Antibacterial Pharmacology Flashcards
Discovery of abx
Alexander Fleming 1928 Penicillium mold on Petri dish Later used as a “cure all” drug, resulting in resistance
Cycle of ID
susceptible host -> causative agent -> reservoir -> Portal of Exit blood -> Mode of transmission -> portal of entry blood
Properties of bacteria
- Prokaryotic cells - no membrane enclosed organelles - single cellular - reproduce through binary fission - plasmids and nucleoid DNA are easy to transport and communicate because they are free -> cause for resistance
Gram Positive Bacteria
- thick peptidoglycan - relatively featureless - no outer membrane - susceptible to cell wall disruption
Gram Negative Bacteria
- cytoplasmic and outer membranes - thin peptidoglycan - lots of lipids because of outer membrane - resistant to cell wall disruption
Cell wall structure
Peptidoglycan Layer: rigid glycerin cross-linked by flexible peptide bridges Periplasmic spaces: Very small on gram (+), multiple on gram (-): generate B-lactamases which inhibit abx Wall tetracholic acid: accessory protein on g(+) Lipoprotein, Porin protein, LPS: on gram (-) Lipoprotein: protection layer Porin: if needed bacteria can down regulate LPS: for inflammatory response
PBP
- Important for MoA for abx - enzymes that catalyze: transglycosylation, transpeptidation, carboxypeptidation, endopetidation - for: cell wall synthesis (peptidoglycan), cell wall remodeling, cell division, cell shape
Bactericidal
direct action of bacteria - kill/lysis biochemical pathways in wall assembly compromised cell wall progressively weaker cells - daughter cells don’t have what is needed to keep cell wall up. eventually integrity of cell wall fails
Bacteriostatic
does not directly kill may be reversible - or relapse target nucleic acid synthesis and protein synthesis slow bacteria growth allows immune system to act and destroy the cells
Broad spectrum
Treat many kinds of infections - wide range of bacteria - targets common structures so can also go against commensal bacteria -> LEADS TO SUPERINFECTION - Once the agent is identified it should be discontinued
Superinfection
Bacteria that aren’t supposed to grow well in a particular area but do because the niche (normally keeps it away) is dead.
Narrow spectrum
Against a single or few bacteria (specific) - when agent is known - reduces chance of superinfection and abx resistance
Classification of bacteria
With 16s ribosome which share amplified DNA from a single cell. Polymer chain reaction is used to compare (DNA template to RNA to ribosomal subunits)
Where do abx come from?
Soil (but hard to isolate) Bottom feeders like roaches, catfish, alligators, bacteriophages (viruses that infect bacteria), cannabinoids. They are exposed to more bacteria than anyone else so they evolved to develop mechanisms to protect themselves.
MoA of abx
- inhibition of bacterial cell wall synthesis - direct action on cell membrane - inhibition of protein synthesis - modification of protein synthesis (change how it works) - inhibition of nucleic acid synthesis - inhibition of biosynthetic pathways
Inhibition of Cell wall synthesis
Attack cell wall synthesis - Beta Lactams (PBP in periplasmic space)
Penicillins, cephalosporins - inhibit transpeptidase from creating long chains of glycopeptide polymer chains (D-ala addition) carbapenems, monobactams
Inhibit pathways of peptidoglycan and sugars: Vancomycin (periplasmic space) & Bacitracin (cytoplasm)
Attack cell membrane Polymyxins
3 places to attack
- cell wall synthesis
- Protein synthesis
- Nucleic acid synthesis
Nucleic acid synthesis
Attack DNA and/or biosynthetic pathways
Folate synthesis Sulfonmides, Trimethoprim
DNA Gyrase/ topoisomerase (mRNA translation- unwinding and unkinking DNA) Quinolones
RNA polymerase (reads sequencing) Rifampin
Protein synthesis
Intracellular - interfere with translation Together 50s and 30s make 70s subunit. 50s subunit: Macrolides, clindamycin, linezolid, chloramphenicol, streptogramins 30s subunit: Tetracyclines, aminoglycosides
Detergents
Cell wall is degraded because it suck out lipids.
Daptomycin
Inhibits cell wall by squishing lipid tail into cell wall lipids -> forms complexes -> forms into channels (from the subunits coming together) -> disrupts the normal order of cell/ influx and eflux of materials
Penicillins and other B-lactam MoA
5 AA peptide ends in D-ala D-ala. The PBP removes the end alanine to form a cross-link with a nearby peptide (gives cell wall rigidity). B-lactam abx are analogues of D-ala D-ala which covalently bonds to PBP - inhibiting transpeptidation reaction and stops peptidoglycan synthesis - cell dies.
Half life of penicillins & clinical
penicillins = 30 mins / 10 hours for renal failure. 1-2 hours before or after meals. without regard with amoxicillin amplicillins = 1 hour these are cleared with kidney so adjust when needed nafcillin - biliary excretion oxacilin, dicloxacillin - biliary and kidney -> no dose adjustment
Tetracyclines MoA
Binds to 30s active site. can’t make proteins to let the chain grow
Macrolides MoA
binds to 50s - interferes with peptide conjugation
Aminoglycoside MoA
blocks initiation complex of 50s binding to 30s -> causes miscoding of proteins which won’t fold and bind to active site -> can’t move out of ribosome (translocation step)
Folate synthesis Inhibition
PABA->Dihydrofolic acid->tetrahydrofolic acid ->purines ->DNA Sulfonamides competes with PABA at dihydropteroate synthase Trimethoprim inhibits dihydrofolate reductase
Bacterial Resistance
- lots of bacteria - few are resistant
- use of abx - kills bad bacteria and good bacteria
- still some resistant that are left and grow (no good bacteria to protect)
- sharing of information to other bacteria -> more reisistance
Topoisomerase 4
Divides/ seperates part of DNA so daughter cells can get equal amounts
Used in inhibition of nucleic acid synthesis
think DNA gyrase - unwinding DNA inhibited by fluroquinolones
Origin of drug resistance
- bacteria in inactive site (non dividing)
- Genetics (horizontal gene transfer - ex) PBP dont bind to B-lactams on MRSA)
- Spontaneious mutation: misreading, mutation
- plasmid-encoded resistant gene products
- cross resistance of one type: same MoA
drug doesnt reach the target
drug activity is decreased/ destroyed
drug target is altered
How do bacteria exchange genetic information?
Transduction - bacterial virus - transfer its genes into bacteria ->resistance from virus
Transformation - naked DNA transfer
Ex) shock E. Coli then transfer DNA -> gets sucked up by another
Conjugation - transfer by direct cell-cell contact - through pilli of fusion of membrane
Transposition - transposon medicated exchange
: small segments jump out of DNA and go elsewhere to disrupt chromosomes
Production of enzymes that destroy or inactivate the drug
B-lactamases inactivate B-lactam Abx
B-lactamases are normally in bacteria and activate Antibodies -> too much B-lactamases = resistance
Aminoglycosides altered by acetylation, phosphorylation. or adenylation
just enough change to not work with antibodies
Ex) kinases (protein that phosphorylates) can mutate so that it disrupts normal order
Chloramphenicol acetyltransferases in inactive chloramphenicol
Decrease entry or increased efflus
Decreased active transport across membrane in anaerobic conditions - effect on channels -> can’t get in, can’t get out
Down regulation of porin expression -> throws everything out of the cell
Mutation in efflux transporter
Altered structural target for the drug
Altered:
binding sites on ribosonal subunits (decreased affinity for macrolides - protein syn inhibitors)
binding proteins (B-lactams no longer able to bind to PBP)
mutation in DNA genes (decreased affinity for abx-fluroquinolones)
Alterante metabolic pathway
Resistant strains produce D-ala D-lactate instead of D-ala D-ala (affinity for Vancomycin reduced)
Resistant strains overproduce PABA which antagonizes sulfonamide abx.
MIC
- Minimum inhibitory concentration
- lowest concentration of abx required to inhibit bacterial growth
- defines susceptibility of drug
- DOES NOT indicate bactericidal activity
MBC
- Minimum Bacerial Concentration
- concentration of abx required to inhibit bacterial growth by 99.9%
- more quantitative than MIC
PAE
- Post abx effect
- period of bacterial growth supression after brief exposure to drug
- abx with PAE requires LESS frequent administration
[abx] < MIC
time afterward is still slowing growth
PALE
- Post-antibiotic Leukocyte effect
- period during which bacteria are more susceptible to leukocyte action
- After drug has cleared, stimulation of phagocytosis mechanism still at work
- also explains drug efficacy below MIC
Broth/Agar dilution Test
Same number of bacteria in each tube but at different concentrations of the drug.
The minimum inhibitory concentration of drug = not cloudy
Disk diffusion test
Filter paper disks concentrated with abx.
Check for zone of inhibition.
No zone = resistant
Little zone = intermediate
Large zone = sensitive
Gradient Diffusion Test
- gradient of abx
- higher concentration of abx as go up on strip
- Find MIC/ decreasing growth as you go down (lower concentration of abx)
