Antimicrobial Agents And Antibiotic Susceptibility Testing Flashcards
Limited spectrum of action
Narrow spectrum
Wide spectrum of action
Broad spectrum
Kill or destroy organism
Bacteriocidal agents
Inhibits the growth of microorganisms
Bacteriostatic agents
Agents that target the peptidoglycan layer
Inhibition of cell wall synthesis
- Beta Lactam drugs
- Glycoproteins
- D-Cycloserine
- Bacitracin
MOA: formation of covalent complexes with enzymes that generate peptidoglycan molecule
-target: enzyme producing the link
Beta Lactam drugs
Similar structure of Beta Lactam drugs. This bond is found in the peptidoglycan layer
D-alanyl D-alanine
Examples of beta lactam drugs
Penicillin
-Penicillin G
-Penicillin V
-Aminopenicillins (Ampicillin, amoxicillin)
-Penicillinase Resistant Penicillina (methicillin, oxacillin)
Cephalosporins
MOA: binds to terminal D-Ala D-Ala of the pentapeptidyl-glycosyl peptidoglycan intermediates
- target: substrate (D-Ala D-Ala) needed for the enzymatic reaction
- inhibiting the transpeptidation step of cell wall synthesis
- Vancomycin
Glycopeptides
Activity is limited to Gr+ org.
Treatment of infections caused by staphylococci, streptococci, and enterococci
Glycopeptides
True or false:
Gr- organisms are resistant to vancomycin
True
MOA: inhibit the synthesis of the peptidoglycan precursors in the cytoplasm
Cycloserine
MOA: inhibits the recycling of certain metabolites required for peptidoglycan synthesis
-toxic: limited to topical application
Bacitracin
MOA: act like detergents which interact with phospholipids increasing permeability leading to leakages of macromolecules and ions essential for cell survival
-Gram-
Polymyxins (Ploymyxin B and Collistrin)
More effective against Gr- organisms
Agent of P. aeruginosa and acinetobacter infections
Polymyxins
Why are polymyxins toxic?
Because it do not just target the cell membrane of the bacteria, but also the cell mem. of humans
It is an important precursor in DNA synthesis of bacteria
Folate
What are the enzymes mediationg folate synthesis?
- Dihydropteroate synthase
- Dihydrofolate reductase
MOA: blocks formation of 7,8 dihydropteroate by competitively inhibiting the binding of the analogue paraaminobenzoic acid (PABA) with dihydropteroate synthase
Sulfonamides (Sulfamethoxazole)
MOA: blocks the step leading to formation of tetrahydrofolate by preventing dihydrofolate reductase mediated recycing of folate coenzymes
Trimethoprim
MOA: bind and interfere with DNA gyrase and topoisomerase IV
- bacteriocidal
- toxicity: tendinitis
- Nalibdic acid (example)
- for enterics, pseudomonads, staphylococcus, streptococcus, neisseria
Fluoroquinolones (Quinolones)
MOA: nitro group is REDUCED by nitroreductase leading to generation of cytotoxic compounds and free radicals that disrupt DNA
-must be in reduced form to work
Metronidazole
What is the effective environment of metronidazole?
Anaerobic environment
For anaerobes, microaerophiles, and protozoans
MOA: binds to DNA dependent RNA polymerase to inhibit RNA synthesis
-primarily for gram+ org
-for tb
Side effect: red urine
Rifamycins (rifamin/rifampicin)
MOA: inhibits translation through inhibition of elongation step
-broad spectrum
Toxic: aplastic anemia (pancytopenia), gray baby syndrome
-used for typhoid fever back then
Chloramphenicol
MOA: inhibits translation through inhibition to 23s of RNA of the 50s ribosomal subunit
-mostly bacteriostatic
For gr+ (mycoplasma, treponemes, reickettsia)
Macrolides
Causes pseudomembranous colitis
Clindamycin
Drug of choice for legionnaire’s disease, community acquired pneumonia
Erythromycin
Inhibits protein synthesis by interacting with 23s rRNA
Inhibits initiation ofbtranslocation of mRNA
For gr+ and mycobacteria
Linezolid (Oxazolidinones)
MOA: inhibits protein synthesis by binding reversibly to the 30s ribosomal subunit
-broad spectrum
Toxicity:
-GI irritation
-phototoxic dermatitis
-toxic to liver and kidney
-discolored teeth and depressed bone growth
Take this with full stomach
Don’t give to pregnant woman
Tetracycline and Doxycycline
Often used together with penicillins in order to diffuse and enter bacterial cell
Ex. Streptomycin, gentamicin, tobramycin, amikacin, neomycin
Toxicity: ototoxic, nephrotoxic
Aminoglycosides
MOA:
- inhibits mycolic acid
- inhibit DNA dependent RNA protein synthesis
Aminoglycosides
1st line drugs for aminoglycosides
- isoniazid
- rifampicin
- pyrazinamide
2nd line drugs for aminoglycosides
- streptomycin
- ethambutol
Changes that rest in observably reduced susceptibility of an organism to a particular antimicrobial agent
Biologic resistance
Antimicrobial susceptibility has been lost
Drug is no longer effective for clinical use
Clinical resistance
Physical or chemical factors that alter the antimicrobial agent for the microorganism’s physiologic response to agent
pH
Anaerobic atmosphere
Cation concentration
Metabolites
Environmentally mediated antimicrobial resistance
Types of microorganism mediated antimicrobial resistance
Intrinsic: inherent, known from the start
Acquired: if antibiotic is abused
