ABSTRACT
Introduction: Intestinal bacteria are exposed many external influences, including drugs, causing the emergence of strains resistant to the effects of antibiotics. Consequently, the discovery of new antibiotics that affect resistant strains is required. Marine algae offer a source of renewable natural compounds with antimicrobial effects. Therefore, the aim of this study was to detect some of these compounds and examine their impact on enteric bacteria. Methodology: Escherichia coli, Salmonella typhi, Shigella dysenteriae, Klebsiella pneumoniae, and Enterobacter aerogenes were tested with extracts of Turbinaria triquetra and Halimeda opuntia extracted with methanol, ethanol, petroleum ether, or dimethyl formamide solvents. We measured bacterial growth inhibition, the minimal inhibitory concentrations (MICs), and potassium leakage, and analyzed the bacterial cells with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Results: The T. triquetra extract produced with methanol strongly affected the bacteria tested. When the results for T. triquetra and H. opuntia were compared with those of omacillin, the T. triquetra and H. opuntia extracts in most solvents were more effective than the antibiotic. Differences in the bacterial growth inhibition and MICs depended on the type of alga and the solvent used. At the end of the incubation period, potassium leakage had increased by 62.98% for E. coli, 61.24% for S. typhi, 61.32% for S. dysenteriae, 64.02% for K. pneumoniae, and 63.10% for E. aerogenes when treated T. triquetra. Conclusion: Turbinaria triquetra extracted with methanol strongly affected the growth of the bacteria tested. Therefore, it is a potential source of natural antibacterial compounds.