What is the recommended treatment for a positive Actinomyces neuii wound infection?

Treatment of Actinomyces neuii Wound Infection

For a wound infection positive for Actinomyces neuii, treat with amoxicillin-clavulanate combined with surgical debridement and meticulous wound care, with a treatment duration of 6 weeks to several months depending on infection severity and clinical response. 1, 2

Antibiotic Selection

First-line therapy should be amoxicillin-clavulanate (oral: 875/125 mg twice daily; IV: ampicillin-sulbactam 1.5-3.0 g every 6 hours). 1, 2 This beta-lactam/beta-lactamase inhibitor combination has demonstrated successful outcomes in documented A. neuii wound infections and provides appropriate coverage for this facultative anaerobic gram-positive rod. 1

Alternative Antibiotic Options

If beta-lactam allergy or intolerance exists, consider:

• Cephalexin (for mild infections) 2
• Clindamycin 2
• Ceftriaxone (particularly for more severe infections or prosthetic involvement) 3
• Ertapenem or ciprofloxacin (documented successful use in case series) 2

The antimicrobial susceptibility pattern of A. neuii generally parallels other Actinomyces species, showing good susceptibility to penicillins, cephalosporins, and carbapenems. 4, 5

Treatment Duration

The duration of antibiotic therapy should be 6 weeks minimum for uncomplicated soft tissue infections, extending to several months (up to 12 months) for complex cases with fistulous tracts, tunneling, or extensive tissue involvement. 1, 3

• Uncomplicated soft tissue infections: 6 weeks of therapy 3
• Infections with communicating abscesses or sinus tracts: Up to 12 months 1
• Prosthetic joint infections: Minimum 6 weeks following surgical debridement 3

Surgical Management

Surgical intervention is essential and should include incision and drainage of any abscesses, debridement of necrotic tissue, and exploration for communicating sinus tracts. 1, 2 A. neuii characteristically causes multiple abscesses that communicate through sinus tracts, particularly in the groin, axilla, and pressure ulcer sites. 1, 4

Key surgical principles:

• Perform thorough incision and drainage of all purulent collections 2
• Debride necrotic tissue aggressively to reduce bacterial load 1
• Explore for and address fistulous tracts and tunneling, which are common with this pathogen 1
• Consider resection of infected prosthetic material if present 3

Clinical Characteristics to Recognize

A. neuii differs from typical Actinomyces species in several important ways:

• Grows aerobically (unlike most Actinomyces) 4
• Does not show branching on microscopy 2, 4
• Does NOT cause typical actinomycosis (cervicofacial, thoracic, or abdominal) 4, 5
• Most commonly causes abscesses and infected atheromas rather than classic actinomycotic lesions 4, 5

Microbiological Diagnosis

Ensure the microbiology laboratory cultures specimens both aerobically and anaerobically, as A. neuii is a facultative anaerobe that grows well aerobically. 2 The organism appears as a catalase-positive, gram-positive coryneform bacillus without branching. 2

MALDI-TOF mass spectrometry has significantly improved identification of this organism, leading to increased recognition of its pathogenic role. 2 Traditional biochemical testing with API-CORYNE may provide preliminary identification, but confirmation with MALDI-TOF or DNA sequencing is recommended. 2

Prognosis

The prognosis is generally excellent with appropriate combined antibiotic and surgical therapy. 2, 4, 5 All documented cases in recent case series showed favorable outcomes when treated with adequate drainage and appropriate antibiotics. 2 However, rare cases of fatal septicemia have been reported, emphasizing the importance of prompt recognition and treatment. 5

Common Pitfalls to Avoid

• Do not rely on antibiotics alone—surgical drainage is essential for successful treatment 1, 2
• Do not use inadequate treatment duration—premature discontinuation may lead to recurrence given the organism's indolent nature 1, 3
• Do not overlook communicating sinus tracts—failure to address these will result in treatment failure 1
• Do not dismiss as a contaminant—A. neuii is a true pathogen when isolated from normally sterile sites or purulent material 2, 4