In Vitro Evaluation of the Antibacterial Activity and Antibiotic-Modulatory Effect of Gracilaria cervicornis (Tuner) J. Agardh

Background: The marine macroalgae are very diverse group of benthonic photosynthetic organisms. These organisms are a source of a high variety of phytocompounds useful to the human kind, demonstrating several applications in the human and animal nutrition, in the pharmaceutical, cosmetic, food and biotechnological industries. Several bioactivities were reported, as antioxidant, anti-inflammatory, immune-modulatory, antiviral and antimicrobial, indicating the huge pharmacological potential of this group. Gracilaria cervicornis (Turner) J. Agardh, (Gracilariaceae) is a red macroalgae which is studied less for its pharmacological applications, mainly against multi-resistant bacteria. Objective: The objective of this work was to determine the Minimal Inhibitory Concentration (MIC) and the antibiotic-modulatory effect of the dichloromethane/methanol extract of G. cervicornis (DEMGC) against standard and multi-drug resistant clinical isolates (MDRs). Methods: The MIC of the antibiotics (aminoglycosides) were determined alone or in association with ECG by the microdilution method. The assays were performed in triplicate and the results were statistically analyzed using the geometric mean. Results: The ECG did not demonstrate a clinically relevant antibacterial effect (MIC >= 1024 mu g/mL), however, when in association with gentamicin, ECG potentiated significantly the antibiotic effect against the MDR strains of Pseudomonas aeruginosa 10 and Escherichia coli 06 (p< 0.001), indicating a synergism. Conclusion: These results indicated that products from G. cervicornis can be used to combat the bacterial drug multi-resistance, being a source of new drugs or formulations of antibiotics.