Coccus bacteria, known as cocci, are oval-shaped or spherical bacteria. When cocci divide or reproduce they create different patterns, depending on the type. Types of coccus bacteria include Diplococcus bacteria, Streptococcus bacteria, Staphylococcus bacteria and Enterococcus bacteria. They are named depending on how their bacterial cells are arranged.

While coccus bacteria are generally round or spherical, rod bacteria (bacillus) are cylindrical or rod-shaped. Examples of rod bacteria are ​Escherichia coli​ (​E. coli​) and ​Bacillus subtilis​ (​B. subtilis​).

​E. coli​, a large, varied group of bacteria, are found in the environment, intestines and food of humans and animals. While most ​E. coli​ strains are harmless, others can cause diarrhea, urinary tract infections, pneumonia and respiratory illness.

​Bacillus subtilis​ are pervasive bacteria commonly found in areas of air, soil and water that are not toxic or pathogenic to the environment, and as such do not pose danger to plants, animals or humans. Some strains of ​B. subtilis​ are registered as microbial pesticides.

If you've seen bacteria described as gram-positive or gram-negative, this simply comes down to the bacterial organism's protective outer covering, known as a membrane. Gram-negative bacteria have a thin but difficult to penetrate membrane, while gram-positive bacteria have a large, thick membrane. The properties of a gram-negative bacterial membrane makes it particularly resistant to antibiotics.

Diplococcus bacteria (diplococci) are arranged in pairs, i.e. the two coccus cells are connected. This type of bacteria may be gram-positive or gram-negative. They can cause gonorrhea (​Neisseria gonorrhoeae​), pneumonia (​Diplococcus pneumoniae​) and a type of meningitis (​Neisseria meningitidis​).

Streptococcus bacteria (streptococci) are arranged in chains or rows, which vary in length. Many are hemolytic, meaning the attack red blood cells in the body. This gram-positive bacteria can cause many diseases, including pneumonia, scarlet fever, rheumatic fever, the skin disorder erysipelas, strep throat and tooth decay.

Staphylococcus bacteria (staphylococci) are arranged in grape-like clusters of cells. They are gram-positive, non-motile and have a high salt tolerance. Staphylococcus species growth is normal in skin and mucous membranes but they can cause disease when introduced into normally sterile sites in the body, causing abscesses, wound infections, toxic shock syndrome, skin infections and, most commonly, food poisoning.

Enterococcus bacteria (enterococci) are arranged in pairs or short chains. They are gram-positive, non-motile and found in the enteric nervous system. While enterococci have a limited potential to cause disease, they can cause urinary tract infections, bacteremia (bacteria in the blood) and wound infections.