First report of subcutaneous abscess caused by Porphyromonas gingivalis

Highlights

• •P. gingivalis is a gram-negative bacterium, frequently found in dental plaque.
• •Porphyromonas infection of the skin is considered rare.
• •Skin abscesses have known involvement with Streptococcus and Staphylococcus species.
• •Porphyromonas is more commonly associated with oral infections.

Abstract

Approximately 90% of skin infections are thought to be attributable to Staphylococcus aureus and Streptococcus pyogenes, along with some anaerobic bacteria such as Bacteroides and Prevotella species, which are considered significant causative agents in post-operative skin infections especially in diabetics. Species from the anaerobic Porphyromonas genus are known to cause oral infections, but rarely cause infection of the skin. In this case report, we describe a subcutaneous abscess caused by Porphyromonas gingivalis in a 67-year-old man who had started chemotherapy for lung cancer (cT3N3M0 stage Ⅲ B) three days prior to consulting a dermatologist. On clinical examination, a fist-sized mass with a hot sensation was observed in the left temporal region of the face, and treatment with cefazolin was commenced at 6 g/day. After three days, the mass was drained via skin incision and pus culture was performed, which revealed infection with P. gingivalis. The patient was successfully treated with abscess drainage and antibiotics therapy. We suggest that in tandem with immunosuppression, P. gingivalis could be a cause of skin infections.

Introduction

Porphyromonas gingivalis was previously known as Bacteroides gingivalis, and renamed P. gingivalis after numerous rounds of taxonomic reclassification. P. gingivalis is a gram-negative anaerobic bacterium, said to be frequently detected in dental plaque [2].

While skin infections caused by Bacteroides and Prevotella, from the same taxonomic class, play a significant role in post-operative infections, infections caused by Porphyromonas are considered rare. Skin abscesses have known involvement with aerobic and anaerobic bacteria, including Streptococcus anginosus, Streptococcus pyogenes, and Staphylococcus aureus, all of which are common causes of skin infections [1,3]. However, Porphyromonas species are more commonly associated with oral infections [2].

In this case study, we describe the onset and treatment of a skin abscess caused by P. gingivalis in a 67-year-old man who was undergoing chemotherapy for lung cancer. Drainage of the abscess via skin incision and treatment with antibioticss resulted in satisfactory resolution.

Case Report

A 67-year-old man attended the Dermatology Department at JR Tokyo General Hospital with swelling to the left side of his head. He had commenced chemotherapy (weekly Paclitaxel [80 mg/m²] + Carboplatin [300 mg/m²], the 1^st line regimen used for lung cancer.) for lung cancer cT3N3M0 stage Ⅲ B three days prior to his consultation with Dermatology. Clinical examination revealed a fist-sized mass with a hot sensation to the left temporal region of the face. Initial laboratory workup on the day of consultation showed an elevated serum C-reactive protein level of 416 nmol/L. The patient was diagnosed with a skin infection and started on cefazolin at 6 g/day, but his symptoms did not improve. Therefore drainage via skin incision was performed three days later, and the exudate was collected and submitted for laboratory culture. Cefazolin at 6 g/day was continued, along with treatment of the wound, and P. gingivalis was detected from the pus culture. Sensitivity of the bacteria to various antibioticss is shown in Table 1. The patient’s symptoms improved within one month, and chemotherapy was resumed.

Table 1.

Antibacterial sensitivity test report of P. gingivalis cultured from exudate collected from the patient’s lesion.

Drug	MIC1	Interpretation
Amoxicillin	≤0.06	S2
Piperacillin	≤0.03	S
Cefazolin	≤0.12	S
Gentamicin	≤0.12	S
Arbekacin	1	R3
Clarithromycin	≤0.12	S
Clindamycin	>4	R
Minocycline	0.5	S
Fosfomycin	≤4	S
Vancomycin	≤1	NA4
Levofloxacin	>8	R

¹MIC: minimum inhibitory concentration; ²S: sensitive; ³R: resistant; ⁴NA: not assessed.

Discussion

This patient experienced a skin abscess caused by P. gingivalis. While this is a common cause of oral infections, it is thought to infect the skin and other systems only rarely [2]. Due to undergoing treatment for lung cancer, the patient was considered immunocompromised [4]. Unfortunately, as the exudate culture was submitted after administration of cefazolin, it is not known whether other causative bacteria could have been involved. However, formation of the abscess and detection of cefazolin-sensitive P. gingivalis only, with no other pathogens, suggests that P. gingivalis was the likely cause. Additionally, the patient uses dentures, which may be a contributing factor for P. gingivalis activity.

There has been suggestion of P. gingivalis involvement in oral cancer [5], but its association with lung cancer has not been reported and remains unknown. No skin infection or skin abscess due to P. gingivalis is reported within the PubMed search range, and this case is considered to be the first of skin abscess due to Porphyromonas gingivalis.

ICMJE Criteria Authorship Statement

Both authors meet the International Committee of Medical Journal Editors authorship criteria (ICMJE criteria). Both authors are the attending physicians for this patient. Yuta Norimatsu wrote the manuscript.

Author statement

Authorship statement: Both authors meet the International Committee of Medical Journal Editors authorship criteria (ICMJE criteria). All authors are the attending physicians for this patient. Yuta Norimatsu wrote the manuscript.

Declarations of Competing Interest

None.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Informed consent

We obtained written signed consent from the patient to publish his clinical details.