Antibiotics bacterial cell metabolism inhibitors

In general, penicillins exert their biological effect, as do the other p-lactams, by inhibiting the synthesis of essential structural components of the bacterial cell wall. These components are absent in mammalian cells so that inhibition of the synthesis of the bacterial cell wall structure occurs with little or no effect on mammalian cell metabolism. Additionally, penicillins tend to be irreversible inhibitors of bacterial cell-wall synthesis and are generally bactericidal at concentrations close to their bacteriostatic levels. Consequendy penicillins have become widely used for the treatment of bacterial infections and are regarded as one of the safest and most efficacious classes of antibiotics. 

An extensive database has demonstrated that many chemicals that are positive in this test also exhibit mutagenic activity in other tests. There are, however, examples of mutagenic substances, which are not detected by this test reasons for these shortcomings can be ascribed to the specific nature of the endpoint detected, differences in metabolic activation, or differences in bioavailability. On the other hand, factors which enhance the sensitivity of the bacterial reverse mutation test can lead to an overestimation of mutagenic activity. The bacterial reverse mutation test may not be appropriate for the evaluation of certain classes of chemicals for example, highly bactericidal compounds (e.g., certain antibiotics) and those which are thought (or known) to interfere specifically with the mammalian cell replication system (e.g., some topoisomerase inhibitors and some nucleoside analogues). In such cases, mammalian mutation tests may be more appropriate. 

Inhibitors are substances that tend to decrease the rate of an enzyme-catalysed reaction. Although some act on the substrate, the discussion here will be restricted to those inhibitors which combine directly with the enzyme. Inhibitors have many uses, not only in the determination of the characteristics of enzymes, but also in aiding research into metabolic pathways where an inhibited enzyme will allow metabolites to build up so that they are present in detectable levels. Another important use is in the control of infection where drugs such as sulphanilamides competitively inhibit the synthesis of tetrahydrofolates which are vitamins essential to the growth of some bacteria. Many antibiotics are inhibitors of bacterial protein synthesis (e.g. tetracyclin) and cell-wall synthesis (e.g. penicillin). 

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