©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
MICB 2121- Midterm 2 Exam Study Guide
Solutions
Microbiota - ANSWER✔✔Surface tissues like skin and mucous membranes are in contact with
microorganisms all the time
Microbiota: colonies of bacterial species in the same anatomical sites in all people
Some organisms have permanent residence within the host, while others are more transient and present
for limited periods of time, from days to weeks to months
Bacteria are the most numerous and obvious microbial components of microbiota, but some eukaryotic
fungi and methanogenic Archaea colonize lower intestinal tract
Some organisms can only be found in association with a host whereas others can also be found in
environment
Host and Microbiota Interactions - ANSWER✔✔Association between host and microbiota is dynamic,
and a relationship that benefits both host and bacteria
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, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
1. The bacteria benefit- host environment is a continuous source of nutrients and a stable environment,
as well as a mode of transportation, protection benefit: host is a place for bacteria to colonize
2. The host benefits- Minimizing hosts susceptibility to pathogens, through microbial antagonism. When
colonization of native microbiota inhibits colonization by pathogens, this is done by many mechanisms
(i.e. occupying adherence sites, utilizing nutrients, chemical inhibition, and modulating pH and oxygen
availability)
a. Nutritional synergism- in the gastrointestinal tract, bacteria synthesize and excrete vitamins such as
vitamin K and b12. These can be absorbed by host cells. Bacteria can convert bile acids to steroids that
can be used by the host.
- Immune stimulation: microbiota can stimulate immune system through induction of antibody response.
Low levels of antibodies can cross react with pathogens and prevent infection or invasion.
The microorganisms of the microbiota are adapted to their host:
We live synergistically with our microbes
Bacteria of microbiota have adapted to survive specifically within their host. Physical association
between the microbiota and host involves biochemical interactions between bacterial surface
components (ligands or adhesins) and host cell molecular receptors. E.g. microbiota resist innate
Page 2/33
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
immune defences and do not elicit strong adaptive immune responses that would lead to their
elimination.
Harmful aspects of the host-microbiota relationship include:
Not all host-microbiota interactions are beneficial. Translocation of bacteria from one niche to another
can be harmful. (e.g E. coli in urinary tract)
Other products of host-microbiota relationship can impact systems outs
Opportunistic pathogens: - ANSWER✔✔take advantage of reduced health or lowered immunology,
considered commensal if you are healthy
Microbiota obtained immediately from environment: - ANSWER✔✔Passage through birth canal
Exposure to other humans (pets)
Ingestion of food and fluids
Inhalation of air borne microogranisms
Variety of bacterial species enter the infant but only those capable of colonizing a particular
microenvironment will remain. Once stable microbiota is established, composition of microbiota remains
Page 3/33
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
relatively constant, although changes can be induced (diet changes). Bacterial colonizers are acquired
quickly.
Factors that affect the composition of the microbiota - ANSWER✔✔Diet (milk produces lactic acid
bacteria in microbiota)
Infection (increase in pathogen numbers)
antibiotic treatment (decrease overall microbiota), in GI tract, this leaves the host susceptible to
colonization by opportunistic bacteria
After antibiotic therapy is completed, the microbiota will re-establish itself.
Location of the microbiota - ANSWER✔✔Three reasons why microbiota are located at a particular
anatomical site:
Certain species of bacteria only are located in one locale; exhibit a tissue preference for colonization.
Host provides essential growth factor needed by the bacterium. Some locations of host are inherently
inhospitable for colonization of bacteria
At colonization sites, bacteria attach to host receptors using specific bacterial ligands (capsules, cell wall,
fimbriae). These host receptors that interact with the bacterial ligands are expressed only at certain
locations in the host's body.
Page 4/33
FIRST PUBLISH OCTOBER 2024
MICB 2121- Midterm 2 Exam Study Guide
Solutions
Microbiota - ANSWER✔✔Surface tissues like skin and mucous membranes are in contact with
microorganisms all the time
Microbiota: colonies of bacterial species in the same anatomical sites in all people
Some organisms have permanent residence within the host, while others are more transient and present
for limited periods of time, from days to weeks to months
Bacteria are the most numerous and obvious microbial components of microbiota, but some eukaryotic
fungi and methanogenic Archaea colonize lower intestinal tract
Some organisms can only be found in association with a host whereas others can also be found in
environment
Host and Microbiota Interactions - ANSWER✔✔Association between host and microbiota is dynamic,
and a relationship that benefits both host and bacteria
Page 1/33
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
1. The bacteria benefit- host environment is a continuous source of nutrients and a stable environment,
as well as a mode of transportation, protection benefit: host is a place for bacteria to colonize
2. The host benefits- Minimizing hosts susceptibility to pathogens, through microbial antagonism. When
colonization of native microbiota inhibits colonization by pathogens, this is done by many mechanisms
(i.e. occupying adherence sites, utilizing nutrients, chemical inhibition, and modulating pH and oxygen
availability)
a. Nutritional synergism- in the gastrointestinal tract, bacteria synthesize and excrete vitamins such as
vitamin K and b12. These can be absorbed by host cells. Bacteria can convert bile acids to steroids that
can be used by the host.
- Immune stimulation: microbiota can stimulate immune system through induction of antibody response.
Low levels of antibodies can cross react with pathogens and prevent infection or invasion.
The microorganisms of the microbiota are adapted to their host:
We live synergistically with our microbes
Bacteria of microbiota have adapted to survive specifically within their host. Physical association
between the microbiota and host involves biochemical interactions between bacterial surface
components (ligands or adhesins) and host cell molecular receptors. E.g. microbiota resist innate
Page 2/33
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
immune defences and do not elicit strong adaptive immune responses that would lead to their
elimination.
Harmful aspects of the host-microbiota relationship include:
Not all host-microbiota interactions are beneficial. Translocation of bacteria from one niche to another
can be harmful. (e.g E. coli in urinary tract)
Other products of host-microbiota relationship can impact systems outs
Opportunistic pathogens: - ANSWER✔✔take advantage of reduced health or lowered immunology,
considered commensal if you are healthy
Microbiota obtained immediately from environment: - ANSWER✔✔Passage through birth canal
Exposure to other humans (pets)
Ingestion of food and fluids
Inhalation of air borne microogranisms
Variety of bacterial species enter the infant but only those capable of colonizing a particular
microenvironment will remain. Once stable microbiota is established, composition of microbiota remains
Page 3/33
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
relatively constant, although changes can be induced (diet changes). Bacterial colonizers are acquired
quickly.
Factors that affect the composition of the microbiota - ANSWER✔✔Diet (milk produces lactic acid
bacteria in microbiota)
Infection (increase in pathogen numbers)
antibiotic treatment (decrease overall microbiota), in GI tract, this leaves the host susceptible to
colonization by opportunistic bacteria
After antibiotic therapy is completed, the microbiota will re-establish itself.
Location of the microbiota - ANSWER✔✔Three reasons why microbiota are located at a particular
anatomical site:
Certain species of bacteria only are located in one locale; exhibit a tissue preference for colonization.
Host provides essential growth factor needed by the bacterium. Some locations of host are inherently
inhospitable for colonization of bacteria
At colonization sites, bacteria attach to host receptors using specific bacterial ligands (capsules, cell wall,
fimbriae). These host receptors that interact with the bacterial ligands are expressed only at certain
locations in the host's body.
Page 4/33
