Singular coccus; plural cocci is the type of bacteria which is of spherical, oval or round in shape.
Coccus mainly refers to the bacteria shape and can grow in chains, clusters or pairs depends on their attachments during cell division.
let us discuss some examples of cocci bacteria
- Moraxalla catarrhalis
- Diplococcus pnemoniae
- Enterococcus spp.
- Streptococcus spp.
- Stapylococcus spp.
- Micrococcus spp.
- Sarcina spp.
Bacteria are classified mainly into three types depending on their shapes.
- Cocci – they are spherical in shape
- Bacillus– they are rod or cylindrical in shapes
- Spirochetes– they are spiral in shape
Characteristics of coccus bacteria
The name ‘coccus’ is derived from the Greek word ‘kokkus’ which means Berry. Their size ranges vary from 0.5 to 1.0 µm in diameter. These are smallest and simplest form of bacteria.
Structure of cocci
The cell wall structure of cocci may vary from gram –ve bacteria having thin peptidoglycan layer and Gram +ve bacteria which have thick peptidoglycan layer in their cell wall. Cocci bacteria may be of pathogenic, symbiotic or commensally in nature.
Comparison with other bacteria
Coccus bacteria v/s bacillus bacteria
Coccus bacteria are spherical or oval in shape while bacillus bacteria is of rod or cylindrical in shape e.g., Escherichia coli, Bacillus subtilis.
Gram +ve bacteria v/s Gram –ve bacteria
Bacteria can be differentiated into two categories based on the property of dye attained by bacterial call wall used in gram staining method. Gram –ve bacteria have a thin peptidoglycan cell wall whereas gram +ve bacteria have large, thick membrane.
Types of cocci bacteria
Cocci bacteria can exist in mainly four categories depand on their grouping and arrangement of cocci cell.
- Diplococcus bacteria- As the name indicate ‘diplo’ means in pairs that is when two coccus cells are connected in pairs. They can be of any type gram +ve or gram –ve bacteria. Example – Neisseria gonorrhoea causes disease gonorrhoea, Neisseria meningitidis causes a type of meningitis, Diplococcus pneumoniae causes pneumonia disease.
- Streptococcus bacteria- these are the bacteria arranged in chains or row. The length of chain may vary. These are gram +ve bacteria. Example – Streptococcus pneumonia causes pneumonia, meningitis and bronchitis; Streptococcus pyogene cause tonsilitis and strep throat.
- Staphylococcus bacteria- These are the bacteria are arranged in grape like cluster of coccus cells. These are gram +ve and halo tolerant (can survive at very high concentration of salt). They are also non-motile in nature. Example- Stapylococcus aureus causes pneumonia and skin infection; Staphylococcus epidermis causes common part of normal skin flora; Stapylococcus haemolyticus found in hospital skin infections.
- Enterococcus bacteria- These are the bacteria arranged in pairs or short chains. These are gram +ve, non- motile, and live in enteric nervous system. Enteric bacteria has limited capacity to cause diseases. Example- Enterococcus faecalis and Enterococcus facieum causes infection in intestine.
Arrangement of cocci cells
During the cell division, cocci cells may remain single or attached. Cells which are attached can be divided depend on their arrangement.
- Diplococci – cocci cell are remain in pairs (group of two cells). e.g. Streptococcus pneumoniae and Neisseria gonorrhoeae.
- Streptococci – cocci are present as chains e.g. Streptococcus pyogene.
- Staphylococci – cluster of cocci are irregular like grapes shape e.g. Staphyococcus aureus.
- Tetrad- cluster of four cocci arranged in the same plane e.g Micrococcus sp.
- Sarcina– eight cocci are found to be cuboidal arrangement e.g. Sarcina ventriculi.
Common example of cocci bacteria
Gram negative diplococci – Neisseria spp. And Moraxella catarrhalis.
these are the bacteria that make colony on mucosal surfaces of many animals. Out of 11 species that colonize human but only two are pathogens which are N. meningitis and N. gonorrhoeae. When they are examined under microscopically appeared as coffee beans. N. gonorrhoeae also called gonococcus responsible to causes gonorrhea disease and N. meningitidis also called meningococcus is the common cause of bacterial meningitis and responsible for meningococcal septicaemia
it is a non motile, oxidase positive and aerobic diplococcus that is responsible for infections of central nervous system (CNS), respiratory system, middle ear, eye and human joints.
. Gram negative diplococci– Streptococcus pneumoniae and Enterococcus spp
they are non motile and do not form any find of spores. D. pnemoniae is the significant human pathogenic bacteria were recognised to be cause pneumonia in late 19th century. It lives asymptomatic in healthy carrier mainly in respiratory tract, nasal cavity and sinuses. While in persons with weak immune system like young children and elderly people, it may become pathogenic and cause diseases by spreading to other locations. It can be causative agent of neonatal infections. It spreads by person to person contact directly through respiratory droplets.
Pneumonia diseases caused by the bacteria D.pnemoniae, different type of vaccines have been developed to protect from its infections. The WHO (World Health Organisation) recommends routine pneumococcal vaccinations in childhood.
In the past Enterococcus bacteria thought to be harmless to humans but within last decade, there has been influx of nosocomial pathogens that were originating from Enterococcus bacteria. The bacteria cause enterococcal meningitis, a nosocomial disease. These nosocomial infections (originates from a hospital) also affects the urinary tract (UT) and post- surgical wounds that still in healing condition.
in streptococci, cell division occurs along a single axis, so at successive division they may appear bent or twisted. Most of them are catalase negative, oxidase negative and facultative anaerobes (able to grow in both aerobic and anaerobic conditions).
In addition to streptococcal pharyngitis (strep throat) certain type of Streptococcus species causes many diseases like pink eye, meningitis, bacterial pneumonia, endocarditic, necrotizing fasciitis (flesh eating bacterial infection) and erysipelas.
Many species of streptococcal are not pathogenic whereas commensally human microbiota of skin, mouth, upper respiratory tract and intestine. Streptococci bacteria are also helpful in producing Emmentaler (swiss) cheese.
Streptococcus species further classified based on their hemolytic properties.
- Alpha-haemolytic species – these are species which cause iron oxidation in haemoglobin molecules within red blood cells.
- Beta-haemolytic species- species that cause complete red blood cells (RBCs) rupture.
- Gamma-haemolytic species – these species do not causes any type of haemolysis
they appear spherical (cocci) and form in the grape like cluster. Staphylococcus species are facultative anaerobic (able to grow in both aerobic and anaerobic conditions).
Many species cannot cause diseases and inhabit normally on skin and mucous membrane of human and other animals. Certain species found to be nectar inhabiting microbes and also a small component of soil microbiome.
Two species of Stapylococcus (S.epidermidis and S. arlettae) identified as halotolerant (salt tolerant).
these are species found in a wide range of environments like soil, water and dust. These are gram- positive spherical cells vary from 0.5 to 3 µm in diameter and typically arranged in tetrad. They are oxidase positive, catalase positive, citrate negative and indole negative.
Earlier Micrococcus is thought to be a commensal or saprotrophic bacteria but it can be an oppotunistic pathogen, which particularly found in the hosts with compromised (weak) immune systems, such as HIV patients. Micrococci may be involved in many type of other infections like recurrent bacteremia, septic arthritis, septic shock, meningitis, endocarditis and cavitating pneumonia (immunosuppressed patients).
its name from the Latin word “sarcina” means pack or bundle. They divide in the three planes and arranged in cubodial (2×2×2) arrangement of cocci cells. Most of the members of this genus are human flora and microbial cellulose synthesizer.
The species Sarcina ventriculi found in the cereal seeds surfaces, mud, soil and in the stomachs of humans, rabbits and guniea pigs.
Frequently asked questions-
Q1 what is the shape of cocci bacteria.
- 1. Rod shaped
- 2. Cylindrical
- 3. Spiral
- 4. Spherical
Ans. The correct answer is option 4
Q2 What are arrangement of cells in Staphylococcus bacteria
- 1. Tetrad
- 2. Cuboidal
- 3. Grape like
- 4. Irregular
Ans the correct answer is option 3
Q3 what kind of cell arrangement found in the Streptococcus bacteria
- 2. Chain
- 4.Both a and b
Ans the correct option is option 4
Q4 What is Nature of cocci bacteria
- 1. Gram positive
- 2. Gram negative
- 3. Both a and b
- 4. None of the above
Ans the correct option is option 3
Q5 The disease gonorrhoea is caused by which bacteria
- 1. Neisseria gonorrhoea
- 2. Staphylococcus aureus
- 3. Streptococcus pnemoniae
- 4. Bacillis subtilis
Ans the correct answer is option 1.