Lipopolysaccharides are substances that have both lipid and polysaccharide. LPS layer is the characteristic feature of gram-negative bacteria. The LPS layer is present in the outer membrane of the cell envelope of gram-negative bacteria. It is not found in Gram-positive bacteria.
Broad-spectrum drugs are the chemotherapeutic agents that are effective against several kinds of pathogens while the narrow spectrum drugs target only a limited type of microbes. Therefore, an antibiotic that attacks the LPS layer would be effective against Gram-negative bacteria only which in turn makes it a narrow-spectrum drug.
