Miscellaneous Bacterial Infections with Cutaneous Manifestations
Miscellaneous bacterial infections with skin involvement form a broad group of conditions caused by uncommon, opportunistic or waterborne bacteria and by organisms acquired from animals (zoonoses). Unlike the classic staphylococcal, streptococcal or Gram-negative infections, this group includes coryneform bacteria (Corynebacterium minutissimum, Kytococcus sedentarius), filamentous bacteria (Actinomyces israelii, Nocardia brasiliensis), zoonotic bacilli (Erysipelothrix rhusiopathiae, Bartonella henselae) and opportunistic pathogens in immunocompromised patients. The ways these organisms damage the skin vary widely: keratin-digesting enzymes that pit the stratum corneum of the soles, buildup of coproporphyrin III that makes lesions fluoresce, rapid pseudo-malignant capillary proliferation driven by Bartonella, and deep suppurative infection with sulfur granules caused by filamentous bacteria. At Haute-Derma, we use a detailed microbiological work-up (Wood's lamp fluorescence screening, Gram, Kinyoun and Warthin-Starry stains, and skin biopsy for histopathology) combined with targeted antibiotics to clear persistent infections at their source.
How these infections affect skin cells and the immune response:
- Keratinase-Driven Breakdown of the Stratum Corneum and Coproporphyrin III Deposition (Coryneform Epidermotropism):
- In warm, moist, occluded skin (maceration), Kytococcus sedentarius and Corynebacterium spp. multiply rapidly in the stratum corneum. They release serine proteases and keratinases that dissolve keratin directly, producing the many tiny pits (1–3 mm) typical of pitted keratolysis.
- At the same time, Corynebacterium minutissimum produces large amounts of coproporphyrin III. Under long-wave ultraviolet light (Wood's lamp, 365–400 nm), this porphyrin gives off the coral-red fluorescence that is characteristic of erythrasma.
- Bartonella-Induced Vascular Proliferation via HIF-1α and VEGF (Bacterial-Induced Angiogenesis):
- The Gram-negative bacilli Bartonella henselae and Bartonella quintana invade the endothelial cells of dermal blood vessels in immunocompromised patients (for example, those with HIV/AIDS).
- The bacteria block endothelial cell apoptosis and switch on signaling that stabilizes hypoxia-inducible factor 1-alpha (HIF-1α), triggering a surge of vascular endothelial growth factor (VEGF). The resulting runaway capillary growth forms vascular tumors rich in necrotic endothelial cells, known as bacillary angiomatosis.
- Deep Suppurative Infection and Sulfur Granules (Filamentous Granulomatous Infiltration):
- The Gram-positive filamentous bacteria Actinomyces israelii (anaerobic) and Nocardia brasiliensis (aerobic) enter the dermis and subcutaneous fat through open wounds.
- They form abscesses with a hard, woody induration and burrow through fascial planes to create draining sinus tracts. The pus contains sulfur granules: clumps of bacterial filaments coated with calcium phosphate and host proteins.
Clinical Features
| Condition / Organism | Typical Clinical Features | Mechanism and Key Clues |
|---|---|---|
| Erythrasma (Corynebacterium minutissimum) | Well-defined reddish-brown macules or light-brown patches with fine scale; coral-red under Wood's lamp. | Produces coproporphyrin III; common in obesity, diabetes and hot, humid weather. |
| Pitted Keratolysis | Tiny pits (1–3 mm) on pressure-bearing areas of the soles, moist skin and a strong foot odor (malodor). | Secretion of keratinases and volatile sulfur compounds. |
| Erysipeloid (Erysipelothrix rhusiopathiae) | Sharply defined violaceous plaque with a dark-red edge and paler center, itchy and burning; appears on the hand after a cut from handling raw fish or meat. | Opportunistic infection through a wound from animals or seafood; non-suppurative; intrinsically resistant to vancomycin. |
| Bacillary Angiomatosis (Bartonella spp.) | Dark-red to purple, raspberry-like papules and nodules that bleed easily when knocked; mainly in immunocompromised people (HIV). | Capillary proliferation driven by bacterial stimulation of VEGF; bacilli stain with Warthin-Starry silver stain. |
| Cutaneous Actinomycosis (Actinomyces israelii) | Woody, indurated mass that suppurates and forms multiple sinuses draining pus with pale-yellow sulfur granules. | Anaerobic filamentous bacteria causing chronic necrotizing granulomatous inflammation with sinus tracts; follows trauma or dental/oral infection. |
Our Approach
At Haute-Derma, diagnosing these unusual bacterial infections combines optical skin examination with morphological microbiology:
- Wood's Lamp (365–400 nm) and Dermoscopy:
- Wood's lamp examination in a dark room: bright coral-red fluorescence confirms erythrasma within 30 seconds and immediately separates it from fungal infection or contact dermatitis.
- Dermoscopy: in pitted keratolysis, magnification shows round, punched-out pits with steep walls in the stratum corneum; in bacillary angiomatosis, it shows red-purple dome-shaped vascular structures surrounded by a white scaly collarette.
- Rapid Microscopic Staining Panel:
- Gram stain: identifies short Gram-positive coryneform rods in erythrasma and pitted keratolysis, or Gram-negative Bartonella bacilli.
- Warthin-Starry silver stain: shows black-staining clusters of Bartonella in the interstitial stroma of bacillary angiomatosis.
- Modified Kinyoun (partial acid-fast) stain: distinguishes Nocardia (partially acid-fast) from Actinomyces (not acid-fast).
- Skin Biopsy, Histopathology and Molecular PCR: A 3–4 mm punch biopsy is taken from angioma-like lesions or long-standing indurated, draining lesions to rule out malignancy (Kaposi sarcoma, lymphoma), and PCR is used to identify the exact Bartonella or Nocardia species.
Treatment Options at Haute-Derma
Our treatment protocols are tailored to the specific microbiology of each group of organisms:
- Coryneform Infections (Erythrasma and Pitted Keratolysis):
- Localized erythrasma: erythromycin 2% or clindamycin 1% solution or cream, applied twice daily for 14 days.
- Extensive erythrasma or severe pitted keratolysis: oral erythromycin (250 mg four times daily for 14 days) or azithromycin (500 mg on day 1, then 250 mg daily for 4 days).
- Local control of pitted keratolysis: aluminum chloride 20% solution applied at night to reduce foot sweating, plus an antibacterial spray containing benzoyl peroxide 5%.
- Erysipeloid:
- First-line antibiotics: penicillin V (500 mg orally four times daily) or amoxicillin (500 mg orally three times daily) for 7–10 days.
- Penicillin allergy: ciprofloxacin (500 mg orally twice daily) or levofloxacin.
- Important: do not use vancomycin, teicoplanin or daptomycin, because Erysipelothrix rhusiopathiae is intrinsically resistant to glycopeptides.
- Bartonella-Driven Vascular Proliferation (Bacillary Angiomatosis): Preferred drugs are erythromycin (500 mg orally four times daily) or doxycycline (100 mg orally twice daily) for 3–4 months, to eradicate bacteria hiding inside endothelial cells and prevent relapse.
- Deep Filamentous Bacterial Infections (Actinomycosis and Nocardiosis):
- Cutaneous actinomycosis: intravenous penicillin G (18–24 million units/day) for 2–6 weeks, followed by oral amoxicillin (500 mg three times daily) for 6–12 months, with surgical debridement and drainage of the sinus tracts.
- Cutaneous nocardiosis: trimethoprim-sulfamethoxazole (TMP-SMX), 5–10 mg/kg/day based on the TMP component, for 3–6 months.
