American Society of Hirudotherapy

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

Microbiology published in Infect Immun (1999)

Last Updated: June 18, 2026Reviewed by: ASH Editorial Board
Research article — evidence reviewArticle reference
Evidence: Research reportSafety & Infection ControlGenomics & ProteomicsGraf J · Infection and immunity, 1999

Abstract

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.

Publication typeJournal ArticleResearch Support, Non-U.S. Gov't
Indexed MeSH termsAeromonasAnimalsColony Count, MicrobialDNA, RibosomalDigestive SystemFecesHumansKineticsLeechesMolecular Sequence DataRNA, Ribosomal, 16SSymbiosis

Summary

First definitive identification of Aeromonas veronii biovar sobria as the dominant culturable bacterium in the Hirudo medicinalis crop, with up to 20% rate of post-procedure infections absent prophylaxis.

Why This Matters for Hirudotherapy

This study cultivated and characterized bacteria from the digestive tract of Hirudo medicinalis, identifying the main culturable bacterium as Aeromonas veronii biovar sobria through biochemical testing and 16S rRNA gene sequence comparison. The abstract reports that a rifampin-resistant derivative of a symbiotic isolate rapidly colonized the leech crop (in vivo doubling time 1.2 h at 23°C), reaching native flora densities, and that human fecal isolates of A. hydrophila and A. veronii biovar sobria could also colonize. This is directly relevant to ASH's domain because Aeromonas infection occurs in up to 20% of leech therapy patients, and characterizing the symbiotic flora is essential for understanding and managing this clinically significant complication. The study provides foundational microbiological data rather than clinical hirudotherapy outcomes.

Citation

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

Graf J · Infection and immunity, 1999

DOI

Added to ASH library: May 26, 2026 · Site last updated: June 18, 2026

This website provides educational information and does not constitute medical advice, diagnosis, or treatment recommendations. Medicinal leech therapy carries clinically meaningful risks and should be performed only by qualified clinicians under institutionally approved protocols. FDA 510(k) clearance for medicinal leeches is limited to specific indications; investigational and off-label discussions are labeled accordingly. For patient-specific guidance, consult a qualified healthcare provider.