Antibiotics Flashcards
Abx Bactericidal
kills susceptible bacteria without host defenses
if immumocompromised you want these
the vast majority of ABx
use these if not too severe ONLY
ABX Bacteriostatic
inhibit bacterial growth
destruction of organism dependent on host defenses (still rely on host defenses)
inhibiting their role
abx work best on
actively dividing and growing bacteria.
BETA lactam abx mechanism
binds to transpeptidase enz complexand block the crosslinking of peptidoglycan.
beta lactam acts on what
and 2 of them
act on cell wall
pennicilin S
cephalosporins
vancomycin acts on
cell wall
vancomycin mechanism
stops the extension of peptidoglycan chain (NAM and NAG
vancomycin affects Gram __ bacteria only
+
vancomycin is a
glycopeptide
vancomycin administered via
IV
for more serious G+ infections.
inhibitors of protein synthesis
bind to either 30S or 50S subunit of ribosome inhibit: activation chain initiation chain elongation chain termination
nucleic acid inhibitors
prevent supercoiling of DNA (DNA Gyrase)
excellent drugs with broad spectrum
metabolic inhibitors
combo of trimethoprim/sulfonamides => bactrim
strong drug for UTI
sulfonamides
structural analog of PABA and competitively inhibits synthesis of dihydrofolic acid (precursor of tetrahydrofolic acid)
trimethoprim
Structural analog of dihydrofolic acid and competitive inhibitor of dihydrofolate reductase (final enz in pathway to tetrahydrofolic acid)
Spread of resistance (3)
- plasmid
- conjugation
- transformation
plasmid
circular dsDNA that can exist and replicate independent of chromosome
may integrate with host chromosome
conjugation
gene transfer and recombination in bacteria that requires direct cell-cell contact
Sex bridge - DNA can spread
Transformation
naked DNA taken up by a bacterial cell and incorporated into the recipient genome
must be a competent cell to take tup the DNA
usually in the gut - lots of bacteria
Maintaining resistance
Selective pressure
selective pressure
ensures the resistance gene is maintained
keep giving abx - keep having to continue producing PBP that is different and resistive
selective pressure occurs from
common abx usage - ex kids ear infections
not completely finshing a prescription
using a leftover prescription
abx in animal feed
Mechanisms of resistance
enzymes that inactivate the drug
target site alteration
ribosome alteration
efflux pumps
enzymes that inactivate the drug
beta lactamase
aminoglycoside
ESBL - only been around for 3-5 Years
beta lactamase
plasmid spread (rapid emergence)
danger organism with ESBL
E. Coli
resistant to all beta lactam abx.
target site alteration
pennicilin binding proteins
beta lactam abx can no longer bind
2 examples with altered PBPs
MRSA
S. pneumoniae.
gram negative cell extra aces
PBP changed
porin proteins
enzymes
once inside cell may not be able to bind.
Metabolism mechanism of resistance
organism alters the metabolic pathway and overcomes the blocked pathway.
Evolution of S. Aureus resistance
S. Aureus
- pennicilin resistent aureus (1950)
- methicilin (1980)
- MRSA
- Vancomycin (1997)
- VRE (1990s)
- VRSA (2002)
MRSA
20% of Staph infections in canada
MRSA tx
vancomycin
vancomycin
hospital IV use
expensive
Community acquired MRSA
found in common animals - not infected
but giving it back to humans once healed.
control of CA MRSA
detergent
hot dryer
Hospital screening programs MRSA
Nasal swab +/- perineum - 24 hours
Isolation room, contact precautions
enterococci
relatively harmless bacteria found in the bowel (normal flora), skin, vagina, environment
occasionally causes infection.
history of VRE
avoparcin (similar abx) used in animal feed - colonized animals - colonized humans
exponential growth in VRE colonization incidence (but not infection incidence)
Screening for VRE
rectal swab
do not do it routinely anymore because so common
VRE patients - we do this
contact precautions
CDAD
clostridium difficile associated diarrhea
background of c diff
abx associated diarrhea (AAD)
recognized as a pathogen in 70s
epidemiology of c diff - how does it survive
spores - last months despite drying and disinfectants.
Clinical disease options
asymptomatic
moderate diarrhea
lifethreatening colitis
Life threatening c diff (2)
pseudomembranous colitis
toxic megacolon - emergency needs surgery
can lead to death ( 30% ).
treatment of c diff
abx:
metronidazole
vancomycin - adds to selective P
Fecal bacteriotherapy
stool sample liquified, filtered and given to patient - reestablishing normal gut flora to repopulate
fecal bacteriotherapy route options
- enema
- gastric tube
- Colonoscope - most effective
Fecal bacteriotherapy success
94% cure rate
normal bowel restoration in 24 hours.
