L13 Antibiotics Flashcards
What is an antibiotic?
A compound that inhibits the growth of or kills bacteria, either derived from natural sources or synthesised.
What is the difference between an antibiotic and an antimicrobial?
- Antibiotic: Specifically targets bacteria.
- Antimicrobial: Targets a broader range of microbes, including viruses, fungi, and protozoa.
What is selective toxicity in antibiotics?
The ability of an antibiotic to target bacteria specifically without harming the host.
What are the two main uses of antibiotics?
- Treatment of bacterial infections.
- Prophylaxis to prevent bacterial infections (e.g., surgery or outbreaks).
How do antibiotics benefit society?
They reduce mortality, prevent disease spread, and enable complex medical procedures like organ transplants and chemotherapy.
Name five bacterial targets of antibiotics.
- Cell wall biosynthesis.
- Cell membrane integrity.
- DNA and RNA synthesis.
- Protein synthesis.
- Metabolic pathways.
What is the Minimum Inhibitory Concentration (MIC)?
The lowest concentration of an antibiotic that inhibits bacterial growth.
What is a breakpoint concentration?
The antibiotic concentration below which bacteria are considered susceptible to the drug.
What are the two main ways bacteria develop resistance?
- Mutations in chromosomal genes.
- Acquisition of foreign DNA (e.g., plasmids).
What is the Mutant Prevention Concentration (MPC)?
The antibiotic concentration that prevents the growth of resistant mutants.
What are beta-lactams, and how do they work?
A class of antibiotics that inhibit bacterial cell wall synthesis (e.g., penicillins, cephalosporins).
Name an example of a fluoroquinolone and its target.
Ciprofloxacin, which targets DNA synthesis.
What is the main use of aminoglycosides like gentamicin?
Treating severe infections caused by gram-negative bacteria.
What does pharmacokinetics (PK) study in antibiotics?
How the body absorbs, distributes, metabolises, and eliminates the drug.
What does pharmacodynamics (PD) study?
The effects of the drug on the bacteria, including potency and time-dependent or concentration-dependent killing.
How do quinolones differ in their distribution compared to beta-lactams?
Quinolones penetrate more effectively into tissues like sputum and alveolar macrophages.
How do gram-positive bacteria differ from gram-negative bacteria structurally?
- Gram-positive: Thick peptidoglycan layer, no outer membrane.
- Gram-negative: Thin peptidoglycan layer, outer membrane present.
Name two gram-positive and two gram-negative pathogens.
- Gram-positive: Staphylococcus aureus, Streptococcus pneumoniae.
- Gram-negative: Escherichia coli, Pseudomonas aeruginosa.
What strategies are being pursued to combat resistance?
- Modifications to existing antibiotic classes.
- Development of combination therapies.
- Targeting gram-positive pathogens.
What is synergy in antibiotic combinations?
When the combined effect of two antibiotics is greater than their effects individually.
Why is combination therapy sometimes necessary?
To prevent resistance, broaden spectrum, or enhance efficacy.
What colour do gram-positive bacteria stain, and why?
Purple, because the thick peptidoglycan layer retains the crystal violet stain during the Gram-staining process.
What colour do gram-negative bacteria stain, and why?
Pink or red, because the thin peptidoglycan layer does not retain the crystal violet stain and takes up the counterstain (safranin).
What is the role of the outer membrane in gram-negative bacteria?
- Acts as a barrier to many antibiotics.
- Contains lipopolysaccharides (LPS) which can trigger strong immune responses in humans.
Why are gram-negative bacteria often more resistant to antibiotics?
- The outer membrane acts as an additional barrier to antibiotic entry.
- Many produce beta-lactamases, which degrade beta-lactam antibiotics.
Which antibiotics are most effective against gram-positive bacteria?
- Penicillin.
- Vancomycin.
- Clindamycin.
- Macrolides (e.g., erythromycin, azithromycin).
Which antibiotics are most effective against gram-negative bacteria?
- Aminoglycosides (e.g., gentamicin).
- Fluoroquinolones (e.g., ciprofloxacin).
- Carbapenems (e.g., meropenem).
- Third-generation cephalosporins (e.g., ceftriaxone).
Why are beta-lactam antibiotics sometimes combined with beta-lactamase inhibitors?
To overcome resistance in beta-lactamase-producing bacteria (e.g., augmentin = amoxicillin + clavulanic acid).
What are the steps of the Gram-staining process?
- Crystal violet stain: Both gram-positive and gram-negative bacteria are stained purple.
Iodine treatment: Forms a complex with the crystal violet. - Alcohol/acetone wash:
- Gram-positive: Retains the purple stain.
- Gram-negative: Loses the stain. - Counterstain (safranin):
- Gram-positive: Remains purple.
- Gram-negative: Stains pink/red.
What is the purpose of iodine in Gram staining?
It binds to the crystal violet, forming a complex that is harder to wash out.
Why do gram-negative bacteria lose the crystal violet stain during alcohol washing?
The thinner peptidoglycan layer and the presence of an outer membrane allow the crystal violet-iodine complex to be washed out.
Which types of infections are commonly caused by gram-positive bacteria?
Skin infections (e.g., cellulitis by Staphylococcus aureus).
Respiratory infections (e.g., pneumonia by Streptococcus pneumoniae).
Endocarditis (infection of the inner lining of the heart)
How do gram-positive bacteria develop resistance to antibiotics?
- Modification of penicillin-binding proteins (e.g., MRSA).
- Efflux pumps to expel antibiotics.
- Enzymatic inactivation (e.g., beta-lactamase production).
How do gram-negative bacteria develop resistance to antibiotics?
- Outer membrane prevents drug entry.
- Production of extended-spectrum beta-lactamases (ESBLs).
- Efflux pumps and porin mutations reduce antibiotic uptake.
