Do agrobacteria pose a danger to humans?

Agrobacterium tumefaciens is a plant pathogen with oncogenic potential for plants. The host range of A. tumefaciens includes more than 600 plant species from nearly 100 families of dicotyledonous and gymnospermous plants. In contrast, only a few representatives of monocotyledonous plants are susceptible to A. tumefaciens. Despite their phytopathogenic properties due to the tumor-inducing (Ti) plasmid, there have been isolated reports of the detection of Ti plasmid-free A. tumefaciens variants (also called "A. radiobacter") in human specimens (e.g., blood, cerebrospinal fluid, peritoneal fluid, or on probes and catheters).

However, detections are extremely rare compared to other opportunistic pathogens. Agrobacteria essentially only cause human infection under two conditions: severe immune deficiency or long-term incorporation of alloplastic implants (e.g., venous catheters). Furthermore, A. tumefaciens does not produce exotoxins, and animal studies indicate very low pathogenicity. Likewise, escape of the organism is not expected to pose a threat to the environment, as Agrobacteria are widespread in the soil worldwide (up to 500 bacteria per g of soil).

Due to these properties and the low pathogenicity as well as the very rare clinical detection as an opportunistic bacterium in humans, the Central Commission for Biological Safety (ZKBS) concludes in its statement on the classification of Agrobacterium tumefaciens ( Ref.: 6790-10-52 ) that A. tumefaciens is an organism of the Risk group 1 The unexpectedly long persistence of Agrobacteria in transgenic plants (cf. Under these circumstances, the AGCT-Gentechnik.report of August 30, 2024 , does not necessarily lead to a reassessment of the risk and, consequently, an adjustment of personal and organizational protective measures when handling Agrobacteria. However, a clear system for marking plants in genetic engineering facilities, e.g., in the form of a graduated color system, is recommended.

A traffic light labeling system is conceivable for marking newly transformed plants and transgenic plants of the subsequent generation with a high or moderate risk of contamination (generation T0-T1: red), subsequent transgenic generations with a low or negligible risk of contamination (generation ≥T2: yellow), and non-transgenic wild-type plants (green). The full statement can be found at File number 6790-05-02-41 on the ZKBS website.

The criteria to be applied for classifying other plant pathogens as donor and recipient organisms for genetic engineering work will be discussed in the next AGCT-Gentechnik.report.