Medicinal plant extracts protect epithelial cells from infection and DNA damage caused by colibactin-producing Escherichia coli, and inhibit the growth of bacteria

AIMS

To investigate the biological activity of Thai medicinal plant extracts and their active substances on the inhibition of growth and the transcription of colibactin genes of colibactin-producing Escherichia coli, and effect on the pathogenesis from colibactin toxin including transient infections and colibactin-induced DNA damage.

METHODS AND RESULTS

Among 16 medicinal plants examined, aqueous extracts of Terminalia catappa, Psidium guajava and Sandoricum koetjape demonstrated the growth inhibition against E. coli ATCC 25922, which is known to produce colibactin toxin. These plant extracts contain the active phytochemical compounds, tannin and quercetin, which are able to inhibit the growth of E. coli ATCC 25922. Interestingly, the extracts of T. catappa, P. guajava and S. koetjape, and their compounds tannin and quercetin, protected the eukaryotic epithelial cells of Vero cells and Caco-2 cells from infection and DNA damage by E. coli ATCC 25922. Moreover, these plant extracts and compounds exhibited efficacy to downregulate the expression of five genes (clbA, clbB, clbM, clbN and clbP) that are required for colibactin biosynthesis.

CONCLUSIONS

The extracts of T. catappa, P. guajava and S. koetjape, and their compounds of tannin and quercetin had ability to inhibit the growth and transcription of colibactin genes of colibactin-producing Escherichia coli. Hence, these plant extracts and compounds could protect the transient infection and DNA damage of the eukaryotic epithelial cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first of its kind to report on the enhancement of the biological properties of T. catappa, P. guajava and S. koetjape, and to support the exogenous compound usage of tannin and quercetin, which may be able to protect against the transient infection and DNA damage of eukaryotic cells from E. coli carrying colibactin toxin.

Inhibitory effect of Spirogyra spp. algal extracts against herpes simplex virus type 1 and 2 infection

AIMS

To determine the antiviral activities of Spirogyra spp. algal extracts against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2).

METHODS AND RESULTS

Spirogyra spp. was extracted using water, ethanol and methanol. Aqueous extract of Spirogyra spp. had the lowest toxicity on Vero cells with the 50% cytotoxicity concentration (CC₅₀ ) of 4363·30 μg ml^-1 . As for potent inhibitory effect, the ethanolic extract presented the highest inhibition of viral infection on HSV-1 in the treatment during viral attachment on Vero cells with 50% inhibitory concentration (IC₅₀ ) and selective index (SI) values of 164·20 and 2·17 μg ml^-1 . However, the methanolic extract showed the highest inhibition of HSV-2 when treated during viral attachment with IC₅₀ and SI values of 75·03 and 3·34 μg ml^-1 . The methanolic extract of Spirogyra spp. also demonstrated significant virucidal effects on viral particles. Therefore, anti-HSV activity at various stages of the viral multiplication cycle was shown. The main active compounds in the active fractions of Spirogyra spp. ethanolic extract against HSV were found to be alkaloids, essential oils and terpenoids.

CONCLUSIONS

The highest anti-HSV activity was obtained from the ethanolic extract of Spirogyra spp. The extract inhibited the HSV viral particles and the inhibition was during the viral attachment and the viral multiplication.

SIGNIFICANCE AND IMPACT OF THE STUDY

Anti-HSV activity of extract of freshwater green macroalga Spirogyra spp. in Thailand was demonstrated. Therefore, anti-HSV product containing the Spirogyra spp. extract should be developed for treatment of HSV infection.

Anti-herpes simplex virus activities of Eugenia caryophyllus (Spreng.) Bullock & S. G. Harrison and essential oil, eugenol

In this study, an extract from the flower buds of Eugenia caryophyllus (Spreng.) Bullock & S. G. Harrison and the essential oil, eugenol, were evaluated for their anti-herpes simplex virus properties on standard HSV-1(F), standard HSV-2(G) and ten HSV isolates. The plaque reduction assay showed that HSV-1(F), HSV-2(G), two HSV-1 isolates (2, 30) and four HSV-2 isolates (1, 2, 3, 21) were inhibited by E. caryophyllus. Only HSV-1 isolates 1 and 30 were inhibited by eugenol. Thus, strains or isolates of viruses may affect the range of inhibition. Moreover, particles of HSV standard strains were directly inactivated by E. caryophyllus and eugenol. The total virus yield of HSV standard strains and isolates at 30 h also declined after treatment with E. caryophyllus and eugenol. The E. caryophyllus extract exerted higher antiviral replication on HSV-2(G) than on HSV-1(F). The inhibition of the viral yield of HSV-1 isolates was higher than standard HSV-1(F) and standard HSV-2(G) was also inhibited more than most of the HSV-2 isolates. The anti-HSV activity of eugenol against HSV-1(F) and HSV isolates was stronger than with the E. caryophyllus crude extract. However, the percentage inhibition was more pronounced on HSV-1(F) than on HSV-2(G). Moreover, HSV-1(1) and HSV-2(1, 32) could not replicate when eugenol was included in the assay.