Antibiotics Flashcards
What are the characteristics of antibiotics?
Bactericidal - kill bacteria.
Bacteriostatic - Inhibit growth of bacteria.
What is the mode of action of antibiotics?
They interfere with essential cellular structures/processes. They target bacteria-specific structures/processes. Essential cell structures include: cell wall, plasma membrane and protein synthesis.
Explain gram positive bacteria.
Stain purple. Include staphylococci, streptococci, enterococci. Cell walls have thick layers of peptidoglycan
Explain gram negative bacteria.
Colour pink. E.coli, pseudomonas, salmonella. Cell walls have a think peptidoglycan layer.
What are the antibiotics that act on peptidoglycan biosynthesis?
Penicillins, Cephalosporins, Carbapenems, Vancomycin.
What are B-lactam antibiotics?
They are effective against growing and dividing cells. Kill bacteria by autolysis. Resistant bacterial species will produce B-lactamase.
How do B-lactam antibiotics work?
Inhibit the enzymes that are involved in the transpeptidase cross-linking reaction. Interfere with linking the chains together. Disrupt PG synthesis.
Name the B-lactam antibiotics.
Penicillins e.g amoxicillin, Cephalosporins e.g cefalexin, Carbapenems e.g meropenem.
What are the key characteristics of penicillins?
Very effective against gram +ve bacteria. Some allergy reactions. Aminopenicillins are better tolerated.
What are the key characteristics of Cephalosporins?
Gram +ve, Anaerobes, Gram -ve and Pseudomonas.
What are the key characteristics of carbapenems?
Broad spectrum, generally effective against all BUT: MRSA and VRE. Only available IV.
What is Vancomycin?
An inhibitor of CW biosynthesis. Different mode of action to B-lactams and different chemical structure. It is a Glycopeptide abx which causes more allergic reactions. Effective against MRSA. Administered IV.
What cell structure is involved in protein synthesis?
Ribosome. Bacterial ribosomes are smaller than human ribosomes.
Which antibiotics bind to and inhibit protein components of the 30S subunit?
Tetracycline. Aminoglycosides e.g Gentamycin.
Which antibiotics bind to and inhibit protein components of the 50S subunit?
Macrolides e.g Erythromycin. Chloramphenicol.
What are the characteristics of abx that inhibit protein synthesis?
Broad spectrum - effective against both gram +ve and gram -ve species. Most are bacteriostatic. Associated with greater toxicity.
What are the antibiotics called that inhibit DNA synthesis?
Fluroroquinolones e.g Ciprofloxacin, Norfloxacin, Levofloxacin etc
What do fluoroquinolones do?
Broad spectrum. Inhibit bacterial enzymes with essential roles in DNA replication. Effective against Gram-ve bacteria and intracellular pathogens.
What does Rifampicin do?
Inhibits bacterial but not human RNA polymerases. Used predominantly for treating TB.
What does biosynthesis of nucleotides require?
Folic acid - only produced by bacteria. Folic acid synthesis is a target of man-made antibiotics.
What are the antibiotics called that inhibit folic acid synthesis?
Trimethoprim, Sulphonamide, Co-trimoxazole.
