Antibiotics (or antibacterials) are substances that are capable of either killing bacteria or inhibiting bacterial growth but are not effective against viruses. They are widely used as drugs to treat diseases caused by bacterial infections like tuberculosis, meningitis or salmonella infections. Antibiotics are grouped into families, with Penicillins being one of the first discovered antibiotics.
The antibacterial effect is mediated through different mechanisms:
• Binding to the bacterial 30S ribosomal subunit with subsequential inhibition of protein synthesis (e.g. Aminoglycosides)
• Inhibition of the synthesis of the peptidoglycan layer in bacterial cell walls (e.g. Penicillins)
• Inhibition of protein synthesis by preventing the initiation step of translation (e.g. Oxazolidinones)
• Preventing DNA replication and transcription by inhibition of the DNA gyrase or the topoisomerase IV (e.g. Quinolones)
• Folate synthesis inhibition resulting in the disability to synthesize nucleic acids (e.g. Sulfonamides)
Antibiotics are very effective to handle bacterial diseases and are readily available. This results in an overuse and an increasing resistance of bacteria against antibiotics. Especially in the animal husbandry antibiotics are routinely used.
In research, antibiotics are of high importance for various techniques.
In molecular cloning procedures, they are used to distinguish between bacteria that have incorporated exogenous DNA through transformation and bacteria where transformation has failed. The selection is achieved by introducing an antibiotic resistance into the bacteria together with the genetic modification. Only successfully transformed cells are able to survive on the antibiotic supplemented agar plates.
Protein Synthesis/Gene Expression
For the synthesis of recombinant proteins or conditional gene expression, systems that alter the expression of specific genes depending on the presence or absence of an antibiotic are available. One example of such a system is the Tet-On system which switches on gene expression in the presence of tetracycline or the more stable derivate doxycycline. These systems may also be used in generating transgenic mice with a conditionally expressed gene of interest.
In cell culture, you may use a mix of penicillin and streptomycin (Pen-Strep) to decrease the risk of bacterial infection of your cell lines. Many cell lines are contaminated with Mycoplasma, a genus of bacteria which lack a cell wall. When detected, you can treat a Mycoplasma infection with several antibiotic-containing antimycoplasma reagents.