24 Questions
What is the minimum inhibitory concentration (MIC)?
The concentration needed for visible growth of a microorganism to be inhibited
Why are penicillins used mainly to treat Gram-positive bacterial infections?
They are resistant to beta-lactamases
Why is benzylpenicillin given by injection rather than orally?
It is inactivated by gastric acid
Which penicillin is effective against beta-lactamase producing staphylococci?
Flucloxacillin
What is the main reason ampicillin is rarely used now?
It is inactivated by beta-lactamase
Why is amoxicillin often given in combination with clavulanic acid?
To extend the spectrum of activity
What is a key structural difference between human cells and bacterial cells?
Human cells have a membrane-bound nucleus while bacterial cells do not.
Which type of bacteria has a poorly-defined cell wall and does not hold the Gram stain?
Atypical bacteria
What is the main purpose of the Gram stain in classifying micro-organisms?
To classify them based on their cell wall characteristics
Which component of bacterial cells is essential to their survival?
Peptidoglycan in the cell wall
What is the difference in staining outcome between typical and atypical bacteria with the Gram stain?
Typical bacteria stain red/pink, while atypical bacteria remain colorless.
What characteristic distinguishes most bacterial species classified as Gram-positive from those classified as Gram-negative?
Color in the Gram stain
What is the main structural component of bacterial cell walls, essential for their survival?
Peptidoglycan
Which type of bacteria do not hold the Gram stain due to their poorly-defined cell wall?
Chlamydia
What is the main purpose of the Gram stain in microbiology?
To classify microorganisms based on cell wall characteristics
Why are penicillins primarily used to treat Gram-positive bacterial infections?
They bind to peptidoglycan in the thick cell walls of Gram-positive bacteria
What distinguishes most bacterial species classified as Gram-positive from those classified as Gram-negative?
Thickness of the cell wall
What is the measure of antimicrobial susceptibility that indicates the lowest concentration of an antimicrobial that inhibits bacterial growth?
MIC (Minimum Inhibitory Concentration)
Why must the minimum inhibitory concentration (MIC) be exceeded for antibacterial agents to be effective?
To inhibit the growth of micro-organisms
What is the main difference between minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)?
MIC is higher than MBC for bacteriostatic agents, MBC is higher for bactericidal agents
Why is ampicillin rarely used now?
It has low absorption properties
Why are penicillins like Benzylpenicillin and Phenoxymethylpenicillin given orally?
They are stable against gastric acid
Why are the antipseudomonal penicillins, piperacillin and ticarcillin, administered with an aminoglycoside in Pseudomonas septicaemias?
To create a synergistic effect against Pseudomonas aeruginosa
Which penicillin is effective against beta-lactamase producing staphylococci?
Flucloxacillin
Test your knowledge on antimicrobial agents by understanding the differences between human and bacterial cells, the main sites of bacterial cell affected by antimicrobial agents, MIC and MBC measures, and the main issues for each class of antimicrobial agents.
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