ABSTRACT
Bacterial cultures are grown either on solid media or in broth. Smears of bacterial cultures are prepared by aseptically transferring a loopful of the material from the broth culture on a clean glass slide. The Gram stain is a differential stain developed by Dr. Hans Christian Gram, a Danish physician, in 1884. The staining is called Gram staining, after Dr. Gram. It is a very useful stain for identifying and classifying bacteria into two major groups: Gram-positive and Gram-negative. Most bacteria have a defined shape that falls into one of three morphological categories: Spherical straight rods and spiral- or corkscrew-shaped organisms. A few bacteria change their shape and are called pleomorphic. The outermost layer of the cytoplasm is called the cytoplasmic membrane. This layer is 75 Å units thick. The cytoplasmic membrane in bacteria is a phospholipids–protein bilayer similar to that present in eukaryotic cells.
