HTHSCI 2HH3 Lecture Notes - Lecture 2: Peristalsis, Botulism, Antigen
26 May 2018
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MICROBIOLOGY OF PATHOGENIC FACTORS
Interaction Within the Microbe
The Microbe
• Few are pathogenic
• Many benefit the host, or simply colonize the host without causing disease
• Human body: 10 trillion cells + 100 trillion bacterial cells
The Host: influence the relationship between microbe and host
Interactions Between Microbe and Host- Symbiosis
Commensalism
• One organism benefits from the relationship
• Saprophytic mycobacteria of the ear and external genitals (nutrients = benefit)
o Live on secretions and sloughed-off cells (host = no benefit or harm)
Mutualism
• Both organisms benefit from the relationship
• Escherichia Coli in the large intestine synthesize Vitamin K
o Vitamin K is absorbed into the blood stream and is used by the host (benefit)
• the large intestine of the host provides nutrients used by the bacteria, facilitating their survival
(benefit)
Parasitism
• One organism benefits from the relationship at the expense of the other
• Mutualism: both benefit
• Commensalism: one organism benefits, the other is neither harmed nor benefited
o Both are uniquely specified to that area of the body, when a new pathogen (that may be
harmful to us) is present, the flora must defend its nutrients by fighting off the bacteria
• Amensalism: one is harmed, the other is neither harmed nor benefited
• Parasitism: one benefits, the other is harmed
Interaction Between Microbe and Host- Normal Flora
Normal flora
• Resident microbiota permanently colonize the host, never change
• Transient microbiota temporarily colonize the host, new bacteria may become part our normal
flora while in a specific environment, only resident while the host is exposed to that bacteria
• Do not produce disease under normal conditions
• Distribution and composition determined by the following factors:
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1. Nutrients
• Secretory and excretory products of cells
• Bodily fluids
• Food in the gastrointestinal tract
2. Physical and Chemical Factors
• Temperature
• pH, O2, CO2, salt, sunlight
3. Mechanical Factors
• Chewing
• Flow of saliva and peristalsis of gastrointestinal tract
• Mucous and ciliary action of respiratory system
4. Other Host Factors
• Age- quality of flora decreases as we age
• Nutritional Status
• Disability- a person who is a wheelchair will have areas of the body that are more moist than
others, therefore some bacterial will accumulate in that environment
• Personal hygiene
• Lifestyle- lots of traveling may expose us to transient flora
• Geography
• Occupation
• Stress- can decrease immune status and our ability to fight bacterial infections
• Gravity- normal flora associated with the GI will slowly move upwards and migrate from the GI
in clients who are bed bound
Interactions Between Microbe and Host- Normal Flora
• Under normal conditions, normal flora colonizes the host without causing disease
Microbial Antagonism: normal flora actually benefits the host by preventing growth of pathogenic
microbes
Normal flora
• Competes with the pathogen for nutrients
• Produces substances harmful to the pathogen- bacteriocins
• Manipulates the host environment
o Increases or decreases pH
o Increases or decreases O2 levels
Microbial Antagonism
Escherichia coli -> bacteriocins
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Bacteriocins: proteins produced by bacteria that inhibit the growth of closely related species of bacteria
such as Salmonella and Shigella, proteins that make it difficult for other bacteria to survive ->
bacteriocins protect us from microorganisms -> we must be exposed to the organism in much greater
amounts in order to get sick
When the balance between the normal flora and a pathogenic microbe is altered (ie: microbial
antagonism fails), disease can result
Disruption of this balance may be induced by a number of factors, including:
• Age
• Antibiotic use
• Changes in hygiene
• Nutritional status
Clostridium difficile- C.diff
• causes a range of gastrointestinal symptoms, from mild diarrhea to severe, or even fatal colitis
• Presence of normal flora in the large intestine inhibits the growth of C. diff (bacteriocin)
• Antibiotic-mediated destruction of the GI normal flora creates an environment conducive to C.
diff growth, resulting in disease
• Do’t easily auie utiets eause ou gut’s floa outopetes .diff (bacterial antagonism)
for nutrients, c.diff becomes spores until conditions are favorable (opportunistic)
Opportunistic Infections
Oppotuisti ifetios ou he…
1. Microbes from the host normal flora move from their normal habitat, causing disease
Escherichia coli gains access to other body sites such as the urinary tract or wounds it causing urinary
tract infections
2. The host’s iue syste is eakeed/compromised
Pneumocystis jirovecii causes pneumonia in the immunocompromised patient, but has no effect on
healthy individuals
3. Changes occur in the composition of the host normal flora
Shift in the relative abundance of microbes (antibiotic therapy) creates opportunity for one species to
thrive and cause disease
Interaction Between Microbe and Host- Pathogenesis
Microbial mechanisms of pathogenesis
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Document Summary
The microbe: few are pathogenic, many benefit the host, or simply colonize the host without causing disease, human body: 10 trillion cells + 100 trillion bacterial cells. The host: influence the relationship between microbe and host. Commensalism: one organism benefits from the relationship, saprophytic mycobacteria of the ear and external genitals (nutrients = benefit, live on secretions and sloughed-off cells (host = no benefit or harm) Interactions between microbe and host- normal flora: under normal conditions, normal flora colonizes the host without causing disease. Microbial antagonism: normal flora actually benefits the host by preventing growth of pathogenic microbes. Normal flora: competes with the pathogen for nutrients, produces substances harmful to the pathogen- bacteriocins, manipulates the host environment. When the balance between the normal flora and a pathogenic microbe is altered (ie: microbial antagonism fails), disease can result. Disruption of this balance may be induced by a number of factors, including: age, antibiotic use, changes in hygiene, nutritional status.
