Flashcards in Infection - Antimicrobials Deck (28)
What is the difference between a bactericidal and a bacteriostatic agent?
Bactericidal kills the bacteria, while bacteriostatic inhibits the growth of an organism
What is the strict definition of an antibiotic?
A type of antimicrobial drug derived from another living creature, eg. fungi
What is the basis of an 'antibacterial class'?
They are sorted by chemical structure
Give some ideal features of antimicrobial agents
- selectively toxic
- few adverse effects on host
- reaches site of infection
- oral/IV formulation
- long half-life to allow infrequent dosing
- no interference with other drugs
What are the four main ways that antibacterials work on bacteria?
They interfere with:
1) cell wall synthesis
2) protein synthesis (tetracyclines, aminoglycosides, macrolides)
3) cell membrane function (polymixins)
4) nucleic acid synthesis (quinolones)
How does penicillin affect the bacterial cell wall?
Cell wall is composed of cross-linked chains of peptidoglycans which are joined by penicillin bonding protein.
Penicillin binds to the protein, preventing it from joining the chains together and destabilising the wall.
How does vancomycin disrupt the bacterial cell wall?
It binds to the end of the links between the chains, meaning that they cannot bind to penicillin binding protein and they are not joined
How do fluoroquinolones interfere with protein synthesis?
They inhibit enzymes involved with DNA replication, one of which is responsible for supercoiling the DNA
What are the three types of antibiotic resistance?
- INTRINSIC (no target/access for the drug, usually permanent)
- ACQUIRED (acquires new genetic material/mutates, usually permanent)
- ADAPTIVE (organism responds to a stress, usually reversible)
Give some mechanisms of antibiotic resistance
- bacteria may produce enzyme which inhibits the drug, eg. beta-lactamases
- target enzyme has lowered affinity for antibacterial agent
- may be altered uptake of drug (eg. decrease in permeability of cell wall or increased efflux)
How does chromosomal gene mutation lead to an antibiotic resistant strain of bacteria developing?
- mutated gene confers resistance in one bacterium
- other bacteria are killed by antibiotics
- the resistant strain multiplies and becomes dominant
How can the gene for antibiotic resistance move directly from one bacterium to another?
Horizontal gene transfer - plasmid moves from one bacterium to another via a pilus
How does disc sensitivity testing measure antibiotic activity?
Filter paper disc is impregnated with antibiotic and placed on a petri dish which has been covered with a sample of bacteria. It is incubated to see whether the organism grows or not. How much/little it grows = how well the antibiotic works
What is the 'minimum inhibitory concentration'?
The lowest concentration at which the antibiotic still kills bacteria in a solution
What are beta-lactams?
A class of broad-spectrum antibiotics consisting of all antibiotic agents that contain a beta-lactam ring in their molecular structures. Group includes penicillins, cephalosporins, carbapenems and monobactams
Give some examples of penicillins and what they work against
- penicillin (streptococci mainly)
- amoxicillin (streptococci and gram-negatives)
- flucloxacillin (staphlococci and streptococci)
- co-amoxiclav and piperacillin (all of the above and gram negative)
Give two examples of drug classes that are very broad spectrum and work against most gram negatives
Cephalosporins and carbapenems (there are other answers too)
Do glycopeptides work better against gram positive or gram negative?
Active against most gram positive
Why are tetracyclines sometimes given in the place of another drug?
In penicillin allergy, they are given instead of penicillin
Why shouldn't tetracyclines be given to children younger than 12 years old?
They stain teeth and bone yellow
What situation are aminoglycosides usually reserved for?
Severe gram negative sepsis
Give some examples of macrolides
Erythromycin and clarithromycin
What are macrolides active against?
Atypical respiratory pathogens and mild gram positive infections
How do quinolones work?
They inhibit DNA gyrase
What is trimethoprim often used to treat?
How does trimethoprim and sulphonamides work?
They inhibit folic acid synthesis
Give some examples of antifungals
- azoles (active against yeasts and molds, inhibit cell membrane synthesis)
- polyenes (inhibit cell membrane function)