Microbiology- a clinical approach by Anthony Strelkauskas et
al. 2010
Chapter 1: What is Microbiology and Why does it matter?
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Think of your future professional goal.
Write down three reasons why you think it is
important to take this class and do well in this
class.
Keep this note. We will revisit it later on in the
quarter.
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“Infectious disease is one of the few genuine
adventures left in the world. The dragons are all dead
and the lance grows rusty in the chimney corner…About
the only sporting proposition that remains unimpaired
by the relentless domestication of a once free-living
human species is the war against those ferocious fellow
creatures, which lurk in dark corners and stalk us in the
bodies of rats, mice and all kinds of domestic animals;
which fly and crawl with insects, and waylay us in our
food and drink and even in our love.”
Hans Zinsser was an American bacteriologist known for
work on typhus and a poet.
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The following case studies illustrate how
microbiology is part of our everyday lives:
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Special Delivery
Ivan Goes to Chicago
Hamburger Havoc
The Hospital Can Be Dangerous
Did You Wash Your Hands
Mary, Mary, Quite Contrary
It’s For the Birds
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Microbiology has relevance to everyday life.
We are not sterile and we do not live in a
sterile environment; we interact with microbes
all the time.
Travel allows the movement of infectious
diseases around the world in a relatively short
period of time (less than 48h for respiratory
infectious diseases).
http://learn.genetics.utah.edu/archive/sars/images/world_spread
.gif
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Infectious diseases
Treatment of infectious diseases
Beneficial use of microbes
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Only a small fraction of all microbes cause
disease
◦ Many more microbes form part of our normal
microbiota (trillions...)
◦ Microbial agent that causes disease is called a pathogen
◦ Potential to cause disease is referred to as virulence
◦ Some microbes become pathogens only under certain
circumstances and are called opportunistic pathogens
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Infectious diseases have been around as long as
humans lived
Oil painting by Nicolas Poussin, 1630
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Advances in public health awareness and intervention
lessened the effects of infection
•Sanitation
•Antibiotics
•Vaccination
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However, infectious diseases still account for a large
percentage of health care
◦ Among top ten causes of death
 Lower respiratory tract infections, diarrhea, tuberculosis, HIV/AIDS
(http://www.who.int/mediacentre/factsheets/fs310/en/index.html)
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Healthcare professionals need to understand how pathogens
cause disease
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New threats
◦ Antibiotic resistance
◦ Emergence of new pathogens
 Swine flu
◦ Bioterrorism
A fundamental understanding of
microbiology has never been more
relevant.
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Most pathogens can be looked at from the
following 3 perspectives:
◦ Epidemiology
◦ Pathogenesis
◦ Host defense
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Epidemiology is the study of factors determining
the frequency and distribution of disease.
In epidemiology, pathogens are studied by how well
they meet the five requirements of infection:
◦ Entry (Get in)
◦ Establishment (Stay in)
◦ Defeat the host defense
◦ Damage the host
◦ Exit (Get out) and be transmissible
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In epidemiology, pathogens are classified by
the transmission mechanisms they use. Such as:
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Air
Food or water
Insect vectors
Person-to-person contact
Pathogens can also be classified according to
their geographic distribution
◦ Some are found worldwide, others are restricted to
certain geographic areas.
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Providing the best care for infected individuals
and protection of others involves a clear
understanding of the 5 requirements for
infection.
Knowing how an organism gains entry and how it
spreads are vital to care for infected
individuals
◦ It allows for the implementation of strategies to limit
spread.
◦ It also helps in understanding of the spread of
disease.
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Epidemics are caused by a variety of factors,
including the following:
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Poor socioeconomic conditions
Ignorance of how infections occur
Poor hygiene
Natural disasters
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Virulence factors are required for a pathogen
to do the following:
◦ Persist in the patient
◦ Cause disease
◦ Escape or defeat host defenses
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Pathogens employ a
variety of methods to
accomplish infection.
Bacterial pathogens can:
◦ Produce digestive enzymes
◦ Produce toxins
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Viral pathogens can kill
the host cells.
Sometimes, damage
associated with an
infection is due to over
active host defenses.
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Infection is a complex and competitive
struggle.
It can be characterized as pathogens versus
host defense.
The outcome of this struggle depends on the
success or failure of the host defense.
Failure of the host defense = infection!
Defense
Healthy
Defense
Healthy
Primary pathogen
Opportunistic pathogen
Infectious Disease
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Many pathogens have developed methods to
defeat host defenses.
◦ Some directly attack host defenses.
◦ Some change their looks (a form of camouflage).
◦ Some hide.
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Many potent and successful tools are available
to defeat infection. These include:
◦ Antimicrobics
◦ Disinfectants and antiseptics
◦ Vaccinations
Prevention
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Are toxic chemicals and therefore must act
selectively.
◦ They must kill the disease-causing microorganisms but
not harm the patient.
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Antibiotics (antibacterial)
Anti-viral drugs
Anti-fungal drugs
Anti-parasitic drugs
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Public health measures
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Disinfection of water supplies
Monitoring food supplies
Proper hygiene and sanitation
Proper waste removal and treatment
Insect and pest control
Immunizations
◦ Requires that we understand immune mechanisms and
that we design vaccines that will successfully
stimulate protection.
◦ An ability to ensure the safety of vaccines
◦ Public health control of the immunization of children
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Bioremediation and recycling
◦ Oil spill clean up
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Insect control
◦ Bacillus toxin and caterpillars
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Biotechnology
◦ Recombinant drugs like insulin
◦ Gene therapy with virus vectors
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Microbiology is very relevant to our everyday lives.
We are exposed to potentially dangerous pathogens
on a daily basis.
These pathogens possess virulence factors that allow
them to persist in the host, evade host defenses, and
cause disease.
Pathogens must accomplish five tasks to be
successful in causing disease. They must get in, stay
in, defeat the host defenses, damage the host, and
be transmissible.
Microbiology is not just about infection and disease.
In many cases, microbes can be very beneficial to
humans.
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Virulence can be defined as
A. Opportunistic infection
B. Adequate nutrition
C. Degree of pathogenicity
D. Limited rates of growth
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Epidemic outbreaks of disease are fostered by all
of the following except
A. Poor hygiene
B. Decreased birth rates
C. Poor nutrition
D. Poor socioeconomic conditions
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Treatment of disease relies on which of the
following?
A. Antiseptics
B. Disinfectants
C. Antibiotics
D. None of the above
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Which of the following uses of microbes is not
beneficial to man?
A. Insect control
B. Crop fertilization
C. Mineral decomposition
D. All of the above are useful