Extracts of Hesperozygis ringens (Benth.) Epling: in vitro and in vivo antibacterial activity against fish pathogenic bacteria.

AIMS: This study investigated the in vitro antibacterial activity of Hesperozygis ringens (Benth.) Epling leaf extracts against fish pathogenic bacteria, as well as the in vivo activity of the most active extract in silver catfish (Rhamdia quelen) experimentally infected with Aeromonas hydrophila. Moreover, the chemical composition of the extract used in the survival assay was evaluated.

METHODS AND RESULTS: Only hexane extract (HEHR) showed in vitro antibacterial activity (MIC and MBC ranging from 1600 to 3200 μg mL-1 ) against clinical isolates of A. hydrophila, Raotella ornithinolytica and Citrobacter freundii, obtained from naturally infected silver catfish, and A. hydrophila ATCC 7966. The major compound of the volatile fraction of HEHR was determined as pulegone. HEHR promoted a 93·33% relative survival rate of silver catfish experimentally infected with A. hydrophila seven days after a single therapeutic bath at 30 mg L-1 , while florfenicol at 4 mg L-1 , which promoted a 60% relative survival rate.

CONCLUSIONS: The antibacterial activity of H. ringens (Benth.) Epling leaf extracts seem to be related to phytochemicals of apolar character, since HEHR promoted better survival rate of infected animals than florfenicol.

SIGNIFICANCE AND IMPACT OF THE STUDY: The HEHR has potential to be used in the control and treatment of bacterial infections in organic aquaculture. This article is protected by copyright. All rights reserved.