While gram-negative bacteria of the genus Actinomyces were initially described in the 19th century, the species Actinomyces odontolyticus was only first described in the 20th century.1 In humans, these bacteria occur mainly on the mucous membranes of the mouth, digestive tract, and female reproductive organs. After tissue continuity is disrupted, bacteremia, sepsis, and endocarditis often develop.2 Individual cases of Actinomyces odontolyticus infections causing meningeal or brain abscesses have been reported in the literature.3-5

We present a case of a 45-year-old man of Algerian nationality. The patient was an information technology specialist by profession and a former sportsman (weightlifter). He has been living in Poland for 5 years.

In January 2018, the previously healthy patient presented to an emergency room (ER) with cervical spinal pain (pain intensity, 7/10 on the visual analogue scale) radiating to the upper limbs that had been increasing for 2 weeks. Physical examination showed negative meningeal signs. Laboratory tests showed a C-reactive protein (CRP) level of 80 mg/l (reference range [RR], 0–5 mg/l) and a white blood count of 9 × 103/μl (RR, 4–10 × 103/μl), while magnetic resonance imaging (MRI) revealed a massive hernia of the C3/C4 intervertebral disc. The patient was referred to a neurosurgeon, and the hernia was removed (Figure 1A); however, the tissue material was neither tested for the presence of bacteria nor sent for a histologic examination. The patient presented to the ER again in September 2018 due to pain recurrence (7/10) and fluid leakage from the postoperative wound. The CRP level was 56 mg/l, and the patient underwent another surgery (no data available regarding the nature of this treatment). Due to continuous pain, in November 2018, another MRI of the cervical and thoracic spine was performed, and a diagnosis of spondylodiscitis in Th8/Th9 with epidural and paraspinal inflammatory infiltrations was made (Figure 1B and 1C). The CRP level was 123 mg/l. The patient was referred to a neurosurgeon again, and a biopsy of the Th8/Th9 intervertebral disc was performed. Bacterial culture resulted in isolation of Actinomyces odontolyticus; infection with bacteria of the species Nocardia and Mycobacterium was ruled out. The patient underwent a dental consultation, and the condition of his teeth was determined to be normal. Oral therapy with amoxicillin with clavulanic acid at a dose of 2 × 1 g/day for 4 weeks, together with clindamycin 2 × 500 mg/day for 4 weeks was implemented.

Figure 1. A – magnetic resonance imaging (MRI) of the cervical spine in the sagittal plane, T2-weighted fast spin echo (FSE) sequence, showing large, mid-left lateral herniation of the C3/C4 intervertebral disc (arrows) causing spinal stenosis (sagittal dimension, 5 mm), compressing the dural sac, spinal cord, and left spinal nerve root; B, C – MRI of the thoracic spine, T2-weighted FSE sequence in the sagittal plane (B) and 2-dimensional multiple echo recombined gradient echo sequence in the transverse plane (C), showing spondylodiscitis with infiltration of inflammatory epidural changes, with left-lateral modeling of the spinal cord present at the Th8/Th9 intervertebral disc level (blue arrows). Massive infiltrative inflammatory lesions in soft tissues are present paraspinally, 90 mm long and 15 mm wide (white arrows); D, E – gadolinium-enhanced MRI of the thoracic spine, T1-weighted FSE sequence in the sagittal plane (D) and T2-weighted FSE sequence in the transverse plane (E), showing spondylodiscitis with postcontrast enhancement of the Th10 and Th11 discs and vertebrae, and infiltration on the ventral side of the spinal canal, without compression of the spinal cord present at 3 intervertebral discs: Th8/9, Th9/10, and Th10/11 (white arrows). A paraspinal inflammatory infiltration in soft tissues, 86 mm long and 17 mm wide, and an abscess in the antero-left side of the Th12 vertebra (blue arrow) are also visible; F, G – MRI of the lumbosacral spine, T2-weighted short tau inversion recovery sequence in the sagittal plane (F) and T2-weighted FSE sequence in the transverse plane (G), showing spondylodiscitis with an abscess in the spinal canal, infiltrating the nerve roots (white arrows). Numerous abscesses in the dorsal and lumbar muscles are visible (blue arrows).

In January 2019, the thoracic spine pain increased again (5/10). A follow-up contrast-enhanced MRI of the thoracic spine was performed, which showed spondylodiscitis in Th8–Th11, an abscess of the antero-left side of the vertebral body in Th10, and inflammatory infiltration of the prespinal tissues in Th8–Th12 (Figure 1D and 1E). The patient was referred to a neurosurgeon once more, but no indications for surgery were identified. Anti-infective treatment was continued. In March 2019, the patient was referred to an infectious diseases clinic and treatment with amoxicillin was initiated (3 × 500 mg/day), which he continued for 3 months. In July 2019, due to continuing pain, he was hospitalized at the infectious diseases department, and his CRP levels were 8.3 mg/l. He received intravenous ceftriaxone therapy for 6 weeks and continued oral amoxicillin (3 × 500 mg/day) for the following 5 months, which resulted in disappearance of the subjective symptoms.

In January 2020, the patient reported to the ER once again with severe back pain (8/10) which made it difficult for him to move around and function normally.

Contrast-enhanced MRI of the whole spine revealed changes resembling spondylodiscitis at the L4/L5 level, with formation of an abscess inside the spinal canal compressing the nerves, and numerous small abscesses in the back, lumbar muscles, and part of the left iliac muscle (Figure 1F and 1G). The patient was again referred to the infectious diseases department with a CRP level of 37 mg/l. Intravenous ceftriaxone (2 × 2 g/day) and vancomycin (2 × 1 g/day) were added to the therapy. After 2 weeks, significant clinical improvement was observed; the patient was able to walk smoothly without pain. He was discharged due to the outbreak of the COVID-19 pandemic. On an outpatient basis, he continued treatment with intravenous ceftiraxone, 1 × 2 g daily for up to 365 days. Control MRI examination performed prior to the end of the treatment showed reduced inflammation and resolution of most of the lesions. No symptom recurrence has been observed to the present day.

Actinomyces odontolyticus infection can be iatrogenic and associated with a history of a neurosurgical procedure. Infection of the central nervous system caused by the strain of Actinomyces odontolyticus, rarely observed in Poland, poses diagnostic difficulties, and oral antibiotic therapy is not effective.