Cocci bacteria are spherical or round-shaped microorganisms. They can grow in clusters, chains, or pairs depending on their orientation and attachment during cell division. Cocci bacteria can be divided into gram-positive and gram-negative depending on the gram-staining method. Some of the common cocci bacteria are Staphylococcus aureus, Streptococcus pyogenes, and Neisseria gonorrhoeae. They cause various diseases in humans, including skin infections, pneumonia, endocarditis, septic arthritis, osteomyelitis, and abscesses.
Cocci Bacteria
The word cocci originated from the Greek word kokkos, meaning seed or berry. Bacteria with round, ovoid, and spherical shapes are called cocci bacteria. They belong to various genera, such as staphylococci or streptococci. They can grow in clusters, pairs, or chains depending on their attachment and position during cell division. Most cocci bacteria do not have flagella and are non-motile. Cocci bacteria are present in a variety of species and they are identified and classified based on their morphology or configuration. Some cocci bacteria cause infection and diseases while others are useful in various processes like fermentation and food production.
Examples of Cocci Bacteria
Some example of cocci bacteria are given below:
- Staphylococcus aureus: Responsible for skin infections, abscesses, and more.
- Streptococcus pyogenes: Causes strep throat and other infections.
- Neisseria gonorrhoeae: A sexually transmitted infection causing gonorrhea.
- Micrococcus luteus: A non-pathogenic species found in soil, dust, and on human skin.
- Streptococcus pneumoniae: Commonly associated with pneumonia, sinusitis, and otitis media (ear infections).
- Enterococcus faecalis: Part of the normal gut flora but can cause urinary tract infections and infective endocarditis in humans.
Types of Cocci Bacteria
Cocci after cell division are present either as single cells or remain attached. Those cocci bacteria that remain attached are categorized based on their cellular arrangement and characteristics. These arrangements help in their classification and identification. The various types of cocci are as follows:
- Staphylococci: These bacteria are arranged in the form of grape like clusters. Eg: Staphylococcus aureus
- Streptococci: These bacteria form either pair or chain. E.g:Streptococcus mutans
- Diplococci: These bacteria are arranged in pairs. Eg: Neisseria gonorrhoeae
- Tetrads: These bacteria are present in groups of four. Eg: Micrococcus luteus
- Sarcina: These bacteria are present in groups of eight, forming cubical shape. E.g: Sarcina ventriculi
- Monococci: These are the single cocci present.
Structure of Cocci
Cocci bacteria vary in size from 0.5 to 2 micrometers in diameter. They are round or spherical in shape. Their structure consists of cell wall which consists of thick peptidoglycan layers that provides structural support and protection. After the cell wall, a cell membrane or plasma membrane is present that surrounds the cytoplasm,a site for various essential cellular processes. The DNA is located in the nucleoid, as cocci bacteria lack a true nucleus. Some cocci bacteria may contain plasmids, small circular pieces of DNA. Optional features include a protective capsule, flagella for motility, and pili for attachment or other functions.
Gram Positive Bacteria and Gram Negative Bacteria
Group of bacteria that are positive for gram staining or turns violet are called gram positive bacteria. They share same morphology and have a thick peptidoglycan cell wall, which retains the crystal violet stain during the Gram staining process. Unliken gram negavtive bacteria they lack outer membrane. Gram-positive bacteria include Staphylococcus aureus that is causes disease in humans like skin infection, Streptococcus pyogenes causes strep throat, and Clostridium difficile causes colitis. There certain beneficial species of cocci bacteria like Lactobacillus and Bifidobacterium that form an important part of human gut microbiome and are used in various food processes.
Bacteria which do not retain violet stain during gram-staining are called gram negative bacteria. Instead they take up counterstain like safranin and appear red in colour. Their cell wall contain a thin-peptidoglycan layer. Gram negative bacteria include Acidaminococcus, Veillonella, Megasphaera, and Negativococcus.
Also Read: Difference between Gram Positive and Negative Bacteria
Diseases Caused by Cocci Bacteria
Cocci are major human pathogen and cause various infections that are described below:
- Staphylococcus aureus: Causes various skin infection like boils, cellulities. They cause infection of respiratory tract including pneumonia and bloodstream infection like sepsis. They are also responsible for causing food poisioning due to the production of toxins in contaminated food.
- Streptococcus pyogenes (Group A Streptococcus): Causes common throat infection and various skin infection like cellulitis and necrotizing fasciitis. They are also responsible for Rheumatic fever that is an autoimmune reaction following untreated strep infections.
- Peptostreptococci: They are commensal bacteria present in the human gut, mouth, vagina, urinary tract, etc. They can cause septicemia and abscesses in the brain, liver, breast, and lungs.
- Neisseria gonorrhoeae: Causes Gonorrhea which is a sexually transmitted infection that can affect the genital, rectal, and throat areas.
- Enterococcus faecalis: These are Gram-positive, facultative anaerobic organisms and causes urinary tract infections.