Disease outbreak is one of the major challenges of the rapidly growing aquaculture sector. Plant derivatives, especially with a long history of ethnobotanical use, can be a potential alternative to fight diseases. Bangladesh is one of the major aquaculture producers and has rich plant diversity. The present study was aimed to screen potential plants with antibacterial activity against target fish pathogens.
A total of f ifty-five plants were collected from Bangladesh and extracted using ethanol, acetone, hexane, and water . Screening of a ntibacterial activity of all plant extracts and determination of minimum inhibition concentration of active plant extracts was conducted using the broth microdilution method against the target fish pathogens: Aeromonas hydrophila, Pseudomonas fluorescens, Pseudomonas aeruginosa, Flavobacterium columnare, and Streptococcus iniae . The initial concentration of tested extracts was 1 mg/ml.
The average extraction yields varied with the solvent used; water demonstrated the highest yield (on average 25 mg/mL , range: 10-47mg/ml) and hexane the lowest ( average 4 mg/mL, range: 2-10mg/ml). Acetone, ethanol, and hexane extracts typically exhibited greater growth inhibition activity than water extracts. H exane extracts displayed n o inhibition against A. hydrophila, P. aeruginosa, and P. fluorescens, whereas, 100% and 84%, of hexane extracts inhibited Streptococcus iniae and F. columnare respectively. Aeromonas hydrophila, Pseudomonas aeruginosa, and Pseudomonas flourescens exhibited more resistance against tested plants, while Streptococcus iniae and Flavobacterium columnare were more susceptible. Terminalia arjuna, Terminalia bellirica, Mikania micrantha, Peperomia pellucid, Lawsonia inermis, Phyllanthus emblica, Eryngium foetidum, Amaranthus spinosus, Barringtonia acutangula, Clitoria ternatea, Alstonia scholaris and Sphagneticola trilobata displayed broad-spectrum antibacteri al activities against the tested pathogens. MIC50 value of active extracts varied from 1 to 444 µg/ml.; 53% of the active extracts had MIC 50 value less than 25 µg/mL against Flavobacterium columnare . Terminalia bellirica fruit active extracts had MIC50 ranging from of 4-51 µg/mL, with broad-spectrum activity against Pseudomonas fluorescens, Pseudomonas aeruginosa, Flavobacteriaum columnare and Streptococcus iniae.
The preliminary screening results provide a foundation for further studies that aim to identify potential compounds with antibacterial activity applicable in aquaculture to control bacterial infections.