Symbiosis of Aeromonas veronii biovar sobria and Hirudo medicinalis, the medicinal leech: a novel model for digestive tract associations

Hirudo medicinalis, the medicinal leech, is applied postoperatively in modern medicine. Infections by Aeromonas occur in up to 20% of patients unless a preemptive antibiotic treatment is administered. The associated infections demonstrate the need for a better understanding of the digestive tract flora of H. medicinalis. Early studies reported the presence of a single bacterial species in the digestive tract and suggested that these bacteria were endosymbionts contributing to the digestion of blood. In this study, we cultivated bacteria from the digestive tract and characterized them biochemically. The biochemical test results identified the isolates as Aeromonas veronii biovar sobria. This species identification was supported by sequence comparison of a variable region of the genes coding for 16S rRNA. In a colonization assay, a rifampin-resistant derivative of a symbiotic isolate was fed in a blood meal to H. medicinalis. The strain colonized the digestive tract rapidly and reached a concentration similar to that of the native bacterial flora. For the first 12 h, the in vivo doubling time was 1.2 h at 23 degreesC. After 12 h, at a density of 5 x 10(7) CFU/ml, the increase in viable counts ceased, suggesting a dramatic reduction in the bacterial growth rate. Two human fecal isolates, identified as Aeromonas hydrophila and A. veronii biovar sobria, were also able to colonize the digestive tract. These data demonstrate that the main culturable bacterium in the crop of H. medicinalis is A. veronii biovar sobria and that the medicinal leech can be used as a model for digestive tract association of Aeromonas species.

Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.

Classical paper establishing Aeromonas veronii biovar sobria (not A. hydrophila) as the predominant culturable symbiont of Hirudo medicinalis crop, with characterization of colonization kinetics in a leech model of digestive tract symbiosis.

Explore how this research connects to clinical practice

More peer-reviewed studies in Safety & Infection Control.

• Leech-Assisted Flap Salvage — Systematic Review of 277 Cases — Whitaker et al. (2012)
• Effects of hirudotherapy on liver functions, lipid profile, and insulin sensitivity in rats with metabolic syndrome — Bilden A et al. (2026)
• AIF-1 and RNASET2 Play Complementary Roles in the Innate Immune Response of Medicinal Leech — Baranzini N et al. (2019)
• [Hirudo medicinalis-leech applications in plastic and reconstructive microsurgery--a literature review] — Knobloch K et al. (2007)
• Bacterial symbioses of the medicinal leech Hirudo verbana — Nelson M, Graf J (2012)
• Leech related Aeromonas complex infection after reconstruction with a microvascular forearm flap — Beger B, von Loewenich F, Goetze E, Moergel M, Walter C (2016)
• Aeromonas septicemia after medicinal leech use following replantation of severed digits — Levine SM, Frangos SG, Hanna B, Colen K, Levine JP (2009)
• Outcomes of flap salvage with medicinal leech therapy — Nguyen MQ et al. (2012)
• The role of leech water sampling in choice of prophylactic antibiotics in medical leech therapy — Wilmer A et al. (2013)
• The development and application of mini-barcodes from mitochondrial DNA for identifying medicinal leeches from traditional medicines — Liu Y et al. (2025)

Browse all ASH-analysed research →