Presentation for nursing students on basic principles of microbiology

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Microbiology
Sonja Ray, RN PHN

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Objectives
1. Discuss basic characteristics of bacteria, including
structures that lead to pathogenicity, drug susceptibility,
and accurate identification
2. Discuss basic characteristics of fungi, helminths, and
viruses
3. Describe three main modes of disease transmission
4. Describe how bacteria penetrate host defenses and cause
damage

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Objectives
6. Describe how bacterial infections are diagnosed and
treated
7. Describe how viruses enter the host can cause illness, and
how do we diagnose and treat viral infections
8. Describe how fungi invade and damage host cells, and how
fungal infections are diagnosed and treated
9. Discuss methods of microbial control

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Overview of basic
principles
A quick reference

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The Basics:
 Cell Theory: All living things are composed of cells (circa
1665)
 Biogenesis: All living cells can arise only from preexisting
cells
 Formed basis of aseptic techniques: techniques that prevent
contamination by microorganisms, because we know that
microorganisms can only come from living microorganisms.
 Heritable material (DNA) is passed from parent to offspring
and dictates specific traits expressed in the offspring.
 Germ Theory: Germs can cause disease

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Perspective

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Important Terms:
 Normal microbiota – microorganisms present inside a
healthy human body that do not cause harm and in some
cases benefit the host.
 Infection – the ability of an organism to invade and establish
residency in a host
 Note: Infection ≠ Disease!
 Pathogen – organisms found in the environment that are
capable of replication either independently or with the host
AND are capable of provoking an adverse response in the
host (aka disease)
 Examples include bacteria, viruses, fungi, parasites, and prions
 Range from 20 nm (polio virus) to 10 m (tapeworms)

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Koch’s Postulates
 The microorganism must be found in abundance in all
organisms suffering from the disease, but should not be
found in healthy organism.
 The microorganism must be isolated from a diseased
organism and grown in pure culture.
 The cultured microorganism should cause disease when
introduced into a healthy organism
 The microorganism must be reisolated from the inoculated,
diseased experimental host and identified as being identical
to the original specific causative agent.

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Koch’s Postulates

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Tools in Microbiology: Microscopy
 Most initial observations of microorganisms are made with
stained preparations under the microscope
 Stains:
 Stains are used to color the microorganisms in a way that
emphasizes what you want to look at.
 Microscopy can aid in classification of microorganism
 Determine overall cell shape, size, and capsule
 Using microscopy, you can tell if the microorganism is unicellular
(like a bacteria) or multicellular (like a parasite)
 Based on the organisms response to dyes, you can also note
characteristics of the organisms cell wall (see gram stain and acid
fast stain)

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Bacteria

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Anatomy of a Bacterial Cell
 Bacteria are Prokaryotic, Unicellular
Organisms
 No nucleus – Their DNA is usually a
singular circularly arranged
chromosome
 Their DNA is not associated with
histones
 They lack membrane-enclosed
organelles (i.e. mitochondria)
 Their cell walls almost always
contain the complex polysaccharide
peptidoglycan
 They usually divide by binary
fission. During this process, the DNA
is copied and the cell splits into two
cells.

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Shape: Cocci, Bacilli, Spiral

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Why shape matters: Classification!

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Structures External to the Cell Wall
 Glycocalyx
 A viscous, gelatinous polymer that is composed of
polysaccharides, polypeptides, or both
 If it is organized and firmly attached to the cell wall, it is called a
capsule
 If it is unorganized and loosely attached, it is described as a slime
layer
 Contributes to virulence:
 Protects pathogenic bacteria from phagocytosis (i.e. Bacillus
anthracis and Streptococcus pneumoniae)
 Enables bacterium to survive by attaching to various surfaces
(Streptococcus mutans)
 Protects bacterium against dehydration and can inhibit
movement of nutrients out of the cell

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Visualizing Bacteria: Capsule
Stains
 Showing that a microorganism
has a capsule can help identify
that microorganim and tell you
something about its
pathogenicity
 Capsules to do not accept
most biological dyes, so they
appear as halos surrounding
each stained cell

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Structures External to the Cell Wall
 Flagella
 Long filamentous
appendages made of
protein that propel bacteria
 The flagellar protein called
H antigen is useful for
distinguishing among
serovars (variations within a
species)
 Example: Serovars
identified as E. coli
O157:H7 are associated
with foodborn epidemics

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Structures external to the cell wall
 Axial Filaments
 Found on spirochetes
 Allow motility through
corkscrew movement
 Example: Treponema
pallidum (Syphalis) and
Borrelia burgdorferi (Lyme
disease)

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Structures external to the cell wall
 Fimbriae and Pili
 Hairlike appendages, that are
shorter, straighter, and thinner
than flagella and used for
attachment and transfer of
DNA rather than motility
 Fimbriae
 Can enable a cell to adhere
to surfaces (i.e. Neisseria
gonorrhoeae)
 Pili
 Usually longer than
fimbriae and only one or
two pili per cell
 Join bacterial cells in
preparation for the transfer
of DNA from one cell to
another in a process called
conjugation

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The Bacterial Cell Wall
 Composed of a peptidoglycan network
 Repeating disaccharide attached by polypeptides to form a
lattice that surrounds and protects the cell
 Disacharide portion is made up of monosaccharides called N-
acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
 Alternating NAM and NAG molecules are linked in rows of 10-65
sugars to form a carbohydrate backbone
 Adjacent rows are linked by polypeptides
 The structure of the polypeptide link varies by species, but it
always includes a tetrapeptide side chain attached to NAMs.
 Many antibiotics work by targeting the cell wall (i.e. penicillin
interferes with final linking of pepdidoglycan rows by peptide
cross-bridges

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Bacterial Cell Wall: Images

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Gram Stain

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Gram Positive vs. Gram Negative

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Usefulness of Gram Stain

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Acid Fast Stain

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Bacterial Metabolism: Generating
Energy
Energy Growth End Product ATP molecules
Process Conditions produced
Aerobic Aerobic Water 38/glucose
Respiration
Anaerobic Anaerobic Us. an inorganic Between 2 and 38
Respiration substance (i.e.
methane, hydrogen
sulfide)
Fermentation Aerobic or An organic molecule 2
anaerobic (i.e. lactic acid)

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Objective 1
 Discuss basic characteristics of bacteria, including structures
that lead to pathogenicity, drug susceptibility, and accurate
identification
 Glycocalyx - Protects pathogenic bacteria from phagocytosis,
Enables bacterium to survive by attaching to various surfaces
(Streptococcus mutans), Protects bacterium against dehydration
and can inhibit movement of nutrients out of the cell
 Flagella – H-antigen is useful for distinguishing among serovars
 Axial filaments – allows motility so bacterium can travel to site
of infection
 Fimbriae – allows bacterium to adhere to surfaces
 Components of the cell wall allow bacteria to be identified
through the gram stain and acid fast stain

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Fungi

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Fungi: the basics
 Easily visible by Light Microscopy (1-200 u)
 Plant-like
organisms which grow by
continuous extension and branching
(hyphae)
 Growth
 Some grow only as yeasts (ie. Candida
Albicans, Cryptococcus )
 Some grow only as molds (ie. Aspergillus)

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Growth of Fungi

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Fungi: The basics (continued)
 All fungi require some organic compounds for energy (not
phototrophs)
 Most fungi are aerobic
 Fungi can reproduce via a few routes:
 Asexually by fragmentatino of their hyphae
 Suxually or asexually by formation of spores
 Fungi usually grow better in an environment with a pH of
about 5
 Fungi can also grow on substances with very low moisture
content and are relatively resistant to osmotic pressure

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Helminths
worms

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Helminths: the basics
 Multicellular
 Eukaryotic
 Most possess digestive, circulatory, nervous, excretory, and
reproductive systems
 Most Helmonths that cause disease are parasitic, there are
some distinguishing features of parasitic helminths:
 They may lack a digestive system
 Their nervous system is reduced
 Their means of locomotion is occasionaly reduced or completely
lacking
 Their reproductive system is often complex. An individual
produces a large number of eggs, by which a host is infected

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Life Cycle: Tapeworm

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Viruses

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Size of Viruses

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Viruses: The basics
 Viruses are considered to be obligatory intracellular
parasites
 They require living host cells in order to multiply
 They use host machinery to synthesize their own proteins and
replicate their own DNA
 Viruses have few or no enzymes of their own for metabolism
 They lack enzymes for ATP generation and protein synthesis
 This makes it difficult when designing antivirals, because most
antimicrobial drug targets are enzymes unique the to pathogen,
when an organism has no unique enzymes, you have no potential
drug target

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Viral Anatomy
 Nucleic Acid
 DNA or RNA (But never both)
 ssDNA
 ds DNA
 ss RNA
 ds RNA
 Capsid (Coat Protein)
 protects viral genome from host endonucleases
 capsomeres
 Binding Sites
 Envelope (not present on all viruses)
 Derived from the host cell
 Made up of lipids, proteins and carobhydrates
 Binding Sites

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Shape of Viruses
Helical Polyhedral

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Shape of Viruses
Enveloped (can be
Complex
helical or polyhedral)

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Life Cycle of A virus: Papovavirus

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Differences in biosynthesis among
viruses

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Objective 2
 Discuss basic characteristics of fungi, helminths, and viruses
 Fungi
 multicellular or unicellular (yeasts)
 Prefer acidic (pH ~5) environments
 Can thrive in dry environments and are relatively resistant to
osmotic pressure
 Helminths
 Multicellular
 Most that cause disease are parasitic and have the following
features:
 They may lack a digestive system
 Their nervous system is reduced
 Their means of locomotion is occasionally reduces or completely
lacking
 Their reproductive system is often complex

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Objective 2 (cont)
 Viruses
 Require a host to multiply
 Use hosts machinery to multiply
 Made up to 2-3 main components:
 Nucleic Acid (DNA or RNA)
 Capsid
 Envelope (mot present on all viruses)

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Disease transmission

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Stages of Infection

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Spread of infection throughout
population

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Contact Transmission
 Spread of agent of disease by direct contact, indirect contact,
or droplet transmission
 Direct contact (aka person to person) occurs when agent is
transferred by physical contact between its source and a
susceptible host, no intermediate object is involved
 Indirect contact occurs when pathogen is transmitted from its
reservoir to susceptible host by means of a nonliving object
(fomite).
 Droplet transmission occurs when microbes are spread in
droplet nuclei that travel short distances

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Vehicle Transmission
 Transmission of disease agents by a medium, such as water,
food, or air
 Note: The difference between airborne and droplet
transmission
 Airborne transmission refers to the spread of agents of infection
by droplet nuclei in dust that travel more than 1 meter from the
reservoir to the host (in droplet transmission the droplet travels
less than 1 meter from the reservoir).
 Example: Measles, Tuberculosis can also be spread by airborne
transmission, even though it is also considered to be spread by
droplet transmission

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Vector-based Transmission
 Vectors – animals that carry pathogens from one host to another
 Arthropods are an important group of vectors. They transmit
disease by 2 general methods:
 Mechanical transmission:
 Passive transport of pathogens on the insect’s feet or other body
parts
 Example: houseflies can transfer pathogens of typhoid fever and
bacillary dysentery
 Biological transmission
 Arthropod bites an infected person or animal and ingests some of
the infected blood
 Pathogen then reproduce in the vector
 Pathogen either migrates to salivary gland of vector or gut
 Vector spreads pathogen to susceptible host by defecating,
vomiting, or biting the host
 Example: malaria

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Objective 3
 Describe three modes of disease transmission
 Contact transmission: Spread of agent of disease by direct
contact, indirect contact, or droplet transmission
 Vehicle based transmission: Transmission of disease agents by a
medium, such as water, food, or air
 Vector based transmission: transmission of disease through an
animal vector (i.e. arthropod)

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Nosocomial (hospital acquired)
infections
 In the US, the CDC estimates that 5 to 15% of all hospital
patients acquire some type of nosocomial infection
 The rate of nosocomial infections has increased 36% during
the last 20 years.
 2 million people per year contract nosocomial infections, and
nearly 20,000 die as a result.
 This means, nosocomial infections are the 8th leading cause
of death in the US.

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Transmission based precautions

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Transmission based precautions

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Transmission based precautions

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How do pathogens cause injury?
What do we do about it? (dx and tx)

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Progression of infection

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Step 1: Entry into human host
A pathogen must overcome the host’s barriers to
infection in order to cause disease

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Portal of Entry: Mucous
Membranes
 Lining of respiratory tract, GI tract, GU tract, and conjunctiva
(lining of the eye)
 Respiratory tract – easiest and most frequently traveled.
 Examples: cold, flu, tuberculosis, pertussis, measles, strep throat,
diptheria, pneumonia
 GI – via contaminated food, water, and fingers
 Examples: Hepatitis A, shigellosis, cholera
 GU – some microbes can penetrate and unbroken mucous
membrane, others require a cut or abrasion
 Example: chlamydia, syphilis, herpes, gonorrhea

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Other portals of entry
 Skin  Parenteral
 Skin is the largest organ of  Microorganisms are
the body. When unbroken is deposited into the tissues
an effective barrier for most below the skin or mucus
microorganisms. membranes
 Some microbes can gain  Punctures, injections, bites,
entrance thru openings in scratches, surgery, splitting
the skin: hair follicles and of skin due to swelling or
sweat glands dryness
 Example: Nectoriasis
 Caused by hookworm
 Example: Athletes Foot
 Caused by Fungi: Tinea
pedis

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Step 2: Travel to site of infection
 The blood stream, lymphatic system, and interstitial fluids
provide mediums for pathogens to travel throughout the
body, once inside

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Step 3: Cause damage
 Pathogens can cause damage via three main pathways:
 Direct damage
 Release of Exotoxins, Endotoxins and/or irritant enzymes/
proteins
 Induction of host immune response

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How Bacterial Pathogens Penetrate
Host Defenses
 Capsules
 Capsule resists host’s defenses by impairing phagocytosis
 Human response: produce antibodies against the capsule
 Cell wall components
 Enzymes (produced by some bacteria)
 Coagulases: coagulates (clot) the fibrinogen in blood
 Hyaluronidase: hydrolyzes hyaluronic acid, a type of
polysaccharide that holds together certain cells of the body
 Collagenase: breaks down the protein collagen, facilitating
spread of infection through connective tissue
 IgA proteases: destroys hosts IgA antibodies found on mucosal
surfaces

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How Bacterial Pathogens Penetrate
Host Defenses (cont)
 Antigenic variation
 Adaptive (acquired) immunity is a specific defensive response of
the body to an infection that relies on remembering antigens
associated with specific pathogens.
 Some pathogens can alter their surface antigens, so by the time
the body develops an immune response specific to those
antigens, the pathogen has changed and is unaffected by the
body’s immune response
 Penetration into the host cytoskeleton
 Adhesins: molecules on the surface of bacteria that are used to
attach to host cells
 Actin: the major component of the cytoskeleton of host cells. Used
by some microbes to penetrate host and to move through the host
cell

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How Bacterial Pathogens Cause
Damage
 Using host’s nutrients: Siderophores
 Direct Damage
 Production of Toxins
 Exotoxins
 Endotoxins
 Inducing a hypersensitivity reaction

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Siderophores
 Proteins secreted by some pathogens that allow the pathogen
to obtain free iron from the host
 Iron is required for the growth of most pathogenic bacteria,
but the concentration of free iron is low because most iron is
tightly bound to proteins
 When iron is needed by a pathogen, siderophores are
released into the medium where they take the iron away from
iron transport proteins by binding the iron more tightly.
 Once the iron-siderophore complex is formed, it binds to the
bacterial surface and is used by the bacteria

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Direct damage
 Bacteria can cause direct damage as they use the host cells
for nutrients and produce waste products
 As bacteria metabolize and multiply in cells, the cells usually
rupture

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Toxins
 Exotoxins:
 produced inside some bacteria as a part of their growth and
metabolism and secreted by the bacterium into the surrounding
medium or released following lysis
 Many exotoxins are encoded by genes on the bacterial plasmid
 They destroy particular parts of the host cell or inhibit certain
metabolic functions
 The body produces antitoxins, which are antibodies that provide
immunity to exotoxins

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Toxins (Cont)
 Endotoxins
 Are part of the outer portion of the cell wall of gram-negative
bacteria
 Are lipopolysaccharides
 Are released when gram negative bacteria die and their cell walls
undergo lysis
 Antibiotics used to treat diseases caused by gram-negative
bacteria can lead to release of endotoxin and thus may lead to
immediate worsening of the symptoms, but the condition usually
improves as the endotoxin breaks down
 Stimulates macrophages to release cytokines in very high (toxic)
concentrations. Symptoms include: chills, fever, weakness,
generalized aches. Can lead to miscarriage, shock, and death

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Objective 4
 Describe how bacteria penetrate host defenses and cause
damage
 Penetrate host defenses:
 Capsules
 Cell wall components
 Enzymes
 Antigenic variation
 Penetration into cytoskelton
 Cause damage
 Using host’s nutrients
 Direct damage
 Toxins
 Hypersensitivity reaction

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Diagnosing and treating a
bacterial infection
 Culture
 Gram stain
 Set up culture with best specimen for symptoms
 Identification based on biochemical reactions
 Sensitivities to determine best antibiotic therapy
 All usually completed in 24-72 hours
 Special consideration for Mycobacteria
 distinctive waxy cell coat requiring Acid Fast Stains
 virulence is related to cell wall “cord factor” which inhibits
phagosome-lysosome fusion
 Special culture methods used; may take up to 6 weeks
 TX: antibiotics

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Objective 5
 Describe how bacterial infections are diagnosed and treated
 Diagnosis
 Culture
 Drug sensitivity tests
 Gram stain/ acid fast stain
 Treatment
 antibiotics

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Example of Bacterial Infection: C.
diff
 Clostridium difficile is a
bacteria that can cause
symptoms ranging from acute
diarrhea to life-threatening
inflammation of the colon
 Gram-positive, spore-forming
bacillus
 Part of normal flora in 1 to 3%
of humans
 Tx. with broad-spectrum
antibiotics predisposes person
to colonization by C. diff

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C. diff infection (cont)
 C. diff releases toxins that
cause mucosal damage and
inflammation
 Pseudomembranous colitis
occurs when an adherent
inflammatory membrane
covers areas of mucosal injury
 Life threatening
 Prompt therapy is needed to
prevent perforation of bowel
 C. diff is transmitted via fecal-
oral route

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C. diff infection (cont)
 Symptoms:
 Diarrhea (mild to moderate)
 Lower abdominal cramping
 If due to antibiotics, they typically begin within 1 to 2 weeks after
antibiotic tx started, but this varies from 1 day to 6 weeks
 Symptoms tend to subsitde after antibiotic has been d/c’d
 Diagnosis:
 History (look for antibiotic use)
 Lab tests to confirm C. diff in stool by culture and measuring
presence of C. diff toxin
 Rapid dx can be done with flexible sigmoidoscopy or abdominal
CT

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C. Diff (cont)
 Treatment
 Immediate d/c of antibiotics
 Specific tx aimed at eradicate C. diff if symptoms are severe or
persistent
 Metronidazole (PO) is first choice, but vancomycin (PO) is used
in people who can’t tolerate metronidazole or don’t respond
 Nursing concerns
 Maintaining and monitoring hydration
 Maintaining and monitoring skin integrity
 Monitoring stool output and response to tx
 Contact precautions to prevent spread

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Viral Mechanisms for Invading
Host
 Viruses need a host for replication
 Viruses gain access to cells because they have attachment
sites for receptors on their target cells.
 When an attachment site is brought together with an
appropriate receptor, the virus can bind to and penetrate
those cells

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Common terms in viral infection
 Active Infection: After recent entry, the virus replicates
with the production of antigens. Antibodies and/or a cell
mediated response is usually absent in early acute
infection.
 Past Infection: The virus entered long ago, an immune
response occurred and the virus has been cleared. This is
characterized by the absence of antigen and the presence
of antibodies and/or a cell-mediated response.
 Latent Infection: The virus entered in the past and remains
there, BUT is inactive. Antigens are absent, but antibodies
and/or a cell mediated response is present. The virus can
reactivate.
 Recurrent Infection: The latent virus has become active.
Antigen and antibodies are present.

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Viral induced injury
 Infection of a host cell by a virus usually leads to the death of
the host cell. This can occur one of a few ways:
 Accumulation of large numbers of multiplying viruses
 Effects of viral proteins on the permeability of the host cell’s
plasma membrane
 Inhibition of host DNA, RNA, or protein synthesis
 Some viruses cause lysosomes to release their enzymes
 Some viruses cause adjacent infected cells to fuse to form a vary
large multinucleate call called a syncytium
 Some viruses cause antigenic changes on the surfface of infected
cells. This elicits a host antibody response against the infected
cell, and thus targets the cell for destruction by the host’s immune
system
 Some viruses cause chromosomal damage to the host cell

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Diagnosis: methods of identifying a
virus
 Detection of virus by Culture
 Detection of Antigens-- ELISA
 Detection of specific Antibodies

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Prevention and treatment of viral
diseases
 Let them run their course and treat symptoms
 Antivirals (there are not as many antiviral medications
available)
 Vaccines

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Objective 6
 How do viruses enter the host can cause illness, and how do we
diagnose and treat viral infections?
 Viruses gain access to cells because they have attachment sites for receptors
on their target cells.
 Viruses can cause damage in the following ways:
 Accumulation of large numbers of multiplying viruses
 Viral proteins effect the permeability of the host cell’s plasma membrane
 Inhibition of host DNA, RNA, or protein synthesis
 Cause lysosomes to release their enzymes
 Cause adjacent infected cells to fuse to form a vary large multinucleate call
 Cause antigenic changes on the surface of infected cells, targeting them for
destruction by the host’s immune system
 Cause chromosomal damage to the host cell
 Diagnosis through culture and nucleic acid matching, ELISA, Western Blot
 Treatment: treat symptoms, give antivirals (rare), prevent spread with vaccines

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Example of a viral infection:
Influenza (flu)
 Influenza is caused by RNA viruses in the family
Orthomyxoviridae
 Can affect birds and mammals (which can serve as reservoirs)
 There are 3 types that cause epidemics in humans: A, B, and C
 Airborne transmission and direct contact transmission
 Coughs and sneezes (air)
 Contact with bird droppings or nasal secretions (direct-contact)
 A person is contagious beginning about the day before
symptoms appear to 5 to 7 days later

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Influenza (Cont)
 Influenza binds to epithelial
cells in nose, throat and lungs
(See diagram)
 Viral proteins can degrade
host cell mRNA, inhibit
translation of host cell mRNA
 New viruses buds off from the
host cell to spread infection
and the host cell dies
 Influenza evades immune
response through antigenic
variation

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Influenza
 Most Common Symptoms:
 Chills
 Fever
 Sore throat
 Muscle pains
 Severe headache
 Coughing
 Weakness/fatigue
 General discomfort
 Nausea and vomiting (esp
children)

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Influenza diagnosis
 Symptom assessment
 Tests (rare)
 Rapid flu test
 Done in a doctor’s office
 Direct fluorescent antibody stain (DFA)
 Done in a lab
 Viral culture
 Done in a lab
Takes 3-10 days

 Nucleic acid amplification
 Influenza A or B antibody tests

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Influenza treatment
 Treatment:
 Fluids, rest
 Treat symptoms (acetaminophen for fever, etc)
 Neuraminidase inhibitors (antiviral)
 Prevent the release of new infectious viruses and halt viral
replication
 M2 inhibitors (antiviral)
 Prevent uncoating of virus once in cell, thus preventing
replication
 Preventing spread:
 Handwashing
 Seasonal Vaccines (esp. health care workers, over 50, etc)

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Influenza: Nursing concerns
 Encourage rest
 Encourage fluids
 Monitor lung sounds
 Provide supportive therapy as indicated (antipyretics, or
antitussives)

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Fungal Infection
 Infection is called mycoses or mycotic infection.
 Fungal infections tent to be chronic because fungi grow
slowly
 Do not have well defined set of virulence factors
 Classified into one of five groups according to extent of
tissue involvement and mode of entry into the host
 Systemic
 Subcutaneous
 Cutaneous
 Superficial
 Opportunistic

91. +
Systemic Mycoses
 Fungal infections deep within the body
 Not restricted to any particular region of the body, but can
affect a number of tissues and organs
 Usually caused by fungi that live in the soil
 Inhalation of spores is the route of transmission; infection
typically begins in the lungs and then spreads to other
tissues.
 Do not tend to be contagious from animal to human or from
human to human
 Example: Histoplasmosis and coccidioidomycosis

92. +
Subcutaneous mycoses
 Fungal infections beneath the skin
 Caused by fungi that live in soil and on vegetation
 Infection often begins by direct implantation of spores or
mycelial fragments into a puncture wound on the skin
 Example: Sporotrichosis (acquired by gardeners and
farmers)

93. +
Cutaneous mycoses
 Dermatophytes: fungi that infect only the epidermis, hair, and
nails
 Cutaneous mycoses (aka dermatomycoses) are infections
caused by dermatophytes.
 Dermatophytes secrete karatinase, an enzyme that degrades
karatin, a protein in hair, skin, and nails
 Infection is transmitted from human to human or animal to
human by direct contact or by contact with infected hairs and
epidermal cells
 Example: Epidermophyton floccosum

94. +
Superficial Mycoses
 Caused by fugni localized
along hair shafts and in
superficial (surface)
epidermal cells
 Prevalent in tropical climates
 Example: Pitvriases versicolor
(shown on the right, above),
Tinea Capitus (shown on right,
below)

95. +
Opportunistic Mycoses
 Opportunistic pathogen:  Example: Pneumocystis and
generally harmless in normal Candidiasis (shown below)
habitat, but can become
pathogenic in a host who is:
 seriously debilitated or
traumatized
 under treatment with broad-
spectrum antibiotics
 Immunocompromised due
to drugs or an immune
disorder
 diagnosed with a lung
disease

96. +
How do fungi invade host cells?
 Candida albicans and Trichophyton secrete proteases that
modify host cell membranes to allow attachment of the fungi
 Cryptococcus neoformans produces a capsule that helps it
resist phagocytosis

97. +
How do Fungi cause damage?
 Some produce metabolic products that are toxic to humans
 i.e. Trichothecenes: fungal toxins that inhibit protein synthesis in
host cells
 i.e. Alfatoxin is produced by a mold that can be found in peanut
butter. Excessive amounts of this toxin is known to have
carcinogenic properties.
 Some provoke allergic reactions

98. +
Diagnosis and Treatment of Fungal
Infection
 Cultures may be done.
 Many
fungi can be identified by light
microscopy.
 Specimens and biopsies: Special stains
 Medications are available for treatment.
 Topicals: end in –azole
 Systemic: ketoconazole, amphotericin B, Nystatin
 Note: Some fungi have developed resistance to
antifungals

99. +
Objective 7
 Describe how fungi invade and damage host cells, and how
fungal infections are diagnosed and treated
 Invade host:
 Secrete proteases that allow attachment
 Produce a capsule that resists phagocytosis
 Cause damage:
 Producing toxins
 Elicit allergic response
 Diagnosis: culture and light microscopy, gross assessment
 Treatment: antifungals

100. +
Helminth induced injury
 Use host tissues for their own growth or produce large
parasitic masses; the resulting cellular damage evokes
symptoms
 Waste products of these parasites can also contribute to
disease

101. +
Protozoa induced injury
 Reproduce within host cell, causing it to rupture
 Example: Plasmodium
 Prevent normal cell function
 Example: Toxoplasma
 Digest cells and tissue fluids
 Example: Giardia lamblia
 Note: some protozoa can avoid host defenses by varying their
antigens like viruses. For example Trypanosoma (causes
sleeping sickness) can produce up to 1000 different antigens

102. +
Control of Microbial
Growth

103. +
Requirements for Growth
Temperature
 Every bacterium has an ideal
temperature range and
temperatures outside that
range prohibit growth and life
 Psychrophiles (cold-loving)
 Mesophiles (moderate temp-
loving)
 Thermophiles (heat loving)

104. +
Requirements for Growth
 pH  Trace Elements (i.e. zinc, iron,
 Most bacteria prefer a pH copper, molybdenum)
between 6.5 and 7.5
 Oxygen (in some bacteria)
 Human immune response
often uses pH to destroy  Organic Growth Factors
bacteria
 Organic compounds that an
 Osmotic Pressure organism is unable to
synthesize and must be
 Carbon directly obtained from the
environment (i.e. vitamins,
 Nitrogen, Sulfur and amino acids, purines,
Phosphorus pyrimidines)

105. +
Terms used in microbial control
 Sterilization: destroying all forms of life
 Disinfection: destroying pathogens or unwanted organisms
 Disinfectant: antimicrobial agent used on inanimate objects
 Antiseptic: antimicrobial agent used on living tissue
 -cidal: kills (i.e. bactericidal = kills bacteria)
 Static: inhibits growth (i.e. bacteristatic = inhibits growth of
bacteria)

106. +
Actions of microbial control agents
 Alteration of membrane  Damage to proteins and
permeability nucleic acids
 Plasma membrane is located  Many bacterial proteins are
just inside the cell wall enzymes that are vital to all
cellular activities
 Membrane actively
 Destroying the shape of
regulates passage of proteins destroys the
nutrients into the cell and function of proteins
the elimination of wastes
 H-bonds and disulfide
from the cell bridges are critical to
 Damage to the membrane protein structure but can
causes cellular contents to be broken by heat and
leak into the surrounding chemicals
medium and interferes with  Heat, radiation, or chemicals
growth can destroy bacterial DNA
and RNA

107. +
Microbial Control
Physical Methods Chemical Agents
 Heat  Phenols
 Moist heat  Phenolics
 Dry heat  Bisphenols
 Filtration  Biguanides
 Cold  Halogens
 High Pressure  Alcohols
 Dessication  Heavy metals
 Osmotic Pressure  Surface-Active Agents
 Radiation  Chemical Food preservatives
 Aldehydes
 Gaseous Chemosterilizers
 Peroxygens

108. +
Objective 9
 Discuss methods of microbial control
 Physical: Heat, Filtration, Cold, High Pressure, Dessication,
Osmotic Pressure, Radiation
 Chemical: Phenols, Phenolics, Bisphenols, Biguanides, Halogens,
Alcohols, Heavy metals, Surface-Active Agents, Chemical Food
preservatives, Aldehydes, Gaseous Chemosterilizers, Peroxygens
 The above act either by altering the membrane permeability of
the microorganism or damaging proteins and nucleic acids of the
microorganism