Coccus: Bacterial Shape / Structure Brief

Any bacteria or archaeon with an ovoid, spherical-shaped bacteria or usually round shaped bacteria is called a coccus (plural cocci). Bacteria are divided into three groups based on their coccus shape: bacillus (rod-shaped), cocci (spherical shaped bacteria), and spirochetes (spiral-shaped).

The genus Coccus refers to the form of bacteria and may include several genera, including staphylococci and streptococci. Based on the orientation and connection throughout cell division, the coccus shape may develop in pairs, lines, or bundles. Numerous cocci bacteria lack flagella and therefore are non-motile, in comparison to so many other bacilli-shaped bacteria.

Cocci is an English loanword for a traditional or neo-Latin noun that comes from the Greek masculine noun κόκκoς (cóccos), which implies "berry."

Coccus Bacterial Shape/Structure

The coccus bacterial shape varies depending on whether the bacterial wall is gram-positive or gram-negative.

Gram-positive (thick peptidoglycan layers) as well as gram-negative (thin peptidoglycan layers) cocci have different cell wall structures (thin peptidoglycan layers). Cocci may be pathogenic (e.g., streptococcus), commensal, or symbiotic when residing in their host organism.

Gram-Positive Cocci:

Gram-positive cocci are a diverse group of bacteria that share a common morphology. They're all approximately spherical, but they're all of the different sizes. The manner in which the cells are bound with one another distinguishes members of a certain genera: in bags, loops, or grape-like clusters. The dynamics of cell division as well as the reality that cells remain together are reflected in such arrangements.

Sarcina cells, for instance, are organized in cubical pockets since cell division occurs in three perpendicular planes during frequent intervals. Since division often happens in the same plane, Streptococcus spp. resemble a string of beads. S. pneumoniae, for particular, has strings that are just two cells long. Diplococci is the scientific name for them. Staphylococcus species do not divide in a normal plane.

Physiologically and geographically, the different gram-positive cocci vary. Micrococcus spp. are skin-inhabiting obligate aerobes. Human skin is indeed home to Staphylococcus spp., although they are facultative anaerobes. Sugars are fermented, and lactic acid is produced as a byproduct. Most of these organisms generate carotenoids, which give their colonies a yellow or orange colour. A significant human pathogen is Staphylococcus aureus. This could damage about every body tissue, most commonly the skin. Nosocomial (hospital-acquired) infections are normal.

Examples of Cocci Bacteria:

The cocci bacteria can be found as single cells or as cells that stay attached after cell division. Those that stay attached may be divided into three categories based on their cellular arrangement:

• Cocci that are in pairs are known as diplococci (examples include, Streptococcus pneumoniae and Neisseria gonorrhoeae).

• Streptococci are cocci strings (e.g. Streptococcus pyogenes).

• Staphylococci are colonies of cocci that are irregular (grape-like) (e.g. Staphylococcus aureus).

• Tetrads are groups of four cocci that are organized in the same plane (e.g. Micrococcus sp.)

• Sarcina is a bacterial genus that consists of eight cocci arranged in a cuboidal pattern (e.g. Sarcina ventriculi).

Types of Cocci Bacteria 

Depending on the type of cocci, as they divide or reproduce, they form distinct patterns. Diplococcus bacteria, Streptococcus bacteria, Staphylococcus bacteria, and the Enterococcus bacteria are all the types of coccus bacteria. They are given names based on the arrangement of their bacterial cells. 

Diplococcus:

Cocci bacteria definition states that a diplococcus (plural diplococci) is a coccus (round bacterium) that usually appears as two joined cells. They are grouped in pairs, implying two coccus cells are linked together. They can also be both gram-negative and gram-positive. Neisseria spp. and Moraxella catarrhalis are examples of gram-negative diplococci whereas Streptococcus pneumoniae and Enterococcus spp. are representatives of gram-positive diplococci. Diplococcus has most likely been linked to encephalitis lethargica. Pneumonia, Meningitis, Gonorrhea can also be caused by them.

Different types of Diplococcus

1. Gram-Negative Diplococci:

• Neisseria Spp : The family Neisseriaceae includes the genus Neisseria. The genus Neisseria contains more than ten various species, the majority of which are gram-negative and coccoid. Neisseria cinerea, Neisseria oralis, Neisseria polysaccharea, Neisseria gonorrhoeae, Neisseria mucosa, Neisseria meningitidis, Neisseria lactamica, and Neisseria subflava are gram-negative coccoid species. Another very important and common pathogenic Neisseria species are Neisseria gonorrhoeae and Neisseria meningitidis.

• Moraxella Catarrhalis: The family Moraxellaceae includes the genus Moraxella. Moraxella saccharolytica, Moraxella lacunata, Moraxella bovis, Moraxella boevrei, Moraxella atlantae, Moraxella caprae, Moraxella caviae, Moraxella canis, Moraxella equi, Moraxella cuniculi, Moraxella nonliquefaciens, Moraxella lincolnii, Moraxella ovis, Moraxella pluranimalium and Moraxella osloensis. Just one of them, Moraxella catarrhalis, has a diplococcus morphology. M. catarrhalis is a significant pathogen that causes infections in humans.

2. Gram-Positive Diplococci:

• Streptococcus Pneumoniae: Streptococcus pneumoniae is a member of the Streptococcus genus and Streptococcaceae family. Streptococcus is a genus of bacteria with 129 species and 23 subspecies which benefit a variety of microbiomes mostly on the human body. Many organisms have non-pathogenic features; furthermore, certain species, such as S. pneumoniae, have pathogenic attributes in the human body. 

• Enterococcus Spp.: The Enterococcus genus belongs to the Enterococcaceae family. There are 58 species as well as two subspecies throughout this genus. Such coccoid bacteria, which are gram-positive, were formerly believed to be harmless to humans. Nevertheless, over the last ten years, an influx of nosocomial pathogens derived from Enterococcus bacteria has emerged.

Brief on Streptococcus: 

Streptococcus belongs from the genus of gram-positive coccus (plural cocci) or spherical bacteria belonging to the Streptococcaceae family, which is part of the Lactobacillales (lactic acid bacteria) order in the Firmicutes phylum. Since streptococci divide across a single axis, they appear to make pairs or chains which seem bent or distorted as they grow. Streptococcus / Streptococci or bacteria are grouped in rows and chains. In addition, the length of the chain or row varies. 

Staphylococci, on the other hand, differentiate along several axes, resulting in irregular, grape-like colonies of cells. The majority of streptococci lack oxidase and catalase, and most are facultative anaerobes (have the capacity of growing in both the manner, namely aerobically and anaerobically). Furthermore, many of them are hemolytic, meaning they damage the body’s red blood cells. They are gram-positive bacteria that can cause pneumonia, scarlet fever, erysipelas, tooth decay, rheumatic fever, and step threat, among other disorders.

Staphylococcus: 

Staphylococcus is a Gram-positive, non-motile bacteria genus belonging to the Bacillales order's Staphylococcaceae family. Staphylococcus bacteria (staphylococci) form clusters of cells that resemble grapes. They seem spherical (cocci) when observed under the microscope and create grape-like groups. Staphylococcus species are anaerobic organisms that can live in the absence of oxygen (can grow under both aerobic and anaerobic conditions) with a high salt tolerance.

Staphylococcus species develop regularly on the skin and mucous membranes, but when they enter usually sterile areas of the body, they can cause wound infections, abscesses, toxic shock syndrome, skin infections, and, most often, food poisoning. The bacteria of the Enterococcus genus (enterococci) are found in pairs or short chains. They are non-motions, gram-positive bacteria that live in the entire nervous system. Enterococci can cause urinary tract infections, bacteria in the blood, and wound infections, to despise their low disease potential.

There are at least 40 species of Staphylococcus. These species have been categorised in such a way that nine species amongst these have two subspecies, one with four subspecies and one with three subspecies. Many organisms do not lead to causing disease and live naturally on humans as well as other animals' skin and mucous membranes. A nectar-inhabiting microbe has indeed been discovered in Staphylococcus. They also make up a minor part of the soil microbiome.

What is Sarcina?

Sarcina is a Gram-positive cocci bacteria genus belonging to the Clostridiaceae family. Numerous members of the genus constitute human flora and can be used in the skin and large intestine as microbial cellulose synthesisers. After the cuboidal cellular connections they generate while divided along three planes, the genus gets its name from the Latin word "sarcina," which means "pack or bundle." Sarcina ventriculi are the type species of the genus, and they can be located on the surface of cereal seeds, in mud, dirt, and in the human stomach, rabbits, and guinea pigs.

1. Coccus bacteria vs Rod bacteria

Bacillus rod bacteria are cylindrical or rod-shaped bacteria. Coccus, on the other hand, has a round or spherical shape. Rod bacteria examples are Bacillus subtilis (B. Subtilis) and Escherichie coli (E. coli).

2. Gram-Negative vs Gram-Positive 

If you’re ever heard bacteria referred to as gram-negative or gram-positive, it all boils down to the bacterial organism’s protective outer layer, also known as the membrane. Gram-positive bacteria have thick and broad membranes, whereas gram-negative bacteria have thin membranes that are difficult to penetrate. Furthermore, gram-negative bacteria are resistant to antibiotics due to this feature.

Conclusion

We have covered all the major aspects of Coccus Bacterial Shape. You can download the PDF format from Vedantu website to learn more.