Abstract
Background. The combination of natural products like the bioactive stingless bee nest materials with conventional antibiotics offers a promising strategy to enhance antibacterial efficacy and contend with antimicrobial resistance.
Objective. This study evaluated the potential synergistic effects of Tetragonisca angustula pot-pollen extract combined with amikacin and meropenem against six extensively drug-resistant Gram-negative bacteria of clinical origin.
Methodology. The inhibitory and bactericidal tests of T. angustula pot-pollen extract, amikacin, and meropenem were determined by minimum inhibitory concentration and minimum bactericidal concentration. The checkerboard method was employed to quantify the effect of T. angustula pot-pollen extract in combination with the selected antibiotics. Fractional inhibitory concentration indices were calculated to determine the interactions between T. angustula pot-pollen extract-amikacin and T. angustula pot-pollen extract-meropenem.
Results. The ethanolic extract of T. angustula pot-pollen showed inhibitory activity against all strains tested, with ranging minimum inhibitory concentration from 16 to 128 mg/ml. The minimum bactericidal concentration remained within two ranges above the minimum inhibitory concentration. Based on the fractional inhibitory concentration indices values, 12 interactions were evaluated (T. angustula pot-pollen extract-amikacin and T. angustula pot-pollen extract-meropenem). Of these, 9 (75%) exhibited total synergism, while 3 (25%) showed partial synergistic interactions or addition effects. The combination of T. angustula pot-pollen extract-amikacin indicated a two-to three-fold reduction in the minimum inhibitory concentration for Enterobacterales and Pseudomonadales. The T. angustula pot-pollen extract-meropenem association showed a notable synergistic effect on Klebsiella pneumoniae, Enterobacter ludwigii, Pseudomonas aeruginosa, and Acinetobacter baumannii, with a fractional inhibitory concentration indices ranging from 0.313 to 0.380.
Conclusion. These results revealed that T. angustula pot-pollen extract may enhance the efficacy of existing antibiotics against extensively drug-resistant Gram-negative bacteria, offering a promising alternative in the fight against antimicrobial resistance. Further research is necessary to elucidate clinical applications and underlying mechanisms of the observed synergistic interactions.