Antibacterial Agents Flashcards
Define antibiotic
Chemical products of microbes that inhibit/kill other organisms
Define Antimicrobial agents
- Antibacterial, antiviral, antifungal
- Antibiotics
- Synthetic/semi-synthetic compounds with similar effects
What are the different types of bacterial killing?
- Bacteristatic= inhibit bacterial growth (protein synthesis inhibitors)
- Bactericidal= kill bacteria (cell-wall active agents)
What is the minimum inhibitory concentration?
Minimum conc of antibiotic at which visible growth is inhibited
-Some antibiotics are bacteriostatic at low conc and bactericidal at high conc
What types of antimicrobial interactions are there?
- Synergism (activity of 2 antimicrobials given together is greater than the sum of their activity separately)- B-lactam/aminoglycoside combination for strep endocarditis
- Antagonism (one agent diminishes activity of another)
- Indifference (activity unaffected by addition of another agent)
Name some cell wall synthesis inhibitors
- B-lactams
- Glycopeptides
- Cycloserine (antiTB agent)
Describe the structure of a bacterial cell wall
- Peptidoglycan major component in gram +ve & -ve bacteria
- Polymer of glucose-derivatives NAG & NAM
How do B-lactam antibiotics work?
Interfere with function of penicillin binding proteins- Transpeptidase enzymes involved in the peptidoglycan cross-linking
Describe the general structure of B-lactams
- Four membered B-lactam ring structure (C-C-C-N)
- Structural analogue of D-alanyl-D-alanine
Name the groups of B-lactam antibiotics, members of each family and their spectrum
- Penicillins (benzylpenicillin, amoxicillin, flucloxacillin- narrow spectrum)
- Cephalosporins (Cefuroxime, ceftasidime- broad spectrum)
- Carbapenems (meropenem, imipenem-extremely broad spectrum)
- Monobactams (aztreonam- gram -ve activity only)
Name types of glycopeptides and how they work
- Vancomycin, teicoplanin
- Bind directly to terminal D-Alanyl-D-alanine on NAM pentapeptides
- Inhibit binding of transpeptidases thus peptidoglycan cross-linking
- Unable to penetrate gram -ve outer membrane porins
How are proteins synthesised in bacteria?
- Translation of RNA to a protein
- Takes place in ribosome
- 50S + 30S= 70S
Give examples of Aminoglycosides, where they bind and what they are known for?
- Gentamicin, amikacin
- Protein synthesis inhibitors
- Bind to 30S ribosomal subunit
Give examples of MLS, what it stands for, where they bind and what they are known for?
- Macrolides, Lincosamides, Streptogramins
- Protein synthesis inhibitors
- M= erythromycin, clarithromycin
- L= clindamycin
- Bind to 50S ribosomal subunit= blockage of exit tunnel or inhibit protein elongation
Where do tetracyclines bind to, what are they known for?
- Protein synthesis inhibitors
- Bind to 30S ribosomal subunit
- Inhibit RNA translocation= interfere with binding of tRNA to rRNA
Give an example of an Oxazolidinone, where it binds and what it is known for?
-Protein synthesis inhibitor
-Linezolid
-Binds to 50S ribosomal subunit- may also bind to 70S subunit
-Inhibits initiation of protein synthesis
-Inhibit assembly of initiation complex
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What are Trimethoprim & Sulphonamides inhibitors of and how? What is their combined name?
- DNA synthesis
- Inhibit folate synthesis (folic acid= purine synthesis precursor)
- T=Dihydrofolate reductase
- S=Dihydropteroate synthase
- Combined= Co-Trimoxazole
Give examples of Quinolones & fluoroquinolones, what they inhibit and how?
- Ciprofloxacin, Nalidixic acid
- Inhibit 1 or more of 2 related enzymes- DNA gyrase & topoisomerase IV
- Involved in remodelling of DNA during DNA replication
What is Rifampicin and how does it do this?
- RNA synthesis inhibitor
- RNA polymerase inhibitor
- Prevents synthesis of mRNA
Name some plasma membrane agents
- Colistin (gram -ve)
- Daptomycin (gram +ve)
- Destruction of cell membrane
What are adverse effects of antibiotics?
- C.Diff
- Antibiotic resistance
- Fungal infection (candidiasis)
- Nausea/vomiting, rashes
What are the adverse reactions of aminoglycosides?
- Reversible renal impairment on accumulation
- Irreversible ototoxicity
- Therapeutic drug monitoring indicated
What are the adverse reactions of B-lactams?
Allergic reactions: Generalised rash or anaphylaxis
What are the adverse reactions of Linezolid?
Bone marrow depression
