In vitro synergistic interactions of Protocatechuic acid and Chlorogenic acid in combination with antibiotics against animal pathogens

The Array of Antibacterial Action of Protocatechuic Acid Ethyl Ester and Erythromycin on Staphylococcal Strains

“…To the best of our knowledge, there are no studies, except ours, on the antibacterial activity of EDHB, but works on the antimicrobial potential of the PCA are worth discussing. Chai et al [ 36 ] studied the action of PCA and chlorogenic acid in combination with antibiotics against Escherichia coli , S. aureus , Streptococcus iniae and Proteus mirabilis . The authors found that the growth of Gram-negative bacteria was inhibited to a lesser extent by PCA and chlorogenic acid than the growth of Gram-positive pathogens, and that the effect of PCA was more prominent than that of chlorogenic acid.…”

“…The MIC value of PCA against S. aureus in their study was 300 µg/mL, so it was close to the median obtained in our work for EDHB (512 µg/mL). Chai et al [ 36 ] also studied an interaction between PCA and antibiotics. A synergistic effect against S. aureus was noted for the PCA with clinafloxacin and gatifloxacin, an additive effect for the combination with ciprofloxacin, and an indifferent effect for the combination with sulfamonomethoxine.…”

“…The susceptibility of staphylococcal strains to the combination of erythromycin and EDHB was assessed by determining the fractional inhibitory concentration (FIC) value for each strain. The checkerboard microdilution method with modifications was used to determine the total susceptibility effect of the tested strains [ 35 , 36 ]. Briefly, the erythromycin and EDHB solutions corresponding to an MIC value of 8 were prepared.…”

“…The MIC was re-established for EDHB and erythromycin for each strain. Then the FIC [ 35 , 36 ] was calculated for EDHB and erythromycin and their sum for each well. The following formula was used: FIC index = FICA + FICB = (MICA + B)/MICA + (MICB + A)/MICB where:…”

“…MICB-MIC of a polyphenolic compound alone. Many different combinations are observed in the checkerboard test; therefore, only the FIC values of the most efficient combination of compounds are used to calculate the FICI [35,36]. Based on the FIC index value for each strain, the relationship between EDHB and erythromycin was assessed according to the following scale: FIC ≤ 0.5-means synergism; 0.5 < FIC ≤ 1-means additive effect; 1 < FIC ≤ 4-means indifference; FIC > 4-means antagonism [1].…”