Conventional and molecular characterization of an Aeromonas isolate recovered from an aquaculture farm with high fish mortality in Kenya

Abstract

Bacterial diseases can pose a significant challenge to aquaculture in Kenya, leading to significant economic losses. A fish farm in Narok County, Kenya, reported mass mortality among its reared fish which included Nile tilapia, catfish and ornamental fish. This study aimed to characterize an Aeromonas isolate recovered from the farm and assess its potential role in the outbreak. Water samples (n=10) were collected randomly from different points within the fish ponds using sterile universal bottles and transported to the bacteriology laboratory at the Department of Veterinary Pathology, Microbiology and Parasitology, University of Nairobi. The bacterial isolate was identified using conventional culture methods, biochemical assays, Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF), BD Phoenix machine tests, and Whole Genome Sequencing. Based on morphological, biochemical, and MALDI-TOF analyses, the isolate was identified as Aeromonas veronii and further confirmed as Aeromonas veronii biovar Sobria using the BD Phoenix system. The genome size of the isolate was approximately 4.6 Mb with a GC content of 59%. Phylogenetic analysis showed that the isolate clustered with fish isolates from South America and Asia and with human isolates from Asia and Australia. The study underscores the need for more studies on this bacterium’s pathogenicity and development of an autogenous vaccine for the prevention of its bacteriosis.