Microbiology 20: Antimicrobials 1 Flashcards
What coverage do Glycopeptides antibiotics have ?
Gram +ve
When would Glycopeptide antibiotics be indicated ?
Gram +ve bacteria resistant to Beta lactams
E.g MRSA
Why are beta lactams considered bactericidal ?
They dont kill existing bacteria, they inhibit cell wall synthesis so stop new bacteria from forming their cell walls and hence causing lysis.
Give 3 examples of classes of beta lactams ?
Penicillins
Cephalosporins
Carbapenems
Give an example of a drug that is a beta lactamase inhibitor ?
Clavulanic acid
tazobactam
As you go up the generations of cephalosporins what happens to their activity against gram +ve and -ve bacteria ?
As you go up the generations the activity against gram -ve goes up and +ve goes down.
What complications can glycopeptides cause ?
Nephrotoxicity
Give 2 examples of Glycopeptides ?
Vancomycin
Teicoplanin
Which Glycopeptide is often used to treat C.difficile infection ?
Vancomycin
Which antibiotic is commonly used to treat meningitis ?
Ceftriaxone (cephalosporin)
Can’t normally penetrate blood brain barrier but does so when there is inflammation ie in meningitis
List 5 classes of Protein synthase inhibitors ?
Aminoglycosides Tetracyclines Macrolides Chloramphenicol Oxazolidinones (Linezolid)
Why are Proteinase inhibitors selective for bacteria and not hum an cells ?
They bind to the ribosomal subunit which is a different size in bacteria (30S) compared to human cells
What antibiotic coverage do Aminoglycosides (gentamicin) have ?
Good gram -ve activity
Poor gram +ve and anaerobe activity
what antibiotic coverage do Tetracyclines (doxycycline) have ?
Mostly gram +ve
Very good for intracellular pathogens e.g chlamydia and mycoplasma
Which class of Protein synthesis inhibitors are contraindicated in children and pregnant women ?
Tetracyclines
Deposit in bone and also cause discolouration of teeth
Chloramphenicol is contraindicated in the 3rd trimester as it can cause “grey baby syndrome”
What is a dangerous complication of giving babies chloramphenicol ?
Grey baby syndrome
Aplastic anaemia
What is the antibiotic coverage of Linezolid ?
Very active against gram +ve bacteria
Poor activity against gram -ve bacteria
In which infection is Linezolid particularly useful ?
MRSA
Give 2 side complications you can get with Linezolid ?
Optic neuritis
Thrombocytopenia
Give 2 classes of DNA synthesis inhibitors ?
Quinolones
Nitroimidazoles
What antibiotic coverage do quinolones (ciprofloxacin) have ?
very active against gram -ves
New quinolones: moxifloxicin and levofloxacin have more gram +ve cover than gram -ve
Give one example of a Nitroimidazole ?
Metronidazole
Which bacteria is Metronidazole particularly effective against ?
Anaerobes (C.Difficile)
Give one example of a class of RNA synthesis inhibitors ?
Rifampicins
Which antibiotic turns your secretions (urine, tears etc) an Orange colour ?
Rifampicin
What is the antibiotic treatment for Pneumocystis jirovecii pneumonia ?
Septrin (Sulphonamides + Trimethoprim) (co-trimoxazole)
Which antibiotic is commonly used to treat skin infections such as cellulitis or impetigo ?
Flucloxacillin
List 2 serious side effects of gentamicin ?
- Ototoxic
- Nephrotoxic
Which antibiotic is often given in the case of penicillin allergy ?
Erythromycin (macrolide)
List 2 mechanisms of resistance that MRSA uses against Beta lactams ?
- Beta lactamses (inactivation)
- PBP2a (altered target) - Normally beta lactams bind to penicillin binding proteins in the cell wall to cause their effect. Binding To PBP2a means the cell wall is not affected.
list 3 examples of selective targets
peptidoglycan layer of cell wall
inhibition of bacterial protein synthesis
DNA gyrase and other prokaryote-specific enzymes
difference between gram -ve and + ve cell walls
gram -ve = outer membrane - peptidoglycan - cytoplasmic membrane
gram +ve - thick peptidoglycan cell wall - cytoplasmic membrane
features of beta lactam antibiotics
inactivate enzymes used in terminal stages of cell wall synthesis
cells will have a weak cell wall
active against rapidly-dividing bacteria
ineffective against bacteria without a cell wall
penicillins, cefalosporins, carbapenems, monobactams
features of penicillins
active against gram-positives
eg streptococci
broken down by beta-lactamase produced by S aureus and many gram -ves
what are beta lactamase inhibitors
clavulanic acid and tazobactam
protect penicillins from breakdown by beta lactamase
increases coverage of antibiotics to include S. Aureus , gram -ves and anaerobes
features of glycopeptides
large molecules
active against gram +ves
inhibit cell wall synthesis
used to treat serious MRSA infections
inc vancomycin and teicoplanin
binds amino acid chains and prevents glycosidic bonds and peptide cross-links from forming
which antibiotics inhibit protein synthesis
aminoglycosides (gentamicin, amikacin, tobramycin) tetracyclines Macrolides (erythromycin) licosamides (clindamycin) chloramphenicol oxazolidinones (linezolid)
features of aminoglycosides
binds to amino-acyl site of the 30s ribosomal subunit
ototoxic and nephrotoxic
no activity against anaerobes
prevents elongation of peptide chain
features of tetracyclines
broad spectum Ab with activity against IC pathogens (chlamydia, mycoplasma)
do not give to children and pregnant women
light-sensitive rash
binds to ribosomal 30S subunit, inhibits protein synthesis
features of macrolides
bacteriostatic
minimal activity against gram -ves
mild staph/strep infections in penicillin allergic
active against: campylobacter spp, legionella, pneumophila
bind to 50S subunit of the ribosome
features of chloramphenicol
bacteriostatic
broad antibacterial activity
rarely used
list antibiotics which inhibit DNA synthesis
quinolones (cipro, levofloxacin, moxifloxacin)
nitroimidazoles (metronidazole, tinidazole)
features of fluoroquinolones
act on the alpha subunit of DNA gyrase
broad antibacterial activity esp against gram negative organisms inc pseudomaonas aeruginosa
uses: UTIs, pneumonia, atypical pneumonia, bacterial gastroenteritis
list antibiotics which are cell membrane toxins
daptomycin - gram positive only, MRSA and VRE infections
colistin - gram -ves inc Pseudomonas aeruginosa, acinetobacter baumanii
klebsiella pneumoniae
features of sulfonamides and diaminopyrimidines
interfere with folic acid metabolism
trimethoprim - community acquired UTIs
what are mechanisms of antibiotic resistance?
1 - inactivation (B lactams, aminoglycosides, chloramphenicol)
2 - altered target (B lactams, macrolides, quinolones)
3 - reduced accumulation (tetracyclines, B lactams)
4 - bypass antibiotic-sensitive step in cell division (trimethoprim, sulphonamides)
how can antibiotic resistance develop via inactivation
beta lactamases
S Aureus and gram negative bacilli
how can antibiotic resistance develop via altered targets
MRSA - mecA gene encoded PBP2a - low affinity for binding beta lactams
Strep pneumoniae - penicillin resistance via stepwise mutations in PBP genes
Macrolides - modified 23S NRA, reducing binding of macrolides
