Antimicrobial Agents Quiz

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Questions and Answers

What is the minimum inhibitory concentration (MIC)?

The concentration needed to kill 99.9% of the original inoculum
The concentration that is many dilutions higher than MBC for bacteriostatic agents
The concentration needed for visible growth of a microorganism to be inhibited (correct)
The concentration at which beta-lactamase is produced by bacteria

Why are penicillins used mainly to treat Gram-positive bacterial infections?

Most staphylococci are resistant to benzylpenicillin
They have a poor spectrum of activity
They are resistant to beta-lactamases (correct)
They are lipids soluble

Why is benzylpenicillin given by injection rather than orally?

It has a poor spectrum of activity
It is inactivated by gastric acid (correct)
It has a high MIC
It is lipids soluble

Which penicillin is effective against beta-lactamase producing staphylococci?

Flucloxacillin (B) Signup and view all the answers

What is the main reason ampicillin is rarely used now?

It is inactivated by beta-lactamase (B) Signup and view all the answers

Why is amoxicillin often given in combination with clavulanic acid?

To extend the spectrum of activity (B) Signup and view all the answers

What is a key structural difference between human cells and bacterial cells?

Human cells have a membrane-bound nucleus while bacterial cells do not. (A) Signup and view all the answers

Which type of bacteria has a poorly-defined cell wall and does not hold the Gram stain?

Atypical bacteria (D) Signup and view all the answers

What is the main purpose of the Gram stain in classifying micro-organisms?

To classify them based on their cell wall characteristics (D) Signup and view all the answers

Which component of bacterial cells is essential to their survival?

Peptidoglycan in the cell wall (C) Signup and view all the answers

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. (B) Signup and view all the answers

What characteristic distinguishes most bacterial species classified as Gram-positive from those classified as Gram-negative?

Color in the Gram stain (C) Signup and view all the answers

What is the main structural component of bacterial cell walls, essential for their survival?

Peptidoglycan (B) Signup and view all the answers

Which type of bacteria do not hold the Gram stain due to their poorly-defined cell wall?

Chlamydia (A) Signup and view all the answers

What is the main purpose of the Gram stain in microbiology?

To classify microorganisms based on cell wall characteristics (C) Signup and view all the answers

Why are penicillins primarily used to treat Gram-positive bacterial infections?

They bind to peptidoglycan in the thick cell walls of Gram-positive bacteria (A) Signup and view all the answers

What distinguishes most bacterial species classified as Gram-positive from those classified as Gram-negative?

Thickness of the cell wall (B) Signup and view all the answers

What is the measure of antimicrobial susceptibility that indicates the lowest concentration of an antimicrobial that inhibits bacterial growth?

MIC (Minimum Inhibitory Concentration) (D) Signup and view all the answers

Why must the minimum inhibitory concentration (MIC) be exceeded for antibacterial agents to be effective?

To inhibit the growth of micro-organisms (D) Signup and view all the answers

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 (D) Signup and view all the answers

Why is ampicillin rarely used now?

It has low absorption properties (D) Signup and view all the answers

Why are penicillins like Benzylpenicillin and Phenoxymethylpenicillin given orally?

They are stable against gastric acid (D) Signup and view all the answers

Why are the antipseudomonal penicillins, piperacillin and ticarcillin, administered with an aminoglycoside in Pseudomonas septicaemias?

To create a synergistic effect against Pseudomonas aeruginosa (B) Signup and view all the answers

Which penicillin is effective against beta-lactamase producing staphylococci?

Flucloxacillin (B) Signup and view all the answers

Flashcards

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial that inhibits bacterial growth.

Gram-positive bacteria

Bacteria that stain purple in the Gram stain due to a thick cell wall.