Antibacterial synergic effect of honey from two stingless bees: Scaptotrigona bipunctata Lepeletier, 1836, and S. postica Latreille, 1807

Abstract

Several studies have tested antimicrobial activity of combinations of honey and various substances. In this study, we tested a combination of two stingless bee honeys against various bacterial strains. In particular: the antibacterial activity of honeys produced by Scaptotrigona bipunctata (SB) and Scaptotrigona postica (SP) was evaluated against Gram-positive and Gram-negative bacterial strains by agar well diffusion assays, minimum inhibitory concentration (MIC) assessment, construction of growth and viability curves and scanning electron microscopy (SEM). The interaction of the two honeys was also evaluated by the checkerboard assay. Inhibition zones ranged from 8 to 22 mm. The MIC values of the individual honeys ranged from 0.62 to 10% (v v(-1)) and decreased to 1/4 to 1/32 when the honeys were combined. SEM images showed division inhibition and cell wall disruption for the SB and SP honeys, respectively, and these alterations were observed in same field when the SB and SP honeys were combined. This study demonstrated that the natural honeys possess in vitro antimicrobial activity against Gram-positive and Gram-negative bacteria, including multidrug-resistant strains. Combination of the SB and SP honeys could lead to the development of new broad-spectrum antimicrobials that have the potential to prevent the emergence of resistant bacterial strains.

Figure 1. Time-kill curves of S. aureus strains exposed to honey at 1×MICs: SB honey used alone, 1.25%; SP honey used alone, 1.25%; and SB/SP honey used in combination, 0.31/0.31%.

The control indicates bacterial growth without honey.

Figure 2. SEM images of the antibacterial effect of SB honey, SP honey and the combined SB/SP honeys against the MRSA N315 strain after 3 h of incubation.

(A) negative control (without honey); (B) cells treated with SB honey (1.25%), showing that the cells formed septa (arrowhead); (C) cells treated with SP honey (1.25%), showing spheroplasts (arrow); (D) cells treated with both the SB (0.31%) and the SP (0.31%) honeys, showing that the cells formed septa (arrowhead) and spheroplasts (arrow). Different morphological alterations can be observed following treatment. The inset images show the detail of the morphological alterations.