Selected medicinal plant extracts as inhibitors of conjugal transfer of plasmid-mediated antibiotic resistance in Escherichia coli

Antibiotic resistance is a global health concern and plasmids are a major mechanism of spreading bacterial resistance. Plasmids transfer the genes responsible for the resistance by four secretion steps. Inhibiting this process is potentially a good therapeutic target identifying substances modulating antibiotic resistance [1]. In this study, selected medicinal plant extracts were screened for their ability to inhibit the conjugal transfer of plasmids in Escherichia coli. Bacteria were transformed with a plasmid containing either the drug resistance gene in E. coli with the PKM 101 plasmid (encoding for ampicillin resistance), or the TP114 plasmid (kanamycin resistance). The donor for the bacterial conjugation assay was E. coli possessing the ER 1793 plasmid, which encodes for streptomycin resistance [2]. The test samples used were extracts and fractions from Quercus robur, Robinia pseudoacacia and Baptisia tinctoria. The methanol extract of Quercus robur showed a strong reduction in the conjugal transfer of plasmid PKM101 with a percentage transfer frequency of plasmids to be 4% in each case and below when compared to the control. The percentage transfer frequencies for Quercus robur hexane extract were found to be greater than 50%, indicating that they were poorly active against conjugal transfer of TP114. This could mean that other plant extracts such as Quercus robur methanol and Quercus robur hexane extract may increase the transfer frequency of TP114. Possibly the conjugal inhibitory activity of these natural products is due to the inhibition of conjugative pili formation. Further studies are ongoing to isolate and characterise the natural products responsible.

Keywords: Plasmids, conjugation, Quercus robur, Robinia pseudoacacia, Baptisia tinctoria.

References:

[1] Fernandez-Lopez R, Machón C, Longshaw CM, Martin S, Molin S, Zechner EL, Espinosa M, Lanka E, de la Cruz F. Unsaturated fatty acids are inhibitors of bacterial conjugation. Microbiology, 2005; 151: 3517 – 3526

[2] Livermore, D.M. Bacterial resistance: origins, epidemiology, and impact. Clinical infectious diseases: an official publication of the Infectious Diseases Society of America, 2003; 36(Suppl 1): S11-S23

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