In vitro and in vivo evaluation of antibacterial activity of 1,8-cineol and the essential oil of Myrciaria pilosa Sobral & Couto

The search for new drugs with antimicrobial activity is a global imperative. Therefore, the aim of the study was to assess the antimicrobial and modulatory activities of the essential oil from Myrciaria pilosa leaf (EOMP) and its main compound, 1,8-cineole (CNL), against resistant bacteria. So, initial the EOMP was obtained by hydrodistillation and analyzed by gas chromatography, identifying CNL as the main compound (34.51 %) present. The Minimum inhibitory concentration (MIC) tests were performed against resistant bacterial isolates of environmental and clinical origin. The results shows that the combination of EOMP and CNL with ampicillin (AMP) significantly reduced MIC values, with FICI values ranging from 0.005 to 1.0 against isolates of Staphylococcus schleiferi, Staphylococcus haemolyticus, Staphylococcus aureus, and Klebsiella oxytoca. As for the results of the growth curve and bacterial kill time assays, for K. oxytoca and S. haemolyticus showed a greater reduction in bacterial load compared to untreated strains. For the in vivo models with Tenebrio molitor, the treatments showed no toxic effects and were effective within the first 24 h in protecting the larvae against infections caused by resistant bacteria. These findings are the first report of the synergistic activity of EOMP with AMP, in addition to its in vivo effectiveness, and reinforce the synergistic potential of essential oils in combating bacterial resistance.