Synergistic Effects of Herbal Extracts in Combination with Conventional Antibiotics

Conventional antibiotic treatment of bacterial infections is hampered by prevalent antimicrobial resistance. In this research, the synergistic antibacterial activity of different herbal extracts and cefixime against resistant clinical isolates is tested. The preliminary antibiotic susceptibility and antibacterial activity of the herbal extracts were evaluated using disc diffusion and microbroth dilution. Checkerboard experiments, time-kill kinetics, and protein content assays were used to establish synergy. RP-HPLC phytochemical profiling showed high levels of gallic acid (0.24-19.7 μg/mg), quercetin (1.57-18.44 μg/mg), and cinnamic acid (0.02-5.93 μg/mg) in the extracts. 13/16 Gram-negative and 4/6 Gram-positive clinical isolates were resistant to intermediate or total cefixime. Aqueous plant extracts were non-synergistic, whereas ethanolic and methanolic were synergistic. Time-kill kinetics demonstrated that the synergistic interaction reduced bacterial load by 2–8 and was time- and concentration-dependent. The fractional inhibitory concentration index (FICI) combination therapy inhibited growth and protein content (5–62%) in the bacterial isolates from the antibiotic or extract. The research indicates herbal extracts are potential adjuvants to standard antibiotics in resistant microorganisms.