Antibacterial activity of avocado extracts (Persea americana Mill.) against Streptococcus agalactiae

Plants contain numerous constituents and are valuable sources of new biologically active molecules. Avocado (Persea americana Mill.) is cultivated and used as food in most tropical and subtropical countries. Its high nutritional value and biological activities, as antioxidant, antimicrobial and analgesic properties, have been thoroughly investigated. Interest in plant extracts with antimicrobial properties has increased as a result of the indiscriminate use of antibiotics, leading to the emergence of resistant bacterial strains. Among bacterial species with clinical importance to multiple hosts, Streptococcus agalactiae is outstanding, as it can cause infections especially in humans, fish and cattle. The current study aimed to evaluate the antimicrobial activity of two extracts (ethanol and dichloromethane) from avocado seeds, 'Margarida' variety, against isolates of S. agalactiae. Extracts were diluted in ethanol / water (1: 1) at a concentration of 100 mg/mL. Antimicrobial activity was tested by the disk diffusion method (antibiogram) against isolates of S. agalactiae of human and fish origin. The ethanol extract showed antimicrobial activity only for some isolates of S. agalactiae of human origin. The dichloromethane extract showed activity against all isolates of S. agalactiae of both origins. A comparison of the results obtained with dichloromethane extract from isolates of S. agalactiae of human or fish origin demonstrated the existence of phenotypic variability among isolates from the same host. However, when comparing measurements obtained in each of the groups, they were statistically similar, showing a lack of interpopulation variability. Thus, it can be verified that the resistance profile of isolates of S. agalactiae was independent of host origin and typical of the species.