Actinomycetales

Actinomycetales are a group of Gram-positive bacteria known for their filamentous growth. 

In medical settings, they are known both as normal human flora and as pathogens capable of causing a range of diseases, particularly in immunocompromised individuals.  

In the environment, they play a crucial role in decomposing organic materials, thus contributing to nutrient cycling and soil health.

By examining the presence, absence, or quantity of Actinomycetales in different settings, scientists and medical professionals can gather critical information about disease dynamics, microbial ecology, and environmental health.

Understanding Actinomycetales  [5., 8., 9.]

Actinomycetales is an order of Gram-positive bacteria belonging to the phylum Actinobacteria.  

Actinomycetales are bacteria that do not have the ability to move on their own. They also grow very slowly compared to other bacteria. 

These bacteria are not stained by certain dyes (acid-fast) and may require low oxygen levels (microaerophilic), or they can live with or without oxygen (facultative anaerobes), or they can only live without oxygen (obligate anaerobes).

Actinomycetales are often distinguished by their mycelial morphology with branched hyphae and the ability to form spores, although not all actinomycetes are sporulating.  Members of the Actinomycetales order exhibit great diversity in characteristics such as moisture tolerance, habitat, optimal pH, and thermophilicity.

They are often found at moderate pH levels, though some acidophilic and alkaliphilic species are known.  While some thermophilic actinomycetes have been recorded, most species appear to prefer moderate temperatures.

Actinomycetales are primarily found in soils and were originally thought to be solely terrestrial.  However, many marine species have been discovered in aquatic systems worldwide.  

They are being evaluated for various industrial applications, including probiotic use in aquaculture, biofuel production, and the production of compounds used in the development of plastics, detergents, and other products.

One of the most well-known genera within the Actinomycetales order is Streptomyces.   Streptomyces spp. are saprophytic bacteria found in soil as well as aquatic environments, which possess a variety of morphological forms that often resemble fungi.  Under unfavorable conditions, aerial hyphae extend away from the mycelium to release spores for dispersal.  

Actinomycetales in the Human Microbiome  [1., 3., 6., 7., 10.] 

Actinomycetales is a normal part of the human gastrointestinal microbiome, particularly on the skin.  Members of the Actinomycetales order, particularly genera like Propionibacterium, Corynebacterium, Rothia, and Actinomyces, are commonly found colonizing the human digestive tract.  [7., 10.]

Actinomycetales species are ubiquitous, occurring in soil and in the animal and human microbiota.  They are distributed widely as part of the microbiome in the alimentary tract, from the oral cavity to the intestinal tract.  [7.]

The most diverse and frequently detected Actinomycetales in the human gut include Propionibacterium and Corynebacterium.  [10.]  Propionibacterium species are major vitamin B12 producers and contribute to the degradation of gluten.  [10.]

Actinomyces graevenitzii has been detected in increased abundance in the small intestine of celiac disease patients.  [10.]

Changes in the composition and interactions of Actinomycetes with other microbiota members may contribute to various alimentary tract diseases.  [7.]

Actinomycetales is also part of the normal human microbiome on the skin.  The Actinobacteria phylum, which includes the Actinomycetales order, is one of the most abundant on human skin.  [1., 3.]

Specific genera within Actinomycetales, such as Propionibacterium and Corynebacterium, are commonly found on the skin.  Propionibacterium acnes colonizes healthy pores and produces compounds that inhibit the growth of certain pathogens.  [1.]

However, under certain conditions, some Actinomycetales species can become opportunistic pathogens.  

Common Diseases Associated with Actinomycetales

Actinomycetales are associated with a variety of diseases, depending on the species and the body's immune response.  [7.] 

Actinomycosis  [DYNAMED>>>>>>>

Actinomyces species, for instance, are known for causing actinomycosis, a condition characterized by the formation of painful abscesses in the mouth, lungs, or gastrointestinal tract.  [2.]

Actinomycosis is characterized by the formation of abscesses, sinus tracts, and sulfur granules.  The infection typically spreads from normally colonized sites like the oropharynx, gastrointestinal tract, or urogenital tract after the mucosal barrier is compromised.  Polymicrobial infections are common.

The most frequent types of actinomycosis are cervicofacial, abdominal/pelvic, and thoracic, while less common forms include extrafacial bone and joint, central nervous system, cutaneous, and disseminated infections.  The disease primarily affects individuals aged 20-60 years, with the highest incidence between 30-50 years. 

Except for pelvic actinomycosis, men are affected three times more often than women.

Risk factors vary depending on the infection site. Poor oral hygiene, oral mucosal trauma, immunocompromise, male sex, and other head and neck infections are associated with cervicofacial disease.  

Actinomycosis typically presents as a chronic, slowly progressive infection with abscesses, fistulas, dense fibrosis, and/or draining sinus tracts. Mortality rates vary between 0% and 28%, with the highest rates in patients with cerebral actinomycosis.

Laboratory Testing for Actinomycetales

To effectively diagnose diseases caused by Actinomycetales and assess their presence in environmental samples, accurate and reliable laboratory testing methods are essential. 

Current Methodologies for Detecting and Quantifying Actinomycetales

Testing for Actinomycetales to diagnose Actinomycosis may include culture of infected tissue or sulfur granules, or sputum or bronchial lavage.

In functional medicine settings, assessment of Actinomycetales as part of the microbiome often utilizes a stool sample.  Some laboratory companies may require special preparation prior to sample collection.

Interpretation of Laboratory Results

Optimal Levels of Actinomycetales

It is important to consult with the laboratory company used to determine optimal levels of Actinomycetales in stool testing.  One company reports Actinomycetales levels on a scale from -3 to +3, with 0 being considered the optimal level.

Clinical Significance of Low Levels of Actinomycetales

Actinomycetales levels have been shown to decrease in irritable bowel syndrome.  [4.]

Clinical Significance of High Levels of Actinomycetales

Proton-pump inhibitor drugs may increase the abundance of Actinomycetales in the gut by reducing stomach acid levels. This allows microbes normally found in the mouth to colonize the intestines.  [6., 7.]

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