Can Cutibacterium acnes be a causative pathogen associated with chronic cough in a patient with a culture report showing little growth of Cutibacterium acnes, with presence of white blood cells (WBC) and epithelial cells?

Cutibacterium acnes and Chronic Cough

Cutibacterium acnes is NOT a causative pathogen of chronic cough and should be considered a contaminant in this clinical context. The presence of "little growth" with WBCs and epithelial cells in your culture strongly suggests specimen contamination from normal skin or oropharyngeal flora rather than true respiratory infection.

Why C. acnes is Not the Cause

C. acnes is a Skin Commensal, Not a Respiratory Pathogen

• C. acnes is a normal skin and mucous membrane colonizing bacterium that commonly contaminates respiratory specimens 1, 2
• The presence of epithelial cells in your culture report indicates oropharyngeal contamination during specimen collection 2
• "Little growth" further supports contamination rather than true infection, as clinically significant respiratory pathogens typically show moderate to heavy growth 3

Chronic Cough Has Well-Established Common Causes

The ACCP guidelines clearly state that in patients with chronic cough and normal chest X-ray who are nonsmokers and not on ACE inhibitors, the diagnostic approach should focus on upper airway cough syndrome (UACS), asthma, non-asthemic eosinophilic bronchitis (NAEB), or GERD—alone or in combination 4. These account for the vast majority of chronic cough cases.

• Tuberculosis, fungi, and parasites should only be considered when more common causes have been ruled out AND the patient has resided in endemic areas 4
• Bacterial infections causing chronic cough typically involve organisms like Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis in the context of chronic bronchitis or bronchiectasis 4

When C. acnes IS a True Pathogen (Not Your Case)

C. acnes can cause true invasive infections, but only in very specific clinical contexts that do NOT include isolated chronic cough:

• Prosthetic joint infections, particularly shoulder implants 5
• Foreign material-associated infections (ventriculo-peritoneal shunts, aortic stent-grafts) 3
• Pneumonia in severely immunocompromised patients on TNF-alpha inhibitors with radiographic findings of pulmonary nodules, hilar adenopathy, and bronchiectasis 1
• Auto-inflammatory bone disorders (CNO, SAPHO syndrome) 6

Critical Distinguishing Features of True C. acnes Infection

When C. acnes is a true pathogen (not applicable to chronic cough):

• Requires presence of foreign material or severe immunosuppression 1, 5, 3
• Presents with systemic signs (fever, weight loss) and specific radiographic abnormalities 1
• Requires tissue biopsy or multiple positive blood cultures, not just sputum culture 1, 3
• One study found that requiring multiple positive cultures may miss true infections, but this applies to bloodstream infections with foreign material, not respiratory specimens 3

What You Should Do Instead

Focus your evaluation on the established common causes of chronic cough:

1. Upper Airway Cough Syndrome (UACS): Look for rhinosinusitis symptoms, postnasal drip, throat clearing 4

2. Asthma: Perform spirometry with bronchodilator response, consider methacholine challenge if spirometry is normal 4

3. GERD: Assess for heartburn, regurgitation, or consider empiric PPI trial 4

4. Non-Asthmatic Eosinophilic Bronchitis (NAEB): Obtain induced sputum for eosinophil count (>3% suggests NAEB) 4

5. Chronic bronchitis: If the patient is a smoker with chronic sputum production 4

Common Pitfalls to Avoid

• Do not treat C. acnes based on sputum culture alone—this leads to unnecessary antibiotic exposure without clinical benefit 2, 3
• Do not assume any bacterial growth in sputum represents infection—the presence of epithelial cells indicates poor specimen quality 2
• Do not pursue exotic infectious causes before ruling out common etiologies—TB and fungi should only be considered after common causes are excluded AND there is epidemiologic risk 4
• Studies show that C. acnes is isolated from asymptomatic patients with foreign material in 62% of open biopsies, demonstrating its propensity for contamination rather than pathogenicity 2