[Campbell Biology P.263] Considering the 'Your Data' and 'Your Approach' sections, what can ... | Practice Question

Considering the 'Your Data' and 'Your Approach' sections, what can be hypothesized about the quorum-sensing pathways based on the combined effect of Peptides 1 and 2, and its implication for treating S. aureus infections?

  • A: Peptides 1 and 2 likely act on the same quorum-sensing pathway because their combined effect is less than the sum of their individual effects, suggesting competitive inhibition, which makes them a poor candidate for combined therapy.
  • B: Peptides 1 and 2 likely act on two different quorum-sensing pathways, or on different steps within the same pathway, because their combined effect is substantially greater than either peptide alone, suggesting a synergistic or complementary action. This makes them a promising candidate for treating antibiotic-resistant S. aureus infections.
  • C: The peptides are only effective individually, and their combination leads to no additional benefit, thus they would not be useful for treating S. aureus infections.
  • D: The experiment does not provide enough information to hypothesize about the quorum-sensing pathways, and thus, no conclusions can be drawn regarding their use in treating infections.

Explanation

The problem states that S. aureus quorum sensing involves two separate signal transduction pathways. If peptides 1 and 2 acted on the same pathway, their combined effect might not be significantly greater than the most effective individual peptide, or might even show diminishing returns. However, the data shows that the combined effect of Peptides 1+2 approx. 0.3 µmoles/mL toxin is substantially lower than either Peptide 1 alone approx. 1.0 µmoles/mL or Peptide 2 alone approx. 0.7 µmoles/mL . This synergistic effect strongly suggests that the two peptides interfere with different pathways, or different critical steps within the same pathway, leading to a more comprehensive inhibition of toxin production. Given that S. aureus can be antibiotic-resistant, this new approach targeting quorum sensing without directly killing bacteria and thus reducing selective pressure for resistance is a promising treatment strategy.