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The Mode of Action of Antibiotics on Gram-Negative Bacilli

Victor Lorian, MD
Arch Intern Med. 1971;128(4):623-632. doi:10.1001/archinte.1971.00310220131022.
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The mode of action of any antibiotic is essentially the same, whether it is against gram-positive or gram-negative microorganisms.1,2

In order to present a schematic version of the modes of action, I will try to give just enough molecular and biochemical information to facilitate understanding without burdening the reader with unnecessary details. The illustrations are more diagrammatic than the expression of the real stereomodel of the many biochemical reactions described. Data presented in this manner is more relevant to the practical aspects of antibiotic tests in vitro as well as in the treatment of patients.

As the mode of action of antibiotics is conditioned in part by the bacterial anatomy of the microorganism and its chemical constituents, let me point out a few essential differences between the gram-positive and gram-negative organisms.

Figure 1 schematically pictures a gram-positive coccus and a gram-negative bacillus. The gram-positive organism has a thick


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