Diplococci Bacteria: Definition, Shape, Examples, Diseases, And Treatments

In this guide, we’ll be taking a look at the diplococci bacteria, including how diplococci are defined, the shape they take, and examples of strains.

Many diplococci are pathogens, and this guide will also cover the diseases they can cause, how the infection spreads, symptoms, and potential treatments.

Read on to learn about diplococci bacteria.

Diplococci Bacteria Definition

Diplococci bacteria, or diplococcus in singular, are rounded bacteria that occur in pairs as joined cells.

Diplococci rarely appear completely round, unlike the staphylococci bacteria which are exactly spherical. Instead, the diplococci can be ovoid, elongated, or bean shaped.

Not all diplococci bacteria appear in pairs. For example, while streptococcus pneumoniae is most often found in pairs, some species of enterococcus are found instead to form short chains. Diplococci can be gram-positive or gram-negative.

Diplococci bacteria cause a range of infections in human beings, including pneumonia and meningitis. However, diplococcus can also be commensal, and live in a healthy human body without causing any issues.

Varieties of diplococci include:

• Neisseria gonorrhoeae
• Neisseria meningitidis
• Moraxella catarrhalis
• Enterococcus faecalis
• Enterococcus faecium
• Streptococcus pneumoniae.

Shape Of Diplococci Bacteria

Diplococcus is typically described as rounded, although some species don’t form a perfectly rounded shape. Instead, diplococcus might be elongated, or have a bean shape. Due to the ovoid shape, diplococci are often described as being ovococcoid.

Studies have shown that the shape of the diplococci is often caused by the peptidoglycan — the cytoplasmic membrane that forms a protective envelope in most species of bacteria.

Different attributes of the peptidoglycan machinery lead to the shaping of the bacteria. In the case of diplococci, this machinery tends to lead to the ovoid shape.

Truly round bacterium, or coccoids, are formed this way due to the cell division machinery that causes the synthesis of septal peptidoglycan and the rounded shape of the cell wall.

This same process is seen in ovococcoid bacteria, or elongated bacteria, as well.

However, in these cells, the synthesis of the cell wall also occurs through the elongation complex, which creates the peripheral peptidoglycan, providing the elongated shape.

Regardless of the form, bacteria typically maintains a regular shape, unlike the irregular forms of eukaryotic cells. The shape of the bacterium is enforced and maintained by peptidoglycan, the polymer that forms the cell wall.

The different types of cell division mechanism can affect the resulting shape that the cell wall creates. Varieties of diplococci take differing rounded shape because of this cell division mechanism.

During the early stages of cell division, dynamic filaments are produced in the center of the cell by FtsZ, a protein that is the first to localize at the division site.

This draws more proteins in, and acts as a base structure for cell division. This initial division site is marked by the wall band, or the equatorial ring,

Division in Streptococcus pneumoniae, for example, takes place perpendicular to the long axis, along the parallel plane. This is true of other diplococcus.

The dynamic filaments then undergo the process of polymerization, and molecules come together to form polymer chains. The proteins then begin binding, leading to the synthesis of septal peptidoglycan, and the equatorial ring becomes split into two.

As the cell divides and the equatorial ring splits into two equally, it sets a limit for the shape of the peripheral peptidoglycan synthesis. Meanwhile, the rings continue to move from the middle outwards, becoming markers of cell division.

The processes of peripheral PG synthesis and septal peptidoglycan synthesis occur with some differences. Septal peptidoglycan synthesis is mediated by proteins including bPBP2x, a class B protein.

They close inwards, and mark a vital role in separating identical daughter cells. During peripheral PG synthesis, proteins such as bPBP2b move outwards from the mid-point of the cell, gradually elongating, and creating the ovoid appearance.

Identifying Gram Positive And Gram Negative Diplococci Bacteria

While some forms of diplococci bacteria are gram-positive, others are gram-negative. Gram-negative diplococci, such as Moraxella catarrhalis, have a thinner peptidoglycan layer, and fewer lipids.

Using the gram staining method, gram-negative bacteria will appear pale pink or red. However, a thicker peptidoglycan layer, between 20 and 80 nm, allows gram-positive bacteria to retain the purple stain of gram testing.

Streptococcus pneumoniae and Enterococcus are two forms of diplococcus that are gram-positive. They are both common within the human body, and feature the same morphological characteristics.

Because of this, they can be difficult to tell apart solely based on morphology.

Enterococcus species is often found in the gut and the bowel of both humans and animals. It’s a typical part of the intestinal flora, and can sometimes be identified in the mouth.

Bile Esculin Agar can be used to grow Enterococcus species, as they produce glucose and esculatin from hydrolyzed esculin.

Streptococcus pneumoniae is also found in the human body, although rather than in the gut, it lives in the mucosal surfaces found on the respiratory system.

It normally acts as a commensal bacterium, but, as an opportunistic pathogen, can lead to pneumonia and other infections in certain conditions.

Streptococcus pneumoniae needs complex nutrition to grow, but it can be successfully grown in a culture containing either blood or chocolate agar.

Gram-negative diplococci include Neisseria species, and Moraxella catarrhalis.

What’s Needed For A Gram Stain?

A gram stain is used to determine the thickness of the cell wall, and quickly categorize bacteria. In order to conduct a gram stain, you will need:

• Gram stain reagents. These are the primary stain, the mordant, the decolorizer, and the secondary stain
• A sample of the bacteria, typically from the culture
• Sterile wire loop
• Bunsen burner
• Slides
• Staining rack
• Water

How To Complete A Gram Stain

1. Begin by placing a small amount of your specimen onto a glass slide using a sterile wire loop. The specimen should be placed in a thin smear at the center of the slide. Leave to air dry.
2. When the slide is dry, pass it through the flame of the Bunsen burner several times, to heat fix. Work carefully, as you don’t want to overheat the specimen.
3. Add several drops of the crystal violet – the primary stain – to the slide, and leave to stand for roughly one minute. The bacteria should be stained purple.
4. Wash the slide quickly under clean water, and gently shake away the excess.
5. Apply several drops of gram’s iodine – the mordant – to the slide. Again, leave it to stand for one minute, before gently rinsing with clean water, and shaking dry.
6. Tilt the slide, and apply several drops of the decolorizer, typically a solvent such as ethyl alcohol. Rinse the slide with the decolorizer until it runs clear, and then immediately rinse under a gentle stream of clean water. The decolorizer will remove the color from gram-negative specimens but, if left too long, can decolorize even gram-positive bacteria.
7. Add the Safranin – the counterstain – and incubate for around one minute. Wash again under a gentle stream of water.
8. Observe under a microscope.

Observing A Gram Stain

Gram-positive bacteria will appear violet, as the primary stain combined with the mordant has been trapped in the peptidoglycan layer by the decolorizer. Gram-negative bacteria will appear pink.

The outer membrane of the cell has degraded, and the violet-iodine complex has escaped, so the Safranin is able to stain the cells red.

When observing both Streptococcus pneumoniae and Enterococcus species under a microscope, they both should be stained purple. This shows that they are a gram-positive form of diplococcus.

Both species of diplococci are also most likely to be seen in pairs, but they do sometimes form short chains or appear as single cells. Streptococcus pneumoniae is typically an elongated cell shape.

Observed under a microscope, Moraxella catarrhalis will be pink. This indicates it’s a gram-negative diplococcus, as the primary stain has been washed away.

This means Moraxella catarrhalis can be quickly identified as a bacterium with a thinner peptidoglycan layer.

Diplococci Bacteria Diseases

Bacteria that occur in pairs are typically classified as diplococci, and some of these can cause diseases in humans. Many diplococci are commensal, and can exist in the human body without causing any harm.

However, they are often pathogens, and can lead to infections and illness. Below, we’ll take a look at some of the most common types of diplococci, and the diseases they are responsible for.

Neisseria Species

Neisseria is a genus belonging to the Neissariaceae family. It can be divided into more than ten species, and most of these are coccoid and gram-negative, with a thinner peptidoglycan layer.

They are most often found on the mucosal surface of humans and animals. When viewed under a microscope, Neisseria diplococci often resemble coffee beans.

There are eleven species of Neisseria that colonize humans, with two of these being pathogens. These are Neisseria meningitidis, and Neisseria gonorrhoeae.

Neisseria Meningitidis

Neisseria meningitidis is a gram-negative bacteria, referred to as a diplococcus because it frequently forms pairs. Also known as meningococcus, the bacteria is responsible for meningitis, among other diseases such as meningococcemia.

It is an exclusively human pathogen, present in roughly 10% of adults. Neisseria meningitidis spreads through contact with saliva and other respiratory secretions.

N. meningitidis enters the body and adheres to the epithelial cells using the long pili extensions. Opa and Opc surface-exposed proteins are then able to interact with the cell, crossing the mucosal barrier and entering into the bloodstream.

From here, the bacteria can travel through the bloodstream, and enter the central nervous system.

Some forms of the bacteria are capsulated, meaning they have a polysaccharide layer outside the cell envelope.

This allows the bacteria to evade the immune response. Several factors, including the capsule layer, can influence the virulence of N. meningitidis.

In many parts of the world, the infection is prevented via the use of vaccines. The term Meningococcal vaccine is used to describe a number of vaccines developed to prevent a Neisseria meningitidis infection.

It’s often given to those traveling to a country with a high risk of meningitis.

In the case of a confirmed Neisseria meningitidis infection, immediate hospitalization and antibiotic treatment is required.

An initial dose of intramuscular antibiotic is given at the earliest stage possible, followed by treatment with a third-generation cephalosporin antibiotic such as cefotaxime or ceftriaxone.

Neisseria Gonorrhoeae

Known as gonococcus (singular), and gonococci (plural) Neisseria gonorrhoeae is a gram-negative diplococcus.

It causes the sexually transmitted infection gonorrhea, and is responsible for other gonococcal diseases such as septic arthritis, disseminated gonococcemia, and gonococcal opthalmia neonatorum.

N. gonorrhoeae is sexually transmitted in adults, and can be transmitted to infants during birth if the mother has an untreated infection.

It’s highly unlikely for non-sexual transmission among adults, although thought to be possible. For the bacteria to successfully transmit, the first thing it must do is adhere to the epithelial cells at the infection site.

The hair-like pili protein appendages that can be found on the cell wall pull the bacteria to the epithelial membrane. Then, the opacity and other surface proteins are able to interact and penetrate the cell.

Once adhered, Neisseria gonorrhoeae can then replicate, creating microcolonies, and can potentially transcytose across the epithelial barrier and into the bloodstream.

The initial adhesion is vital for the development of the disease. Once adhered, N. gonorrhoeae can be very tricky to get rid of.

It has developed numerous defensive mechanisms to evade the immune system, and an ability to alter surface proteins means reinfection is possible.

As the gonorrheal infection adheres itself to the columnar epithelia, it’s most often found in parts of the bodies with mucosal surfaces. Neisseria gonorrhoeae is typically found in the conjunctiva, pharynx, urethra, and rectum.

One common side effect of a gonorrheal infection is pain when urinating. These infections can also be described as purulent infections, as they result in a cloudy or clear discharge.

Treatment for Neisseria gonorrhoeae is typically an injection of ceftriaxone, which is a third-generation cephalosporin antibiotic. This works to prevent the bacteria from adhering to the cell wall.

However, the high-level of antibiotic immunity of N. gonorrhoeae has made treatment difficult.

Moraxella Catarrhalis

A member of the genus Moraxella in the family Moraxellaceae, Moraxella catarrhalis is a gram-negative diplococci bacteria. Not all Moraxella are diplococcus, with many appearing as either short rods, or as a coccobacillus.

Moraxella catarrhalis is one of the most common species of Moraxella, and also the most clinically important.

Moraxella catarrhalis is often a normal part of the gut flora. However, it can pathologize, and be the cause of numerous infections in the human body.

It’s often detected in school age children, with studies suggesting the bacteria tends to colonize the upper respiratory system at an early stage in life.

There’s a significantly larger chance of becoming infected with Moraxella catarrhalis as a child than as an adult, with transmission often occurring due to interaction with infected droplets.

Having entered the body, the bacteria adheres to the host cells via trimeric autotransporter adhesins. These proteins occur on the outer membrane of gram-negative bacteria, and adhere to epithelial cells by binding proteins in the extracellular matrix. Once attached to the host cell, the infection can then avoid the immune system.

Moraxella catarrhalis is responsible for several diseases and infections. It is an opportunistic pulmonary invader, causing most harm in patients suffering with a compromised immune system, or an underlying disease.

Below, we’ve covered some common illnesses resulting from an M. catarrhalis infection:

Otitis Media: Otitis Media is a term used to refer to a group of inflammatory diseases that affect the middle ear. It can lead to ear pain, and eventually hearing loss.

It’s commonly diagnosed in children, with Moraxella catarrhalis being a leading cause of infection. M. catarrhalis migrates from the respiratory tract, via the eustachian tube, toward the middle ear.

The eustachian tube becomes inflamed, causing congestion. The pressure on the ear can then lead to pain and discomfort.

Otitis Media caused by M. catarrhalis is most commonly treated with painkillers, and occasionally antibiotics. Antibiotics are sometimes avoided in children over six months, due to lack of benefit.

However, in some cases, Amoxicillin-clavulanate or trimethoprim-sulfamethoxazole are used as treatment.

Sinusitis: Moraxella catarrhalis is one potential cause of sinusitis, sometimes referred to as rhinosinusitis. Sinusitis is when the mucous membranes lining the sinuses become inflamed. This can result in excessive nasal mucus, and a persistent cough.

Sinusitis is common, and Moraxella catarrhalis is just one potential bacterial origin. Moraxella catarrhalis is thought to be responsible for roughly 16% of sinusitis cases caused by bacteria.

When M. catarrhalis is the cause, sinusitis typically lasts for 7 to 10 days.

Antibiotics are typically used when a case of Moraxella catarrhalis has lasted for longer than 10 days. Antibiotics typically used to treat sinusitis include amoxicillin, or amoxicillin/clavulanate.

Bronchitis: An inflammation of the bronchi airways in the lungs, bronchitis can be the result of a Moraxella catarrhalis infection.

However, bronchitis is most often a result of a viral infection. M. catarrhalis leading to an increased risk of bronchitis is more common among young children.

Antibiotics have historically been used to treat acute bronchitis, but there’s an effort to reduce the number offered as treatment.

Laryngitis: As with bronchitis, laryngitis, an inflammation of the larynx, is most commonly caused by a viral infection.

In some cases, bacteria, including M. catarrhalis, can result in laryngitis. Bacterial causes of laryngitis often develop in conjunction with a viral infection.

Again, antibiotics have previously been offered as treatment to laryngitis, but this practice is becoming less common.

Streptococcus Pneumoniae

Streptococcus Pneumoniae, also known as pneumococcus, is a gram-positive bacteria that’s typically found in pairs. In a healthy carrier, the bacteria can live asymptomatically on the mucosal surfaces of the throat and nose.

However, pneumococcus can become pathogenic in those with a weaker immune system, and is the leading cause of community acquired pneumonia and meningitis in children and the elderly.

Streptococcus pneumoniae is spread from person to person via direct contact with respiratory droplets. The bacteria attach themselves to the nasopharyngeal cells via the surface adhesins.

But the normal colonization can turn infectious if the bacteria are carried to areas including the nasal sinuses, the Eustachian tubes, the lungs, or into the bloodstream.

The polysaccharide capsule enveloping the bacteria helps it to resist phagocytosis, and evade the immune system of the host.

When S. pneumoniae reaches the air sacs of the lungs and begins to colonize, the body initiates the inflammatory response. The alveoli are filled with plasma and white blood cells, causing the condition we know as pneumonia.

Symptoms of pneumonia include coughing, trouble breathing, chest pains, fever, and chills. Among the elderly, pneumonia can also lead to confusion and reduced alertness levels.

Another disease that can be caused by Streptococcus pneumoniae is pneumococcal meningitis. In this case, the bacteria have colonized the tissue surrounding the brain and spinal cord.

This can result in a headache, stiff neck, sensitivity to light, a fever, and confusion.

Other diseases that can be caused by pneumococcal infections include bronchitis, sinusitis, otitis media, conjunctivitis, rhinitis, sepsis, brain abscess, and endocarditis.

Cases of pneumonia are typically treated with antibiotics including amoxicillin and macrodyne for outpatients, and intravenous ampicillin and ceftriaxone for inpatients.

Vaccines have also developed to prevent infections from S. pneumoniae. These vaccines are referred to as pneumococcal vaccines, and are often administered in early infancy.

Enterococcus Species

Enterococci are gram-positive diplococci that sometimes occur in short chains, and can be very difficult to differentiate from streptococci.

Like streptococci, enterococcus can be commensal organisms, forming a harmonious relationship with the intestinal flora. Also like streptococci, species of enterococcus can become pathogenic.

There are two species of Enterococci commonly found in the human intestine: E. faecalis, and E. faecium. Enterococcus faecalis is found in roughly 90% of human intestines, and can be used as a probiotic.

However, as an opportunistic pathogen, it can also lead to fatal infections, particularly strains with a high resistance to antibiotics. E. faecalis is often found in root canal infections, as it can bind to dentin and spread to dentinal tubules.

E. faecalis infections can result in endocarditis, sepsis, meningitis, and urinary tract infections, among others.

Enterococcus faecium is also a common bacterium found in a healthy human intestine, although it occurs less frequently than E. faecalis.

This, along with other virulence factors, have made E. faecium more resistant to antibiotic treatments. Vancomycin-resistant Enterococci (VRE) are more likely to be transmitted by an infected person, and difficult to treat.

VRE infections are often associated with a high mortality rate, due to the difficulties of treatment.

The high antibiotic resistance of both E. faecalis and E. Faecium has made traditional treatment complex, and often a combination of drugs are necessary to fight an infection.

Linezolid, daptomycin, tigecycline, and streptogramins have been used against VRE, and sultamicillin has been shown to be an effective treatment.

Diplococci bacteria are commonly found, and many of the strains show pathogenic characteristics.

Diplococci can be gram-negative or gram-positive, and the infections are typically treated with antibiotics, although the development of antibiotic-resistant bacteria means this treatment is becoming less common.

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