Assessment of antimicrobial activity of ethanolic and aqueous extracts of Aesculus hippocastanum L. (horse chestnut) bark against bacteria isolated from urine of patients diagnosed positive to urinary tract infections.

The search for new antimicrobials is essential to address the worldwide issue of antibiotic resistance which affects all areas requiring the use of antibiotics including the management of diseases such as urinary tract infections (UTIs). AimTo assess the antimicrobial activity of ethanolic and aqueous extract of Aesculus hippocastanum L. (horse chestnut) bark. Material and MethodBioactive compounds were extracted from A. hippocastanum bark using water and ethanol as solvent. The extracts were tested against 10 clinical strains isolated from urine of patients diagnosed positive to urinary tract infections and including five Gram-positive bacteria (Kocuria rhizophila 1542, Enterococcus avium 1669, Staphylococcus simulans 5882, Conybacterium spp 1638, Enterococcus faecalis 5960) and five Gram-negative (Proteus mirabilis 1543, Morganella morganii 543, Citrobacter freundi 426, Acynetobacter baumannii 5841 and Achromobacter xylosoxidans 4892). Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 25922 were used as standard Gram+ and Gram-respectively. The susceptibility of the test strains to antibiotic was assessed using the Kirby Bauer disc diffusion method while the antibacterial activity of the extracts was evaluated using the well diffusion method. We finally determined the Minimum inhibitory concentration (MIC) and the minimum bactericidal concentrations (MBC) by the microdilution method. ResultsA. hippocastanum bark possessed a dry matter content of 65.73%. The volume yield of the ethanolic and aqueous extract (AE) was 77,77% and 74,07% (v/v), respectively, whereas their mass yields were 13,4% and 24,3% (w/w), respectively. All the bacteria were susceptible to amoxiclav, imipenem and ceftriaxone, both standard bacteria (E. coli ATCC 25922 and S. aureus ATCC 6538) were sensitive to all antibiotics while the clinical strains were resistant to at least one antibiotic. K. rizophilia 1542 and Conybacterium spp 1638 were the most resistant bacteria both with multidrug resistance index of 0.45. Except AE on P. Mirabilis 1543 and E. faecalis 5960 (0 mm), both AE and EE were active against all the microorganisms tested with inhibition diameters (mm) which ranged from 5.5-10.0 for AE and 8.0-14.5 for EE. The MICs of EEs varied from 1-4 mg/ml while those of EAs varied from 4-16 mg/ml. Almost all the MBCs of AEs were indeterminate (>64 mg/ml) while those of EE were successfully determined. The ethanolic extracts (EE) were overall more active than the aqueous ones. ConclusionThe A. hippocastanum bark extracts had overall weak antibacterial activity (MIC [≥]0.625 mg/ml) and bacteriostatic potential (MBC/MIC [≥]16) on both Gram-positive and Gram-negative bacteria. Therefore, studies with other solvents (such as methanol and chloroform), other extraction techniques, and synergy tests with conventional antibiotics are needed to conclude on a potential better antimicrobial activity of this plant material.