Final Exam Flashcards
Cell wall synthesis inhibitors
Glycopeptides/lipopeptides- includes
vancomycin, daptomycin and teichoplanin
b-lactam antibiotics-
The four main
types are penicillins, cephalosporins,
carbapenams, and monobactams.
can function as a
barrier to certain antibiotics.
outer membrane
Porins-
proteins in the OM of Gram-
negatives that allow diffusion of nutrients
and other molecules.
how does outer membrane become antibiotic resistant?
mutations in porin genes limit permeability of small molecules like antibiotics
can function as a barrier (relatively rarely) to antibiotics
cytoplasmic membrane
_______ are composed of
membrane proteins that use energy to
pump small molecules out of the
bacterial cytoplasm.
efflux pumps
Two types of efflux pumps:
antiporters and
ABC transporters.
What 3 general ways can bacteria be resistant to antibiotics?
- limiting the antibiotic’s access
- enzymatic inactivation of the antibiotic
- modification or protection of the antibiotic target
enyzmes that cleave the
b-lactam ring of b-lactam antibiotics
b-lactamases
chloramphenicol acetyltransferases will add _____ to chloramphenicol, preventing it from ______
acetyl groups
binding to the 23s rRNA in the 50s subunit
examples of enzymatic inactivation of antibiotics are B-lacamases, _________ and ________
Aminoglycoside-modifying enzymes, Chloramphenicol and streptogramin
acetyltransferases
modification of b-lactams target occurs by-
alteration of the transpeptidase or
one of the other penicillin-
binding proteins (PBPs) in the cell.
what gene in Staph aureus encodes a modified PBP2?
mecA
Resistance to glycopeptide
antibiotics involves alteration of-
the peptide portion of peptidoglycan.
Bacteria resistant to glycopeptide antibiotics can have 3 enzymes that work together to confer resistance. name them and tell how they cause resistance:
VanH catalyzes conversion of pyruvate to D-lactate
VanA or B leads to formation of D-Ala-D-lactate instead of D-Ala-D-Ala (vancomycin’s target)
VanX cleaves any D-Ala-D-Ala that might have formed
Resistance to tetracycline involves-
“ribosome protection” or alteration
of the ribosome
Resistance to macrolides,
streptogramins, and lincosamides involves-
RNA methylases add a methyl group(s)
to 23S rRNA (part of 50S subunit)
Resistance to quinolones, rifampin, and streptomycin (an aminoglycoside) involves-
alterations (through mutation) of the
particular target of the antibiotic
Resistance to trimethoprim and
sulfonamide involves-
alterations (through mutation) of the enzymes in the tetrahydrofolate biosynthesis pathway.
resistance genes are regulated by: (3)
repression, translational attenuation, activation
name the way in which each gene is regulated: tetB- erm- blaZ- ampC- vanH/A/X-
- repression
- translational attenuation
- repression
- activation
- activation
what does each of these genes encode: tetB- erm- blaZ- ampC- vanH/A/X-
- TetB efflux pump
- RNA methylase
- b-lactamase
- b-lactamase
- vancomycin resistance
the 3 general mechanisms for horizontal gene transfer:
transformation, transduction, conjugation
what region of the F plasmid encodes conjugation proteins?
tra region
what is the origin of transfer in the F plasmid?
oriT
name the 5 general characteristics of plasmids:
Extrachromosomal Replicate autonomously Most are circular Often contain resistance genes May be self-transmissible or mobilizable
the plasmid R100 transfers via conjugation among which species?
Escherichia, Klebsiella, Proteus, Salmonella, and Shigella species
the resistance plasmid R100 confers resistance to what?
mercury, sulfonamide, streptomycin, chloramphenicol, tetracycline
what two ways does multi-drug resistance arise in bacteria?
1) A single mechanism that confers
resistance to multiple antibiotics
(e.g., multi-drug efflux pump).
2) Acquisition of a plasmid or other
conjugative genetic element that
contains multiple resistance genes.
How does a plasmid acquire multiple
resistance genes?
transposons or integrons
transposons-
segments of
moveable DNA that can insert into a
chromosome or plasmid independent
of homologous recombination.
integrons-
typically transposons
but they also contain an integrase
gene and an attachment (att) site.
integrons can supply resistance genes with ____ and ____
a promoter and integrase gene
Conjugative transposon-
second type
of conjugative genetic element .
Generally have a broader host range
than most plasmids.
if an antibiotic is improperly prescribed, it can select for resistance in _______. when properly prescribed but improperly used, it can select for resistance in _______
- normal flora
- the pathogen population
Tn5 and Tn3 are both
transposons
Point mutations, gene deletions,
or duplications, and chromosomal
rearrangements (all slow processes) occur at frequencies ranging from:
10^-6 to 10^-9 per nucleotide per generation in bacteria
what are 3 ways pathogen evolution occurs (mechanisms of genetic change and diversification):
- random genetic mutation
- phase variation
- Antigenic variation
how would phase variation benefit bacterial evolution?
On-off control of some bacterial genes, such as those encoding surface proteins, that allow response to rapidly varying environmental conditions.
what kind of phase variation occurs in Salmonella species?
flagellin protein
what alternative types of flagellin protein can salmonella use?
H1 or H2
- Frequency of salmonella flagellar phase variation is ~
10-4 per cell per generation.
Which gene, upon inversion, can activate or inactivate H1 flagellin/H2 flagellin
Hin invertase
in one orientation, a promoter is available to transcribe ____ and ______, but if Hin invertase flips the Hin gene, the promoter is flipped to the other side and ________ are no longer transcribed, allowing _____ to freely be transcribed
- H2 flagellin and H1 flagellin repressor
- H2 flagellin and H1 flagellin repressor
- H1 flagellin
Phase variation inn Bordetella pertussis involves what two proteins?
BvgS and BvgA
The BvgS and BvgA proteins compose a:
two-component signal transduction system that controls expression of a number of virulence genes
Phase variation in pertussis is mediated by:
a reversible mutation in the bvgS gene.
the reversible mutation that causes phase variation in pertussis is:
The result of this mutation is:
- addition or deletion of a GC base pair in a sequence region containing a string of 6 GC base pairs.
- a switch between BvgS+ and BvgS-
adding a GC pair to the bvgS gene switches it from ____ to ____. Removing that GC pair then switches it back.
BvgS+ to BvgS-
Phase variation in Neisseria species involves ____ proteins
Opa
Opa proteins are located in ________ in N. meningitidis and N. gonorrhoeae. They mediate _______________.
- the outer membrane
- adherence and invasion during infection
Each Neisseria species has multiple opa genes, any of which may be ____________
on or off at different stages during infection
opa genes contain _________ that cause_____________
- 5’ tandem repeats of (CTCTT)n
- high frequency slipped strand misrepair and thus frameshifts in the gene
Some bacteria have mechanisms that allow alternative forms of genes to be expressed in what is known as:
These variable forms of a gene are achieved through:
- antigenic variation
- gene shuffling
Gene shuffling mechanisms that allow alternative forms of some genes, such as those encoding surface proteins, to be expressed
antigenic variation
The result of antigenic variation is that:
a range of antigenically distinct forms of a protein can be produced, which helps the bacterium avoid the host immune system.
T4SS are divided into what 3 functional groups?
conjugative, DNA uptake/release (transformation), and effector translocation