The major characteristics of coccus bacteria are its spherical or oval shape and the ability to live on its own or in colonies. Like many forms of bacteria, coccus bacteria can be positive or negative, depending on the strain.
The Greek term coccus refers to the rounded shapes of cocci bacteria. Coccus has the ability to exist either as a single cell or in clusters. This unique ability makes it easy for cocci to spread. Some strains of cocci arrange themselves in chains known as streptococci, and in irregular clusters known as staphylococci. While some cocci are harmless and occur naturally in the human body, others are pathogenic and capable of causing illness. Some are gram-stain positive while others are not. According to “Bacterial Pathogens of Humans,” pathogenic coccus bacteria is the leading cause of many common infections. For instance, Staphylococcus aureus, a common culprit in food poisoning, also causes pneumonia, meningitis and toxic shock syndrome. About 20 percent of the human population carries Staphylococcus aureus. Another common pathogen, Streptococcus pneumoniae, which causes pnemonia and meningitis, also causes sinusitis, otitis, sepsis, endocarditis and peritonitis. Streptococcus pyogenes, which causes strep throat, also causes rheumatic fever, scarlet fever and necrotizing flesh-eating fasciitis.