ANTIMICROBIAL AND ANTIBIOFILM ACTIVITY OF EUCALYPTUS GLOBULUS LEAVES EXTRACT AND ITS MAIN COMPOUNDS ON MASTITIS PATHOGENS OF DAIRY COWS.

Antibiotics are the main therapy for bovine mastitis, but the increase in antimicrobial resistance has improved the use of alternative molecules. In this study, were evaluated the Minimal Inhibitory Concentration (MIC) and Minimal Inhibitory Biofilm Concentration (MBIC) of Eucalyptus globulus leaves (EGL-L) extract, Ursolic (UA) and Asiatic acid (AA) against Staphylococcus aureus (SA), Streptococcus uberis (SU), Streptococcus agalactiae (SAG), and Enterococcus spp. (EN) reference and field strains isolated from infected cows. The ability to produce biofilm was assessed for every strain. Statistical analysis was conducted to evaluate differences in MIC values among bacterial groups for each compound using SPSS software, employing the Kruskal-Wallis non-parametric test and post-hoc analysis with pairwise comparisons of ranks means using Bonferroni correction. No significant differences were found for MIC values of EGL-L among the bacterial groups. For UA significant differences were observed, between SA and SU/SAG groups (P<0.001), while for AA, between SU and SA groups (P<0.001). The highest number of moderate and strongly adherent strains was found in SA (6/15) and SAG (8/17) groups. Regarding antibiofilm activity, only 5/32 strains had MBIC80 values above 256 μg/mL (maximum tested) for both UA and AA. However, 12/32 and 11/32 strains showed MBIC80 ≤ 8 μg/mL for UA and AA, respectively. For EGL-L, 17/32 strains exceeded 2000 μg/mL (maximum tested) and 6/32 ≤ 64 μg/mL. In conclusion, all compounds exhibited antimicrobial activity; however, UA and AA were more effective on Streptococci than Staphylococci. Additionally, both UA and AA were effective on moderate and strong biofilm producer strains.