The growing resistance of bacteria to existing antimicrobial drugs is a major problem, making it essential to find new ways to treat bacterial infections. Sometimes, antibiotics alone are not effective enough. To address this, combining different drugs is often used, and one approach is to use a combination of antibiotics and plant extracts or phytochemicals. This combination therapy is particularly useful for patients with serious infections caused by drug-resistant pathogens.

Eladl, et al. (2024) obtained seven antibiotics (gentamicin, ceftazidime, ciprofloxacin, doxycycline, amoxicillin, ceftriaxone, and azithromycin) from a local pharmacy. Minimum inhibitory concentrations (MIC) were determined using the broth micro-dilution method. Various antimicrobial combinations were tested on 20 multidrug-resistant (MDR) clinical isolates (10 S. aureus and 10 P. aeruginosa). Additionally, the antibacterial activity of several volatile oils (limonene, rosemary, salvia, thyme, and black pepper), plant extracts (moringa seed, curcumin, and capsicum), and phytochemicals (thymol and chitosan) was evaluated against S. aureus and P. aeruginosa using the broth micro-dilution method.

The results showed that combining ceftriaxone with ciprofloxacin or gentamicin had a strong synergistic effect against S. aureus. Additionally, combining amoxicillin with ceftazidime reduced the MIC by five to six times. For MDR P. aeruginosa isolates, the combination of azithromycin with doxycycline reduced the MIC of azithromycin by about five to six times. The combination of gentamicin with ceftriaxone was also significant. Among natural compounds, thymol, rosemary oil, curcumin, capsicum, and moringa seed extract showed the highest synergistic activity with the tested antibiotics against S. aureus and P. aeruginosa.