First evidence of extensively drug-resistant virulent Aeromonas dhakensis isolated from diseased endemic Mascara barb (Dawkinsia assimilis) in India

Abstract

Aeromonas species is ubiquitously present in aquatic habitats, can cause motile Aeromonas septicemia (MAS). However, it is very complex to identify Aeromonas spp. based on its phenotypes. In the present study in mid-November 2018, we investigated a case of severe mortality of wild caught mascara barb (Dawkinsia assimilis) endemic to the Western Ghats, India. No cytopathic effect was observed in DRG and CSK fish cell line after inoculating filtrate of the tissue homogenates and found negative for all major viral pathogens. Here, aetiological agent was identified as bacteria, presumed as Aeromonas hydrophila, and Escherichia coli based on biochemical tests. Later, PCR assay was performed for the molecular confirmation by gyrB gene resulted in confirmation of Aeromonas as A. dhakensis with 99.63% similarity with A. dhakensis from SA1 of diseased pacu. Multiple antibiotic resistance (MAR) index of A. dhakensis was 0.9112. Further, A. dhakensis was positive for ten antibiotic resistance and seven virulence genes with β-hemolysis colonies. The LD50 value was found to be 3.42 × 105 CFU/mL in experimental trails. In the present study, a tetracycline, colistin, and ESBL resistant hypervirulent A. dhakensis was isolated from the diseased endemic mascara barb. Ten natural ingredients and five disinfectants found to be effective against A. dhakensis. To the best of our knowledge, this is the first evidence of extensively drug-resistant (XDR) virulent A. dhakensis associated with disease outbreak in endemic mascara barb in India.