CONICET | Buscador de Institutos y Recursos Humanos

Luteolin (LT) a flavonoid isolated from fruits of Prosopis strombulifera var. strombulifera with antioxidant properties and scavenger capacity of free radicals, has demonstrated in previous studies of our group, a marked protective effect against the production of reactive oxygen species (ROS) induced bygentamicin (GEN), ciprofloxacin (CIP) and chloramphenicol (CMP) in human leukocytes showing besides synergistic effect on GEN antimicrobial activity. These results motivated us to study the effect of LT on the activity of CIP and CMP, in order to determine if its protective action on human cells can modify the antibacterial activity of these antibiotics in different strains of Escherichia coli and Staphylococcus aureus.A reference strain of E. coli ATCC 25922 and a clinical strain of E. coli resistant to GEN and CIP, a reference strain of S. aureus ATCC 29213 and a clinical strain of S. aureus resistant to GEN and CIP were used. The microdilution method was used to determine the Minimum Inhibitory Concentration (MIC) of LT on all strains of E. coli and S. aureus, while the checkerboard method was used to determine the interaction between LT and the antibiotics CIP and CMP employing combinations of these compounds at different concentrations in Mueller-Hinton broth. So, the combinations LT plus CIP and LT plus CMPfor the inhibition of clinical strains of S. aureus demonstrated an increase in bacterial susceptibility to this antibiotics, being observed a decrease of 8-fold in the MIC value of the same when were combinedwith LT. Moreover, when LT was combined whit these antibiotics for the inhibition of S. aureus ATCC a synergistic effect was revealed whit CIP (FICILT+CIP = 0.5) when the MIC of CIP and LT were decreased 4times below their individual MIC and likewise, the combination LT plus CMP demonstrated a synergistic effect (FICILT+CMP = 0.378) when the MIC of CMP decreased 4 times and the MIC of LT decreased 8 times respect their individual MIC. Regarding in both strains of E. coli the presence of LT did not produce changes in the susceptibility to CIP and CMP. On this basis we can conclude that LT significantly increase the antibacterial activity of CIP and CMP in strains of S. aureus, revealing synergistic effects in the clinicalstrains, while the combination of LT with these antibiotics did not alter the sensitivity of reference strains of E. coli. Therefore, LT proved to have a protective effect against oxidative stress induced by CIP and CMP in human leukocytes without modifying the antibacterial effect of these drugs in E.coli and strengthening it against S. aureus strains