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      No Genotoxicity Is Detectable for Escherichia coli Strain Nissle 1917 by Standard In Vitro and In Vivo Tests

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          Probiotic Escherichia coli strain Nissle 1917 (EcN) has a long history of safe use. However, the recently discovered presence of a pks locus in its genome presumably producing colibactin has questioned its safety, as colibactin has been implicated in genotoxicity. Here, we assess the genotoxic potential of EcN. Metabolic products were tested in vitro by the Ames test, a mutagenicity assay developed to detect point mutation-inducing activity. Live EcN were tested by an adapted Ames test. Neither the standard nor the adapted Ames test resulted in increased numbers of revertant colonies, indicating that EcN metabolites or viable cells lacked mutagenic activity. The in vivo Mammalian Alkaline Comet Assay (the gold standard for detecting DNA-strand breaks) was used to determine potentially induced DNA-strand breaks in cells of the gastro-intestinal tract of rats orally administered with viable EcN. Bacteria were given at 10 9–10 11 colony forming units (CFU) per animal by oral gavage on 2 consecutive days and daily for a period of 28 days to 5 rats per group. No significant differences compared to negative controls were found. These results demonstrate that EcN does not induce DNA-strand breaks and does not have any detectable genotoxic potential in the test animals.

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          Most cited references 28

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          A simple technique for quantitation of low levels of DNA damage in individual cells.

          Human lymphocytes were either exposed to X-irradiation (25 to 200 rads) or treated with H2O2 (9.1 to 291 microM) at 4 degrees C and the extent of DNA migration was measured using a single-cell microgel electrophoresis technique under alkaline conditions. Both agents induced a significant increase in DNA migration, beginning at the lowest dose evaluated. Migration patterns were relatively homogeneous among cells exposed to X-rays but heterogeneous among cells treated with H2O2. An analysis of repair kinetics following exposure to 200 rads X-rays was conducted with lymphocytes obtained from three individuals. The bulk of the DNA repair occurred within the first 15 min, while all of the repair was essentially complete by 120 min after exposure. However, some cells demonstrated no repair during this incubation period while other cells demonstrated DNA migration patterns indicative of more damage than that induced by the initial irradiation with X-rays. This technique appears to be sensitive and useful for detecting damage and repair in single cells.
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            Revised methods for the Salmonella mutagenicity test

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              Revised methods for the Salmonella mutagenicity test.

               D Maron,  James Ames (1983)
              The methods for detecting carcinogens and mutagens with the Salmonella mutagenicity test were described previously (Ames et al., 1975b). The present paper is a revision of the methods. Two new tester strains, a frameshift strain (TA97) and a strain carrying an ochre mutation on a multicopy plasmid (TA102), are added to the standard tester set. TA97 replaces TA1537. TA1535 and TA1538 are removed from the recommended set but can be retained at the option of the investigator. TA98 and TA100 are retained. We discuss other special purpose strains and present some minor changes in procedure, principally in the growth, storage, and preservation of the tester strains. Two substitutions are made in diagnostic mutagens to eliminate MNNG and 9-aminoacridine. Some test modifications are discussed.

                Author and article information

                Eur J Microbiol Immunol (Bp)
                Eur J Microbiol Immunol (Bp)
                European Journal of Microbiology & Immunology
                Akadémiai Kiadó (Budapest )
                17 March 2020
                07 April 2020
                : 10
                : 1
                : 11-19
                [1 ]Ardeypharm GmbH , Loerfeldstraße 20, 58313 Herdecke, Germany
                [2 ]Molecular Microbiology and Genomics Consultants , Tannenstraße 7, 55576 Zotzenheim Germany
                Author notes
                *Author for correspondence: Ardeypharm GmbH, Loerfeldstrasse 20, 58313 Herdecke; E-mail: vbuenau@
                © 2020, The Author(s)

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium for non-commercial purposes, provided the original author and source are credited, a link to the CC License is provided, and changes - if any – are indicated.

                Page count
                Figures: 4, Tables: 2, Equations: 0, References: 37, Pages: 9
                Original Research Paper


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