Lecture 9.2: Microbial Adaptations Flashcards
What are Microbial Adaptations?
The ability of microbes to endure the selective pressures of their environment
What is Intrinsic Resistance?
The organism possesses properties that make it naturally resistant to certain
insults
E.g. the more complex outer layer of gram negative bacteria makes it much more difficult for certain antimicrobials to penetrate
What is Acquired Resistance?
Naturally susceptible microorganism acquires ways of not being affected by
the drug
E.g. Mutation, Added Genes…etc
How does gene transfer occur in microorganisms?
Acquisition of foreign DNA coding for resistance determinants through horizontal gene transfer (HGT)
What effect does ‘Antibiotic Pressure’ have on bacteria?
Antibiotic pressure selects for bacteria that have a heightened mutation rate
What is an increased mutation rate is typically associated with?
Typically conferred by alterations in the genes that constitute the mismatch repair (MMR) system:
• mutS
• mutL
• mutH
• mutT
• mutY
• mutM
• uvrD
What are the 3 different types of horizontal transmission for the transfer
of genetic information?
• Conjugation (bacteria-to-bacteria transfer)
• Transduction (viral-mediated transfer)
• Transformation (free DNA transfer)
Mechanism of Conjunction
• The process requires cell-to-cell contact
• The donor cell (F+) has a conjugative
plasmid, an extrachromosomal piece of
dsDNA that codes for the protein
necessary to make a pilus
• The pilus is used to bind to the recipient
(F-) cell bringing it in close proximity to
the donor cell
• A channel is then opened between the two
cells, allowing for a ssDNA copy of the
plasmid to enter the recipient cells
• Both cells then make the complementary
copy to the ssDNA, resulting in two F+ cells
capable of conjugation
Mechanism of Transduction
• Bacteriophage, act as a conduit for
shuttling bacteria genes from one cell to
another, thus negating the necessity for
cell-to-cell contact
• A bacterial host cell is infected with a
bacteriophage engaging in the lytic cycle
of replication
Mechanism of Transformation
• The recipient cell is one that is capable of
taking up the DNA from the environment
and incorporating it into its own genome
• The cell is described as being competent
• Random pieces of DNA bind to receptors
on the outside of the cell and are then
transported into the cell by the DNA
translocase, through the transmembrane
channel, a large structure often involving
numerous different proteins.
• Once inside the cell, the DNA must be
incorporated into the bacterial
chromosome by RecA, for the genes to be
expressed
What is a Transposon?
A class of genetic elements that can “jump” to different locations within a genome
What is Conservative Transposition?
When a transposon can be removed from one location and relocated to another
What is Replicative Transposition?
When a transposon can be copied, with the copy being inserted at a second site
What are the 4 Main Categories of Antimicrobial Resistance Mechanisms?
1) Limiting uptake of a drug
2) Modifying a drug target
3) Inactivating a drug
4) Active drug efflu
Multiple Drug Resistance (MDR)
MDR is that the ability of microbes to show resistance against three or more categories of antibiotics inhibition concentration
