Anti-Acinetobacter baumanniiactivity of selected phytochemicals alone, in binary combinations and in combinations with conventional antibiotics

Acinetobacter baumanniiis one of the emerging multidrug- and pandrug-resistant pathogens. The aim of the study was to determine anti-A. baumanniiactivity of selected terpenes, terpenoids and phenylpropanoids alone, in binary combinations, and in combinations with conventional antibiotics using microdilution-checkerboard and time-kill curve method. The most effective were terpenoids carvacrol (7.0-28.0 mu g mL(-1)) and thymol (22.0-76.0 mu g mL(-1)), as well as phenylpropanoid compound eugenol (90.5-304.0 mu g mL(-1)), with the active concentrations were comparable to antibiotics. The binary combinations showed additive or indifferent effects. The combination gentamicin-carvacrol was synergistic only against reference strain (FICI = 0.50), while other combinations were additive. The best bacteriostatic activity showed carvacrol, thymol or eugenol in combination with ciprofloxacin (FICI range 0.11-0.50) against both the reference and multidrug-resistant strains. The synergistic effect was further confirmed by time kill curve method and obtained after only 15 h. The results indicate a new possible therapeutic strategy against multiple resistantA. baumannii.

Automated summary

The study found that carvacrol, thymol, and eugenol exhibited good antibacterial activity against A. baumannii, especially when used in combination with ciprofloxacin. The synergistic effect was confirmed by the time kill curve method.