The use of Ocimum americanum essential oil against the pathogens Aeromonas hydrophila and Gyrodactylus sp. in silver catfish (Rhamdia quelen).
The bactericidal activity (minimum inhibitory concentration (MIC)-test) of Ocimum americanum (inflorescences) essential oil (OAEO) against Aeromonas hydrophila was determined in this study. Also investigated was the potential of OAEO and the main compound found in the oil (linalool) at subinhibitory concentrations to be inhibitors of haemolysis caused by Aer. hydrophila in fish erythrocytes. An in vivo experiment was conducted to evaluate the survival of fish (Rhamdia quelen) experimentally infected with Aer. hydrophila and exposed to OAEO. A second experiment was conducted to evaluate the in vitro and in vivo activity of OAEO (mix from inflorescences and leaves) against the parasite Gyrodactylus sp. The OAEO showed weak in vitro activity against Aer. hydrophila (6400 μg ml(-1) ). Subinhibitory concentrations of OAEO (100 μg ml(-1) ) inhibited haemolysis (90%) caused by Aer. hydrophila in fish erythrocytes, however, linalool did not inhibit haemolysis activity. At the low concentrations (10 and 20 mg l(-1) ) added to the water, OAEO promoted the survival of fish experimentally infected with Aer. hydrophila. Lastly, the OAEO mix (50 mg l(-1) ) was effective against Gyrodactylus sp., significantly reducing (60%) the number of parasites in the fish.


CONCLUSIONS
Phytochemicals, such as essential oils (EOs) are a great source of new molecules and have shown potential to be used in aquaculture systems. However, additional studies focused on the in vivo efficacy, mode of action and identification of the active compounds are needed. This study determined the potential of Ocimum americanum EO for use against two important fish pathogens, Aeromonas hydrophila and Gyrodactylus sp., as well as providing preliminary information about the role of the main EO compound (linalool) against Aer. hydrophila virulence.
Department of Physiology and Pharmacology, Federal University of Santa Maria (UFSM), Santa Maria, RS, Brazil.
F J
FJ
Sutili
Department of Industrial Pharmacy, UFSM, Santa Maria, RS, Brazil.
A L
AL
Murari
Regional Integrated University of High Uruguay and Missions (URI), Santiago, RS, Brazil.
L L
LL
Silva
Department of Preventive Veterinary Medicine, UFSM, Santa Maria, RS, Brazil.
L T
LT
Gressler
Department of Industrial Pharmacy, UFSM, Santa Maria, RS, Brazil.
B M
BM
Heinzmann
Department of Preventive Veterinary Medicine, UFSM, Santa Maria, RS, Brazil.
A C
AC
de Vargas
Department of Agronomy, UFSM/CESNORS, Frederico Westphalen, RS, Brazil.
D
D
Schmidt
Department of Physiology and Pharmacology, Federal University of Santa Maria (UFSM), Santa Maria, RS, Brazil.
B
B
Baldisserotto
D000080462:Acyclic Monoterpenes; D016980:Aeromonas hydrophila / Q000187:drug effects*; D000818:Animals; D017756:Aquaculture; D002397:Catfishes / Q000382:microbiology* / Q000469:parasitology*; D002590:Cestode Infections / Q000188:drug therapy / Q000662:veterinary*; D004912:Erythrocytes / Q000382:microbiology; D005393:Fish Diseases / Q000188:drug therapy* / Q000382:microbiology; D016905:Gram-Negative Bacterial Infections / Q000188:drug therapy / Q000662:veterinary*; D006461:Hemolysis / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D039821:Monoterpenes / Q000494:pharmacology*; D031339:Ocimum / Q000737:chemistry; D009822:Oils, Volatile / Q000494:pharmacology*; D064209:Phytochemicals / Q000494:pharmacology; D010986:Platyhelminths / Q000187:drug effects*; D014774:Virulence
D000080462:Acyclic Monoterpenes; D039821:Monoterpenes; D009822:Oils, Volatile; D064209:Phytochemicals; C018584:linalool
haemolysis; linalool; monogenea; plant; virulence