PSEUDOMONAS AERUGINOSA: CHARACTERISTICS, MORPHOLOGY, LIFE CYCLE, CONTAGION - BIOLOGY - 2025

Pseudomonas aeruginosa is a gram-negative bacterium found primarily in water, moist soil, and in hospital settings. It is characterized as one of the main opportunistic pathogens in humans.

It was first described by the renowned German mycologist Walter Emil Migula in 1894. It is a bacterium that, among other things, has the ability to synthesize some pigments such as pyoverdin and pyorrubin.

Pseudomonas aeruginosa. Source: Photo Credit: Janice Haney Carr Content Providers (s): CDC / Janice Haney Carr / Public domain

This bacterium is extremely important in the health field, since it is responsible for a high percentage of infections in patients who are confined in health centers. It is capable of generating infections in the skin, respiratory tract and urinary tract, among others.

Characteristics of

Pseudomonas aeruginosa is a bacterium classified within the group of gram negative ones. This implies that when it is subjected to the gram staining process, it acquires a fuchsia coloration. It is because between their two cell lipid membranes they have a peptidoglycan layer. This layer is thin, so it is unable to retain the Gram stain particles.

This battery is aerobic, which means that it requires an environment rich in oxygen in order to develop.

It is also catalase positive. That is, it can synthesize the enzyme catalase and therefore break down hydrogen peroxide into water and oxygen. Continuing with the biochemical reactions, Pseudomonas aeruginosa is also oxidase positive, which means that it synthesizes the enzyme oxidase and, consequently, uses oxygen for energy.

Pseudomonas aeruginosa has the ability to oxidize some carbohydrates, such as galactose. However, you cannot ferment them.

Culture of Pseudomonas aeruginosa on blood agar. Source: HansN. / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Regarding the temperature levels required for this bacterium to develop, it must be at approximately 36 ° C. However, in the laboratory it has been seen to develop even at 41 ° C.

Morphology

Pseudomonas aeruginosa is a non-spore-forming bacterium, approximately 1 to 3 µm long and 0.5 to 1 µm wide.

It has a polar flagellum made up of a complex protein structure that provides mobility in liquid media and response to chemical stimuli. It also allows it to bind to cell membranes.

It has small filaments called pili, which are located on the outside. These structures are used to move in semi-solid media and, like the flagellum, adhere to surfaces.

Pseudomonas aeruginosa. By DataBase Center for Life Science (DBCLS) (http://togotv.dbcls.jp/ja/togopic.2017.38.html), via Wikimedia Commons

Its morphology is heterogeneous, generally its colonies are large, flattened, smooth or with saw-shaped edges, and may show a metallic luster. Extremely slow-growing dwarf colonies called punctate can also be found from chronic infections.

The mutations that occur in the colonies generate genetic and phenotypic changes, being able to identify different morphologies in the same patient depending on their location in the body.

Externally they form lipopolysaccharides and alginac, these biologically active substances have diverse protective functions of the bacterium, such as for example against desiccation, the response of the host's immune system and antibiotics. They also participate in adhesion and anchoring to the surface of cells.

Taxonomy

The taxonomic classification of Pseudomonas aeruginosa is as follows:

• Domain: Bacteria
• Kingdom: Monera
• Phylum: Proteobacteria
• Class: Gamma Proteobacteria
• Order: Pseudomonadles
• Family: Pseudomonadaceae
• Genus: Pseudomonas
• Species: Pseudomonas aeruginosa

Lifecycle

Pseudomonas aeruginosa reproduces, like all bacteria, asexually. The process through which it does this is known as binary fission. This is the most common bacterial reproduction process and through it, a bacterial cell divides to give rise to two cells exactly the same as the parent cell.

The first thing that happens in the binary fission process is that the bacterial DNA must be duplicated. However, this is a relatively simple process, since bacteria only have one circular chromosome.

Once its genetic material has been duplicated, each chromosome goes to one end of the cell. It is important to remember at this point that the Pseudomonas aeruginosa cell is elongated in shape.

When this happens, in the middle zone of the bacteria, the bacterial membrane and wall form a septum or septum that, finally, ends up dividing the cell, giving rise to the two resulting cells.

Contagion and transmission

The Pseudomonas genus of bacteria is responsible for a wide variety of infections in humans. Of all the species that comprise it, Pseudomonas aeruginosa is the one most frequently associated with this type of infection.

This bacterium is mainly found in water, vegetation, sewage, wet soil, and in some hosts such as humans. Likewise, it can also be found present in health institutions, specifically in surgical instruments, catheters and even in the hands of the personnel who work there caring for patients.

For the bacteria to infect an individual, it is strictly necessary that there be a gateway to the body. In this sense, the bacteria usually enter the body through a wound or softened skin, when it comes into contact with a contaminating element (such as contaminated water) or with a surface where the bacteria are found.

Despite the fact that this is the most frequent and effective way of contagion, specialists have affirmed that through the respiratory and digestive tracts contagion can also occur. In this sense, if a person inhales some type of contaminated fluid from another infected person or ingests contaminated water, they could become infected with the bacteria.

Diseases

Because this bacterium has the ability to colonize a wide variety of tissues, it is responsible for a large number of infections and diseases in humans. The best known are listed below.

Ear infections

Taking into account that this bacterium can be found in bodies of water in which people can swim regularly, it is not surprising that it infects this area of ​​the anatomy.

Among the infections that Pseudomonas aeruginosa can cause in the ear, we can mention acute external otitis media, an infection that affects the external auditory canal.

In patients with a chronic underlying disease, such as diabetes, a more aggressive form of the disease may develop, called malignant external otitis.

Respiratory tract infections

When the bacteria enter the body through the respiratory tract, it is possible that it causes some pathology such as pneumonia, bronchitis and even sinusitis.

These infections are more common in patients who are on a respirator and in people with chronic diseases that weaken their immune systems. These pathologies include AIDS, lupus, and cystic fibrosis.

Skin infections

Taking into account that the skin is one of the most frequent routes of contagion and entry for this bacterium, it is common then that it causes infections in it.

Skin infections that are caused by Pseudomonas aeruginosa include cellulitis, folliculitis, osteomyelitis, and ecthyma gangrenous. All these infections are potentially dangerous, if they are not treated in time, since they progressively injure the layers of the skin, until they can even affect much deeper structures, and perhaps access the blood vessels, generating an infection.

Urinary tract infections

The bacteria can enter the body through the urethra, causing a lower urinary tract infection. This is more common in patients who are hospitalized and have a catheter to aid urination.

Infections

When the bacteria has spread in such a way that it enters the bloodstream, it may travel all the way to the heart. There it can adhere to the atrioventricular valves or the semilunar valves and cause an infection known as acute bacterial endocarditis.

This pathology is more frequent in patients who have undergone open heart surgeries in which a valve replacement or any other type of procedure has been done.

Symptoms

The symptoms of Pseudomonas aeruginosa infection will vary, depending on the tissue that is affected.

Ear infections

• Purulent discharge that may be accompanied by a bad smell.
• Sharp pain, especially when pressure is exerted against the tragus of the ear
• Redness and swelling of the ear canal
• Decreased hearing (hearing loss)

If the individual has any pathology such as diabetes, the symptoms worsen, even exposing the bone in the most severe cases.

Respiratory infections

• High fever, which is constant
• Difficulty breathing (dyspnea)
• Cough that does not subside, which, at times, may be accompanied by purulent discharge.
• Chest pain
• Shaking chills
• Decay and general malaise.
• Increased heart rate

In the case of sinusitis, symptoms include:

• Pain in the sinuses, especially when pressure is applied to them.
• Fever
• Transient loss of sense of smell
• Nasal congestion
• Nasal discharge, which can be purulent
• A feeling of pressure may even be experienced when the individual lowers their head.

Infections in the skin and other tissues

• Fever
• Redness and pain in the affected area
• Sensation of heat in the injured area
• Lesions such as pustules or an inflammatory nodule. These lesions may contain purulent material.

In the case of ecthyma gangrenosum, the lesions often have necrotic areas where healthy tissue dies.

Infections

The most common heart infection is endocarditis. Your symptoms are:

• Constant fever
• Shaking chills
• Difficulty breathing and pain in the chest when trying
• Profuse sweating, especially at night
• Appearance of a heart murmur
• General pain and discomfort

Urinary infections

• Urgency to urinate
• Pain and burning when urinating
• Pelvic discomfort

Treatments

Currently there is a mortality of 30 to 40% caused by Pseudomonas aeruginosa, mainly in the first 24 to 48 hours after its onset, especially if the infection is located in the respiratory tract and the treatment applied is not adequate.

These bacteria are resistant to various antibiotics and have a great capacity to acquire new defense mechanisms. They can form biofilms, decrease the permeability of the outer membrane, use ejection pumps for multiple drugs, and have enzymes that modify antibacterials.

The number and choice of antibiotics to be used is controversial; he is divided between the opinion of applying a monotherapy or combining similar antibiotics. Treatment with ceftazidime alone or in combination with amikacin is often recommended.

Several drugs such as penicillins, cephalosporins, carbapenems, monobactams, aminoglycosides, fluoroquinolones, in addition to polymyxins, manage to be active against these bacteria. But sometimes they have no effect due to mutations in strains or information from new genes with acquired resistance.

Alternative investigations have also been carried out on the use of plants with antimicrobial compounds, such as the Sonchus oleraceous species, commonly known as "cerraja", which is distributed throughout the world despite being native to Europe and Central Asia.

Studies indicate that antibiotic resistance profiles in some cases vary within the same country or even within a geographic region.

References

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