Primarily, it detects peptidoglycan, which is present in a thick layer in Gram-positive bacteria. ... In Gram-positive bacteria, the cell wall is thick (15-80 nanometers), and consists of several layers of peptidoglycan. They lack the outer membrane envelope found in Gram-negative bacteria.
Link:https://courses.lumenlearning.com/boundless-microbiology/chapter/cell-walls-of-prokaryotes/
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