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

Plants contain numerous constituents and are valuablesources of new biologically active molecules. Avocado (Perseaamericana Mill.) is cultivated and used as food in most tropical andsubtropical countries. Its high nutritional value and biological activities,as antioxidant, antimicrobial and analgesic properties, have beenthoroughly investigated. Interest in plant extracts with antimicrobialproperties has increased as a result of the indiscriminate use ofantibiotics, 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 especiallyin humans, fish and cattle. The current study aimed to evaluatethe 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 concentrationof 100 mg/mL. Antimicrobial activity was tested by thedisk diffusion method (antibiogram) against isolates of S. agalactiaeof human and fish origin.The ethanol extract showed antimicrobialactivity only for some isolates of S. agalactiae of human origin. Thedichloromethane extract showed activity against all isolates of S. agalactiaeof both origins. A comparison of the results obtained with dichloromethaneextract from isolates of S. agalactiae of human or fishorigin demonstrated the existence of phenotypic variability amongisolates from the same host. However, when comparing measurementsobtained in each of the groups, they were statistically similar,showing a lack of interpopulation variability. Thus, it can be verifiedthat the resistance profile of isolates of S. agalactiae was independentof host origin and typical of the species.