T. thermophilus Rhamnolipids Induce Cytogenetic Damage on Human Lymphocytes and Bind DNA in vitro

Aims: Bacteria including Pseudomonas and T. thermophilus secretes rhamnose–containing glycolipid biosurfactants called rhamnolipids (RLs), known as bacterial virulence factors. The aim of this investigation was the evaluation of DNA damage induced on human lymphocytes by both RLs itself, secreted in a host organism by pathogens during a bacterial attack or symbiosis and in combination with the camptothecin (CPT), and on calf thymus DNA.

Study Design: Human lymphocytes and calf thymus DNA were treated with isolated T. thermophilus RLs for studying DNA damage in vitro.

Methodology: RLs DNA damaging action was evaluated by the Sister Chromatid Exchanges (SCEs) methodology, a method for estimating genotoxicity of human exposure to different chemicals or other mutagenic agents and by DNA electrophoretic mobility experiments.

Results: RLs at concentrations of 100 and 150 μg/mL reveal significant toxicity. The highest concentration of 200 μg/mL reveals higher genotoxicity. The frequency of SCEs/cell was increased two times over the control level. When CPT, an antineoplastic drug with DNA damaging action, was tested together with RLs the genotoxic activity was reduced significantly (P<0.01) compared to the action caused by CPT itself. Sequential increase in the concentration of RLs results in the proportional reduction of Proliferation Rate Index (PRI) which is a cytostatic index. Also, Mitotic Index (MI), a cytotoxic index, was also significantly decreased at concentration of 200 μg/mL RLs. Addition of RLs in the same concentration together with CPT doesn’t affect the MI so much. Moreover, RLs are obviously capable for strong binding to plasmid or calf thymus DNA in vitro.

Conclusion: RLs exert genotoxicity, cytotoxicity and cytostaticity in human lymphocytes and play probably a protective role for cells against CPT due to RLs’ detergent capability to enrobe CPT and DNA, providing a significant property that might support its possible involvement in DNA horizontal transfer phenomena.