PROPIONIBACTERIUM ACNES: CHARACTERISTICS, TAXONOMY, MORPHOLOGY - BIOLOGY - 2025

Propionibacterium acnes is a gram positive bacterium that is part of the normal microbiota of the human being. It is found mainly at the level of the hair follicles, but it is also located in other body cavities.

It was discovered in a patient with a particularly severe case of acne. From there it has been associated with more and more cases of acne. Likewise, it has been associated with other pathologies such as endocarditis or corneal ulcers, although to a lesser extent.

Propionibacterium acnes. Source: By CDC / Bobby Strong (http://phil.cdc.gov ID # 3083), via Wikimedia Commons

This is one of the most well-known and studied bacteria of the genus Propionibacterium. Hence, its pathogenic mechanism is known and fully identified.

Acne is a widely distributed pathology on the planet. It is one of the most frequent conditions, common mainly during adolescence and the second decade of life, although it can occur at any age.

Current treatments are very novel, since they not only involve topical medications with antibiotics, but also the use of other technologies such as lasers.

Taxonomy

Domain: Bacteria

Phylum: Actinobacteria

Order: Actinomycetales

Suborder: Propionibacterineae

Family: Propionibacteriaceae

Genus: Propionibacterium

Species: Propionibacterium acnes

Morphology

Propionibacterium acnes is a rod-shaped bacterium. They are approximately 0.5 - 0.8 microns wide by 1.0 - 5.0 microns long. They are bacteria that do not have cilia or flagella. They also do not have a capsule that surrounds them.

Its cell wall is made up of a thick layer of peptidoglycan. Likewise, it has among its components muramyl dipeptide (MDP), in addition to other lipid components that stimulate the host's immune system.

The most widely used culture medium for this bacterium is blood agar. Once developed, the colonies have an opaque, whitish enameled appearance and a circular morphology.

Its genetic material is made up of a single circular chromosome, which contains a total of 2,351 genes that code for the synthesis and expression of 2,297 proteins. 60% of DNA is made up of cytosine and guanine nucleotides.

General characteristics

It is gram positive

Bacterial cells of Propinibacterium acnes, when subjected to the Gram staining process, acquire an intense violet color.

This is due to the fact that the peptidoglycan found in its cell wall retains the molecules of the dye used, causing the bacteria to adopt its color and thus be seen under the microscope.

Habitat

This bacterium is a common commensal of the human body, specifically in the skin, the oral cavity, the urinary tract and parts of the large intestine. Commensal refers to the fact that the bacterium benefits from the host's body, but does not cause any harm to it.

It is mesophilic

The bacteria grow at an optimal temperature of 37 ° C. This is evidenced by the fact that the bacteria inhabit the human body, whose temperature is the one already mentioned.

It is catalase positive

Propionibacterium acnes has the genes to synthesize the enzyme catalase. This enzyme is responsible for dividing hydrogen peroxide into water and oxygen according to the following reaction:

2H ₂ O ₂ ----------- 2H ₂ O + O ₂

It is indole positive

The indole test is performed on bacteria to determine if they are capable of breaking down the amino acid tryptophan, specifically releasing indole. Indole is a compound that is formed as a consequence of reductive deamination of the mentioned amino acid.

Propionibacterium acnes synthesizes a group of enzymes that together are known as tryptophanases and are those that carry out the process..

Reduces nitrates to nitrites

This bacterium synthesizes the enzyme nitrate reductase. This enzyme allows you to reduce nitrates to nitrites, as indicated by the reaction:

NO ₃ + 2e ^- + 2H -------– NO ₂ + H ₂ O

This property of reducing nitrates, together with that of producing catalase and the indole test, constitute three indispensable indicators when it comes to differentiating Propionibacterium acnes from other bacteria.

Metabolism

Propionibacterium acnes involves the fermentation of glucose in its metabolism. As a product of this fermentation, propionic acid and acetic acid are generated as a by-product. All this according to the reaction:

3C ₆ H ₁₂ O ₆ ------ 4CH ₃ -CH ₂ -COOH + 2CH ₃ -COOH + 2CO ₂ + 2H ₂ O

It is anaerobic

This bacteria is anaerobic. This means that it does not require oxygen to carry out its metabolic processes. However, there are studies that indicate that Propionibacterium acnes is aerotolerant. That is, it can develop in an environment with oxygen, since it is not toxic for it.

Diseases

Propionibacterium acnes is a pathogenic bacterium that is mainly associated with skin lesions known as acne. It has also been linked to other infections such as endocarditis, pericarditis and corneal ulcers, among others.

Acne

It is the pathology most frequently associated with Propionibacterium acnes. This bacteria is housed in the hair follicle and pores. The sebaceous glands produce sebum, which is used by the bacteria as a source of energy and nutrients.

Acne lesions. Source: By Roshu Bangal, from Wikimedia Commons

Sometimes, the sebaceous glands are overactive, generating excess sebum, which can obstruct the hair follicle. This provides the ideal conditions for bacteria to proliferate there, causing the characteristic acne lesions.

Symptoms

The lesions appear mainly on the face and shoulders. Less frequently they are seen on the trunk, arms, buttocks and legs.

• Reddish bumps known as papules.
• Bumps (pustules) that have yellow or white pus.
• Erythema around the lesions
• Crusting of skin rash
• Fever and general poor condition (in advanced and extremely severe cases)

Endocarditis

It is an infection that occurs when bacteria reach the heart through the bloodstream. It affects the endocardium, which is the innermost layer of the heart, as well as the atrioventricular valves, especially if they are synthetic.

Symptoms

• Fever and chills
• Joint and muscle pain
• Chest pain when breathing
• Difficulty breathing
• Fatigue

Pericarditis

It is an infection that occurs in the pericardium, the thin membrane that surrounds the heart. It happens because the bacteria have gotten there through the bloodstream.

Symptoms

• Shooting pain in the chest
• Fever
• Cough
• Difficulty breathing
• Palpitations

Corneal ulcers

These are sore-like lesions that occur in the anterior, transparent layer of the eye, the cornea.

Symptoms

• Pain and inflammation of the eye
• Tearing
• Blurry vision
• Excessive sensitivity to light
• Pus-like secretions
• Sensation of a foreign object.

Treatment

Treatment for diseases caused by Propionibacterium acnes is based mainly on antibiotics that stop the proliferation of the bacteria.

In the case of acne, benzoyl peroxide is used, as well as clindamycin, erythromycin and tetracycline. In the other conditions such as endocarditis and pericarditis, penicillin, cephalosporins, and vancomycin can be used.

It all depends on the susceptibility results that the culture of the pathogenic bacteria produces.

References

1. Corrales, L., Antolinez, D., Bohórquez, J. and Corredor, A. (2015). Anaerobic bacteria: processes that carry out and contribute to the sustainability of life on the planet. Not going. 13 (23). 55-81
2. Guío, L., Sarriá, C., De las Cuevas, C., Gamallo, C. and Duarte, J. Chronic endocarditis of the prosthetic valve due to Propionibacterium acnes: an unsuspected cause of prosthetic dysfunction. (2009). Spanish Journal of Cardiology. 62 (2). 167-177
3. Jaramillo, M. and Bazalar, D. (2006). Etiological significance of Propionibacterium acnes in the development of acne vulgaris. Dermatological folia of Peru. 17 (1). 25-31
4. Propionibacterium acnes. Retrieved from: microbewiki.com
5. Propionibacterium acnes. Retrieved from: antimicrobe.org
6. Schlecht, S., Freudenberg, A. and Galanos, C. (1997). Culture and biological activity of Propionibacterium acnes. 25 (4). 247-249
7. Corneal ulcer. Retrieved from: aao.org