Antimicrobials Flashcards
Classes of antimicrobials used in veterinary medicine?
Aminoglycosides Cephalosporins Macrolides Penicillins Phenicols (NOT USED IN HUMANS) Quinolones Sulfonamindes Tetracyclines
Most commonly prescribed antibiotic?
Clavamox
Why is antibiotics resistance considered a “not new event”?
Most antibiotics have a natural origin
What is the MIC?
Minimum Inhibitory Concentration
Lowest concentration of an antimicrobial agent that prevents visible growth in agar or broth dilution susceptibility test
What is the MBC?
Minimum Bactericidal Concentration
Lowest dilution where NO bacteria survives
What is the breakpoint?
MIC or zone diameter value used to indicate susceptible (S), intermediate (I), and resistant (R)
Some labs report not interpretable (NI) if no established breakpoint
Which groups of antibiotics target the bacterial cell wall?
Beta lactams
Glycopeptides
Bacitracin
Which groups of antibiotics target bacterial DNA?
Fluroquinolones
Novobiocin
Nitromidazoles
Nitrofurans
Which groups of antibiotics target bacterial protein synthesis?
tetracyclines Aminoglycosides Lincosamides Macrolides Streptograminns Chloramphenicol
What is intrinsic resistance?
Innate ability to resist activity of an antimicrobial
Natural insensitivity
What are causes of intrinsic resistance?
Lack of affinity of drug for bacterial target
Inaccessibility of drug into bacterial cell
Extrusion of drug by chromosomally-encoded active exporters
Innate production of enzymes that inactivate drug
What is acquired resistance?
Where a previously susceptible microbe obtains ability to resist activity of a drug
Involves 1) mutation of chromosomal genes involved with bacterial physiology/cell structures, 2) acquisition of foreign resistance genes, 3) both
By which methods can resistance be acquired?
Conjugation
Transformation
Transduction
Mutation
How do bacteria become resistant to beta lactam antibiotics?
Have beta-lactamase or penicillin binding proteins
Block cross-linking of enzymes if peptidoglycan layer of cell wall
How does clavamox overcome bacterial resistance?
Clavulanate inactivates beta-lactamase by forming slowly hydrolysing acyl enzyme intermediate
Amoxicillin blocks cell wall cross-linking transpeptidase, and by forming a slowly hydrolysing covalent acyl enzyme intermediate
Resistance by efflux affects which antibiotics?
Erythromycins
Teteracyclines
How does resistance to macrolides/lincosamides/streptogramins form?
Target modification by rRNA methylases
Dug efflux
Inactivation by enzymes
Which groups of antibiotics are typically broad-spectrum?
Tetracyclines
Phenicols
Fluoroquinolones
3rd and 4th generation cephalosporins
Beta-lactam mechanism of action
Target and bind to penicillin binding protein
Inhibit bacterial cell wall synthesis
Bacterial mechanism of resistance to beta-lactams
Enzymatic destruction of beta-lactam rings
Target (PBP) modification
Reduced intracellular accumulation
Glycopeptide antibiotic mechanism of action
Inhibit the last stages of cell wall assembly by preventing ross-linking reactions
Bacterial mechanism of resistance to glycopeptide antibiotics
Target modification
Production of false targets
Quinolone mechanism of action
Targets DNA gyrase and topoisomerase IV of the bacteria and inhibits the necessary step of supercoiling
Bacterial mechanism of resistance to quinolones
Target modification (mutation of DNA gyrases and DNA topoisomerase IV genes)
Efflux pump (reduced intracellular accumulation)
Aminoglycoside mechanism of action
Target and bind to the 30s ribosomal subunit to cause misreading of the genetic code which results in inhibition of protein synthesis
Targets peptidyl transferase
Bacterial mechanism of resistance to aminoglycosides
Antibiotic (structural) modification
Target modification (rRNA methylation)
Reduced uptake
Enzymatic inactivation
Efflux pump
Macrolide mechanism of action
Targets and binds to 50s ribosomal subunit to inhibit translocation and transpeptidation process, resulting in inhibition of protein synthesis
Bacterial mechanism of resistance to macrolides
Reduced intracellular uptake
Target modification
Mechanism of action of tetracyclines
Target and bind to 30s ribosomal subunit to prevent aminoacyl-tRNA to attach to RNA-ribosome complex, inhibiting protein synthesis
Bacterial mechanism of resistance to tetracyclines
Reduced intracellular accumulation
Drug efflux
Target modification (ribosome protective proteins with homology to elongation factor)
Mechanism of action of rifampin
Interacts with the beta-subunit of the bacterial RNA polymerase to block RNA synthesis
Bacterial mechanism of resistance to rifampin
Target modification
Mechanism of action of sulfonamindes
Targets dihydropteroate synthase (DHPS) and prevents addition of para-aminobenzoic acid (PABA), inhibiting folic acid synthesis
Bacterial mechanism of resistance to sulfonamindes
Target modification
Contraindication of aminoglycoside use
Creatinine >5
Which antibiotics are not effective against anaerobes?
Fluoroquinolones
Which antibiotics are especially particularly effective against Gram negative enteric pathogens an Pseudomonas spp?
Fluoroquinolones
Why should you avoid using fluoroquinolones in immature animals?
Can result in cartilagenous erosion leading to permanent lameness
Mechanism of action of lincosamindes
Targets 23s part of 50s subunit of bacterial ribosomes, causing premature dissociation of peptidyl-tRNA from ribosome
Most frequently prescribed antibiotics overall
Dogs: cephalexin
Cats: clavamox
Most frequently prescribed antibiotic for skin infection
Dog: cephalexin
Cat: clavamox
Most frequently prescribed antibiotic for urinary tract infections
Dogs and cats: clavamox
Most frequently prescribed antibiotics for GI
Dogs and cats: metronidazole
Most commonly prescribed antibiotic for respiratory infection
Clavamox
