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Abstract

Introduction

Unlike physicians practicing in the 1940s, who had only sulfonamides and penicillin to treat infections, practitioners now choose from a broad (and sometimes overwhelming) number of antibiotics. However, trends in emerging antimicrobial resistance may force us to take a giant step backward to that frightening situation of the past of having bacteria that are essentially "untreatable" by any of our available antibiotics.

This article is an overview of some of the microbiology, pharmacology, and physiology critical to the rational use of antibiotics in today's practice. It summarizes the basic mechanisms of action of some commonly used antibiotics and briefly discusses the emergence of resistance to several common pathogens.

Structures of Bacteria Important to Antibiotic Action

The outermost component of most bacteria is the cell wall, a multilayered structure located external to the cytoplasmic membrane. The cell wall is composed of an inner layer of peptidoglycan, a complex interwoven lattice of linear sugars (glycan) that are cross-linked by peptide chains. Peptidoglycan provides the rigid support by which the cell maintains its characteristic shape.

Gram-positive and Gram-negative bacteria differ in their cell wall structures (Figure). In Gram-positive organisms, the peptidoglycan layer is a thick (15 to 80 nm) multilayer and may have a thin layer of teichoic acid outside the peptidoglycan.