Download Exploring the Normal Flora of the Human Body

Welcome to the Wonderful
World of Microbiology and
Infectious Disease!
What are Microbes?
 Microbes are living things that are too small to be
seen with the unaided eye
 They include bacteria, fungi, protozoa and
microscopic algae.
 Typically we view microbes as harmful, causing
diseases, but only a minority of all microbes is
pathogenic (disease-producing).
Bacteria
 Bacteria are microbes, which are single-celled
organisms that are too small to be seen without a
microscope.
 They are considered to be prokaryotes, which
means that their DNA is not enclosed by a
membrane.
 Eukaryotic cells have a nucleus with a membrane.
 Where can bacteria be found?
Bacterial Cell
Basic Bacterial Anatomy
Bacterial Cell Parts
 Capsule – outer covering on some bacteria;
protects the cell and makes it more pathogenic;
considered a glycocalyx or sugar coat
 Cell wall – semi-rigid structure that maintains the
shape of the cell and protects the interior of the
cell from changes in the outside environment
 The bacterial cell wall contains peptidoglycan.
Some bacteria have just a few layers of
peptidoglycan while others have many.
 Peptidoglycan is not found anywhere else in the
biological world.
Bacterial Cell Parts
 Plasma membrane - thin structure inside the cell
wall that surrounds the cytoplasm, serves as a
selective barrier through which materials can
enter and exit
 Ribosomes - appear as small dots in the
cytoplasm; they make proteins
 Nucleoid – the area where the DNA is found in the
cell
 The DNA strand is long, continuous and usually
circular
 Bacteria possess NO chromosomes.
Bacterial Cell Parts
 Plasmids - small circular strands of DNA not
connected to the main DNA strand
 Cytoplasm - everything inside the plasma
membrane; mostly made up of water
 Pili – hair-like structures that allow bacteria to
attach to other cells and transfer DNA
(conjugation)
 Flagella - long tails that help bacteria move
Shapes of Bacteria
 Come in three main shapes
 Bacillus (rod)
 Coccus (sphere)
 Spirillum (spiral)
Arrangements of Bacteria
 Straight chains of bacteria are referred to as
strepto Two cells of bacteria are called diplo A cluster of bacterial cells is known as staphylo-
Gram Stain
 Developed by the Danish bacteriologist Hans
Christian Gram in 1884
 Classifies bacteria into two major groups:
 Gram-positive
 Gram-negative
Gram Stain
Gram Stain
The crystal violet and iodine combine within
the cytoplasm of the bacterial cells.
Gram-positive - The color does not get washed
out from the alcohol wash and the cells remain
purple.
 Have thicker layer of peptidoglycan in cell walls that
enables the cell to retain the crystal violet
 Gram-negative - The color is washed out by the
alcohol and is no longer visible. When the
counterstain safranin is applied, the cells appear
red.
 The crystal violet can be washed out because they
have a thinner layer of peptidoglycan
Gram Stain
Gram-positive
Gram-negative
Gram-positive/Gram-negative
Cell Walls
Normal Flora/Microbiota
 We all live with a variety of microbes on and in us.
 These microbes make up our normal flora and
include fungi, protists, but mostly bacteria.
 Our body is made up of 1013 cells and we harbor
about 1014 bacteria.
 10 times more bacterial cells than human cells!
 They are in most cases beneficial to us because
they protect our bodies from diseases by preventing
the overgrowth of harmful microbes.
Normal Flora/Microbiota
 Normal flora can be found throughout our body
localized in certain regions.
 Skin
 Eyes (conjunctiva)
 Nose and throat (upper respiratory system)
 Mouth
 Large intestine
 Urinary system
 Reproductive system
Factors that influence where
normal flora/microbiota are found
 Availability of nutrients
 Chemical and physical factors
 Defenses of the host
 Age
 Gender
Normal Flora/Microbiota of Skin
 Microbes on our skin must be able to withstand
secretions from the sweat and sebaceous glands
that have antimicrobial properties.
 Keratin, a protein found on the skin, acts as a
resistant barrier and the low pH of the skin can
also inhibit many microbes.
 These factors prevent the microbes that are in
direct contact with the skin from becoming
permanent residents.
Staphylococcus epidermidis
 S. epidermidis is the most abundant inhabitant of the
skin, especially the upper body.
Staphylococcus aureus
 The nose is one of the
most common sites for
S. aureus.
 It is a leading cause of
bacterial disease in
humans. It can be
transmitted from the nasal
membranes of a carrier to
a susceptible host
(immunocompromised).
Propionibacterium acnes
 Located on greasy areas
of the skin, such as the
forehead
 Can become trapped in
hair follicles and cause
inflammation and acne
 Different species of
Propionibacterium can
live on the sides of our
nose and on our armpits.
Symbiosis
 The relationship between the normal flora and
the host is called symbiosis.
 Symbiosis - living together
 Three types of symbiotic relationships
 1. mutualism
 2. commensalism
 3. parasitism
 Animal symbiosis (4:20)
Mutualism
 Where both the host and bacteria are thought to
derive benefits from each other, it is referred to
as being mutualistic.
 Example: E. coli synthesizes vitamin K and some B
vitamins that are absorbed into our blood stream.
The large intestine, in return, provides nutrients
needed by the bacteria.
Commensalism
 Commensalism - where one organism benefits
and the other is unaffected
 Many of the bacteria that make up our normal
flora are commensals.
 These include the bacteria that are on the
surface of our eyes (conjunctiva) and skin and
some bacteria in the ear that live on secretions
and sloughed-off cells.
Parasitism
 Parasitism -when one organism benefits at the
expense of the other organism
 In some situations normal flora can make us sick.
This can occur when the normal flora leave their
habitat.
 Example: When E. coli leave their habitat of the
large intestine and gain access to other body
parts, such as the urinary bladder, lungs or spinal
cord, they can cause infections such as urinary
tract infections, pulmonary infections, meningitis
and abscesses.
Nutrients
 Bacteria can colonize only where they can be
supplied the right nutrients.
 These nutrients can come from excretory
products of the cells, substances in body fluids
and dead cells, and food in the gastrointestinal
tract.
Chemical and Physical Factors
that Affect Bacterial Growth
 Temperature
 pH
 Available oxygen and carbon dioxide
 Salinity
 Sunlight (UV rays)
Mechanical Factors that Affect
Bacterial Growth
 Certain areas of the body have different mechanical
factors that can affect normal flora from colonizing.
 These include:
 Chewing action of teeth
 Tongue movements
 Flow of saliva and digestive secretions in gastrointestinal
tract
 Muscular movements of throat, stomach, intestines
 These mechanical factors can trap or dislodge microbes.
How do Bacteria Make us Sick?
 It’s not the bacteria themselves that make us sick; it’s
what they produce that makes us sick.
 Bacteria produce substances called toxins that cause
illness and disease.
 There are two types of toxins: exotoxins and endotoxins
 Exotoxins are proteins that are secreted by bacteria and
are products of their metabolism.
 Generally produced by Gram-positive bacteria
 Some of the deadliest substances known (C. botulinum toxin)
 Disease examples: food “poisoning”, TSS, tetanus, botulism,
diphtheria, gas gangrene
 Endotoxins are components of the bacterial cell wall
(lipopolysaccharides).
 Generally found in Gram-negative bacteria
 Disease examples: no specific diseases; cause fever, hemorrhaging,
shock, miscarriage, coma, death
Defenses of Host
 The body has many defenses against microbes
that include:
 Activated cells that kill microbes
 Cells that inhibit growth
 Prevent adhesion to cell surfaces
 Neutralize toxins that microbes produce
 These defense mechanisms are helpful in fighting
pathogens.
Biofilms
Plaque
 Masses of microbes attached to a surface; increases
pathogenicity (involved in 70% of infections)
 The “slime” is made primarily of polysaccharides
with some DNA and proteins.
 The microbes are connected to each other,
enabling them to chemically communicate with
each other, transfer DNA, and share nutrients.
Biofilms
 Because of the complex chemical composition of
the slime, biofilms are resistant to immune
systems, disinfectants, and antibiotics (about 1000
times more resistant).
 Significant problem on internal medical devices
such as catheters, stents, and mechanical heart
valves; also problematic on contact lenses
 When microbes grow in biofilms, they
communicate with each other.
 Examples: plaque, pool algae, shower scum
 Bacterial communication (15:00)
Biofilms – Progression of Growth
Virus Characteristics
Viruses contain DNA or RNA, but not both
Possess a protein coat
Some viruses have surface spikes
Most viruses infect only specific types of cells in
one host
Host range is determined by specific host
attachment sites and cellular factors
First isolated and studied in 1935 (tobacco
mosaic virus)
Phage therapy and oncolytic viruses
Are Viruses Alive??
Viruses are inert outside a host cell = nonliving
They have few or no enzymes of their own, so
they need their host cells’ enzymes.
However, once they enter a cell, their nucleic
acids become active and they start multiplying.
They cause infection and disease just like living
pathogens.
They could be considered:
 a very complex mixture of chemicals, or
 a very simple living organism
Viral Structure
Virion - a complete, fully-developed, infectious
viral particle composed of nucleic acid and
surrounded by a protective protein coat
(capsid)
Capsomere – protein subunit of a capsid; can
be used to identify a particular virus
Envelope – lipid, protein, and carb complex
covering capsid; many times contains parts of
host membrane
 Used to help virus enter host cell
Spike – carb-protein complex projecting from
envelope; can be used to ID virus
 Used to attach virus to host cell and clump cells
together
Viral Anatomy
Relative Sizes of Viruses
How do Viruses Reinfect?
 Why do we get influenza more than once?
 The surface proteins (spikes) of many viruses, like
influenza, can easily mutate.
 Although you may have produced antibodies to one
influenza virus, the virus can mutate and infect you
again.
 What is a vaccination?
Influenza viruses –
(notice the spikes)
Virus video (3:38)
History of Vaccination
(4:30)
Multiplication of Bacteriophages
(Lytic Cycle)
 A virus must invade and take over a host cell in order to
multiply; it needs the host cell’s enzymes and nucleic acids.
 Attachment
Phage attaches by tail fibers to
host cell receptors
 Penetration
Phage lysozyme (enzyme) opens cell
wall; DNA is injected into cell
 Biosynthesis
Production of phage DNA and
proteins; no complete phages yet; step
when host cell is taken over
 Maturation
Assembly of phage
 Release
Phage lysozyme breaks cell wall and
“baby” phages are released to wreak
more havoc
Lytic Cycle of a Bacteriophage (a)
Attachment
Penetration
Biosynthesis
Lytic Cycle of a Bacteriophage (b)
Maturation
Release
Lytic/Lysogenic Cycles
Lytic cycle: Phage causes
lysis and death of host cell
Lysogenic cycle: Prophage
DNA (inserted phage DNA)
incorporated in host DNA
 Host cell does not die
 Every time host divides, so
does the prophage DNA.
Lysis of E. coli
Lytic/Lysogenic Cycles
Viruses and Cancer
 Almost anything that alters cellular DNA (oncogenes)
has the potential to make normal cells cancerous.
 Several types of cancer are known to be caused by
viruses (~10% of all cancers).
 Relationship between viruses and cancer first
demonstrated in 1908 (chicken leukemia)
 Oncoviruses – viruses that transform normal cells into
cancerous cells.
 Transformed cells have increased growth, loss of
contact inhibition, and viral-specific T antigens
(antigens that disrupt the normal cell cycle).
 The genetic material of oncogenic viruses becomes
integrated into the host cell's DNA.
Latent/Persistent Viral Infections
Latent Viral Infections
 Virus remains in asymptomatic host cell for long
periods
 Cold sores, shingles, oncogenic viruses
 Many remain latent in nervous tissue
 Can be reactivated by immunosuppression
Persistent Viral Infections
 Disease progresses over a long period; generally
fatal; disease presents years later
 Often caused by another virus
 Measles and fatal encephalitis; HBV and liver
cancer; human papillomavirus and cervical cancer
Plant Viruses and Viroids
• Plants are generally
protected by cell wall
• Plant viruses enter through
wounds or via insects that
suck plant’s sap
• Viruses can multiply inside
insect cells, then get
passed to plant
• Viroids
• Viroids are infectious
pieces of RNA (potato
spindle tuber disease)
• Responsible for millions of
$ in crop damage
tobacco mosaic virus
Prions
 Infectious proteins first explained in 1982
 Inherited and transmissible by ingestion, transplant,
and surgical instruments; can be spontaneous as well
 Treated with proteases or NaOH and autoclave
 Most resistant to chemical biocides because when
altered, they’re extremely stable and resistant to
denaturation
 Many are believed to be inherited (the case with the
five human prion diseases)
 PrPC: normal cellular prion protein; on cell surface
 PrPSc: scrapie protein; accumulates in brain cells
forming plaques (plaques used for postmortem
diagnosis; don’t appear to be cause of cell death)
Prions
Microscopic "holes" are characteristic in prionaffected brain tissue sections, causing the tissue
to develop a "spongy" appearance.
Prions
Section of a normal brain
Prions (1:40)
Section of brain affected by
Creutzfeldt-Jakob disease
Fatal Familial Insomnia (9:55)
QUIZ TIME!!!
Bacteria can be found in the
shape of _____.
 A. spheres
 B. rods
 C. spirals
 D. all of the above
Shapes of Bacteria
Identify each basic shape.
Because they have no nucleus or
organelles, bacteria are
considered to be _____.
The pili of a bacterial cell are
used for _____.
 A. protection from macrophages
 B. making proteins
 C. movement
 D. transferring DNA to other bacteria
(conjugation)
You will never find ______ in a
bacterial cell.
 A. a nucleus
 B. a cell wall
 C. a ribosome
 D. DNA
What is the carb covering of the
bacterial cell that protects it from the
outside environment?
 A. plasma membrane
 B. capsule
 C. cell wall
 D. pili
Normal flora are bacteria that
cause disease.
 True
 False
Normal flora can only be found on
our skin.
 True
 False
Spherical bacteria are called ________.
Rod-shaped bacteria are called ________.
Spiral bacteria are called _______.
When both the host and bacteria
receive benefits from each other it is
considered to be _____.
 A. parasitism
 B. commensalism
 C. mutualism
Bacteria arranged in a straight chain
are referred to as _________.
Bacteria arranged in a cluster are
referred to as ________.
Two side-by-side cells of spherical
bacteria are called ________.
Bacterial cells will burst at the end of the
_____ cycle.
Cancer-causing viruses are called _____.
_____ are masses of a variety of microbes
sticking to a surface.
The carb-protein structure that enables
viruses to attach to host cells:
A. capsule
B. glycocalyx
C. spike
D. pili
Infectious proteins are called:
A. viroids
B. bacteriophages
C. prions
D. normal flora