RESUMO
Diseases of fishes caused by Aeromonas spp. are common, have broad host ranges and may cause high mortality. Treatments of captive-reared populations using antimicrobials are limited with concerns for bacterial resistance development and environmental dissemination. This study was done to determine whether selected plant-derived essential oils were bactericidal to Aeromonas spp. Initially, twelve essential oils were evaluated using a disk diffusion assay to an isolate of A. salmonicida subsp. salmonicida, cause of fish furunculosis. The greatest zones of inhibition were obtained with oils of cinnamon Cinnamomum cassia, oregano Origanum vulgare, lemongrass Cymbopogon citratus and thyme Thymus vulgaris. Minimum bactericidal concentrations (MBC's) were determined for these four oils, Allimed® (garlic extract, Allium sativum) and colloidal silver to sixty-nine isolates representing nine Aeromonas spp. The lowest mean MBCs (0.02-0.04%) were obtained with three different sources of cinnamon oil. MBCs for three sources of oregano and lemongrass oils ranged from 0.14% to 0.30% and 0.10% to 0.65%, respectively, and for two thyme oils were 2.11% and 2.22%. The highest concentration (5%) of Allimed® tested resulted in MBCs to twelve isolates. A concentration of silver greater than 15 mg/L would be required to determine MBCs for all but one isolate.
RESUMO
A polymerase chain reaction (PCR) method was developed for largemouth bass virus (LMBV). This iridovirus can cause a lethal disease of largemouth bass Micropterus salmoides, but also subclinically infects largemouth bass and other species of fishes. Oligonucleotide primers were designed to specifically amplify the major capsid protein gene of LMBV. The protocol for sample processing and PCR provided a method that was more sensitive than cell culture for detection of LMBV in fish. The specific amplification of LMBV also provided an improved method for confirming the identity of cell-culture isolates presumptively identified as LMBV.
