L4 Antimicrobial Flashcards
bacterias ribosomes _____ compared to human ribosomes that are ______
(30S + 50S) = 70S; 80S
classes of protein synthesis inhibitors that affect the 30S
- aminoglycosides 2. tetracyclines
classes of protein synthesis inhibitors that affect the 50S
- chloramphenicol 2. macrolides 3. lincosamides 4. streptogramins 5. oxazolidinones
aminoglycosides are generally bactericidal/bacteriostatic/both
bactericidal
aminoglycosides are generally used againist gram + /gram -
mainly used against gram -
subclasses of aminoglycosides
subclasses: 1. streptomycin 2. gentamicin
anaerobes/aerobes are resistant to aminoglycoside
anaerobes are intrinsically resistant
resistance to aminoglycosides
- alter drug target- methylation of rRNA, mutation of ribosomal protein 2. alter drug exposure- increased efflux, decreased uptake 3. enzymatically inactivate drug- modifications by phosphorylation, methylation adenylation
enzymes are usually encoded on mobile/stationary genetic elements
mobile
combinational therapy
- prevent the emergence of resistance - treatment of emergency cases when etiology is still unknown - take advantage of combinational synergy
B lactam and aminoglycoside combinational therapy
can be sueful becuase aminoglycoside is large and B lactam can puncture cell wall so large aminoglycoside can enter to target 30S
tetracyclines bind to 30S/50S
30S
mycoplasma
do not have anything outside of cell membrane, do not have peptidoglycan
B lactams would not be affective againist mycoplasm becuase
they do not have petidoglycan cell wall
tetracyclines are generally bactericidal/bacteriostatic/both
bacteriostatic
Subclasses of tetracyclines
tetracycline and doxycycline
Tetracyclines attack
G+, G-, mycoplasma, and intracellular bacteria
Which antibiotic would you use to kill intracellular bacteria?
Tetracyclines
tetracycylin is selective for bacteria vs. host cells due to greater uptake in
bacteria
_______ and _______ inhibit the absorptions of tetracyclines
divalent cations (Ca2+ and Mg2+) so avoid anti-acids and milk
contraindications of tetracycline
pregnancy and young children due to inhibition of bone growth and discoloration in teeth
T/F Bacteriostatic and bactericidal agents are not usually combined.
true
resistance to tetracyclines
- alter drug exposure- efflux pumps 2. alter drug target- ribosome protection proteins (prevent drug from binding to the ribosome)
chloramphenicols are generally bactericidal/bacteriostatic/both
bacteriostatic but cidial against encapsulated organisms
chloramphenicol bind to 30S/50S
50 S
resistance to chloramphenicol
enzymatically inactivate drug (modified by acetyl transferases)
macrolides are generally bactericidal/bacteriostatic/both
bacteriostatic
macrolides bind to 30S/50S
50S
macrolides subclasses
erythromycin and azithromycin
macrolides usually work against Gram+ / Gram - with the exception of
gram + ; chlamydia
lincosamides bind to 30S/50S
50S
lincosamides are generally bactericidal/bacteriostatic/both
bacteriostatic
subclass of lincosamide
clindamycin
lincosamide is highly associated with
C difficile
streptogramins A and B lincosamides are generally bactericidal/bacteriostatic/both
individually bacteriostatic together bactericidal synergetic
macrolides, lincosamides and streptogramins B
cross-resistance due to similar mechanisms of action
constitutive
present all the time
erm
the gene that is targeted for alter drug target for resistance against MLSb
inducible
there but not expressed until needed
constitutive is high/low fitness cost compared to inducible
high
D-test
shows inducible
Constitutively resistant to macrolide (ERY) and lincosamide (CL)
Constitutively resistant to ERY, sensitive to CL
Constitutively resistant to ERY, inducibly resistant to CL
You streak bacteria from inside the red zone to a new plate and place a fresh CL disk without an ERY disk nearby. What do you expect to see after incubation for 24h?
A.A symetrical, circular zone
B.No zone
C.A D-shaped zone
A.No zone
oxazolidinones bind to the 30S/50S
50S
oxazolidinones are bacteriostatic/bactericidal
bacteriostatix
oxazolidinones work against
gram +
subclass of oxazolidinones
linezolid
resistance to oxazolidinones
alter drug target mutations in rRNA
isoniazid
targets mycolic acid synthesis
ethambutol
thought to inhibit arabinotransferases
lipopeptides
disrupt the cell membrane of G+ bacteria
lipopetide example
daptomycin
folate syntheiss inhibitors
trimethoprim
sulfonamides
RNA synthesis inhibitors
rifamycin
DNA synthesis inhibitors
fluoroduinolones
agents thatr damage DNA
nitroimidazoles
Which of the following is NOT traditionally used as a b-lactam antibiotic?
A.Cephalosporin
B.Monobactam
C.Penicillim
D.Clavulanic acid
D.Clavulanic acid
Which of the following targets the bacterial tetrahydrofolate synthesis pathway?
A.Fluoroquinolone
B.Trimethoprim
C.Rifamycin
D.Macrolide
B.Trimethoprim
Mutations in bacterial topoisomerases confer resistance to which of the following?
A.Ceftriaxone
B.Ciprofloxacin
C.Chloramphenicol
D.Clindamycin
B.Ciprofloxacin
Which class of bacteria is most susceptible to b-lactam antibiotics?
A.Gram-negative
B.Gram-positive
C.Mycobacteria
D.Mycoplasma
B.Gram-positive
b-lactams bind tightly to M. tuberculosis PBPs
Yet, Mtb is resistant to b-lactams – HOW?
Mycobacterium tuberculosis produces several b-lactamases
For which of the following S. aureus infections would you NOT prescribe daptomycin (a lipo-peptide antibiotic)?
A.Osteomyelitis (bone infection)
B.Pneumonia (lower respiratory tract infection)
C.Endocarditis (heart valve infection)
D.Bacteremia (blood stream infection)
B.Pneumonia (lower respiratory tract infection)
T/F Antibiotic resistance often exacts a
fitness cost
True
VanA locus*
constitutive resistance
VanB locus*
inducible resistance
