Cocci Bacteria: Definition, Types & Diseases Caused by Cocci Bacteria

Coccus is a spherical-shaped bacterium known as a cocci in microbiology. There are a variety of bacterial species, and it is often possible to identify them by their distinctive configurations. Diplococci is a word used to describe pairs of cocci. 

• According to the basic morphologies, bacteria can be divided into five groups.
• For example, spherical (cocci), rod-shaped (bacilli), spiral-shaped (spirilla), comma-shaped (vibrios), or corkscrew-shaped (spirochaetes). 
• They may occur as single cells, pairs, chains, clusters, or chains of cells.
• Cocci can cause certain diseases in humans.
• Pneumonia and UTI (urinary tract infection) are common examples of it.

Key terms: Coccus, Cocci, Diplococci, Staphylococcus, Enterococci, Bacteria, Tetrads, Streptococcus, Gram-Positive, Gram-Negative.

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Definition of Cocci Bacteria

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Any bacteria or archaeon with a round, spherical, or ovoid shape is referred to as a coccus (plural cocci). 

• Staphylococci and Streptococci are two species that are found within the coccus genus of bacteria. 
• Cocci can grow in pairs, chains, or clusters based on their adhesion and position during cell division. 
• Unlike numerous bacilli-shaped bacteria, most cocci bacteria are non-motile and do not contain flagella.

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Structure of Cocci Bacteria

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Cocci might have different structural characteristics for gram-positive and gram-negative types. Additionally, both types of cocci might have different cell formations as well. Cocci are organisms that reside on their host's body and can be commensal or harmful.

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Gram-Positive and Gram-Negative Cocci

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Cocci that turns positive for gram-staining are classified as Gram-Positive cocci bacteria. They have a thick peptidoglycan layer in their cell wall. Common examples of Gram-Positive Cocci are Staphylococcus, Blantia, Ruminococcus, and Streptococcus.

• The diverse gram-positive cocci vary in habitat and physiology. 
• Human skin is home to obligate aerobes called Micrococcus spp. 
• Despite being facultative anaerobes, Staphylococcus species also live on human skin.
• They produce lactic acid as a byproduct of glucose fermentation.
• These species produce a lot of carotenoids, which give their colonies yellow or orange color. 

There are some cocci that do not retain violet stain during gram-staining. They uptake the counterstain- Safranin and appear red in color. These are called Gram-Negative Cocci. Their cell walls have a thin peptidoglycan layer. Examples of Gram-Negative bacteria are Anaeroglobus, Acidaminococcus, Veillonella, Megasphaera, and Negativococcus.

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Types of Cocci Bacteria

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Cocci can exist as solitary cells or as connected cells after cell division. Based on cellular configuration, those that stay connected can be divided into the following categories:

• Cocci that are in pairs are known as diplococci.
• Streptococcus pneumoniae and Neisseria gonorrhoeae grow in pairs.
• Chains of cocci make up streptococci.
• Streptococcus pyogenes is an example of streptococci.
• Staphylococci are those that grow as irregular (grape-like) clusters of cocci.
• Tetrads that are found in Micrococcus species, are collections of four cocci organized on a single plane.
• Bacteria belonging to the genus Sarcina are found in cuboidal formations of eight cocci.
• Sarcina ventriculi is one of the Sarcina genus of cocci.

Types of Cocci Bacteria

Also read: Infectious Diseases 

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Diseases Causing Cocci Bacteria

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Cocci are known to cause various infections in the human body. Few of them are described below.

Staphylococcus

Staphylococcus bacteria cause staph infections. Many healthy people frequently have these kinds of germs on their skin or in their noses. Most of the time, these bacteria just cause mild skin illnesses.

Peptostreptococci

Humans have commensal Peptostreptococcus species, which are part of the gut microbiota and mostly inhabit the mouth, skin, gastrointestinal, vaginal, and urine tracts. These microorganisms can develop septicemic and pathogenic characteristics under immunosuppressed or stressful situations. It can be harmful to the host. In addition to necrotizing soft tissue infections, peptostreptococcus can result in abscesses in the brain, liver, breast, and lungs.

Pneumococcus

Streptococcus pneumoniae, often known as pneumococcus, is the bacterium that causes pneumococcal illness. Those who have pneumococcal illness can spread the bacterium to others when they cough or sneeze. The bacteria pneumococcus can infect several bodily areas including Lungs (Pneumonia). 

Enterococci

Enterococci are Gram-positive, facultative anaerobic organisms. Numerous diseases, including endocarditis, urinary tract infections, prostatitis, intra-abdominal infections, cellulitis, and wound infections as well as concomitant bacteremia, are caused by Enterococcus faecalis and E. faecium.

Also Read:

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Things to Remember

• Bacteria can be classified according to their fundamental shapes.
• The bacteria can be either spiral, bacillus, vibrios, spirochaetes or coccus.
• The coccus’ shape and growth type can classify them in diplococcus, streptococcus, tetrad, sarcina, or staphylococcus.
• Cocci includes both Gram-positive and Gram-negative bacteria.
• Cell wall and cellular structure of both types of cocci may differ from each other.
• Most cocci bacteria are non-motile and lack flagella.
• Cocci like streptococcus, Pneumococcus, Enterococcus causes infections in the human body.