Microbiology - Chapter 14
Non-Specific defenses to invasion and
infection
Lines of defense against infection or invasion
– both non-specific and
specific
Microbiology - Chapter 14
Know for test
Microbiology - Chapter 14
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)
Microbiology - Chapter 14
b. mucous membranes and secretions
1. 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
Microbiology - Chapter 14
4. sweat glands on skin produce perspiration that wash the
skin
5. lysozyme in the sweat breaks down cell wall of gram
positives
6. sebum in the skin is acidic-oily substance, pH of 3 to 5,
inhibits growth of some microbes
7. stomach secretions, very acidic, kills most pathogens,
some toxins are resistant
Microbiology - Chapter 14
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
Microbiology - Chapter 14
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
Microbiology - Chapter 14
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
Microbiology - Chapter 14
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
damage
2. many things cause an inflammation
reaction – infection, injury, even chemical
action
3. purpose of inflammation reaction
a. to destroy and remove the disease
agent if possible
b. limit the effect of the invading agent
c. repair the damage at the site of injury
Microbiology - Chapter 14
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
Microbiology - Chapter 14
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
Microbiology - Chapter 14
Process of Phagocytosis – simplify into 4 stages
1. Chemotaxis – phagocytes are chemically attracted to a
site where invaders are present
a. chemotactic mediators – peptides from damaged
tissues, microbial waste products, components from
white blood cells
b. these chemicals released at site of infection or
injury attract the phagocytes (some in the tissue
already, some circulating in the bloodstream)
Microbiology - Chapter 14
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
Microbiology - Chapter 14
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 packaged
b. the waste particles are expelled
c. 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
Microbiology - Chapter 14
5. Expulsion: End products are expelled and filtered out
and removed by other organ (liver)
See next slide for diagram
Process of
phagocytosis
Microbiology - Chapter 14
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 combat
most all of the body invaders (bacteria, viruses, helminthes,
protozoans)
see slide to follow – we will follow that diagram
1. injury or invasion, at site chemical signals are released
2. blood vessels dilate, opening up of diameter of blood
vessel, increase blood flow,
causing redness (erythema) and heat
3. Vasodilation and increased permeability of blood vessels
are caused by chemicals
released by damaged tissues
Microbiology - Chapter 14
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.
Microbiology - Chapter 14
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 to
the 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)
Microbiology - Chapter 14
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 invaders
and 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.
Microbiology - Chapter 14
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.
Microbiology - Chapter 14
Complement
1. affect blood vessels – permeability and dilation
2. actually attract leukocytes (phagocytes), activate
phagocytes
3. produce inflammatory mediators
4. actually can act on microbes and cause them to lyse
(rupture) cytolysis
5. 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
Microbiology - Chapter 14
INTERFERONS – non-specific antiviral proteins
produced by host cells when host is
infected by a virus
1. general – not specific
2. 3 types - alpha, beta, gamma
3. alpha and beta IF cause uninfected cells to produce
antiviral proteins (inhibit some
function of the virus – mRNA synthesis, or viral protein
synthesis
4. gamma IF can cause neutrophils to kill bacteria
5. Recombinant DNA technology, production of
interferon by bacteria in pure
form and in large quantities to treat some diseases
(herpes, hepatitis B and C)
INTERFERONS – non-specific antiviral proteins
produced by host cells when host is
infected by a virus
1. general – not specific
2. 3 types - alpha, beta, gamma
3. alpha and beta IF cause uninfected cells to produce
antiviral proteins (inhibit some
function of the virus – mRNA synthesis, or viral protein
synthesis
4. gamma IF can cause neutrophils to kill bacteria
5. Recombinant DNA technology, production of
interferon by bacteria in pure
form and in large quantities to treat some diseases
(herpes, hepatitis B and C)