Sphingobium yanoikuyae is a short, rod-shaped, strictly aerobic, gram-negative, non-motile, non-spore-forming bacterium of the Sphingomonadaceae family. It is a hydrophilic bacterium capable of forming biofilms.

Bacteria of the Sphingomonadaceae family have been described in various terrestrial and aquatic environments, including dialysis and water supply equipment (1). Sphingobium yanoikuyae is implicated in the degradation of polycyclic aromatic hydrocarbons. This could be exploited in the development of bioremediation technologies (2).

Peritonitis in peritoneal dialysis is associated with significant morbidity and mortality, and in 4% of cases it can lead to death, damage to the peritoneal membrane, and withdrawal of the dialysis catheter, with temporary or permanent recourse to hemodialysis.

Also belonging to the Sphingomonadaceae family, the Sphingomonas genus was described in 1990 by Yabuuchi et al. (3), identifying Sphingomonas paucimobilis as the type species, and new species in the genus including Sphingomonas yanoikuyae.

The first description of the Sphingobium genus was made by Takeuchi et al. in 2001 (4), distinguishing it from Sphingomonas after phylogenetic analyses of 16S rRNA gene sequences. Sphingobium yanoikuyae is the type species of the genus Sphingobium (5).

Sphingomonas yanoikuyae is the basionym of Sphingobium yanoikuyae, although nomenclature defines them as two distinct species.

While a dozen human Sphingomonas infections of different types have been described (6,7), only two cases of human infections caused by Sphingobium species have been reported. These latter cases involved infection of peritoneal dialysis fluid:

- Sphingobium olei peritonitis (8)

- Sphingobium lactosutens peritonitis (9)

We describe here an 87-year-old patient followed in nephrology for end-stage renal failure of diabetic and vascular origin. He has been treated with peritoneal dialysis since the end of May 2023, after catheter placement in mid-April. The patient was trained and then educated in continuous ambulatory peritoneal dialysis (CAPD). After this education phase, the patient was able to carry out his care independently at home. The peritoneal dialysis protocol included two isotonic bags during the day and one Icodextrin bag at night, six days a week.

A few days after initiation of peritoneal dialysis, the patient presented a deterioration in general condition, accompanied by diabetic imbalance, warranting hospitalization due to the intensity of the anorexia. Clinical examination was unremarkable except for constipation for three days.

Initial laboratory workup revealed an infectious syndrome, with C-reactive protein at 223 mg/l, hyperleukocytosis at 10.9 G/L, and slightly increased procalcitonin at 0.67 ng/ml.

On 2023-06-06, analysis of the dialysate showed a cloudy appearance, with a negative blood agar culture on the first bag. Nevertheless, cellular analysis of this first dialysate sample showed an increase in leukocytes to 750/mm3, including 472 neutrophils per mm3, with numerous mesothelial cells and macrophages.

While analysis of the second bag showed no significant increase in leukocytes (48/mm3 including 13% neutrophils, 43% lymphocytes, 25% histiocytic cells), a culture on blood agar identified in 36 hours:

—

-Numerous Sphingobium yanoikuyae:

– -Sensitive: meropenem, ceftazidime + avibactam

– -Intermediate: ceftazidime, ciprofloxacin

– -Resistant: ceftriaxone, amoxicillin

— -Fairly numerous Sphingomonas sp.:

– -Sensitive: amoxicillin and ciprofloxacin

– -Resistant: meropenem, ceftazidime, ceftriaxone, ceftazidime + avibactam

These two bacteria are closely related in genus but remain distinct.

On both bags, neither direct examination nor blood cultures on dialysate taken simultaneously identified any germs.

The patient was initially treated with vancomycin 1 gram and ceftriaxone 2 grams IV probabilistic therapy. As soon as the Sphingobium antibiogram was obtained, the patient was switched to meropenem 1 gram/d IV, then intraperitoneally with 6-hour stasis for a total of three weeks. A second bacterium, Sphingomonas sp. (resistant to MEROPENEM), was also identified later. Given the favorable clinico-biological course, only Sphingobium was considered to be responsible for the disease.

During hospitalization, the patient developed a peripheral a frigore facial paralysis, with sudden deafness, which did not regress. No etiology was identified for these symptoms. There was possible neurotoxicity of meropenem (10,11) but no plasma meropenem assays were performed to support this hypothesis. Nevertheless, this prescription was in line with antibiotic therapy recommendations for dialysis patients.

Bacteriological analysis of the dialysate came back sterile after 48 hours of treatment, with an improvement in clinical condition and a favorable evolution of biological inflammatory markers.

This clinical case reports the first case of human infection with Sphingobium yanoikuyae, and it is the third case of Sphingobium infection, all in the context of peritoneal dialysis fluid infection.

This picture of pauci-symptomatic peritonitis, which progressed favorably under antibiotic therapy targeting Sphingobium yanoikuyae and not covering the susceptibility of Sphingomonas sp., is in favor of low virulence in our patient.

However, although rare, descriptions in the literature of infections with Sphingomonas species suggest an increase in the incidence of nosocomial infections with the Sphingomonadaceae family, whose resistance profile is still poorly studied (nevertheless, an intrinsic resistance to colistin and an extended resistance to beta-lactams have been described). Their omnipresence in the environment and their adaptability constitute a natural reservoir of antibiotic resistance, which is potentially dangerous for humans due to their opportunistic nature (12).

The patient has given his consent for the publication of this clinical case.

Sara Mouradi: patient management, article writing

Gérard Motte: proofreading the article

Stéphane Torner: proofreading the article

Pierre Lebugle: patient management

Nelly Petitboulanger: bacteriological analysis of samples

Aziz Bemmerzouk: final proofreading of the article

Pierre-Yves Charles: bibliography, article writing, proofreading, final corrections