By Ethan Covey
A case of cellulitis, tenosynovitis and arthritis caused by Mycoplasma arginini has been identified in an immunocompromised kidney transplant recipient in Slovenia. Historically, this has not been considered a human pathogen.
An investigation into the case found the infection likely resulted from a bite from a pet cat, making it one of the few documented published cases supporting the zoonotic potential of M. arginini (Emerg Infect Dis 2025;31[6]:1207-1210).
“This case highlights the potential of zoonotic and environmental mycoplasmas, such as M. arginini—which has historically been considered non-pathogenic in humans—to cause clinically significant infections in immunocompromised individuals, including solid organ transplant recipients,” said Željka Veceric-Haler, MD, PhD, of the Department of Nephrology at the University Medical Centre Ljubljana, in Slovenia. “Our findings emphasize the importance of heightened diagnostic vigilance and the use of molecular methods when evaluating infections in which conventional microbiological testing fails to identify a causative pathogen.”
The 56-year-old woman had undergone two kidney transplants since 2011 and had been treated for multiple opportunistic infections related to her immunosuppressive drug regimen. Roughly two years after her second kidney transplant, which took place in 2022, she noticed a small lump in the left mid-forearm with redness that progressively spread toward her wrist and elbow. Treatment with oral amoxicillin-clavulanic acid failed to resolve the symptoms, and she was hospitalized. She reported frequent contact with cats and a dog and noted she’d been bitten on her forearm by one of her cats approximately one week prior to hospital admission.
Broad-range bacterial polymerase chain reaction with sequencing from synovial fluid revealed the presence of M. arginini. A combination of doxycycline and moxifloxacin resulted in clinical improvement. Treatment was de-escalated to doxycycline monotherapy after eight days. Following a 10-week course of doxycycline treatment, the patient recovered without any lingering signs of M. arginini infection.
The researchers hope future studies will clarify lingering questions regarding M. arginini transmission and the risk for infection among immunocompromised individuals.
“Important questions remain—particularly regarding the true incidence of M. arginini in human disease, its natural reservoirs, and possible transmission routes,” Dr. Veceric-Haler said. “Targeted surveillance in high-risk populations, including immunosuppressed patients and especially those with profound hypogammaglobulinemia (a condition marked by low antibody levels, leading to a weakened immune system and increased susceptibility to infections), together with the application of advanced molecular diagnostics, will be essential to determine whether this case represents an isolated incident or a previously underrecognized clinical threat.”
Dr. Veceric-Haler reported no relevant financial disclosures.
