Detection of Virulence-Associated Genes and in vitro Gene Transfer From Aeromonas sp. Isolated From Aquatic Environments of Sub-himalayan West Bengal

Abstract

Aeromonas is omnipresent in aquatic environments and cause disease within a wide host range. A total of thirty-four isolates from water samples of small fish farms were identified as Aeromonas based on biochemical characteristics and 16S rRNA gene sequence. A total of six virulent factors were analyzed which indicated 100% of isolates as beta-haemolytic and proteolytic, whereas 44.1, 38.2, and 70.6% of isolates produced DNAse, siderophore, and amylase, respectively. Studies on the occurrence of four genetic determinants of virulence factors revealed that aer/haem (haemolytic toxin) and flaA (polar flagella) genes were present in 44.1% of strains whereas ascV (type 3 secretion system) and aspA (serine protease) genes were detected in 21.5 and 8.82% of strains, respectively. Fish (Anabas testudineus) challenge studies showed that the isolate GP3 (Aeromonas veronii) bearing five virulent factors with the combination of aer/haem+/ascV+/fla+ genes induced severe lesions leading to 100% of mortality. In contrast, RB7 possessing four virulence factors and three genes (aer/haem+/ascV+/aspA+) could not produce severe lesions and any mortality indicating the absence of correlation between the virulence factors, its genes, and the pathogenicity in fishes. GP3 was cytotoxic to human liver cell line (WRL-68) in trypan blue dye exclusion assay. The 431 bp aer/haem gene of GP3 was transferable to E. coli Dh5α with a conjugational efficiency of 0.394 × 10–4 transconjugants per recipient cell. The transfer was confirmed by PCR and by the presence of 23-kb plasmids in both donor and transconjugants. Therefore, the occurrence of mobile genetic elements bearing virulence-associated genes in Aeromonas indicates the need for periodic monitoring of the aquatic habitat to prevent disease outbreaks.

Aeromonas veronii Is a Lethal Pathogen Isolated from Gut of Infected Labeo rohita: Molecular Insight to Understand the Bacterial Virulence and Its Induced Host Immunity

“…Similarly, the alt gene accountable for producing cytotoxin and enterotoxin is crucial in establishing the infection [60]. Dnase (Exu) production primarily depends on the nutritional requirement of the pathogen [61]. The production of the Dnase protein leads to the breakdown of DNA.…”

Characterization of a hemolytic and antibiotic-resistant Pseudomonas aeruginosa strain S3 pathogenic to fish isolated from Mahananda River in India

“…Following incubation, the cells were observed under phase-contrast inverted microscope (Olympus CK40-SLP) at 200X magnification. The percentage of viable cells of treated and control sets was determined following the trypan blue dye exclusion assay described previously [ 31 ]. Percent viability was determined as: [total number of viable cells per ml of aliquot/ total number of cells per ml of aliquot] × 100.…”