Antibacterial & Antifungal Agents Flashcards
What is the purpose of antimicrobial agents?
In which 2 circumstances are they used?
they are used to kill microorganisms while preserving the life of the patient
they are used in treatment of established infections
and
prophylaxis of possible infections
What is the difference between treating an established infection and prophylactic treatment?
established infections:
- these are infections that have already been diagnosed
prophylactic treatment:
- this involves treatment of infections that haven’t yet happened, but may happen
- e.g. giving an antibiotic to someone in close contact with an infected person
What is meant by an antibmicrobial agent having selective toxicity?
they must kill the organisms whilst preserving the life of the patient
the antimicrobial must be non-toxic to the person with the infection
What are the 3 stages involved in the strategy of antibiotic use?
1. empiric therapy
- this is known as “best guess” therapy
2. targeted therapy
- this is used once the organism has been identified through laboratory tests
3. susceptibility-guided therapy
- you know exactly what the organism is and what it is susceptible to after antimicrobial susceptibilty results
What is the first stage in diagnosing an infection?
What type of antibiotic therapy should be used at this stage?
clinical diagnosis based on history and examination
you know the organism that is involved, but not exactly what is causing the disease
empiric therapy is used based on where the infection is, the organisms which are likely to cause it and the antibiotics that are effective against the suspected organisms
Once you have received results from laboratory examinations, what type of antibiotic therapy is used?
the lab results identify the organism that is causing the infection
targeted therapy is used based on the organism’s likely antimicrobial sensitivity
What type of therapy is used once you have received the antimicrobial susceptibility results?
susceptibility-guided therapy
you now know exactly what organism is causing the infection and which antibiotics it is sensitive to
How does the antimicrobial spectrum change as knowledge increases?
as the level of knowledge of the infecting organism increases, the antimicrobial spectrum of the agent(s) used decreases
What are the 3 stages involved in choosing the right empiric antimicrobial agent?
1. know the likely organism causing infection
- body site
- immunological status of patient
- microbiological history
2. select agent with appropriate antimicrobial spectrum
3. match pharmacokinetics with patient
- distribution
- interactions
- adverse effects
Why is it important to know a patient’s immunological status when choosing the right empiric antimicrobial agent?
an immunocompromised patient will have a different spectrum of organisms which are able to cause infection
What are the definitions of antimicrobial agents and antibiotics?
antimicrobial agents:
- these are any agents which kill microorganisms
- e.g. antibacterial, antifungal, antiviral
antibiotics:
- these are chemical products of microbes that inhibit or kill other organisms
What are the 3 main categories of antimicrobial agents?
- antibiotics
- synthethic compounds with similar effect e.g. sulfonamides
- semi-synthetic compounds i.e. modified from antibiotics
Why are semi-synthetic antimicrobials used?
these are antibiotics that have been chemically modified to improve them in some way
e.g. to make it less toxic or more broad spectrum
What is meant by a bacteriostatic/fungistatic organism?
What is an example?
this will not actually kill the organism, it will just inhibit growth
the immune system then destroys the organism
e.g. protein synthesis inhibitors
What is meant by a bacteriocidal/fungicidal antimicrobial?
What is an example?
these will kill the organism that they are targeting
e.g. cell wall-active agents
without a fully functional cell wall, the bacteria or fungi will die
What is meant by minimum inhibitory concentration (MIC)?
minimum concentration of antimicrobial agent at which visible growth is inhibited
What is meant by minimum bactericidal/fungicidal concentration (MBC/MFC)?
the minimum concentration of antimicrobial agent at which most organisms are killed
What is meant by synergy / synergism?
when the activity of two antimicrobials given together is greater than the activity of either if given separately
“additive effect” is used to describe this
What is meant by antagonism?
when the activity of two antimicrobials given together is less than the activity of either if given separately
i.e. the second antibiotic that is given will inhibit the function of the original antibiotic
Why is synergy and antagonism important in clinical practice?
there are some combinations of antibiotics which can be used together to improve patient outcome
there are some combinations which should not be used together
What is meant by the antimicrobial spectrum?
the range of bacterial/fungal species likely to be sensitive to a particular antibacterial/antifungal agent
What is the difference between a broad spectrum and a narrow spectrum antimicrobial?
broad spectrum:
- kills most types of bacteria/fungi encountered
narrow spectrum:
- kills only a narrow range of organisms
Why is it important to have knowledge of the antimicrobial spectrum?
it is important in choosing appropriate empiric antimicrobial therapy
the narrowest spectrum antibiotic that is appropriate should be used at all times
In general, how do antimicrobial agents work?
through inhibition of critical process in bacterial/fungal cells
“antimicrobial targets” are the critical processes in the cell that the antibiotic inhibits
What processes / molecules act as antimicrobial targets?
enzymes, molecules or physical structures
- cell wall
- protein synthesis
- DNA synthesis
- RNA synthesis
- membrane function
what is meant by the antimicrobial agent exhibiting selective toxicity?
the target is not present in the human host
or the target is present in the human host, but it is inaccessible to the antimicrobial agent
What is the bacterial cell wall made from?
What is the structure like?
peptidoglycan
this makes up the cell wall of gram-positive and gram-negative bacteria
it is a polymer of glucose derivatives - N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG)
Why is the peptidoglycan cell wall a good target for selective toxicity?
there is no cell wall present in human cells
What are examples of cell wall synthesis inhibitors?
B-lactams and glycopeptides
B-lactams are most commonly used, but some patients have an allergy to penicillin, so the second line is glycopeptides
What do all the B-lactam antibiotics have in common?
they all contain the B-lactam ring
this is a four-membered ring structure (C-C-C-N)
How do B-lactam antibiotics work?
they interfere with the function of penicillin binding proteins
these are transpeptidase and carboxypeptidase enzymes that are involved in the cross-linking process that forms the peptidoglycan cell wall
What are the 4 main categories of B-lactam antibiotics?
- penicillins
- cephalosporins
- carbapenems
- monobactams