Antimicrobial chemotherapy Flashcards
(42 cards)
How do bactericidal antibiotics work?
They kill the bacteria E.g penicillin.
How do bacteriostatic antibiotics work?
They inhibit the growth of the bacteria. E.g. erythromycin
What is meant by saying an organism is sensitive?
Sensitive means the organism has been inhibited or killed by the drug available at the site of infection.
What is meant by saying an organism is resistant?
The organism is not killed nor inhibited by the drug at the site of infection.
What is MBC?
Minimum bacterial concentration - needed to kill the organism.
What is MIC?
Minimum Inhibitory concentration - needed to inhibit growth.
What are an antibiotics mechanism of action?
Inhibition of cell wall synthesis
Inhibition of nucleic acid synthesis
Inhibition of protein synthesis
What is the role of Glycopeptides?
Used in the inhibition of cell wall synthesis
Only act on gram positive bacteria.
Inhibit assembly of a peptidoglycan precursor.
Only given parenterally.
E.g Vancomycin
What is the role of Beta lactams?
Used in the inhibition of cell wall synthesis.
Inhibits the enzymes (penicillin-binding proteins, PBPs)
responsible for cross-linking the carbohydrate chains.
Works on all bacteria
E.g penicillin, cephalosporins
What are the role of Aminoglycosides?
Used in the inhibition of protein synthesis
Enter ribosome and inhibit the translation of mRNA.
Gram negative bacteria
E.g Gentamicin
What is the role of Macroslides?
Used in the inhibition of protein synthesis.
Enter ribosome and inhibit the translation of mRNA.
Gram positive bacteria
Alternatives to penicillin
E.g erythromycin
What is the role of Tetracyclines?
Used in the inhibition of protein synthesis
Enter ribosome and inhibit the translation of mRNA.
Staph. aureus, Strep. pyogenes and Strep. pneumoniae
strains are resistant
What is the role of Oxalzolidones?
Used in the inhibition of protein synthesis.
Enter ribosome and inhibit the translation of mRNA.
Given orally
E.g Linezolid - kept for serious infections only.
What is the role of Cyclic Lipopeptide?
Used in the inhibition of protein synthesis.
Enter ribosome and inhibit the translation of mRNA.
Gram positive bacteria
E.g Daptomycin - especially MRSA.
What is the role of Fluoroquinolones?
Used in the inhibition of nucleic acid synthesis
Inhibits DNA gyrase
Given orally or parentally
Particularly effective on gram negative bacteria
E.g ciprofloxacin
What are streptococci always resistant to?
Aminoglycosides.
What drug are gram negative bacteria always resistant to?
Vancomycin.
How can resistance be acquired?
Spontaneous mutation - change in structure or function which no longer allows the antibiotic to act (target may have changed)
Spread of resistance - the gene/s that code for resistance can spread from organism to organism or from species to species. Genes can be carried on plasmids or on transposons (packets of DNA which insert themselves into the chromosome).
What are beta-lactamases?
Bacterial enzymes which cleave the β–lactam ring of the antibiotic and thus render it inactive.
In what organisms are beta-lactamases most common?
Gram negative bacilli
Staphh aureus
What are the methods of combating beta-lactamases?
To introduce a second component to the antibiotic
(β-lactamase inhibitor) protecting the antibiotic
from enzymatic degradation E.g co-amoxiclav
To modify the antibiotic side chain producing new antibiotic resistant to the actions of β-lactamase. E.g flucloxacillin
How do micro-organisms develop resistance to beta-lactams?
Changing the structure of their PBPs
Mutations in PBP genes result in a modified target site to which β–lactams will no longer bind.
E.g Staph. aureus, known as Meticillin Resistant Staph. aureus or MRSA.
What are some adverse reactions to antibiotics?
Allergic reactions- commonly associated with the β-lactam (penicillins and cephalosporins).
Immediate hypersensitivity- Anaphylactic shock This is IgE mediated occurs within minutes of administration.
Characterised by itching, urticaria, nausea, vomiting, wheezing and shock. Laryngeal oedema may prove fatal unless the airway is cleared.
Delayed hypersensitivity- Takes hours/days to develop.
Rashes, fever, serum sickness and erythema nodosum may also occur.
Which group of antibiotics is most likely to cause nephrotoxicity?
Aminoglycosides
