Overview antimicrobials Flashcards
Difference between cocci and bacilli
Cocci: spherical
Bacilli: rod-shaped
Difference between staph and strept
Staph: clusters
Strept: chains
Differential diagnosis examples of staphylococci based on coagulase
Positive: S. aureus
Negative: S. epidermis
Differential diagnosis examples of streptococci based on haemolysis
A-haemolytic: Pneumococcus
B-haemolytic: Group A strep
Non-haemolytic: enterococcus
Staphylococci and streptococci are gram…
Positive cocci
Listeria, Cornynebacterium and Clostridium (AnO2) are gram…
Positive Bacilli
Examples of gram negative cocci
- N. meningitidis
- N. gonorrhoea
Examples of gram negative bacilli
- Bacteroides
- Pseudomona
- Haemophilus
- Enterobacteriaceae
Examples of enterobacteriaceae
- E.coli
- Kebsiella
- Enterobacter
- Proteus
Examples of atypical bacteria
Mycoplasma
Chlamydia
Plasmodium spp. can be stained with
aniline dyes
Arsphenamine killed…
spirochaetes
Antibiotics that inhibit cell wall synthesis
Beta lactams (penicillins, cephalosporin, carbapenems) Glycopeptides (e.g. vancomycin, Teicoplanin)
Bacitracin, fosfomycin, isoniazid)
Antibiotics that inhibit protein synthesis
Macrolides (e.g. erythromycin & clarithromycin) Aminoglycosides (e.g. gentamicin, amikacin)
Tetracyclines (Doxycycline, tigecycline)
(Lincosamides, rifamycins, mupirocin, linezolid)
Antibiotics that interfer with DNA synthesis and replication
Nucleotide synth:
- Sulphanoamides (e.g. suplamethoxazole)
- Diaminopyrimidines (e.g. trimethoprim)
DNA gyrase inhibition:
- Quinolones (e.g. ciprofloxacin)
- Nitroimidazoles (e.g. metronidazole)
Antibiotics that disrupt cell membrane
Polymixins (e.g. colistin)
Lipopeptides (e.g. daptomycin)
Penicillin structure
Ring of: 3C, 1N, 1S
ONE modifiable residue.
Pen V better oral absorption than Pen G
- Flucloxacillin - better agains Staphyolococci
Cephalosporin structure
A beta-lactam Ring of: 4C, 1N, 1S
TWO modifiable residues
Cefalexin: absorbed orally
Ceftazidime: active against pseudomonas
Carbapenems
A beta-lactam Ring of: 4C, 1N
THREE modifiable residues
Ertapenem: long halflife
Meropenem: very broad spectrum
Beta lactams, mode of action:
β-lactam antibiotics are bacteriocidal, and act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls. The peptidoglycan layer is important for cell wall structural integrity, especially in Gram-positive organisms,
Function and examples of Beta lactamase inhibitors
B-lactamase produced by many bacteria Hydrolysis of B-lactam ring results in inactivation. inhibitors like cavulanic acid have a B-lactam ring; binds lactamases andstops destruction of AB. Co-amoxiclav
Glycopeptides, mode of action:
Vancomycin (IV) and teicoplanin (IV/IM) are most commonly used
Broad gram positive spectrum:
- MRSA, Coagulase negative Staphylococci
- Penicillin resistant Enterococci and Streptococci -
Clostridium difficile (PO Vanc.)
Macrolides structure and example
Protein synthesis
Large ring forms core e.g. clarithromycin: CA-pneumonia, Legionalle, Mycoplasma
Tetracycline structure and example
Four ringed structure, avoid in pregnancy and children(teeth) Doxycycline: oral and longacting
TIgecycline: glycylcycline with very broad spectrum
Aminoglycosides structure and example
Inhibit protein synthesis
- Three rings linked via oxygen residues
- Narrow therapeutic window (toxicity)
Gentamicin – single doses for sepsis
Tobramycin – anti-pseudomonal in Cystic Fibrosis
Locations at which protein synthesis is inhibited
Macrolides function and example
Protein synthesis inhibitors (early)
Sulphamethoxazole: combined with Trimethoprim to form ‘Co-trimoxazole’.
- Toxicity a concern.
- Used to treat/prevent PCP.
Diaminopyrimidines function and example
Folate synthesis inhibitors (late)
Avoid in first trimester of pregnancy
Trimethoprim
- Commonly used to treat urinary tract infections. Considered to be ‘bacteriostatic’.
Quinolones function and example
Addition of fluorine atom
- fluoroquinolones Stops DNA unwinding before replication
Ciprofloxacin
- versatile antibiotic
- Concerns: MRSA and C. difficile CNS and musculoskeletal
Considerations in treating fungal infections
Fungi are eukaryotes – fungal cells share more in common with human cells than bacteria Grouped as yeasts, molds and dimorphic Lead to mycosis
Exxamples of antifungal drugs
Azoles: - triazoles (fluconazole)
Imidazoles (clotrimazole)
Polyenes - amphotericin B - nystatin
Echinocandins - Caspofungin - Micafungin
Exxamples of antifungal drugs
Azoles: - triazoles (fluconazole)
Imidazoles (clotrimazole)
Polyenes - amphotericin B - nystatin
Echinocandins- Caspofungin Micafungin
Triazole structure, function and example
Inhibit ergosterol synthesis, essential for fungal cell membranes
Triazole rings have 3 nitrogens, 2 carbons
Fluconazole: Broad spectrum including dermatophytes, Candida spp. and Cryptococcus spp.
Polyenes structure, function and example
Binds ergosterol in fungal cell membranes
Macrocyclic with C to C double bonds
Amphotericin B – Given IV will treat most systemic mycoses. AmBisome is liposomal form to reduce toxicity.
Echinocandins structure, function and example
Inhibit glucan synthesis in fungal cell wall Macrocyclic with carbon tail
Caspofungin – Effective for systemic mycoses but less toxic than Amph. B. Only given intravenously.
Sites of antifungal action
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