ACTINOMYCES ISRAELII: CHARACTERISTICS, MORPHOLOGY, PATHOGENESIS - BIOLOGY - 2024

Actinomyces israelii is the most important species of bacteria in the Genus Actinomyces. It was described by Kruse in 1896 and was previously known by the Israeli name Streptothrix.

Due to their morphological characteristics, at some point the members of this genus were mistaken for fungi. However, when they observed that they responded satisfactorily to antibiotic treatment, they were classified within the Bacteria Domain.

Species: israelii.

Morphology

They are Gram-positive branched rods, which often appear filamentary on Gram stain. On blood agar the colonies are white and rough.

Under the electron microscope, the ultrastructures of Actinomyces israelii can be observed. It reveals the presence of hair-like fimbriae protruding through a thick surface coating.

For its part, the thin section reveals a Gram-positive cell wall surrounded by a diffuse outer coating. These structures are believed to be important for the pathogenicity of A. israelii.

Pathologies

Actinomycosis can develop almost anywhere, as long as the mucous membrane is disrupted. Once Actinomyces invades the tissue of a violated mucous membrane, it slowly expands and becomes an abscess.

Classic actinomycosis generally occurs after trauma, tooth extractions, or other similar surgical procedures, at sites where these bacteria can reside as part of the normal flora.

There are several risk factors for the development of actinomycosis. It occurs more commonly in men. Other risk factors can include poor oral hygiene and the use of intrauterine devices.

In addition, immunosuppression and other conditions, such as diabetes, alcoholism, infections with immunosuppressive agents, and the use of steroids predispose individuals to the development of actinomycosis.

On the other hand, the concomitant presence of other organisms can play an important role in reducing oxygen tension, making it more conducive to the growth of anaerobes.

Among the most frequent pathologies are:

Cervicofacial actinomycosis

It is called a bulging jaw, it occupies 55% of actinomycosis.

Inadequate oral hygiene has been associated with major oral diseases such as severe periodontitis, which may be the entry point for A. israelii.

Another entry point may be tooth extraction or oral trauma.

Pelvic actinomycosis

The use of the Intrauterine Device (IUD) is considered the main predisposing factor for pelvic infection in women.

A. israelii in the presence of copper intrauterine devices (IUDs) has been shown to cause the formation of a biological foam within the uterine cavity containing fibrin, phagocytic cells, and proteolytic enzymes.

In the case of progesterone-secreting IUDs, they produce an atrophic endometrial tunic.

These devices allow the ascent of bacteria from the vagina to the endocervix by means of their projecting threads. Subsequently, it favors damage to the endometrial mucosa, due to a foreign body reaction.

Subsequently, the microorganism invades the tissue, where low oxygen concentrations allow its growth, forming abscesses, fistulas, and characteristic fibro-dense tissue such as "sulfur granules."

The clinical manifestations are characterized by brown, dark and foul-smelling leucorrhoea, menorrhagia or abnormal bleeding, fever, dyspareunia, a variable pattern of inflammation with abdominal-pelvic pain, weight loss, and abdominal pain.

This pathology can lead to pelvic inflammatory disease, woody pelvis, endometritis, Tubo-ovarian abscesses, sterility, liver abscesses and death if not diagnosed in time.

Actinomycosis of the respiratory tract

Actinomycosis of the respiratory tract includes pulmonary, bronchial, and laryngeal actinomycosis. Pulmonary actinomycosis is the third most common type of actinomycosis.

Pulmonary actinomycosis

Pulmonary actinomycosis is primarily a consequence of aspiration of oropharyngeal or gastrointestinal secretions. Also due to the direct or indirect extension of a cervicofacial infection or by hematogenous route.

In the early stages of the disease, a focal pulmonary consolidation occurs, which may be surrounded by pulmonary nodules. There are often no associated physical symptoms at this stage.

Primary pulmonary involvement can progress slowly to the formation of a peripheral mass, with or without cavitation, that could invade the adjacent tissue.

At this stage, pulmonary actinomycosis is usually characterized by a slow-growing, contiguous fibrotic lesion that passes through anatomic barriers. The mass is often mistaken for a malignant tumor.

The most common symptoms are nonspecific, similar to those of other chronic lung infections such as tuberculosis or chest cancer: mild fever, weight loss, productive cough, hemoptysis, dyspnea, and chest pain.

Pulmonary actinomycosis could cause extrapulmonary spread, extending from the lung to the pleura, mediastinum, and chest wall, with fistulas and chronic suppuration.

Bronchial actinomycosis

Bronchial actinomycosis is rare. It can occur after mucosal barrier disruption, especially in patients with an endobronchial stent, or with a bronchial foreign body aspiration (eg, from a fish bone).

Laryngeal actinomycosis

With regard to laryngeal actinomycosis, several different forms have been described. Actinomycosis of the vocal cord can mimic primary carcinoma or papilloma.

In patients with a history of laryngeal carcinoma and radiation therapy, actinomycosis can simulate a relapse of laryngeal cancer, since it can present as an ulcerative lesion, most often without abscess or sinusitis.

Osteoradionecrosis

The therapy used in oncology, with irradiation of the head and neck area, can lead to devitalization and necrosis of the jaw.

Actinomyces israelii has been the most frequent microorganism of this genus isolated in this type of pathology.

Diagnosis

In invasive pelvic actinomycosis, it is diagnosed by pathological study of the lesion (fistulas, abscesses, masses) or the endometrium. It can be grown on blood agar or Brucella agar, however the culture is not very useful, since the sensitivity is low and it is generally polymicrobial.

Another possibility of diagnosis is through imaging techniques, although they are often confused with neoplastic processes. In the cervical cytology or Papanicolaou the presence of Actinomyces can be detected in 44% of symptomatic women.

However, in asymptomatic women, the presence of this microorganism in the Pap smear only refers to colonization, but it cannot be guaranteed that it is an ongoing disease.

On Pap smears, Actinomyces appear as basophilic aggregates. These can be small without leukocyte infiltrate, or large with amorphous material and abundant leukocyte infiltrate. Radiated filaments start from the center.

In the case of pulmonary pathologies of doubtful origin, with nonspecific symptoms, repetitively negative microbiological tests and radiological images suspicious of pulmonary neoplasia, the existence of pulmonary actinomycosis should be considered.

Especially in smoking patients, of low socioeconomic status with poor oral status. Also in immunosuppressed patients such as HIV positive, alcoholics, diabetics, transplants etc.

Treatment

Appropriate treatment is penicillin G and drainage of actinomycotic abscesses.

Macrolides (erythromycin, clarithromycin, and azithromycin), clindamycin, tetracycline, or doxycycline can be used in penicillin-allergic patients.

Conventional therapy dictates treatment with an intravenous antimicrobial agent for 6 to 8 weeks, followed by treatment with an oral antimicrobial agent for 6 to 12 months.

Premature termination of antimicrobial therapy can cause a relapse of actinomycosis.

Forecast

At present, the good practice of oral hygiene, the availability of antibiotics and the improvement of surgical techniques have resulted in a decrease in mortality.

References

1. Bouza Y, Jam B, Tartabull Y. Pulmonary actinomycosis. Presentation of a case. Medisur 2015; 13 (6): 795-800. Available at: scielo.sld.
2. Actinomyces. Wikipedia, The Free Encyclopedia. 30 May 2018, 17:49 UTC. 24 Sep 2018, 22:07 en.wikipedia.org
3. Sánchez J. Mercado N, Chilaca F, Rivera J. Use of the IUD associated with secondary infection by Actinomyces in the female genital tract. Rev Esp Patol. 2004; 37 (4): 383-390.
4. López-Olmos J, Gasull J. and Vivar B. Actinomyces and mixed infections in cervicovaginal cytology, in IUD carriers. Clin Invest Gin Obst. 2010; 37 (4): 134–140
5. Cardona J, Herrera D, Valencia M. Prevalence of Actinomyces spp and distribution according to some demographic and clinical factors, Medellín-Colombia 2010-2012. iMedPub Journals Arch med. 2015; 11 (4): 1-9.
6. Sharma S, Valentino III DJ. Actinomycosis. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2018.
7. Figdor D, Davies J. Cell surface structures of Actinomyces israelii. Aust Dent J. 1997; 42 (2): 125-8.
8. Honda H, Bankowski MJ, Kajioka E, Chokrungvaranon N, Kim W, Gallacher ST. Thoracic Vertebral Actinomycosis: Actinomyces israelii and Fusobacterium nucleatum. Journal of Clinical Microbiology. 2008; 46 (6): 2009-2014.
9. Valor F, Sénéchal A, Dupieux C, et al. Actinomycosis: etiology, clinical features, diagnosis, treatment, and management. Infection and Drug Resistance. 2014; 7: 183-197. doi: 10.2147 / IDR.S39601.
10. Ryan KJ, Ray C. Sherris. Medical Microbiology, 6th Edition McGraw-Hill, New York, USA; 2010.
11. Koneman, E, Allen, S, Janda, W, Schreckenberger, P, Winn, W. (2004). Microbiological Diagnosis. (5th ed.). Argentina, Editorial Panamericana SA