1. Infection-viv
1. Define infection, host, infectivity, virulence, immunogenicity, toxigenicity,
symbiosis, mutualism, commensalism, and pathogenicity. (M294, M295)
• Infection-direct damage of cells, interference with cellular metabolism, and
rendering a cell dysfunctional because of the accumulation of pathogenic substances
and toxin production
• Host-by which a pathogen microorganism infects
• Infectivity-ability of the pathogen to invade and multiply in the host.
• Virulence-potency of a pathogen measured in terms of the number of
microorganisms of µg of toxin required to kill a host. (ie. Measles virus is of low
virulence; rabies virus is highly virulent)
• Immunogenicity-ability of pathogens to induce an immune response.
• Toxigenicity-a factor important in determining a pathogen’s degree of virulence,
that is, the ability to produce disease by production of a soluble toxin.
(ie.hemolysin, a product of streptococci, destroys erythrocytes).
• Symbiosis-benefits only the human, no harm to the organism.
• Mutualism-benefits both the human and organism.
• Commensalism-benefits only the organism, no harm to the human.
• Pathogenicity-benfits the organism, harms the human. (Opportunism is when
benign human organisms become pathogenic because of decreased human host
resistance).
2. List five innate host defense mechanisms that will impact the host’s ability to
prevent invasion by a pathogen. (M295)
• The first lines of defense against infectious microorganism are external barriers:
o 1) skin
o 2) mucous membranes
o 3) genitourinary tract
o 4) digestive tract
o 5) respiratory tract
3. Describe the concept of host-microorganism interaction by using the definition of
symbiosis, mutualism, commensalism, and pathogenicity to provide examples of
interactions. (M295)
• Symbiotic relationships occur when there is benefit to the human and no harm to
the organism, such as some gut bacteria, as they help digest food.
• Mutualistic relationships occur when there is benefit to both the human and the
organism, as in normal flora of the skin, gut, mouth.
Page 1 of 5

2. • Commensalistic relationships occur when the organism benefits, and there is no
harm to the human. (no examples in McCance).
• Pathogenicity arises in situations where the organism benefits, the human is
harmed, an example would be a tape worm living in the human gut.
Term To Host To Bact
Symbiotic Benefit no harm
Mutualistic Benefit Benefit
Commensalistic No Harm Benefit
Pathogenisity Harmed Benefit
4. Describe 6 microbial factors that improve the chance of a pathogen establishing
an infection in a host. (M296-299)
• Antigenic variation allows the pathogen to change appearance by altering antigens,
thus challenging the specificity of the immune system. This is accomplished by
mutation, recombination, and gene switching. Antigenic variation can occur during
the course of infection, and spread of infection through the environment.
1. Antigenic drift is the change that results from mutations (ie. Flu viruses)
2. Antigenic shifts are major changes in antigenicity that occur from
recombination of genomes (can result in pandemics).
3. Gene switching is used to avoid immune response. Involves pathogens
switching on and off surface proteins to allude immune system.
4. Microorganisms can produce thick capsules of carbohydrate or protein that are
antiphagocytic preventing opsonization & phagocytosis.
5. Exotoxin production - damage the plasma membrane of host cells or prevent
phagocytosis.
6. Endotoxins production - activate inflammatory response and produce fever.
5. Identify eight classes of infectious organisms, their individual site of reproduction,
and provide an example of an organism that fits within the class. (M295)
Class of pathogen Site of reproduction Example
Virus Intracellular Poliomyelitis
Chlamydia Intracellular Trachoma
Rickettsiae Intracellular Rocky Mountain Spotted Fever
Mycoplasma Extracellular Mycoplasm pneumonia
Page 2 of 5

3. Bacteria Skin, Staphylococcal wound infection
mucous membranes, Cholera
Intracellular, Streptococcal pneumonia
Extracellular Tuberculosis
Fungi Skin, Tinea pedis
mucous membranes, Candida
Intracellular, Sporotrichosis
Extracellular Histoplasmosis
Protozoa Mucosal Giardiasis
Extracellular Sleeping sickness
Helminths Intracellular Trichinosis
Extracellular Filariasis
6. Describe the process used by bacteria to establish an infection in a susceptible
host. Make sure to include a discussion of the role of endotoxins, exotoxins, and the
role of proteases that digest IgA.
Bacterial survival and growth depend on effectiveness of the body’s defense mechanisms
and on the bacterium’s ability to resist those defenses and obtain nutrients and multiply.
a) Bacteria must have Iron to multiply, and some express siderophores (iron receptors)
that acquire iron from iron binding proteins (i.e., lactoferrin, transferrin, and hemoglobin)
b) Some pathogens have ways of preventing destruction by the inflammatory and
immune systems. They produce thick capsules of carbohydrate or proteins that are
antiphagocytic, example is the thick polysaccharids covering of the pneumococcus and
waxy capsule surrounding tubercle baccilus.
c) Some pathogens have developed the ability to proliferate at rate that surpass the
development of a protective response.
d) Other bacteria survive and proliferate in the body by producing Exotoxins and
endotoxins that injure cells and tissue.
e) Exotoxins are proteins released during bacterial growth. Can damage cell membranes,
activate second messengers, and inhibit protein synthesis (available vaccines for this
are: tetanus)
f) Endotoxins: are libopolysacharids (LPS) -contain cell walls of gram-negative bacteria
and released during lysis (destruction)
7. Describe the process used by viruses in establishing an infection in a susceptible
host. Make sure to include a discussion of the cellular effects of viruses.
Page 3 of 5

4. Viruses are intracellular parasites that take over the genetic and metabolic machinery of
the host cells and use them for their own survival and replication. Viruses contain genetic
information in either DNA or RNA. Infection with viruses requires it to bind a specific
receptor on the plasma membrane of the host cell. Viral replication depend on absorption,
penetration, uncoating , replication , assembly and release of new viruses.
Once inside the host cell, virions have many harmful effects which includes the
following:
a) Inhibition of the host cell DNA, RNA, or protein synthesis
b) Disruption of lysosomal membranes, resulting in release of digestive lysosomal
enzymes that can kill the cell
c) Promotion of infected, adjacent host cells, thereby producing multinucleated giant
cell
d) Alteration of antigenic properties, or identity of the host cell, causing the host’s
immune system to attack the cell as if it were foreign
e) Transformation of host cells into cancerous cells
f) Promotion of secondary bacterial infection in tissues or organs damage by virusesu
8. Describe the process used by fungi in establishing an infection in a susceptible
host.
Fungi are large microorganisms with thick walls that grow as either single-celled yeast or
multicelled molds. Same fungi can exist in either form and are called Dimorphic. The cell wall of
the fungi is rigid and multilayered. The cell wall is composed of polysaccharides different
from peptidoglycans of the bacteria.
a) The lack of peptidoglycans allows fungi to resist the action of bacterial cell wall inhibitors such
as Penicillin and cephalosporin.
b) The fungi can produce infection by adopting the host environment. Fungi can colonize the skin
can digest keratin; other fungi can grow with wide temperature variations in low oxygen
environment.
c) Fungi has capacity to suppress the host immune defenses, lymphocytes and phagocytes are
important in controlling fungi, low white blood cell counts promotes fungal infection.
9. Describe both local and systemic clinical manifestations of infection and relate to
the process of inflammation.
Clinical manifestations of infectious disease vary, depending on the pathogen, the organ
affected and the severity. The effect of the infection may be acute or chronic, related to immune
responses, or consequence of bacterial toxins. Manifestation can arise directly from the infecting
microorganism or its products; however the majority of manifestation result from the host’s
inflammatory and immune responses.
Page 4 of 5

5. Infectious disease typically began with the nonspecific or general symptoms of fatigue, malaise,
weakness, and loss of concentration. General aching and loss of appetite are common
complications. However, the hallmark of most infectious disease is Fever.
Body temperature is regulated by nervous system feedback to the hypothalamus, which functions
as a central thermostat. A large number of agents ( pyrogens) can produce fever. In current
classification those pyrogens derived outside the host are termed Exogenous Pyrogens and those
produced by the host are termed Endogenous Pyrogens. There is little evidence that exogenous
pyrogens cause fever directly.
Available data favors an indirect effect of such pyrogens on the hypothalamus that is mediated by
endogenous pyrogens released by the cells of the host .
A number of hormones like mediators (cytokines) in cellular and immunologic adaptations have
been identified as endogenous pyrogens. They are Interleukins 1 and 6 ( IL 1 and 6 ),
Interferon (IFN) , tumor necrotizing factor ( TNF) and other cytokines.
The mechanism by which these cytokines raise the thermoregulatory set point seems to be
through stimulation of prostaglandin synthesis and turnover in both thermoregulatory
(brain) and nonthermoregulatory ( peripheral) Tissue.
10. If given a case study of a patient with an HEENT, Respiratory, or GU infection,
be able to identify the most common organisms that can cause disease.
There are a whole bunch of different organisms that cause dz. If you refer to table 9-4 on
page 295 in McCance, there is a list. I will list some common ones for each.
GU: e-coli
HEENT: herpes simplex, fungal, Chlamydial
Respiratory: Tuberculosis, Influenza, C. pneumoniae
Page 5 of 5