Piper betle L. (betel quid) shows bacteriostatic, additive, and synergistic antimicrobial action when combined with conventional antibiotics

• P. betle (PB) is commonly chewed as betel quid (paan) and is reputed as a famous medicinal spice.
• We studied the antibacterial activities of PB extracts and its antibiotic modulating activity.
• PB were evaluated via the broth microdilution assay against 6 ATCC bacterial strains.
• Antibiotics modulating effects was assessed using a modified Checkerboard method.
• Five extracts inhibited at least one of the six bacterial strains tested.
• Greatest synergy was observed against ATCC strain of Pseudomonas aeruginosa.
• Lower MICs occurred with increasing phenol and flavonoid content.

Piper betle L., commonly chewed as betel quid (paan), has been extensively acclaimed in a panoply of countries for both its nutritive and medicinal values. The present study was geared towards investigating the antibacterial activities of P. betle extracts and its antibiotic modulating activity. A decoction of P. betle (AQE) leaves as used traditionally, as well as ethanolic (EE), ethylacetate (EAE), acetone (ACE), and dichloromethane (DCME) extracts were evaluated using the broth microdilution assay against six bacterial ATCC strains. The minimum inhibitory concentration (MIC), bacteriostatic and bacteriocidal activities of the extracts were evaluated. Additionally, the ability of the extracts to modulate conventional antibiotics (synergistic, additive, indifference, antagonistic) was assessed using a modified Checkerboard method and the fractional inhibitory concentration index (ƩFIC) was calculated. The phytochemical profile of each extract was determined and the Pearson’s correlation coefficient was used to establish any association between the MIC, ƩFIC, and phytochemical content. All the five extracts inhibited at least one of the six bacterial strains tested with EAE and ACE exhibiting the most potent antibacterial activity. The lowest MIC (0.2500 μg/μl) recorded was against Staphylococcus aureus. Piper betle has been further shown to exhibit only bacteriostatic effect. Results from the Checkerboard indicated additive and synergistic effects of P. betle extracts especially in the 50% EAE-50% antibiotic and 50% ACE-50% antibiotic combinations. The greatest synergy was observed against Pseudomonas aeruginosa (ƩFIC 0.09) in the 70% ACE-30% Chloramphenicol combination. Synergy was also observed against S. aureus, Propionibacterium acnes, Staphylococcus epidermidis, and Streptococcus pyogenes. Phytochemical screening revealed that ACE and EAE contain the highest amount of phenols while DCME contains the highest amount of flavonoids. Statistical analysis showed that lower MICs occurred with increasing phenol content (R = − 0.392, p ≤ 0.05) and increasing flavonoid content (R = − 0.551, p ≤ 0.01). However, no correlation was established between ƩFIC and phytochemical content which could indicate a different mechanism of action employed by the combinations. Data amassed have provided insight into the antibacterial activity, antibiotic modulating activity, and the phytochemical profile of P. betle.