Case 1
A 70-year-old woman presented for evaluation of a tender lesion on her left lower back in April 2017 (Fig. 1). There was no fever or associated systemic symptoms. Her past medical history was significant for basal cell carcinoma, melanoma in situ, and seronegative rheumatoid arthritis. She was currently being treated with methotrexate.
Nine days prior to presentation, she was at the beach and felt her back being bitten by an insect. The affected area became red and painful and increased in size over the next few days.
Cutaneous examination showed an erythematous patch—the presumed bite site—with an underlying cystic component on the left lower back (Fig. 2). A small amount of pus was expressed from the lesion and cultured. The bacterial culture grew S. lugdunensis (Table 1) and antibiotic susceptibility testing was performed (Table 2).
Table 1 Characteristics of patients with S. lugdunensis infections
Table 2 Susceptibility results from bacterial cultures of patients with S. lugdunensis cutaneous infection
She was treated with incision and drainage; empiric treatment with cephalexin 500 mg, four times daily for 10 days, was also initiated. A wound check performed 5 days later did not show any significant improvement. Therefore, doxycycline 100 mg, twice daily for 10 days, was added. The infection resolved during the subsequent 3 weeks. There was no recurrence of the infection within 60 days following treatment.
Case 2
A 30-year-old man presented for evaluation of a tender lesion on his right great toe in September 2015. There was no fever or associated systemic symptoms. His past medical history was significant for psoriasis and psoriatic arthritis. He was currently being treated with adalimumab and methotrexate.
Cutaneous examination showed erythema of the medial right great toe nail fold with an underlying abscess. A small amount of pus was expressed from the abscess and cultured. The bacterial culture grew S. lugdunensis, Staphylococcus aureus (S. aureus), and Streptococcus agalactiae (S. agalactiae) as the pathogens (Table 1). Antibiotic susceptibility panels were performed (Table 2).
He was treated with incision and drainage. Empiric oral antibiotic treatment with cephalexin 500 mg, four times daily for 10 days, was initiated. Six days after starting the antibiotic, the patient mentioned that the infection had improved by 70%. The cephalexin treatment was extended for another 20 days, for a total of 30 days of treatment. One month after the initiation of antibiotic therapy, the patient presented to the office for a wound check; the infection had resolved. After an additional 30 days, there were no signs of infection.
Case 3
A 67-year-old man presented for the evaluation of a tender lesion on his left upper back in February 2015. There was no fever or associated systemic symptoms. His medical history was significant for elevated fasting glucose levels. The lesion initially appeared a few months earlier.
Cutaneous examination showed an inflamed cystic lesion with surrounding erythema on the left upper back. A small amount of pus was expressed from the lesion and cultured. Bacterial culture grew S. lugdunensis (Table 1) and antibiotic susceptibility tests were performed (Table 2).
He was treated with incision and drainage; empiric oral antibiotic treatment with cefdinir 300 mg, twice daily for 10 days, was initiated. Two days later, the patient reported that he experienced severe diarrhea. Therefore, the cefdinir was stopped and doxycycline 100 mg, twice daily for 10 days, was initiated. The infection resolved within the 10 days of treatment. There was no clinical evidence of recurrent infection 2 months after completion of treatment.
Case 4
A healthy 80-year-old man presented with right index finger pain and swelling in March 2016. There was no fever or associated systemic symptoms. His past medical history was significant for nodular basal cell carcinoma.
The patient stated that a few days prior to the presentation he was doing some gardening and scraped his finger on a plant. He subsequently developed a large blister with localized throbbing, numbness, and redness.
Cutaneous examination showed an abscess with surrounding erythema on the nail fold of the radial aspect of the right index finger. The finger was cleaned and a small amount of pus was expressed from the abscess and cultured. The bacterial culture grew S. lugdunensis and Streptococcus intermedius (S. intermedius) (Table 1). Antibiotic susceptibility tests were performed (Table 2).
He was treated with incision and drainage; empiric oral antibiotic treatment was initiated with cephalexin 500 mg, four times daily, and sulfamethoxazole–trimethoprim 800–160 mg, twice daily, for 10 days. The infection resolved within 10 days of treatment. Sixty days following completion of treatment, there were no clinical signs of recurrent infection.
Case 5
An 82-year-old man presented for evaluation of a tender lesion on his left lower back in May 2017. There was no fever or associated systemic symptoms. His past medical history was significant for diabetes mellitus and metastatic lentigo maligna melanoma. He was being treated with pembrolizumab.
Cutaneous examination showed an inflamed cyst with surrounding erythema on the left lower back (Fig. 3). A small amount of pus from the cyst was expressed and cultured. Bacterial culture grew S. lugdunensis (Table 1) and antibiotic susceptibility tests were performed (Table 2).
He was treated with incision and drainage. Empiric oral antibiotic treatment with cephalexin 500 mg, four times daily for 30 days, was initiated. The infection cleared within the 30 days of the antibiotic regimen (Figs. 4, 5). There was no recurrence of the infection 60 days after completion of treatment.
Informed consent was obtained from the patients who were included in the study.