Module 6 Flashcards
What are most antimicrobial agents?
Antibiotics or chemically reproduced agents
What are the criteria for clinical use of antimicrobials?
Selective toxicity
Shouldn’t cause allergic reactions
Soluble in body fluids and capable of penetrating infected tissue
Microorganisms shouldn’t readily develop resistance
How can antimicrobials be described?
In terms of activity (broad or narrow)
In terms of effect (bactericidal or bacteriostatic)
What are the modes of action of antimicrobials?
Cell wall synthesis Protein synthesis DNA/RNA synthesis Cell membrane function Other metabolic processes
What are the two major groups of beta lactam antibiotics?
Penicillins and cephalosporins
What is the mode of action of beta lactam antibiotics?
Ring structure combined with cell wall enzymes (PBPs) so no cross linking occurs, the cell wall weakens and the cell dies.
What are the different types of penicillins and their characteristics?
Natural- narrow G+ spectrum, sensitive to B-lactamase, penicillin G and V, class concept applies
B-lactamase resistant- bulky side chain protects from B-lactamase, narrow G+ spectrum, resistant bacteria can alter PBPs, eg) cloxacillin, class concept applies
Extended spectrum- amine group added to side chain, broad spectrum (better for G-), sensitive to B-lactamase, amoxicillin and ampicillin, class concept applies
Anti-pseudomonal- increased activity against amp-resistant, carboxypenicillins and ureidopenicillins, broad spectrum (better for G-), sensitive to B-lactam are, class concept doesn’t apply
How do cephalosporins differ in action from penicillins?
B-lactam ring is fused to a different structure
More resistant to B-lactamase
Easier to manipulate
What are the different generations of cephalosporins and their characteristics?
1st- broad spectrum (more G+), class concept applies, cephalothin and cefazolin
2nd- broad spectrum (increased G-), no class concept, cefador, cefonicid, cefotiam
3rd- broad (less G+), no class concept, crosses BBB easier, cefixime, cefotaxime, ceftizoxime, cefoperazone
4th- broader spectrum, cefipime (less likely to induce resistance), cepirome
What is the “other” B-lactam antibiotic and what are its characteristics?
Aztreonam
B-lactam core with no ring structure
Attaches to PBPs
Narrow G- spectrum (ineffective against anaerobes)
Effective against enteriobacteriaceae and pseudomonas
What are B-lactamase inhibitors?
Weak antibiotics, inhibit some B-lactamases
Given in combination with B-lactam antibiotics
What are the two types of B-lactamase inhibitors and what are they given with?
Clavulanic acid- given with amoxicillin or ticarcillin
Sulbactan- given with ampicillin
What are extended spectrum B-lactamases?
Enzymes that mediate resistance to extended spectrum (gen 3) cephalosporins.
What bacteria produce ESBLs?
G-
What if a microorganism is positive for ESBLs?
All penicillins, cephalosporins and aztreonam should be reported as resistant.
What other antimicrobials act against the cell wall? What are their characteristics?
Imipenem- carbapenum class, resistant to most B-lactamases, binds PBPs, broadest spectrum, not effective against MRSA or VRE
Vancomycin- glycopeptide class, binds cell wall precursors, not affected by B-lactamase, narrow G+, reserved for MRSA, C. diff and resistant enterococcus
Teicoplanin- similar to vancomycin
What are antimicrobial agents?
Chemotherapeutic agents used for the treatment of infectious diseases.
How do antimicrobials that inhibit protein synthesis work?
They function where tRNA brings amino acids into place in the ribosomes.
Why aren’t antimicrobials that target protein synthesis excessively toxic?
Bacterial ribosomes differ from human.
What antimicrobials inhibit protein synthesis?
Erythromycin
Clindamycin
Chloramphenicol
Tetracyclines
Aminoglycosides
Describe the characteristics of erythromycin.
Macrolides group
Binds 50S subunit to stop amino acid addition and halt protein synthesis.
Bacteriostatic
Narrow G+ spectrum
Absorbed into tissues except CNS
Destroyed by gastric acid, vomiting
Describe the characteristics of clindamycin.
Lincosamide group
Better absorption and penetration than erythromycin
Effective against anaerobics
Diarrhea in 20% of patients, may develop pseudomembranous colitis
Describe the characteristics of chloramphenicol.
Small molecule with nitrobenzene ring and small side chain.
Competes with erythromycin to bind 50S subunit
Broad spectrum, G+ and some enteriobacteriaceae
Penetrates most tissues
Very toxic, reserved for when other antimicrobials can’t be used
What are some side effects of using chloramphenicol?
Gray syndrome- toxic levels of the antimicrobial accumulate
Aplastic anemia- marrow asplasia
Dose-related marrow depression
