Actinomyces spp

🦠 What is Actinomyces?

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Taxonomy

Despite its name meaning "ray fungus," Actinomyces is actually a bacteria that reproduces by binary fission, not spores or budding.

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Normal Flora

Opportunistic pathogens that are part of normal human microbiota, typically colonizing oral cavity, GI tract, and female urogenital tract.

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Species Count

Currently more than 30 species identified, with Actinomyces israelii being the main causative agent.

                    Key Fact: Actinomycosis is a relatively rare and generally polymicrobial infection that often requires prolonged treatment.
                

                    🔄 Taxonomic Reassignments: Several clinically significant species have been recently reassigned to alternative genera. Common examples include:
                    Schaalia odontolytica (used to be Actinomyces odontolytica)
Winkia neuii (used to be A. neuii)

                

🔍 Morphology & Laboratory

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Branching, beaded, filamentous bacteria
Gram-positive bacilli

Gram Stain Characteristics: Branching, beaded, filamentous, diphtheroid-shaped or coccobacillary Gram-positive bacilli

                    ⚠️ Important: Actinomyces can appear Gram-negative or Gram-variable if not carefully Gram-stained, potentially leading to misidentification.
                

                    🧫 Colony Characteristics: "Breadcrumb/molar-tooth" colonies are classic. Only a few species (e.g., A. israelii) produce the classic breadcrumb/molar tooth colonies. The majority are white or grey in colour, with some producing pigmentation following prolonged incubation periods.
                

Laboratory Identification

                    🔬 Identification Methods: Lab processing usually follows checking for colony morphology, Gram stain and other phenotypic characteristics, followed by identification via MALDI-TOF or molecular methods. Identification using biochemical methods is unreliable - if used, manufacturer's recommendations should be followed.
                

Test	Result	Notes
Spot Indole	Negative	Propionibacterium/Cutibacterium acnes is positive
Catalase	Negative (most species)	Exceptions: A. viscosus, A. neuii subsp. neuii, A. neuii subsp. anitratus, A. radicidentis, A. hominis
Culture Time	10-14 days	Slow-growing organism
Oxygen Requirement	Facultative anaerobe	Except A. israelii, A. gerencseriae, A. meyeri (strict anaerobes)

🎯 Clinical Presentations

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Site	Typical Presentation	Key Predisposing Factors
Cervicofacial (Most common)	Mandibular mass, draining sinuses, "lumpy jaw", lacrimal canaliculitis, pain and trismus	Poor oral hygiene, dental extraction, peri-implantitis with dental implant failure, bisphosphonate-associated osteonecrosis
Thoracic	Chronic pneumonia, lung abscess, chest-wall sinus, indolent course with fever, weight loss, shortness of breath, chest pain, productive cough	Aspiration, dental sepsis, oesophageal perforation
Abdominal	Ileocaecal mass, fistulae mimicking Crohn's, mass, weight loss, fever	Appendicitis, perforated viscus
Pelvic/Genitourinary	Tubo-ovarian abscess, PID, IUD-associated mass, pelvic pain and vaginal bleeding	Long-term copper IUD, pelvic surgery
Central Nervous System	Solitary brain abscess, occasionally cranial osteitis	Haematogenous spread

                    🔍 Diagnostic Hallmark: Actinomyces spreads disregarding tissue and fascial planes, evident in imaging studies.
                

Differential Diagnosis

                    🩺 Key Differentiating Features:
                    Unlike Nocardia: Actinomyces is a commensal bacterium
Disease pattern: Disease occurs when there is a breach in the mucosal barrier, allowing bacteria to invade deeper tissues
Lymphatic involvement: Late/rare in actinomycosis, which may help differentiate from other conditions
Associated conditions: DD includes malignancy, TB, Crohn's disease (abdominal), etc.

                

⭐ Sulfur Granules

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                    🟡 Sulfur Granules: Despite their name, these granules do not contain sulfur. The term comes from their yellow color.
                

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Composition

Made up of tangled masses of filamentous Actinomyces bacteria cemented together by a polysaccharide and protein complex.

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Structure

Show a central tangle of bacteria with peripheral "clubs" arranged in a rosette, encapsulated by the polysaccharide-protein complex.

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Formation

Form as part of a chronic granulomatous infection, resulting from the body's immune response to the bacteria.

⚠️ Other Organisms Producing Similar Granules:

Nocardiosis - Nocardia species
Botryomycosis - Staphylococcus aureus
Eumycetoma - Streptomyces madurae
Other bacteria: Monosporium spp, Cephalosporium spp
Fungi: Aspergillus spp

Important distinction: These other sulphur granules do not have peripheral clubs, unlike those seen in actinomycosis.

Finding sulfur granules in a pus sample or tissue biopsy is considered:

A) Definitive diagnosis of actinomycosis

B) Highly suggestive of actinomycosis

C) Not significant for diagnosis

D) Only found in fungal infections

Correct Answer! While highly suggestive of actinomycosis, similar granules may occasionally be seen in other infections such as nocardiosis, Streptomyces madurae, Staphylococcus aureus (botryomycosis), and others.

💊 Treatment

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Preferred Regimens:

High-dose penicillin is the first-line treatment

For Severe/Extensive Actinomycosis:

Initial parenteral therapy: Penicillin G
Alternative: Ampicillin or Ceftriaxone
Transition to oral: Penicillin V after clinical improvement

For Mild Actinomycosis:

Oral therapy: Penicillin V or Amoxicillin
Alternatives: Tetracycline, Doxycycline, Erythromycin, or Azithromycin

Duration:

Mild disease: 2-6 months total
Severe disease: 6-12 months total
Treatment continues for 1-2 months after clinical/radiologic resolution

Treatment Approach:

75-95% of actinomycosis cases have co-pathogens

Broad-spectrum coverage recommended when significant co-pathogens are present

Preferred: Piperacillin-tazobactam for abdominal infections
Alternative: Amoxicillin-clavulanate for oral-cervicofacial cases

For Penicillin-Allergic Patients:

Ceftriaxone
Doxycycline
Macrolides (erythromycin, clarithromycin, azithromycin)
Carbapenems

Indications for Surgery:

Critical space infections (epidural, brain abscesses)
Massive hemoptysis
Large abscesses not amenable to drainage
Treatment failure
Devitalized tissue present

                            Note: Most actinomycosis can be managed with antimicrobials alone. Surgery should always be combined with antimicrobial therapy.
                        

Monitoring:

Imaging (CT/MRI) after first 4 weeks, then every 6 weeks
Clinical response assessment throughout treatment
Treatment failure warrants evaluation for superinfection or source control issues