Provides an overview of the structures and functions of the external structure, cell envelope, and organelles of prokaryotic cells and their clinical relevance.
External characteristics of bacteria
Name as many of the structures bacteria can have on the outside of their cell as you can,
and discuss each structure’s function. Of these, which can make a bacterial species more
virulent (able to cause serious disease)?
- Flagella: make bacteria motile and allow them to wrap around things —> virulent
- Pili: sticky external structure in gram negative bacteria —> virulent
- Fimbriae: structure that form hair like bristles sticking out from the cell and act as a velcro —>
virulent
- Glycocalyx: slime layer / capsule structure encasing the bacteria make it sticky, help it survive,
and cover up molecules the immune system recognizes —> virulent
Describe the structures that allow motility in bacteria, and how they are arranged on the
surface of the bacterium.
- Flagella allow motility and have different arrangements:
Monotrichous = single flagella
Peritrichous = flagella all over cell —> bunch all flagella up at one end to move and let
all flagella out to “tumble”
Amphitrichous = flagella only at ends of cell (polar arrangement)
Lophotrichous = have a bunch of flagella in a polar arrangement
Compare and contrast the way bacterial cells of different shapes move around.
- Cocci: sphere shaped
do not have flagella —> cannot move around
- Bacilli: rod shaped
range of flagellar arrangement (some may not have any)
, - Spirilla: corkscrews
polar flagella
Spirochetes - flagella wrapped around the cell —> moves in a twisting motion like a
corkscrew through the environment
Describe the movements associated with a bacteria responding to “good” chemicals, and
“bad” chemicals.
- “Good” chemicals like nutrients or other bacteria
Positive chemotaxis = bacteria runs towards desired source, tumbles to make sure it’s on
the right scent, and repeats this pattern up the concentration gradient
- “Bad” chemicals like poisons or antibiotics
Negative chemotaxis = bacteria runs away from negative source, tumbles to make sure
it’s moving away from the scent, and repeats this pattern down the concentration gradient
Name the external structures of bacteria that make them “sticky”. Why is this important
clinically?
- Fimbriae: structure that form hair like bristles sticking out from the cell and act as a velcro
- Pili: sticky external structure in gram negative bacteria
- Pili are important to bacterial evolution
What is conjugation, and what structures do Gram negative cells need to have to undertake
it? Can Gram positive cells undertake this process, and if so, what structures do they
need? Why is any of this stuff this important to us?
- Conjugation = the exchange of genetic material between members of the same or closely
related species —> good way to pass on virulence factors
- Gram negative cells needs Pili to undertake it
- Gram positive cells do not have Pili but conjugation can occur through a structure called a
conjugation bridge
- DNA can be passed between cells, and sometimes the plasmid (circular DNA piece) can carry
an antibiotic resistance trait
Antibiotic resistance is one of the biggest problems in clinics
What is a biofilm, of what is it made and how is it made? On what kinds of clinical
instruments could biofilm be formed? Why is it so important to keep microbial biofilm
from forming in the clinical environment?
- Biofilm = ecosystems of bacteria
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