Antibacterial activity and interaction in vitro of extract from Piper montealegreanum Yuncker on antibiotics of clinical use

Wilma Wilma, Harley Harley, Luanne Luanne, Baldoíno Baldoíno, Maria Célia Chaves, Raïssa Raïssa

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Introduction: Antibiotic and combination therapies are very commonly used nowadays to treat infectious diseases, and over the years new treatment strategies have been searched for and developed. Few chemical studies have been conducted about the biological activity of Piper montealegreanum Yuncker, a shrub native to northern Brazil.
Objective: Evaluate the antibacterial activity and in vitro interaction of crude ethanolic extract (CEE) of P. montealegreanum leaves against Escherichia coli ATCC 25922 with clinical antibiotics.
Method: Leaves from the plant were collected in Belém (Pará, Brazil) and identified at the Botany Department of the Federal University of Rio de Janeiro in Brazil. The plant material was dried, crushed in a mechanical mill and thoroughly extracted with ethanol (4 x 2.0 l). The solvent was removed by reduced pressure and a green residue was obtained. Determination was made of the antibacterial activity of the P. montealegreanum crude ethanolic extract (CEE) against E. coli using the disk diffusion method. Minimum inhibitory concentration (MIC) and interaction with clinical antibiotics such as ampicillin, ciprofloxacin, chloramphenicol, sulfamethoxasol and tetracycline, were determined by adding 20 ·l of the 400 mg/ml-1 crude ethanolic extract (CEE) solution to the antibiotic disks. The results of the interactions were subjected to the Wilcoxon test (p < 0.01).
Results: The CEE was not found to display any activity against E. coli ATCC 25922. However, interaction with the antibiotics was revealed by an increase in the diameter of the growth inhibition halo consistent with synergy interactions.
Conclusions: It was concluded that the crude ethanolic extract of P. montealegreanum was capable of modifying the behavior of antibiotics, hence the importance of the study. Further research should be conducted to identify and quantify plant substances and reveal the interaction mechanisms of CEE of P. montealegreanum with antibiotics.

Key words: Piperaceae; Escherichia coli; interactive effects.