Magnetic Field and Biot-Savart Law

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Questions and Answers

Why might physicians not invariably prescribe antimicrobials with the broadest zone of inhibition?

  • To prevent the development of 'superbugs' resistant to multiple antibiotics.
  • Broad-spectrum antibiotics are invariably more expensive.
  • To minimize disruption of the patient's normal microbiota. (correct)
  • Because narrow-spectrum antibiotics are more effective against viral infections.

A researcher is evaluating a new antibiotic. They perform a series of MIC and MBC tests. If the MIC is smaller than the MBC, which statement is most accurate?

  • The antibiotic is more effective at preventing bacterial growth than at killing the bacteria. (correct)
  • The antibiotic is more effective at killing bacteria than preventing bacterial growth.
  • The antibiotic will only be effective against Gram-positive bacteria.
  • The antibiotic is bacteriostatic at the tested concentrations.

A bacterium exhibits resistance to a beta-lactam antibiotic through enzymatic degradation. Which of the following mechanisms is most likely responsible for this resistance?

  • The bacterium produces an enzyme that alters the antibiotic's target site preventing binding.
  • The bacterium produces beta-lactamase, hydrolyzing the beta-lactam ring. (correct)
  • The bacterium actively pumps the antibiotic out of the cell before it can bind to its target.
  • The bacterium has altered its cell wall structure to prevent antibiotic entry.

Which mechanism of action is LEAST likely to be associated with selective toxicity (harming microbes but not the host)?

<p>Disruption of cytoplasmic membranes that contain sterols. (A)</p> Signup and view all the answers

Why is understanding the mechanisms of antimicrobial action important for preventing the development of drug resistance?

<p>It allows for the development of strategies to bypass or counteract resistance mechanisms. (D)</p> Signup and view all the answers

A patient is prescribed an antimicrobial drug that inhibits protein synthesis. Which cellular component is most likely targeted by this drug?

<p>The ribosome. (A)</p> Signup and view all the answers

How do bacteria in biofilms resist antimicrobials?

<p>All of the above. (D)</p> Signup and view all the answers

Why are fungal infections often more difficult to treat than bacterial infections?

<p>Fungal cells are structurally and metabolically more similar to human cells. (B)</p> Signup and view all the answers

Why is it important to avoid prescribing antimicrobials prophylactically (i.e., in the absence of infection) when they aren't needed?

<p>Prophylactic use increases the risk of antimicrobial resistance and disruption of the microbiome. (B)</p> Signup and view all the answers

Reverse transcriptase inhibitors are used to treat which type of infection?

<p>Retroviral (A)</p> Signup and view all the answers

Flashcards

Broad-spectrum agents

Agents that are selectively toxic against a wide range of pathogens

Minimum Inhibitory Concentration (MIC)

The lowest concentration of a drug that inhibits microbial growth

Adverse Effects of Antimicrobials

Toxic effects on the kidneys, liver, or nerves due to antimicrobial drugs.

Bacitracin

Blocks transport of NAM and NAG from cytoplasm

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Disruption of Cytoplasmic Membranes

Some drugs form channels through cytoplasmic membrane and damage its integrity.

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Mupirocin

Selectively binds to isoleucyl-tRNA synthetase

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Inhibit Nucleic Acid Synthesis

Drugs that block DNA replication or RNA transcription.

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Antagonism of drug

Antagonism occurs when drugs interfere with each other.

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Study Notes

Magnetic Field Created by an Electric Current

Biot–Savart Law

  • Defines the magnetic field $d\overrightarrow{B}$ created by a current element $Id\overrightarrow{s}$ at a point P at distance r.
  • $d\overrightarrow{B} = \frac{\mu_0}{4\pi} \frac{Id\overrightarrow{s} \times \hat{r}}{r^2}$
  • $\mu_0 = 4\pi \times 10^{-7} Tm/A$ represents the permeability of free space.
  • The total magnetic field is the integral of the expression for $d\overrightarrow{B}$: $\overrightarrow{B} = \int d\overrightarrow{B}$.
  • $d\overrightarrow{B}$'s direction is perpendicular to both $d\overrightarrow{s}$ and $\hat{r}$.
  • The magnitude of $d\overrightarrow{B}$ is inversely proportional to $r^2$ (r = distance from current element to point P).
  • The magnitude of $d\overrightarrow{B}$ is proportional to the current I and the length of the element $d\overrightarrow{s}$.
  • The magnitude of $d\overrightarrow{B}$ is proportional to $sen\theta$ ($\theta$ is the angle between $d\overrightarrow{s}$ and $\hat{r}$).
  • The magnetic field dB is zero at points along the wire's extension ($\theta = 0$).

Ampère's Law

  • The line integral of $\overrightarrow{B} \cdot d\overrightarrow{s}$ around any closed path equals $\mu_0 I$.
  • I is the total current through any surface bounded by the closed path: $\oint \overrightarrow{B} \cdot d\overrightarrow{s} = \mu_0 I$.
Strategy to Solve Problems
  • Ampère's law is suited for calculating magnetic fields from current distributions with high symmetry.
  • Select a closed path where the magnetic field is constant where $\overrightarrow{B} \neq 0$.
  • Where the magnetic field is tangent to the path, $\overrightarrow{B} \cdot d\overrightarrow{s}$ simplifies to $Bds$.
  • Where the magnetic field is perpendicular to the path, $\overrightarrow{B} \cdot d\overrightarrow{s} = 0$.
  • Where the magnetic field is zero, the integral of $\overrightarrow{B} \cdot d\overrightarrow{s}$ over that portion of the path is also zero.

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