Evaluation of the synergistic effect of tomatidine with several antibiotics against standard and clinical isolates of Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Escherichia coli

Antibiotic resistance is an important problem in antibiotic treatment of infections, particularly in hospitals. Tomatidine is a plant secondary metabolite with antimicrobial and antifungal effects. This study examined the possible synergistic effect tomatidine with several antibiotics against standard and clinical strains of Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Escherichia coli. After determining the minimum inhibitory concentrations (MICs) of antibiotics and tomatidine against the bacterial isolates using broth microdilution method, the synergistic effect between tomatidine and antibiotics was evaluated by checkerboard method and calculation of FIC indices. Tomatidine alone did not show any antimicrobial effect. However, it had synergistic effect with gentamicin and cefepime against standard and clinical isolates of S. aureus and P. aeruginosa, respectively. It also had synergistic effect with ampicillin and ciprofloxacin only against standard strains of E. faecalis and P. aeruginosa, respectively. In conclusion, tomatidine could be considered as a potential antibiotic potentiator for gentamicin, cefepime and ciprofloxacin, and ampicillin against Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis infections, respectively. However, the toxicological and pharmacological properties of tomatidine for use as a therapeutic agent remain to be determined.