microbiology - chapter 14 non-specific defenses to invasion and infection lines of defense against...

Microbiology - Chapter 14

Non-Specific defenses to invasion and infection

Lines of defense against infection or invasion – both non-specific and

specific


Know for test


1st – body systems that normally keeps microbes out of tissue and prevent

disease

a. intact skin

1. outer epidermis of dead epithelium cells, dry and unfavorable environment

2. keratin protein resist invasion

3. normal flora of skin microbes only a threat if skin is damaged (opportunists)


b. mucous membranes and secretions1. epithelium tissue lining the respiratory, GI tract, and

genitourinary tract

2. have specialized goblet cells that secrete stick substance

called mucous

3. respiratory tract have ciliated epithelial cells that move

mucous up – mucous traps microbes and particles, cilia move

the material up - ciliary escalator-very efficient at protecting

delicate tissues that are more easily invaded


4. sweat glands on skin produce perspiration that wash the skin5. lysozyme in the sweat breaks down cell wall of grampositives6. sebum in the skin is acidic-oily substance, pH of 3 to 5,inhibits growth of some microbes7. stomach secretions, very acidic, kills most pathogens, some toxins are resistant


c. normal microbial flora – microbial antagonism, ecosystem on cellular level,

1. normal balance, keeps pathogens in check

2. if upset in balance, then microbe imbalance can result in problems – yeast infections, or in broad spectrum antibiotics, organisms grow that usually wouldn’t grow – C.difficile, diarrhea


Clostridium difficile is a bacterium that can be found in the colon. It can cause low-grade Diarrhea or severe colitis. It most commonly occurs when an individual is placed on antibiotics. The antibiotics kill off the good bacteria in the colon, and allow room for Clostridium difficile bacterium to grow. In addition, it can be contagiously spread from one person to another, especially in hospital and nursing homes

http://www.ecureme.com/emyhealth/data/Diarrhea.asp


2nd line of defense, system elements, non-specific, go into action if 1st line is

breached

a. PHAGOCYTES – VERY IMPORTANT, these cells engulf and destroy invaders and particulate matter

1. All of the phagocytes are types of white blood cells

2. circulating in the blood and found to some extent in tissue (modified forms), ready to respond to invasion

3. more later


b. Inflammation and fever – if tissue is damaged, inflammation reaction occurs and it is characterized by redness, pain, heat, swelling

1. non-specific response to tissue damage or invasion to limit and stop the infection or damage2. many things cause an inflammation

reaction – infection, injury, even chemical action

3. purpose of inflammation reactiona. to destroy and remove the disease agent if possibleb. limit the effect of the invading agentc. repair the damage at the site of injury


4. Several specialty proteins are involved at the injury site that aid in the processes that limit the invader and help destroy the invader, even help clean up and repair the damage

complement, kinins, interferon, fibrin

Blood cell formation illustrated on next slide


3rd line of defense - this is specific, a production of specific counteracting

chemicals, called antibodies that can recognize and act on invaders to

destroy them

a. usually proteins

b. produced by specialized lymphocytes (B and T cells)

c. Cover in detail in chapter 15


Process of Phagocytosis – simplify into 4 stages1. Chemotaxis – phagocytes are chemically attracted to a

site where invaders are presenta. chemotactic mediators – peptides from damaged tissues, microbial waste products, components from white blood cellsb. these chemicals released at site of infection or injury attract the phagocytes (some in the tissue already, some circulating in the bloodstream)


2. Adherance – attachment of phagocyte to invader or particle,

a. opsonization – some particles or agents are coated with serum proteins, thus allowing the phagocyte to more easily attach, some of the

complement proteins act as opsonins

b. some microbes produce capsules or proteins that

resist phagocytic adherance, more virulent


3. Ingestion – pseudopods of phagocytes surround invader or particle, once completely surrounded, the particle is said to be enclosed in a phagosome

4. Digestion – a cellular organelle, a lysosome, fuses with the phagosome and the digestive enzymes of this new phagolysosome kill the microbe quickly (lipases, proteases, lysozyme, other digestive enzymes, plus strong oxidants and other radicles that can kill the microbe and break it down)

a. the waste products are kept packagedb. the waste particles are expelledc. some microbes survive inside the phagocyte, get a free ride and phagocyte may actually help spread the agent to other tissues –Shigella and Listeria, HIV virus, tubercle bacilli


5. Expulsion: End products are expelled and filtered out and removed by other organ (liver)

See next slide for diagram

Process of phagocytosis


Acute Inflammation – Remember this is a non-specific reaction to the breach of the body primary defense barriers. The reaction is general and can be used to combatmost all of the body invaders (bacteria, viruses, helminthes, protozoans)see slide to follow – we will follow that diagram1. injury or invasion, at site chemical signals are released2. blood vessels dilate, opening up of diameter of blood vessel, increase blood flow,

causing redness (erythema) and heat3. Vasodilation and increased permeability of blood vessels are caused by chemicals

released by damaged tissues


i. histamine- found in mast cells of connective tissue, ad other tissue elements

(a histamine reaction can be very serious – in hypersensitivity reactions –

more later)

ii. kinins – several varieties, also increase permeability and vasodilation

iii. prostaglandins are also released by damaged cells – these chemicals allow more phagocytes to be attracted to the site and they in turn produce more chemicals that attract more phagocytes to the damaged area (mobilization of

defenders) The movement into the damaged tissues of these cells is vital to stop the invaders at the local site.


iv. Leukotrienes – Chemicals produced by mast cells and basophils, they increase permeability of blood vessels (more phagocytes can leave blood to get into tissue that has the invader). They also help the phagocyte to attach tothe invader cells.v. increased permeability allows blood elements that result in clot formation to exit into tissue to wall off area and prevent further invasion or tissue damage (fibrin net)

vi. pus forms – collection of dead cells and tissue fluid

vii. localization of the site and walling off to prevent the spread of infection often produces an abscess (like a boil, or pustule) (remember what a fire ant bite looks like)


4. This acute inflammation activity, producing swelling , redness, pain, heat etc. limits and stops the invasion. The cells that migrate to the site then destroy the invadersand even begin the process of clean up repair. Ultimately healing of the site occurs.

a. Mast cells (fixed tissue macrophages, contain histamine, very important in inflammation and repair of damaged tissue) are real involved in clean up and repair.


b. Role of the group of chemicals called generally – Complement.

Complement is a series of proteins found circulating in blood plasma.

These chemicals are inactive until needed and then activated to perform their role in helping prevent further invasion by microbes. Injury or infection

triggers their activation. They then help trigger the body’s inflammation reaction.


Complement1. affect blood vessels – permeability and dilation2. actually attract leukocytes (phagocytes), activate phagocytes3. produce inflammatory mediators4. actually can act on microbes and cause them to lyse

(rupture) cytolysis5. the activation of complement is complicated and proceeds in a step wise

process called a cascade see pg 441,6. The complement cascade happens quickly and then is

quickly shut off to prevent host cell damage.7. Opsonization – one complement cascade results in a

fragment that attaches to invader cells and oposonizes them – making them easier for phagocytes to attach to and thus destroy them


INTERFERONS – non-specific antiviral proteins produced by host cells when host isinfected by a virus1. general – not specific2. 3 types - alpha, beta, gamma3. alpha and beta IF cause uninfected cells to produce antiviral proteins (inhibit somefunction of the virus – mRNA synthesis, or viral protein synthesis4. gamma IF can cause neutrophils to kill bacteria5. Recombinant DNA technology, production of interferon by bacteria in pureform and in large quantities to treat some diseases (herpes, hepatitis B and C)

microbiology - chapter 14 non-specific defenses to invasion and infection lines of defense against...

Documents