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Host Defenses
Microbiology 2314
A Healthy Host Has a
Variety of Defenses to
Prevent Infection
Definitions
• Resistance
- Ability to ward off disease.
• Susceptibility
- Lack of resistance.
Two Types of
Resistance
Nonspecific Resistance / Defense
Against All Invaders
• First Line of Defense
1. Skin
2. Mucus Membranes
• Second Line of Defense
1. Phagocytes
2. Inflammation
3. Fever
Specific Resistance / Defense
Against Specific Microorganisms
• Antibodies
• Lymphocytes (B and T Cells)
Skin
Structure and
Composition
(Waterproof
Keratin) Provide
Resistance to
Infection.
It is not a great
place for bacteria
to live…
Dries
Sheds
Secretes
Epidermis of the Skin
• Epidermis consists
of four layers.
• Top layer is dead
• 15-40 Rows of
Dying Cells
• Keratin a
waterproof protein
• pH of 3-5
Symbiotic bacteria living on the skin decompose dead skin cells.
The process results in a strong odor as the number of bacteria increase.
Fungus Can Penetrate
Keratin to Cause
Infection When
Excessive Moisture is
Present
Best Areas for Organisms
to Occupy are
Scalp
Ears
Underarms
Genital Regions
Why?
Lachrymal Apparatus
Protects the eyes from irritating substances and microorganisms.
The conjunctiva has only a small number of bacteria present due to
continuous blinking and lachrymal secretions which contain
bactericidal substances.
The lacrimal glands underneath
the skin of the upper eyelids make
a fluid that is mostly salt and
water. This salty water gets to the
eye through small openings inside
the upper eyelids.
When the eyelid blinks, the watery liquid is
spread across the eye. There are other glands
on edges of the eyelids that make oils. The
most important of these glands are called the
meibomian glands. The oils from these
glands actually float on top of the watery
fluid in the tears. This keeps the water from
evaporating too quickly.
Some of the oils stay along the edge of the
eyelid, and they help keep the tears from
"leaking" over the eyelashes. If there is not
enough of these oils, tears will keep
overflowing from the eyes. Oddly enough, a
problem with the meibomian glands can
lead to overflowing tears and dry eye
syndrome at the same time
Salivary
Glands
Produce
Saliva
Saliva Washes
Microorganisms from
Teeth and Gums
Saliva isn’t always enough.
S. mutans  Secretes Sticky Polysaccharide  Plaque
Tooth decay (dental caries) was not a major problem before
the fateful year of 1886. Do you remember why 1886?
That was the year that Coca Cola was first invented and marketed.
European
Teeth
Teeth in skulls from
Europeans prior to the
1500’s showed
remarkably wellreserved teeth. Once
sugar was introduced
into the European diet,
teeth deteriorated
quickly and tooth
decay became a
widespread disease.
Defensive Body Secretions
•
•
•
•
•
•
•
Tears
Saliva
Mucus
Vaginal Secretions
Nasal Secretions
Sebum
Perspiration
Mucus traps many
microorganisms that
enter the respiratory
and gastrointestinal
tracts.
Snotty noses are a
result of the body
trying to rid the
system of the trapped
microorganisms.
The nostrils are
heavy with
bacteria but the
sinuses and lungs
are usually
sterile.
The flow of urine moves
microorganisms out of the urinary
tract.
The kidney and bladder are
usually sterile.
What is Sebum?
Sebum is an oily/fatty substance secreted from the
sebaceous glands (unsaturated fatty acids) that
inhibits the growth of pathogenic bacteria.
Constituent
% by weight
Glycerides and free fatty acids
57.5
Wax esters
26.0
Squalene
12.0
Cholesteryl esters
3.0
Cholesterol
1.5
Unfortunately, Some Bacteria Have Adapted
and Now Metabolize Sebum
Perspiration
• Washes Microorganisms Off
Skin
• Maintains Body Temperature
• Eliminates Cellular Wastes
• Contains Lysozyme
• Lysozyme is Most Effective
Against Gram Positive
Bacteria
Increased
Perspiration
Does Increase
the Growth of
Some
Bacteria.
Lysozyme
• Found In
1. Tears
2. Salava
3. Nasal Secretions
4. Perspiration
The Acidity of Gastric Juice
Prevents Most Microbial Growth in
the Stomach
• Mucus, HCl, Enzymes
• pH 1.2 - 3.0
• No effect on
Clostridium botulinum
• No effect on
Staphylococcus aureus
Helicobacter pylori and Ulcers
Ulcers
• 4 Million Americans Have Ulcers Annually
• H. pylori is Found in Almost 50% of the
Population
• That 50% Could Either Have Gastritis or
Ulcers
Why is H. pylori able to survive
in the acidic environment of the
stomach if it isn’t an acidophil?
Phagocytosis
The Ingestion of Microorganisms or
Particulate Matter by a Cell
We frequently see this when WBC’s engulf bacteria.
Phagocytosis
1. Attraction (Chemotaxis)
2. Attachment (Opsonization / Coating with Protein)
3. Ingestion
4. Digestion (Lysosomal Enzymes and Oxidizing Agents)
5. Expulsion
The Mechanism of Phagocytosis
Chemotaxis is the process by which phagocytes are attracted to microorganisms.
Pus is the accumulation of damaged tissue
and dead microbes and white blood cells.
Removing Pus
From an
Infected Liver
An accumulation of pus in the front of the eye. In this image, the pus
is seen as a pool of whitish fluid between the iris and cornea.
Blood is a Fluid with Formed Elements
White Blood Cells (Leukocytes)
Macrophages are Mature Monocytes that are Phagocytic in Nature
Histiocytes are a special type of macrophage fixed in a particular tissue
1. Kupffer Cells / Liver
2. Alveolar macrophages / Lungs
WBC - Neutrophils
• Increased / Bacterial Infection
• Normally 50-70
• Two Types
1. Segmented (Mature)
2. Banded (Less Mature)
WBC - Basophils
• Allergic Reactions
• Leukemias
• Normally 0-1
WBC - Eosinophils
•
•
•
•
Worm Infections
Skin Disorders
Scarlet Fever
Normally 1-5
WBC - Lymphocytes
•
•
•
•
•
Viral Infections
German Measles
Whooping Cough
Syphilis
Normally 20-30
WBC - Monocytes
• Recovery from Infections
• Fungal, Rickettsial,
Protozoal, Infections
• Normally 2-6
Differential WBC Count (100 Cells)
•
•
•
•
•
Neutrophils
Lymphocytes
Monocytes
Eosinophils
Basophils
50-70
20-30
2-6
1-5
0-1
Wright's stain is a technique that is used to make the differences
between cells visible under light microscopy.
It is used in the examination of peripheral blood smears and bone
marrow aspirates.
Avoid areas in which the blood cells are
clumped or unevenly dispersed.
Also avoid areas where the blood cells are
jumbled together and touching one another
Concentrate your examination in areas
where the cells are individually separated
from one another and fairly uniformly
dispersed
(Segmented)
Neutrophils
Banded
Segmented
Lymphocyte
Monocyte
Eosinophil
Basophil
Mononucleosis
Leukemia
Sickle Cell Anemia
Can We Diagnose From a Blood
Smear?
Slits / Alcoholic Liver Disease
Target Cells / Decreased Iron
Thorn Cells / Severe Burns
Stippling / Heavy Metal Poisoning
Teardrops / Bone Marrow
Malfunction
WBC Hypersegmentation / Chronic
Infection or Liver Disease
WBC Ringed Nucleus / Acute
Myeloid Leukemia
Holes in Cytoplasm of Granulocytes
/ Toxic Effect of Ethanol
• Acanthocytes are
red blood cells
with irregularly
spaced
projections. These
projections vary in
width but usually
contain a rounded
end. They may be
found in
abetalipoproteine
mia and certain
liver disorders.
• Auer rods are elongated, bluish-red rods composed
of fused lysosomal granules, seen in the cytoplasm of
myeloblasts, promyelocytes and monoblasts and in
patients with acute myelogenous leukemia.
• Bacteria in the smear. This image was taken from a
patient with Streptococcus pnemoniae infection.
Sickle Cell Anemia
Döhle Bodies – Small
pale blue cytoplasmic inclusions /
Tuberculosis
• Hairy cells are characterized by their fine, irregular
pseudopods and immature nuclear features. They are
seen only in hairy cell leukemia.
• Howell-Jolly bodies are spherical blue-black inclusions of red
blood cells seen on Wright-stained smears. They are nuclear
fragments of condensed DNA, 1 to 2m in diameter, normally
removed by the spleen. They are seen in severe hemolytic
anemias, in patients with dysfunctional spleens or after
splenectomy.
• Nucleated red blood cells, (nrbcs or normoblasts), represent the
stages of a red blood cell before it matures. Cells of this stage
are usually seen in newborn infants, and in patients with iron
deficiency anemia.
Case Study 1
• This 16 year old male came to the emergency
room complaining of severe abdominal pain in
the right lower quandrant. He had a fever of
101 F. On physical examination, he had a rigid,
board-like abdomen and rebound tenderness in
the right lower quandrant. There were no other
abnormalities.
What is the predominant white blood
cell present?
What does this indicate?
Case Study 2
• This 15 year old female was sent home from
summer camp because of weakness, lassitude,
and sore throat. As her family physician, you
found that on physical examination she had an
inflamed pharynx, enlarged tonsils, several
enlarged and slightly tender lymph nodes in the
neck, a palpable spleen, and a tender palpable
liver edge.
What is the predominant white
blood cell type?
What is your diagnosis in this
case?
Case Study 3
• This 65 year old male was in good health
except for mild hypertension. At his last checkup, a CBC showed a markedly elevated white
blood cell count and physical examination
revealed several slightly enlarged lymph nodes
in the neck and the axillae, and the spleen was
palpable.
What is the predominant white blood
cell type present?
What is the differential diagnosis?
Case Study 4
This 52 year old male had gradually increasing
fatigue together with discomfort in the left
upper quandrant. Physical examination revealed
an easily palpable spleen and liver edge. A few
slightly enlarged lymph nodes were palpable in
the neck.
Inflammation is a bodily response to cell damage.
Inflammation
1.
2.
3.
4.
5.
Redness
Pain
Heat (Local Fever)
Swelling
Possible Loss of
Function
• Vasodilation
Increase in blood vessel diameter to increase
blood flow
1. Histamine / Body Cells
2. Kinins / Blood Plasma
3. Prostaglandin / Damaged Cells
• Margination
Adherence of phagocytes to vessel walls.
• Emigration
Phagocytes leaving blood vessels and
entering tissues.
• Pus
Accumulation of damaged tissue, dead
microbes, and white blood cells
(phagocytes).
Tissue Repair
1. Stroma
(Supporting
Tissue)
2. Parenchyma
(Functioning
Tissue)
Fever
• Abnormally High Body Temperature
• Can Be Induced by Bacterial
Endotoxins
• Chills  Increased Temperature
• Crisis  Decreasing Temperature
• Temperature is Controlled by the
Hypothalamus
How Do We Treat a Fever?
• Do not force food. If diarrhea is present, limit the intake
of fruits and juice.
• Sponging the body with a wet compress, especially
keeping it on the forehead, temples and the feet is a very
effective method of bringing down the temperature. Use
lukewarm water; cool water may cause shivering, which
actually raises body temperature. Don't use rubbing
alcohol, since it can be toxic. Sponging can be repeated
as often as required.
• Overheating due to overdressing can aggravate the fever
so dress lightly, and make sure bedclothes too are light.
• Temperatures lower than 102 degrees F (38.9 degrees C)
usually do not require medication.
• Give acetaminophen or ibuprofen based on the package
recommendations for age or weight. If you don't know
the recommended dose call your doctor. Aspirin is not
recommended for children under age 12.
The Complement System
The complement system consists of a group of serum proteins that
activate one another to destroy invading microorganisms.
The complement system helps clear pathogens from an organism. It is derived
from many small plasma proteins that form the biochemical cascade of the
immune system. Activation of this system leads to cytolysis, chemotaxis,
opsonization, immune clearance, and inflammation, as well as the marking of
pathogens for phagocytosis. The complement system consists of more than 35
soluble and cell-bound proteins, 12 of which are directly involved in the
complement pathways
Interferons
• Antiviral Proteins Produced in Response to
Viral Infection
• Alpha
• Beta
• Gamma