viruses, ect. We should learn lecture for lecture, and lab for lab.
b) Organisms not adapted to man that do not bother us make up 99.9%
c) Opportunistic- Some occasionally cause disease due to immune compromise.
1. These people may be young, aged, immune deficient, AIDS patients and are infected by opportunistic infections.
2. Example is histoplasmosis- fungi growing on droppings of birds. Chicken farmers get this disease because they work with birds.
d) Normal flora- bacteria living in us all the time.
1. We have more live cells in our body that are not part of us than are part of us.
2. Many are dead and anaerobe, and will not grow if cultured.
3. Take our food with them, why excrement is good fertilizer.
e) Disease causing- one group that tries to colonize, that is not normal flora.
1. They try to colonize and invade tissue by fighting with immune system instead of fighting with other bacteria.
2. Ex: Pneumoccocus meningitis- sometimes causes disease.
i. Does not always cause disease, but because it colonizes in tissue it has tools to fight the immune system.
3. Ex: shagella- almost always causes disease. It’s an enteric.
i. Takes tiny amount to cause bloody diarrhea.
ii. Common in wars in deserts where water is not clean.
IX. Normal Flora
a) Reside in gut (especially large intestine), oral cavity, upper airways, genital tract, urinary tract, and skin.
b) Normal flora causes no symptoms
X. Normal Flora
a) Causes no clinical symptoms
b) Often beneficial
1. They exclude pathogens
i. If we are treated with antibiotics very aggressively, we may end with diarrhea because we end up with stuff in gut that shouldn’t be there, because flora is wiped.
ii. We get flora from surfaces of house and other people (reacquire).
2. It produces vitamin K, used in blood clotting.
XI. Attributes of a Pathogenic Microbe **(“Probably one of the most important slides I have”)**
a) Acquisition by a host
b) Exploitation of a niche environment
1. Usually this niche is in sterile tissue (otherwise it would generally not cause disease symptoms).
c) Partially evade host defenses at least well enough to survive in niche
d) Multiplication in the host, because if it doesn’t multiply, they will not be able to make enough to be contagious.
1. We won’t study pathogens that cannot be transmitted, because they would just be gone.
e) Transmission to others
f) Produce disease symptoms- If there were no symptoms we wouldn’t care to study it.
XII. No Label
a) The evolutionary success of a pathogen is measured by its ability to infect or colonize additional hosts, not in its ability to kill.
1. All driving pathogen is ability to get to next host.
2. Usually, if it can exist in a longer period of time, it has more of a chance.
3. Much evolutionary drive not to be too virulent. Hard to find examples that do not care about what happens to us.
XIII. No Label
a) All pathogens have developed ways to be transferred to others, and most have evolved to keep the host alive for a long time to maximize their ability to pass to other hosts.
XIV. No Label
a) Some pathogens such as HIV, which causes AIDS, do not have to be passed efficiently.
1. Frequently may take more than one encounter to transmit.
2. We live a long time with it before getting sick and dying, so there is plenty of time to pass to someone else.
3. If it was a bacteria that was very good at moving from one host to the next, it would be efficient.
4. Public health measures work to prevent transmission
b) They have figured out how to remain in a host a long time to maximize their chance to be passed to others before the original host dies.
XV. No Label
a) Pathogens such as Vibrio cholera (or Anthrax) don’t mind killing their host because in doing so they produce enough bacteria in a watery diarrhea (or spores on the savanna) to guaranty transmission to a new host.
1. It simply induces secretion of fluid into gut at high rate, so that all fluid is taken out of body into the gut, and excreted as diarrhea.
i. This kills the body
2. Treatment is salt water to maintain osmotic pressure. IV given in USA.
i. Undeveloped countries boil rice in salt water. Salt dissolves and makes glucose. This is called oral rehydration. Glucose of rice allows salt to be taken up.
3. Anthrax is not normally a human pathogen.
i. Some ungulate animal picks up anthrax and as animal dies the bacteria make many spores.
ii. The spores can lay in savannas for years until a new ungulate comes along and picks them up, gets anthrax, dies, and makes more spores.
XVI. From the Perspective of the Host: Host Defense Mechanisms
XVII. Major Host Defenses
a) Defense mechanisms start at surface with skin
1. mechanical barrier with cellular tight junctions.
2. Skin has acids and oils that are antimicrobial.
3. Staph aureus is found in the navel because it can adapt. It’s one of most virulent bacteria. Navel is a damned place for bacteria to grow, so clean them.
b) Surface of mucosal epithelium is inside mouth all the way to anus. It has a moist area of about 1.5 tennis courts.
1. One important thing is mucus layer that has charges that bind bacteria and stick to mucus.
2. There is cilia that keeps mucus on the move.
3. In upper airway it comes up through bronchial trees and swallowed to be removed from bronchia. Upper respiratory infection is much more swallowing and moving.
4. This area is kept sterile and swept out.
5. In the lower mucosal epithelium, bacteria is lost through feces. It is a continual cleansing.
6. For pathogen to invade, it must find way to avoid sweeping.
c) Acid in the stomach kills bacteria. Proteases in intestines kill bacteria.
1. Bacteria also make proteases to chop off parts of us before we chop them.
d) Phagocytes- wander through body eating microbes
1. Neutrophils- move to tissue quickly at site of infection. Dead neutrophils excrete pus.
2. Kupffer cells line sinusoids in the liver
e) Complement is a series of proteins that by various mechanisms including Ab can identify microbial surfaces, deposit on surface, and induce macrophage to eat.
f) Pattern Recognition Receptors:
1. C-reactive protein has pattern recognition receptors recognizing microbial surface molecules.
2. TLR (cell wall, flagella, teichoic acids, LPS). Cause phagocytosis.
3. Mannose-Binding Lectin- sticks to things with mannose. If microbe has mannose it will get caught.
g) Cytokines are signaling molecules.
h) NK cells
1. Have pattern recognition receptors
2. Also have receptors to recognize Abs bound to our cells and it will kill our cells on assumption that it is virally invaded or a tumor.
i) T cells (CD4 stimulating inflammation and cytotoxic CD8) and B cells
XVIII. Relative Concentration of Selected Immune Mediators
a) Gives idea about how many cells per mL.
b) 5 million granulocytes or PMNs per mL
c)Mononuclear cells become macrophages in tissues.
d) T cells are low in number, and Ag specific T cells are much smaller.
1. There are only a couple hundred Ag specific T cells per mL. Low chance of encountering.
2. Takes a week or more for cells to recognize Ag and proliferate.
XIX. Phagocytes (PMN & Macrophages)
a) Ingest and destroy microbes
b) Find microbes by:
1. Chance encounters
2. Chemotaxis
i. bacterial breakdown products (N-formyl methionine)
ii. complement fragments (C5a)
iii. leukotriene from stimulated lymphocytes and also cytokines
c) Recognize microbes by molecules on their surface
1. Deposited complement (iC3b)
2. Antibody Fc
3. Repeating structures on microbe surfaces (mannose-binding lectin)
XX. Protective Action of Antibody- What does Ab do?
a) Alone
1. blocks adherence- if Ab recognizes surface of bacteria, it will block adherence and invasion. Just by being there it can prevent adherence.
2. blocks toxin activity- neutralizes
3. blocks enzymatic activity- Ab bind and block enzymes that can kill our tissue
b) In conjunction with complement- when phagocyte sees complement it will eat and digest.
1. Aggregates and opsonizes toxins
2. Aggregates and opsonizes microbes
3. Blocks enzymatic activity
4. lyses host cells bearing bacterial or viral antigens (containing bacteria or viruses)
i. Viruses sometimes accidently display their products on the host cells, which are recognized by Ab to begin complement. Complement causes lysing efficiently.
ii. Body keeps complement from binding uninfected cells.
5. lyses Gram-negative bacteria, but not gram positive because the cell wall is too thick. Gram negative have membrane on outside that can be lysed.
i. Salmonella is fairly resistant to lysis and complement even though it is gram negative.
XXI. Complement role in opsonophagocytosis
a) C3 is Activated (C3 is most important)
1. Through the alternative pathway (factor B) by many microbial surfaces. (Extracellular pathogens generally inhibit this pathway).
i. Every time classical pathway is activated, more C3 is produced to activate the alternative pathway in an enhancing mechanism.
2. Through the classical pathway (C1q) by IgG and IgM antibody bound to pathogen surfaces. C-reactive protein will also activate this.
3. Through the mannose pathway, where mannose is exposed on the bacterial surface.
b) C3 activation and surface deposition Mediates
1. chemotaxis (C5a)
2. Opsonization (iC3b)
3. Lysis (Membrane attack complex- C5b, C6, C7, C8, C9)
XXII. NK Cells
a) NK cells lyse host cells identified by Ab. Called Ab Dependent cellular cytotoxicity
b) Regulate for tumor cells
c) produce gamma interferon which is cell mediated immunity that looks for intracellular bacteria and viruses. Cause inflammation.
XXIII. Cytokines- how immune system communicates.
a)Provide communications between immune cells
b) Activate (or inactivate) immune cells
c) Can stimulate protection against microbial infections
d) Can restore the tissue to a non-inflammatory state as an infection subsides.
1. Sometimes inflammation can kill us; i.e. TB or autoimmune. Host may get hole in lung causing host to cough up blood.
XXIV. Interferons
a) Interfere with viral replication and enhance cell-mediated immunity by activating monocytes and lymphocytes.
XXV. No Label
a) Alpha and beta interferons are produced by virus infected cells.
1. They block the protein synthesis of neighboring cells to prevent viral proliferation.
2. Body chooses to kill virus factory at cost of cells.
b) gamma interferon is produced by immune T cells- also shut down protein synthesis of neighbor.
XXVI. Recognition of pathogens is facilitated by PRRs, which recognize PAMPs
a) PRR= pattern recognition receptors
1) Family of TLRs
2) C reactive proteins
3) Mannose-binding lectin, etc
b) PAMP- pathogen associated molecular patterns
1) Cell walls of bacteria- In sterile tissue, cells are called in to take care of problem
2) LPS- only in gram negative bacteria
3) Flagella of bacteria
4) Lectin binds mannose that is polysaccharide on surface of bacteria
XXVII. Helper (CD4) T cells:
a) Activate (help) B cells to make antibody
b) Mediate cell-mediated immunity
1.Enhance production of cytotoxic T cells
2.Activate macrophages to kill intracellular bacteria and destroy infected host tissue.
3.They do this by secreting cytokines
XXVIII. Inflammation,
a) Enhances microbial killing, often at the expense of host tissue.
1. Happens to person with cavitary TB lesion.
i. T cells bent on getting rid of bacteria, that macrophages are activated and kill everything around.
2. Small pox vaccinations cause a dent in the arm.
i. Vaccine puts Ag in and scratch surface.
ii. The T cell response eats the tissue and makes dent from macrophages eating tissue.
iii. Can look at people’s arm, count dents in arm, and know whether to give next immunization.
b) Cell mediated takes weeks to develop giving time for Ab and complement and innate to clear things out.
1. When it comes in it is last defense and hopefully succeeds in getting rid of pathogen.
XXIX. Inflammation is mediated by,
a) “We talked about this, time for break”