Isolation, biochemical and molecular detection of Aeromonas hydrophila from cultured Oncorhynchus mykiss

Abstract

The isolation of <em>Aeromonas hydrophila</em> from <em>Oncorhynchus mykiss</em> reared in the farms was the aim of the present study. Ninety samples were collected aseptically from the infected fish with signs of hemorrhagic septicemia in gill and skin, exophthalmia, dropsy and 36 water samples were sub-cultured on Tryptic Soya Agar (TSA), as well as kidney. The genotyping by PCR method was used to amplify the gene of 16 SrDNA using primers 27F and 1492R as primer pairs to achieve an approximate length of 1500 bp. The identified motile <em>Aeromonas</em> species were sequenced with electrogram chromas format in chrome version 1/41 software and a phylogenetic tree was drowned by MEGA5.1 software. The results showed that 19% of 24 isolated from gram-negative bacteria were detected as <em>Aeromonas,</em> which the sequencing results revealed that all the isolated bacteria had 99% similarities with the standard <em>A. hydrophila.</em> The results of environmental factors showed when the levels of dissolved oxygen have decreased and the levels of nitrite and ammonia have increased throughout the year, Aeromonasias is increased. Also, when the water has gone alkaline due to increased ammonia, the disease has increased. It may be concluded that fish farmers should take proper management practices to avoid such disease in cultured fishes especially rainbow trout and to get rid of the infection by such serious bacterial pathogen like <em>Aeromonas hydrophila</em> by improving their culture strategy and culture ecosystem.