USMS Bacterial Library
Bacteria are prokaryotic (no organized nucleus), single-celled (0.2-10 um) organisms.
Bacteria are divided into five basic groups based on morphology (shape): coccus, bacillus, spiral, coryneform, and filamentous. When bacteria are Gram-stained, they may be further classified as Gram-positive, Gram-negative, or Gram-variable depending on the ability of their cell walls to hold a specific type of stain. Gram-positive bacteria stain blue-purple and Gram-negative bacteria stain red.
Bacterial names are based on the binomial system: the first name is the genus, the second name is the species. When written, the genus name is capitalized and the species name is not. Both genus and species names are italicized (e.g., Escherichia coli). A genus is a group of related species. A species is a group of microorganisms that have similar genotypic and phenotypic characteristics.