The evaluation of the activity of the aqueous and ethyl acetate extracts of the leaves of
Piper regnellii
was tested against gram-positive and gram-negative bacteria. The aqueous extract displayed a weak activity against
Staphylococcus aureus
and
Bacillus subtilis
with minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of 1000 μg/ml. The ethyl acetate extract presented a good activity against
S. aureus and
B. subtilis with MIC and MBC at 15.62 μg/ml. In contrast to the relative low MICs for gram-positive bacteria, gram-negative bacteria were not inhibited by the extracts at concentrations ≤ 1000 mg/ml. The ethyl acetate extract was fractionated on silica gel into nine fractions. The hexane and chloroform fractions were active against
S. aureus (MIC at 3.9 μg/ml) and
B. subtilis (MIC at 3.9 and 7.8 μg/ml, respectively). Using bioactivity-directed fractionation, the hexane fraction was rechromatographed to yield the antimicrobial compounds 1, 2, 5, and 6 identified as eupomatenoid-6, eupomatenoid-5, eupomatenoid-3, and conocarpan, respectively. The pure compounds 1 and 2 showed a good activity against
S. aureus with MIC of 1.56 μg/ml and 3.12 μg/ml, respectively. Both compounds presented MIC of 3.12 μg/ml against
B. subtilis. The pure compound 6 named as conocarpan was quite active against S. aureus and B. subtilis with MIC of 6.25 μg/ml. The antibacterial properties of
P. regnellii justify its use in traditional medicine for the treatment of wounds, contaminated through bacteria infections.
