Antibiotics: Overview

Antibiotics are low molecular weight secondary metabolites produced by certain strains of bacteria (mainly Bacillus species) and fungi (above all Streptomycetes). At low concentrations, they are either bactericidal by killing other microorganisms or bacteriostatic by reversibly inhibiting growth. The concept of antibiotics includes today also chemically or biochemically synthesized derivatives as well as substances from plants and animals with antibiotic activity. Antibiotics can be classified according to their mechanism ofaction. The major targets in the cell are:

Cell Wall Synthesis

Transcription and replication of genetic material

Protein synthesis

Structure and function of cell membranes

Besides, antibiotics can interact quite specifically in various metabolic pathways. In the research area, antibiotics are used in cell culture toprevent the growth of contaminating bacteria, fungi and mycoplasma. In Molecular Biology, some antibiotics can be used for the selection of resistant cell clones. Due to their specific mechanism of action, antibiotics are alsovaluable tools in the elucidation of cellular functions. In the following section, our antibiotics program is listed according to their mechanism of action.

The table on pages 144-145 lists some of the antibiotics frequently used in mammalian cell culture. It contains useful information about recommended and toxic concentrations,solubility and stability of these substances. All products are listed according to their mechanism of action and their chemical structure.

The indicated concentrations are approximate values in serum containing media. In practice, they may be influencedby various factors, e.g. composition of the medium, cultivated cells, resistance of contaminants etc.

Some comments may elucidate this: Many antibiotics bind toserum proteins, especially to albumin. This decreases thenumber of free molecules that can interfere with microorganisms. In serum- or albumin-free media, the recommended concentration should therefore be reduced by 1/3.

The pH of the medium is another factor which can influenceantibiotic activity. Non-ionized compounds diffuse betterthrough the cell wall and cytoplasmic membrane than do ionized ones. As the pH affects the degree of ionization of abasic or acidic antibiotic, it can influence directly its rate ofpenetration into the microorganism and hence its efficiency.
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