Chloramphenicol was originally isolated from the soil bacterium Streptomyces venezuelae in 1947. Chloramphenicol and a congener thiamphenicol [T2802] can now be made by chemical synthesis. Chloramphenicol has a highly stable which can be stored for prolonged times at room temperature. It has a broad spectrum of antibiotic activity including Staphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli, while it is not effective against Pseudomonas aeruginosa. Chloramphenicol inhibits protein synthesis in susceptible organisms by binding to specific nucleotides in 23S rRNA within the 50S subunit of a bacterial ribosome. However, chloramphenicol causes side effects including bone marrow suppression and aplastic anemia. Chloramphenicol is used in molecular biology as a selective reagent most commonly to isolate bacteria coupled to a gene coding for chloramphenicol resistance, which is one of the most frequently used selection markers for obtaining transgenic cells.