Bacteria are classified into 5 groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), comma (vibrios) or corkscrew (spirochaetes). They can exist as single cells, in pairs, chains or clusters.Bacterial kingdoms are part of the classification scheme that fits bacteria into appropriate groupings based on certain criteria. The kingdom is the broadest classification category. There are two kingdoms of prokaryotes. These are the bacteria (or eubacteria ) and the archaebacteria (or the Archaea ))