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

Background

Bacterial resistance is a serious world wide challenge in both human and veterinary medicine. Some research showed that Protocatechuic acid and Chlorogenic acid have an inhibitory effect on numerous kinds of bacteria.

Objectives

Our research aimed to investigate the role of Protocatechuic acid and Chlorogenic acid in combination with antibiotics against several common veterinary bacteria which showed resistance to antibiotics

Methods

The minimum inhibitory concentrations (MICs) of Protocatechuic acid, Chlorogenic acid and antibiotics against the 4 bacterial strains were tested through micro-dilution method. The fractional inhibitory concentration indices (FICIs) of Protocatechuic acid and Chlorogenic acid combined with antibiotics respectively were measured by microdilution checkerboard technique.

Results

From the 60 tests, 31 were synergistic, 25 additive, 3 indifferent, and only 1 test revealed an antagonistic effect. All synergistic or additive antibacterial effects were seen for combinations of Protocatechuic acid or Chlorogenic acid together with different class of antibiotics such as cell wall / cell membrane synthesis inhibitors, protein synthesis inhibitors and DNA synthesis inhibitors. In general, the combined effects of Protocatechuic acid and Chlorogenic acid with antibiotics against Gram-negative bacteria were better than that of Gram-positive bacteria.

Conclusions

The study showed that Protocatechuic acid and Chlorogenic acid can enhance the antimicrobial activity of most of the tested antibiotics against the bacterial strains of Escherichia coli, Staphylococcus aureus, Streptococcus iniae, Proteus mirabilis.