Introduction

The morphology and arrangement of bacteria are often a key factor in identifying their species. Their direct examination under the

light microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of microsco ...

enables the classification of these

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

and

Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

. Generally, the basic morphologies are spheres (coccus) and round-ended cylinders or rod shaped (bacillus). But, there are also other morphologies such as helically twisted cylinders (example
Spirochetes
'), cylinders curved in one plane (selenomonads) and unusual morphologies (the square, flat box-shaped cells of the Archaean genus ''

Haloquadratum ''Haloquadratum'' (common abbreviation: ''Hqr.'') is a genus of archaean, belonging to the family Haloferacaceae. The first species to be identified in this group, ''Haloquadratum walsbyi'', is unusual in that its cells are shaped like square, ...

)''. Other arrangements include pairs, tetrads, clusters, chains and palisades.

Coccus

coccus A coccus (plural cocci) is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spiral ( of whi ...

(plural ''cocci'', from the Latin ''coccinus'' (scarlet) and derived from the Greek ''kokkos'' (berry)) is any

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

(usually

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

) whose overall shape is

spherical A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ce ...

or nearly spherical. Describing a bacterium as a coccus, or sphere, distinguishes it from

bacillus ''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacilli ...

, or rod. This is the first of many taxonomic traits for identifying and classifying a bacterium according to binomial nomenclature. Important human diseases caused by coccoid bacteria include

staphylococcal ''Staphylococcus'' is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillales. Under the microscope, they appear spherical ( cocci), and form in grape-like clusters. ''Staphylococcus'' species are facultati ...

infections, some types of

food poisoning Foodborne illness (also foodborne disease and food poisoning) is any illness resulting from the spoilage of contaminated food by pathogenic bacteria, viruses, or parasites that contaminate food, as well as prions (the agents of mad cow disease) ...

, some

urinary tract infection A urinary tract infection (UTI) is an infection that affects part of the urinary tract. When it affects the lower urinary tract it is known as a bladder infection (cystitis) and when it affects the upper urinary tract it is known as a kidney ...

toxic shock syndrome Toxic shock syndrome (TSS) is a condition caused by bacterial toxins. Symptoms may include fever, rash, skin peeling, and low blood pressure. There may also be symptoms related to the specific underlying infection such as mastitis, osteomyeliti ...

gonorrhea Gonorrhea, colloquially known as the clap, is a sexually transmitted infection (STI) caused by the bacterium '' Neisseria gonorrhoeae''. Infection may involve the genitals, mouth, or rectum. Infected men may experience pain or burning with ...

, as well as some forms of

meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...

, throat infections,

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...

s, and

sinusitis Sinusitis, also known as rhinosinusitis, is inflammation of the nasal mucosa, mucous membranes that line the paranasal sinuses, sinuses resulting in symptoms that may include thick Mucus#Respiratory system, nasal mucus, a nasal congestion, plugg ...

Arrangements

Coccoid bacteria often occur in characteristic arrangements and these forms have specific names as well; listed here are the basic forms as well as representative bacterial

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

: * pairs or

diplococci A diplococcus (plural diplococci) is a round bacterium (a coccus) that typically occurs in the form of two joined cells. Types Examples of gram-negative diplococci are '' Neisseria spp.'' and ''Moraxella catarrhalis.'' Examples of gram-positiv ...

(e.g. ''

Neisseria ''Neisseria'' is a large genus of bacteria that colonize the mucosal surfaces of many animals. Of the 11 species that colonize humans, only two are pathogens, '' N. meningitidis'' and ''N. gonorrhoeae''. ''Neisseria'' species are Gram-negativ ...

spp. In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate se ...

) * groups of four or eight known respectively as

tetrads Tetrad ('group of 4') or tetrade may refer to: * Tetrad (area), an area 2 km x 2 km square * Tetrad (astronomy), four total lunar eclipses within two years * Tetrad (chromosomal formation) * Tetrad (general relativity), or frame field ** Tetrad fo ...

and

sarcina The ''sarcina'' was the marching pack carried by Roman legionaries, the heavy infantry of the Roman legions. Most of a legionary's equipment other than his arms and armour would, in early times, have been consigned to a baggage train and b ...

(e.g. ''

Micrococcus ''Micrococcus'' (mi’ krō kŏk’ Əs) is a genus of bacteria in the Micrococcaceae family. ''Micrococcus'' occurs in a wide range of environments, including water, dust, and soil. Micrococci have Gram-positive spherical cells ranging from abo ...

'' spp.) * bead-like chains (e.g. ''

Streptococcus ''Streptococcus'' is a genus of gram-positive ' (plural ) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs ...

'' spp.) * grapelike clusters (e.g. ''

Staphylococcus ''Staphylococcus'' is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillales. Under the microscope, they appear spherical (cocci), and form in grape-like clusters. ''Staphylococcus'' species are facultative ...

'' spp.)

Bacillus

(plural bacilli) is a

rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name ''Bacillu ...

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. Although ''

Bacillus ''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacilli ...

'', capitalized and

italicized In typography, italic type is a cursive font based on a stylised form of calligraphic handwriting. Owing to the influence from calligraphy, italics normally slant slightly to the right. Italics are a way to emphasise key points in a printed tex ...

, specifically refers to the genus, the word ''bacillus'' (plural ''bacilli'') may also be used to describe any rod-shaped bacterium, and in this sense, bacilli are found in many different taxonomic groups of bacteria. There is no connection between the shape of a bacterium and its colors in the Gram staining.

Arrangements

Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades. * Diplobacilli: Two bacilli arranged side by side with each other. * Streptobacilli: Bacilli arranged in chains.

Coccobacillus

coccobacillus A coccobacillus (plural coccobacilli), or bacilluscocco, is a type of bacterium with a shape intermediate between cocci (spherical bacteria) and bacilli (rod-shaped bacteria). Coccobacilli, then, are very short rods which may be mistaken for coc ...

(plural ''coccobacilli'') is a type of rod-shaped

. The word ''coccobacillus'' reflects an intermediate shape between ''coccus'' (spherical) and ''bacillus'' (elongated). Coccobacilli rods are so short and wide that they resemble

cocci A coccus (plural cocci) is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spiral ( of whi ...

. ''

Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, non-motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bacteria ...

'' and ''

Chlamydia trachomatis ''Chlamydia trachomatis'' (), commonly known as chlamydia, is a bacterium that causes chlamydia, which can manifest in various ways, including: trachoma, lymphogranuloma venereum, nongonococcal urethritis, cervicitis, salpingitis, pelvic inflamma ...

'' are coccobacilli. ''

Aggregatibacter actinomycetemcomitans ''Aggregatibacter actinomycetemcomitans'' is a Gram-negative, facultative anaerobe, nonmotile bacterium that is often found in association with localized aggressive periodontitis, a severe infection of the periodontium. It is also suspected to b ...

'' is a gram negative coccobacillus which is prevalent in subgingival plaques. ''

Acinetobacter ''Acinetobacter'' is a genus of gram-negative bacteria belonging to the wider class of Gammaproteobacteria. ''Acinetobacter'' species are oxidase-negative, exhibit twitching motility, and occur in pairs under magnification. They are important ...

'' strains may grow on solid media as coccobacilli. ''

Coxiella burnetti ''Coxiella burnetii'' is an obligate intracellular bacterial pathogen, and is the causative agent of Q fever. The genus ''Coxiella'' is morphologically similar to ''Rickettsia'', but with a variety of genetic and physiological differences. ''C. ...

'' is also a coccobacillus.

Spiral

Spiral bacteria Spiral bacteria, bacteria of spiral ( helical) shape, form the third major morphological category of prokaryotes along with the rod-shaped bacilli and round cocci. Spiral bacteria can be subclassified by the number of twists per cell, cell thick ...

are another major bacterial cell morphology. Spiral bacteria can be sub-classified as spirilla, spirochetes, or vibrios based on the number of twists per cell, cell thickness, cell flexibility, and motility.

are known to evolve specific traits to survive in their ideal environment. Bacteria-caused illnesses hinge on the bacteria’s physiology and their ability to interact with their environment, including the ability to

shapeshift In mythology, folklore and speculative fiction, shape-shifting is the ability to physically transform oneself through an inherently superhuman ability, divine intervention, demonic manipulation, sorcery, spells or having inherited the ...

. Researchers discovered a protein that allows the bacterium ''

Vibrio cholerae ''Vibrio cholerae'' is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and oth ...

'' to morph into a corkscrew shape that likely helps it twist into — and then escape — the protective mucus that lines the inside of the gut.

References

External links

Bacteria Picture Gallery
{{anatomy Bacteria Morphology (biology)

Introduction

Coccus

Arrangements

Bacillus

Arrangements

Coccobacillus

Spiral

See also

References

External links