<span>Field of the invention: The invention relates to screening compounds for antimicrobial activity, and, more particularly, to using bacterial proteins in vitro to detect compounds that interfere with cell division. Background: Antimicrobials are developed on the principle of selective toxicity. That is to say, antimicrobials, while toxic to the microorganism, must not be toxic to the patient. The selective toxicity of these drugs is usually relative, rather than an absolute. This means simply that most drugs are given to patients in concentrations that are tolerated by the patient, but are lethal or damaging to the microorganism; higher doses would be toxic to the patient and are avoided. Selective toxicity is often a reflection of the presence of specific receptors present on the microorganism, but lacking in the host system. Other means to achieve selective toxicity commonly rely on the inhibition of biochemical events essential to the microorganism but not the host. As the physiology, structure, and biochemical systems of infectious agents and their hosts are usually quite different, antimicrobial development often relies on these differences. Although the mechanisms of action of many antimicrobials are not well understood, the five major categories of action include inhibition of cell wall synthesis, inhibition of cell membrane function, inhibition of protein synthesis, inhibition of nucleic acid synthesis, and interference with intermediary metabolism. (See e.g., W. K. </span><span>Joklik et al., [eds.], Zinsser Microbiology, 18th ed., Appleton-Century-Crofts, Norwalk, Conn., [1984], p. 193). For example, penicillin, like all .beta.-lactam drugs, is a compound which selectively inhibits bacterial cell wall synthesis. The initial step in the mechanism of action of these .beta.-lactam drugs involves the binding of the drug to cell receptors known as "penicillin-binding proteins" ("PBP"). There are from 3-6 PBPs, with molecular weights ranging from 4-12.times.10.sup.5 ; some of these PBPs are transpeptidation enzymes. (Jawetz, Melnick \A Adelberg&apos;s Medical Microbiology, 19th ed, Appleton \A Lange, Norwalk, Conn. [1991], p. 150). After binding to the PBP, the drug inhibits the transpeptidation reaction and synthesis of peptidoglycan in the organism&apos;s cell wall material is blocked. This results in the eventual triggering of an autolytic cascade which leads to cell lysis. Because of their relatively high concentration of peptidoglycan, gram-positive organisms tend to be much more susceptible to the effects of penicillin and other .beta.-lactams than gram-negative organisms. Importantly, because they affect cell wall synthesis, penicillin and the other .beta.-lactams are only effective against actively growing and dividing cultures. However, one of the benefits of these .beta.-lactam drugs is that animal cells do not have peptidoglycan; consequently, such drugs are remarkably non-toxic to humans and other animals.http://www.google.com/patents?vid=USPAT6809180</span>

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