Bacteria are minute single-celled plants. They lack chlorophyll and depend on other sources for their food. Bacteria come in three shapes: elongated rods called bacilli, rounded or spherical cells called cocci, and spirals called spirilla and spirochaete.
These are round or oval bacteria measuring about .5 – 1. um in diameter. The spherical shaped bacterial may occur singly, in pairs, in tetrads, in chains, and in irregular masses. An association of two such cells is known as diplococcus, a short chain as streptococcus and an irregular arrangement to give an appearance of a bunch is called staphylococcus.
Bacterial pneumonia is caused by cocci bacteria. Sometimes, eight or more cells may form a cuboidal or packet arrangement called as sarcina.
Staphylococcus are the most common (pus producing) microorganisms. Staphylococci cause infections such as boils, urinary tract infections, wound infections and toxic stock.
Coccus or spherical shaped bacteria
