Download Indigenous Microflora of Humans (cont.)

Microbiology
Microbial Ecology
& The Immune
system
(Class 3)
Introduction
• Ecology is the systematic study of the interrelationships
that exist between organisms and their environment.
• Microbial ecology is the study of the numerous
interrelationships between microorganisms and the world
around them.
• Most relationships between humans and microbes are
beneficial, rather than harmful.
• Microorganisms are present both on and in our bodies.
Symbiotic Relationships Involving
Microorganisms
• Symbiosis
– Defined as two dissimilar organisms living together in
a close association.
– The organisms in the relationship are referred to as
symbionts.
– Many microorganisms participate in symbiotic
relationships.
• Neutralism
– Refers to a symbiotic relationship in which neither
symbiont is affected by the relationship.
Symbiotic Relationships Involving
Microorganisms (cont.)
• Commensalism
– A symbiotic relationship that is beneficial to one
symbiont and of no consequence to the other.
– Many organisms in the indigenous microflora of
humans are considered to be commensals.
• Mutualism
– A symbiotic relationship that is beneficial to both
symbionts (example: the intestinal bacterium,
Escherichia coli).
Symbiotic Relationships Involving
Microorganisms (cont.)
• Parasitism
– A symbiotic relationship that is beneficial to one
symbiont (the parasite) and detrimental to the other
symbiont (the host).
• A host is a living organism that harbors another
living organism.
• The parasite may or may not cause disease in the
host.
• A change in conditions can cause one type of symbiotic
relationship to shift to another type.
Symbiotic Relationships Involving
Microorganisms (cont.)
• Synergism (Synergistic Infections)
– When 2 or more organisms “team up” to produce a
disease that neither could cause by itself.
– The diseases are called synergistic infections,
polymicrobial infections or mixed infections.
– Examples:
• Acute necrotizing ulcerative gingivitis (ANUG,
trench mouth or Vincent’s disease).
• Bacterial vaginosis (BV).
Various Symbiotic Relationships
Lichen (mutualistic
relationship)
Demodex mites in
human hair follicles
(commensalistic
relationship)
Cause of African
sleeping sickness
(parasitic relationship)
Indigenous Microflora of Humans
• Also called our “normal flora;” includes all the microbes
(bacteria, fungi, protozoa and viruses) that reside on and
within a person.
• Our indigenous microflora is composed of between 500
and 1,000 different species!
• Blood, lymph, spinal fluid and most internal tissues and
organs are normally free of microorganisms (they are
sterile).
• Transient microflora take up temporary residence on
and within humans.
• Destruction of resident microflora disturbs the delicate
balance between host and microorganisms.
Areas of the body where
most of the indigenous
microflora reside.
Indigenous Microflora of Humans (cont.)
• Microflora of the Skin
– Primarily bacteria and fungi – about 30 different
types!
– Number and variety of microorganisms depend on:
• Amount of moisture present
• pH
• Temperature
• Salinity
• Presence of chemical wastes and other microbes
Indigenous Microflora of Humans (cont.)
• Microflora of the Ears and Eyes
– Middle ear and inner ear are usually sterile; outer ear
and auditory canal contain the same microorganisms
as on the skin.
– Eye is lubricated and cleansed by tears, mucus and
sebum – few microorganisms present.
• Microflora of the Respiratory Tract
– Divided into upper respiratory tract (nasal passages
and throat) and lower respiratory tract (larynx,
trachea, bronchi and lungs).
Indigenous Microflora of Humans (cont.)
• Microflora of the Respiratory Tract (cont.)
– Upper respiratory tract (nasal passages and throat)
has an abundance of microorganisms; many are
harmless, some are opportunistic pathogens.
– Carriers harbor virulent pathogens in their nasal
passages or throats, but do not have the diseases
usually caused by these pathogens.
• Examples: people harboring the bacteria that
cause diphtheria, pneumonia, meningitis and
whooping cough
– Lower respiratory tract is usually free of microbes.
Indigenous Microflora of Humans (cont.)
• Microflora of the Oral Cavity (Mouth)
– A shelter for numerous anaerobic and aerobic
bacteria; remaining food particles provide a rich
nutrient medium for bacteria.
– Careless dental hygiene may cause:
• Dental caries (tooth decay)
• Gingivitis (gum disease)
• Periodontitis
– The most common organisms within the indigenous
microflora of the mouth are various species of alphahemolytic streptococci.
Indigenous Microflora of Humans (cont.)
• Microflora of the Gastrointestinal (GI) Tract
– The GI tract is designed for digestion of food,
absorption of nutrients and elimination of undigested
materials.
– The colon (large intestine) contains the largest
number and variety of microorganisms of any
colonized area of the body; an estimated 500-600
different species - primarily bacteria.
– Colon is anaerobic; bacteria in colon are mostly
obligate-, aerotolerant-, and facultative anaerobes.
– Many of the microflora of the colon are
opportunists.
Indigenous Microflora of Humans (cont.)
• Microflora of the Genitourinary (GU) Tract
– The GU tract consists of the kidneys, ureters, urinary
bladder and urethra, and parts of the female/male
reproductive systems.
– Kidney, ureters and urinary bladder are usually sterile; the
distal urethra and its external opening harbor many
microbes including bacteria, yeasts and viruses.
– Most frequent causes of urethral infections include
Chlamydia trachomatis, Neisseria gonorrhoeae and
mycoplasmas.
– The male and female reproductive systems are usually
sterile, with the exception of the vagina.
Beneficial and Harmful Roles of
Indigenous Microflora
• Humans derive many benefits from their indigenous
microflora; examples - vitamins K and B12.
• Microbial Antagonism
– Means “microbes versus microbes.”
– Many members of our indigenous microflora are
beneficial and prevent other microbes from becoming
established.
– Other examples of microbial antagonism involve:
• Production of antibiotics and bacteriocins
(antibacterial proteins); an example is colicin,
produced by E. coli.
Beneficial and Harmful Roles of
Indigenous Microflora (cont.)
• Opportunistic Pathogens and Biotherapeutic Agents
– Opportunistic pathogens are those microorganisms that
“hang around,” waiting for the opportunity to cause
infection.
• Examples: E. coli, other members of the family
Enterobacteriaceae, S. aureus, and Enterococcus spp.
– Delicate balance of the indigenous microflora can be upset
by antibiotics, chemotherapy, and changes in pH.
– Bacteria and yeasts used to stabilize the microbial balance
are called biotherapeutic agents or probiotics.
Agricultural Microbiology (cont.)
• Infectious Diseases of Farm Animals
– Diseases of farm animals are caused by a wide
variety of pathogens.
– These diseases can be transmitted to humans.
– Of economic concern to farmers and ranchers.
• Microbial Diseases of Plants
– Microbes cause thousands of different plant diseases!
– Most plant diseases are caused by fungi, viruses,
viroids and bacteria.
Bioremediation
• Bioremediation refers to the use of microorganisms to
clean up various types of wastes, including industrial
wastes and other pollutants (e.g., herbicides and
pesticides).
• Some microbes are genetically engineered to digest
specific wastes (e.g., petroleum-digesting bacteria to
clean up oil spills).
• Methanotrophs (bacteria that normally consume methane
in the environment) have been used to remove highly
toxic solvents like trichloroethylene and tetrachloroethylene from the soil.
Parasites
• Parasitology is a branch of microbiology; it is the
scientific study of parasites.
• Parasitism is a symbiotic relationship that is of benefit
to one party or symbiont (the parasite) and usually
detrimental to the other party (the host).
• Parasites are organisms that live on or in other living
organisms (hosts), at whose expense they gain some
advantage.
– Parasites that live on the outside of the host’s body
are called ectoparasites.
– Parasites that live inside the host are called
endoparasites.
Introduction (cont.)
• The life cycle of a parasite may involve one or more
hosts.
– If more than 1 host is involved, the definitive host
is the host that harbors the adult or sexual stage of
the parasite.
– The host that harbors the larval or asexual stage is
the intermediate host.
• An accidental host is one that can serve as a host, but
is not the usual host in the parasites’ life cycle.
• A dead-end host is one in which the parasite cannot
continue its life cycle.
Introduction (cont.)
• A facultative parasite is an organism that can be
parasitic, but does not have to live as a parasite; it is
capable of an independent life.
– Example: the free-living amoeba, Naegleria fowleri,
that causes primary amebic meningoencephalitis.
• An obligate parasite has no choice; it must inhabit a
host or hosts.
– Most parasites that infect humans are obligate
parasites.
Parasitic Protozoa
• Most protozoa are unicellular.
• They are classified taxonomically by their mode of
locomotion; amebae move by means of pseudopodia
(“false feet”); flagellates move by means of flagella;
ciliates move by means of cilia; sporozoans do not move.
• Not all protozoa are parasitic (e.g., Paramecium spp.).
• Protozoal infections are most often diagnosed by
microscopic examination of body fluids, tissue specimens
or feces – specimens are examined for motile
trophozoites and dormant cyst stages.
Helminths
• Helminth means parasitic worm.
– Helminths are multicellular, eucaryotic organisms; 2
major divisions: (1) round worms or nematodes, and
(2) flatworms or Platyhelminthes. The flatworms are
further divided into tapeworms (cestodes) and flukes
(trematodes).
– The helminth life cycle has 3 stages: egg, larva,
and the adult worm.
– Helminth infections are primarily acquired by
ingesting the larval stage; in some helminth
diseases, the larva enters by penetration of the skin.
Helminth Infections of Humans
LOCATION
HELMINTH DISEASE
CAUSE
Skin
Onchocerciasis
Onchocerca volvulus
Muscle/Subcutaneous
Tissue
Trichinosis
Trichinella spiralis
Dracunculiasis
Dracunculus medinensis
Eyes
Onchocerciasis
O. volvulus
Loiasis
Loa loa
Respiratory System
Paragonimiasis
Paragonimus westermani
Circulatory System
Filariasis
Wucheria bancrofti/Brugia
malayi
Schistosomiasis
Central Nervous System
Schistosoma spp.
Cysticercosis
Taenia solium (cysts)
Hydatid cyst disease
Echinococcus granulosis
or Echinococcus
multilocularis.
Parasitic Worms Filariasis.
Helminth Infections of Humans: The GI Tract
• Ascariasis – Ascaris
lumbricoides
• Dwarf tapeworm – Hymenolepis
nana
• Hookworm – Ancylostoma
duodenale or Necator
americanus
• Fish tapeworm –
Diphyllobothrium latum
• Pinworm – Enterobius
vermicularis
• Whipworm – Trichuris trichiura
• Strongyloidiasis – Strongyloides
stercoralis
• Beef tapeworm – Taenia
saginata
• Dog tapeworm – Dipylidium
caninum
• Pork tapeworm – Taenia solium
• Rat tapeworm – Hymenolepis
diminuta
• Fasciolopsiasis – Fasciolopsis
buski
• Fascioliasis – Fasciola hepatica
• Clonorchiasis – Clonorchis
sinensis
Common parasitic roundworms.
Flatworms
• Ribbon-like or
leaf-shaped
– Tapeworms
– Flukes
Arthropods
• 3 classes of arthropods studied in Parasitology courses:
– Insects (e.g., lice, fleas)
– Arachnids (e.g., mites and ticks)
– Crustaceans (e.g., crabs, crayfish and certain Cyclops
species)
• Arthropods serve as mechanical or biologic vectors in the
transmission of certain infectious diseases.
– Mechanical vectors pick up a parasite at point A and
drop it off at point B.
– Biological vectors harbor the parasite in their body,
where the parasite matures and/or multiplies.
Ways in Which Arthropods May Be
Involved in Human Diseases
TYPE OF INVOLVEMENT
EXAMPLE(S)
The arthropod may actually be the
cause of the disease.
Scabies, a disease in which microscopic
mites live in subcutaneous tunnels and
cause intense itching
The arthropod may serve as the
intermediate host in the life cycle of a
parasite.
Flea in the life cycle of the dog
tapeworm. Beetle in the life cycle of the
rat tapeworm.
The arthropod may serve as the
definitive host in the life cycles of a
parasite
Female Anopheles mosquito in the life
cycle of malarial parasites.
The arthropod may serve as a vector in
the transmission of an infectious
disease.
Oriental rat flea in the transmission of
plague. Tick in the transmission of
Rocky Mountain spotted fever and Lyme
Disease.
Arthropods
A. Dermacentor
andersoni, wood tick,
one of the tick vectors of
Rocky Mountain spotted
fever.
B. Xenopsylla cheopis,
oriental rat flea, vector of
plague and endemic
typhus.
Arthropods (cont.)
C. Pediculus humanus,
human body louse; a
vector of epidemic typhus.
D. Phthirus pubis, the
pubic or crab louse.
Body Defense Introduction
• Host Defense Mechanisms
– Ways in which the body protects itself from
pathogens – referred to as 3 lines of defense.
– First 2 lines of defense are nonspecific.
– The 3rd line of defense, the immune response, is
very specific.
• In the 3rd line of defense, special proteins called
antibodies are produced in response to foreign
substances called antigens.
Categories of Host Defense Mechanisms
Nonspecific Host Defense Mechanisms
• Nonspecific host defense mechanisms are general
and serve to protect the body against many harmful
substances.
– Example: innate or inborn resistance.
• Exact factors that produce innate resistance are
not well understood.
– Nonspecific host defense mechanisms include
mechanical and physical barriers to invasion,
chemical factors, microbial antagonism, fever, the
inflammatory response and phagocytic white blood
cells.
First Line of Defense
• Skin and Mucous Membranes as Physical Barriers
• Cellular and Chemical Factors
– In addition to the skin as a physical barrier, there are
other factors (e.g., pH and temperature of skin, mucus,
perspiration, cilia, and various enzymes in secretions such
as lysozyme) that are components of the first line of
defense.
• Microbial Antagonism
– When indigenous microflora prevent colonization of “new
arrivals” as a result of competition for sites and nutrients
and production of lethal substances.
Second Line of Defense
• Transferrin
– Levels of this glycoprotein increase in response to
systemic bacterial infections; binds to iron, depriving
pathogens of this vital nutrient.
• Fever
– Stimulated by pyrogenic (fever-producing)
substances (e.g., pathogens and Interleukin 1, IL-1).
– Augments host’s defenses by stimulating leukocytes,
reducing available free plasma iron and inducing the
production of IL-1.
Second Line of Defense (cont.)
• Interferons
– Small, antiviral proteins produced by virus-infected cells;
they protect nearby cell by preventing them from
producing more virus.
– There are 3 types (alpha, beta and gamma), produced by
3 different types of cells.
– They are induced by different stimuli (e.g., viruses,
tumors, bacteria and foreign cells) and protect the
surrounding cells from viral infection.
– Interferons are not virus-specific, but they are
species-specific
– Are used to treat some viral diseases (Hepatitis C) and
blood cancers (lymphoma)
– Interferons can cause nonspecific flu-like symptoms.
Second Line of Defense (cont.)
• The Complement System
–
A group of about 30 different proteins found in normal blood
plasma – “complementary” to the immune system.
–
Complement components interact with each other in a stepwise
manner known as the complement cascade. Complement
triggers a series (cascade) of reactions that produce tiny protein
rings that create holes in the surface of a foreign cell leading to
death (lysis) of the organism
–
The complement system assists in the destruction of many
different pathogens.
–
Important mechanism of action for antibodies
–
Complement-binding sites on antibody are exposed after
attaching to antigen
–
Complement proteins also aide in the inflammatory response
Second Line of Defense (cont.)
• Acute-Phase Proteins
– Plasma proteins that increase rapidly in response
to infection, inflammation or tissue injury; one
example is C-reactive protein.
• Cytokines
– Chemical mediators released from many different
types of cells in the body; enable cells to
communicate with each other – within the immune
system and between the immune system and other
systems of the body.
– Some cytokines are chemoattractants; they recruit
phagocytes to sites where they are needed.
Inflammation
• The body responds to any local injury, irritation, microbial
invasion, or bacterial toxin by a complex series of events
referred to as inflammation; the 3 major events in
acute inflammation are:
– Mast cells secrete histamine causing an increase in
the diameter of capillaries (vasodilation) which
increases blood flow to the site.
– Increased permeability (also caused by histamine
of the capillaries), allowing the escape of plasma and
plasma proteins.
– Exit of leukocytes from the capillaries and their
accumulation at the site of injury.
Inflammation (cont.)
• The primary purposes of the inflammatory response
are to:
– Localize an infection.
– Prevent the spread of microbial invaders.
– Neutralize any toxins being produced at the site.
– Aid in the repair of damaged tissue.
• The 4 major signs and symptoms of inflammation are:
redness, heat, swelling (edema) and pain.
• Plasma that escapes from the capillaries into the site
causes the area to become edematous (swollen).
The Purposes of Inflammation
Sequence of Events in Inflammation
1. Tissue Injury
2. Vasodilation
3. Increased Permeability
4. Emigration of Leukocytes
5. Chemotaxis
6. Phagocytosis
Inflammation (cont.)
• The accumulation of fluid, cells and cellular debris at the
inflammation site is known as an inflammatory
exudate.
– If the exudate is thick and greenish-yellow,
containing many live and dead leukocytes, it is
known as a purulent exudate or pus.
• In many inflammatory responses (e.g., arthritis or
pancreatitis) there is no exudate and no invading
microorganisms.
• Pyogenic microorganisms (pus-producing
microorganisms) like staphylococci and streptococci
result in additional pus formation.
Phagocytosis
• Phagocytic white blood cells are called phagocytes, and
the process by which they surround and engulf (ingest)
foreign material is called phagocytosis.
• The 3 major categories of leukocytes (white cells) found
in blood are monocytes, lymphocytes and granulocytes.
– The 3 types of granulocytes are: eosinophils,
basophils and neutrophils.
• The most important groups of phagocytes in the human
body are macrophages and neutrophils.
Mechanisms by Which Pathogens Escape
Destruction by Phagocytes
• Capsules; initially serve to protect the organism from
phagocytosis (they serve an antiphagocytic function).
• Some bacteria produce an exoenzyme called leukocidin,
which kills phagocytes.
• Some bacteria (e.g., Mycobacterium tuberculosis) are not
destroyed with phagocytosis.
• The mechanism by which each pathogen evades
digestion by lysosomal enzymes differs from pathogen to
pathogen, and is not yet fully understood.
Additional Factors that Can Impair Host
Defense Mechanisms
• Nutritional status
• Various genetic defects
• Increased iron levels
• Age
• Stress
• AIDS
• Cancer and cancer
chemotherapy
• Drugs (e.g., steroids)
Introduction
• Immunology is the scientific study of the immune system
and immune responses.
• The primary functions of the immune system are to:
– Differentiate between “self’ and “non-self.”
– Destroy that which is “non-self.”
• There are 2 major arms of the immune system:
– Humoral immunity; where special glycoproteins
called antibodies are produced by B cells to destroy
specific microbes.
– Cell-mediated immunity; involves a variety of cell
types, with antibodies only playing a minor role, if
any.
Introduction (cont.)
• Cells involved in immune responses originate in bone
marrow; 3 lines of lymphocytes are derived from lymphoid
stem cells of bone marrow.
– B lymphocytes (or B cells)
– T lymphocytes (or T cells)
– Natural killer cells (NK cells).
• There are 2 categories of T cells:
– Helper T cells and Cytotoxic T cells.
The Two Major Arms of the Immune System
Immunity
• Acquired immunity = immunity that results from the
active production or receipt of antibodies during one’s
lifetime.
• Active acquired immunity:
• Antibodies are produced within the person.
• Usually provides long lasting protection.
• Passive acquired immunity:
• Antibodies are received that were produced by
another person or persons or by an animal.
• Usually provides only temporary protection.
Active Acquired Immunity
• Two types of active acquired immunity:
– Natural active acquired immunity – occurs
naturally.
– Artificial active acquired immunity – artificially
induced.
• Artificial active acquired immunity results when a
person receives a vaccine.
– A vaccine is defined as material that can artificially
induce immunity to an infectious disease, usually
following injection or ingestion of the vaccine.
– Most vaccines are made from living or dead
pathogens or the toxins that they produce.
How Vaccines Work
• Vaccines stimulate the recipient’s immune system to
produce protective antibodies (i.e., antibodies that will
protect the person from disease).
• Types of available vaccines:
– Live
– Attenuated- use of a weakened pathogen (mutated from
being exposed to chemicals or radiation)
– Inactivated vaccines - used of dead pathogens that were
killed by heat or chemicals
– Toxoid- use of inactivated (“detoxified”) toxins
– Conjugate vaccines- use of a linking substance
(polysaccharide) from a microorganisms’ protective
structure to mimic the organism’s antigen which will
trigger an immune response
Passive Acquired Immunity
• Antibodies produced in one person are transferred to
another person to protect the latter from infection –
provides temporary protection.
• Two types:
– Natural passive acquired immunity.
• Small antibodies, IgG, present in mother’s blood
crosses the placenta to reach the fetus.
– Artificial passive acquired immunity.
• Antibodies from an immune person are transferred
to a susceptible person; example, hepatitis B
immune globulin.
Humoral Immunity
• Antigens
– Foreign organic substances
that are large enough to
stimulate the production of
antibodies.
• Antibodies
– Proteins produced by
lymphocytes in response to
the presence of an antigen.
– In a class of proteins called
immunoglobulins – globular
glycoproteins in the blood
that participate in immune
reactions.
Antibody Production
Humoral Immunity (cont.)
• Antibodies (cont.)
– The processing of antibodies results from B cells
developing into plasma cells, which are capable of
secreting antibodies.
– The initial immune response to an antigen is called
the primary response (it takes 10-14 days for
antibodies to be produced).
– The increased production of antibodies following the
second exposure to a particular antigen is called the
secondary response.
Humoral Immunity (cont.)
• Where Do Immune Responses Occur?
– Immune responses to antigens in the blood are
usually initiated in the spleen; responses to microbes
and other antigens in tissues are generated in lymph
nodes located near the infected area.
• Antibody Structure and Function
– Antibodies are a class of glycoprotein called
immunoglobulins; 5 types = IgG, IgA, IgM, IgD, IgE.
– All antibodies are immunoglobulins, but not all
immunoglobulins are antibodies (RhoGAM)!
Antigen-Antibody Complexes
• When an antibody combines with an antigen an antigenantibody complex (or immune complex) is formed.
• Antigen-antibody complexes are capable of activating the
complement cascade; results in some of the following
effects:
– Activation of leukocytes
– Lysis of bacterial cells
– Increased phagocytes being drawn to the area
Cell-Mediated Immunity
• Occurs when antibodies are unable to enter cells.
• Cell-mediated immunity (CMI)
– A complex system of interactions among many types
of cells and cellular secretions (cytokines).
– An arm of the immune system capable of controlling
chronic infections by intracellular pathogens (e.g.,
certain bacteria, protozoa, fungi, and viruses).
– Examples of cells that participate in CMI:
macrophages, Helper T Cells, Cytotoxic T Cells, NK
cells, and granulocytes.
Cell-Mediated Immunity (cont.)
• Helper T cells —release chemicals that attract and
activate macrophages to kill cells by phagocytosis;
produce chemicals that help activate B cells
• Cytotoxic T cells —kill infected or tumor cells by
releasing a substance that poisons infected or tumor cells
• Natural Killer (NK) Cells
– Are large granular lymphocytes.
– Do not proliferate in response to antigen and appear
not to be involved in antigen-specific recognition.
– NK cells kill target cells, including foreign cells, host
cells infected with viruses or bacteria, and tumor
cells.
T Cell
Function
64
Immunosuppression
• Persons whose immune systems are not functioning
properly are said to be immunosuppressed.
• Acquired immunodeficiencies may be caused by
drugs (e.g., cancer therapeutic agents), irradiation, or
certain infectious diseases (e.g., HIV infection).
• Inherited immunodeficiency diseases can be the
result of deficiencies in antibody production, complement
activity, phagocytic function or NK cell function;
examples – DiGeorge syndrome and Wiskott-Aldrich
syndrome.
• People born lacking the ability to produce antibodies (i.e.,
gamma globulins) have agammaglobulinemia; persons
not producing a sufficient amount of antibodies are said
to have hypogammaglobulinemia.
Immunodiagnostic procedures
• Immunodiagnostic procedures (IDPs) are laboratory tests
that are valuable in diagnosing infectious diseases by
detecting either antigens or antibodies in clinical
specimens.
• Skin Testing
– Antigens are injected within or beneath the skin.
– Example: the tuberculosis skin test.