Why is streptomycin more effective against gram negatives?

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A Bradbury

Apr 12, 2005, 7:04:55 AM4/12/05
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I know that streptomycin inhibits protein synthesis, but can anyone
give me more information on how it works and why gram negatives are
more sensitive?

William Knight

Apr 12, 2005, 12:52:29 PM4/12/05
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Streptomycin works by decreasing the accuracy of the decoding step in
protein synthesis. This results in a larger number of incorrect amino
acids that are incorporated into the growing protein chain. It is
believed that the mechanism has to do with the binding of streptomycin
near the decoding center on the 30S subunit of the ribosome, with the
result that it increases the affinity for non-cognate tRNAs into the
A-site (Carter et al, 2000, Nature 407:340-348).

As for why this affects gram negative bacteria more strongly, I can't
say because I'm not familiar enough with the relevant microbiology.
Perhaps gram negative bacteria are more sensitive to certain
incorrectly-synthesized proteins. Another possibility could be that a
mutation that compensates for streptomycin could result in
hyperaccurate phenotypes that make gram-negative bacteria less
competitive/more vulnerable? I'm just speculating at this point. I'm
sure that some microbiologists could offer a better explanation.

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