Cell wall structure of Gram-negative bacteria and their susceptibility to antibiotics.
Gram-negative bacteria are a class of bacteria characterized by an outer layer of LPS (lipopolysaccharide) which does not allow retention of crystal violet stain during the Gram stain process. Gram-negative bacteria do synthesize peptidoglycan; however, the peptidolycan layer is sandwiched between an inner and outer membrane and is not directly exposed to the environment. Because of the outer LPS layer and hidden peptidoglycan layer, certain antibiotics are ineffective against Gram-negative bacteria. Well-known Gram-negative genera include Escherichia (includes E. coli), Pseudomonas, Neisseria (includes N. gonorrhoeae), Klebsiella, Proteus, Enterobacter, and Haemophilus.
The following antibiotics are effective against Gram-negative bacteria.