Occurrence of potential pathogenic Aeromonas species in tropical seafood, Aquafarms and mangroves off Cochin coast in South India

Abstract

Background: The genus Aeromonas include gram-negative, motile, facultative anaerobic, rod shaped and oxidase positive bacteria comprising several species, associated with the aquatic environment. Aeromonas species have been implicated in human pathogenesis and are linked with gastroenteritis, muscle infections, septicemia, and skin diseases. In fish they are renowned as enteric pathogens causing haemorrhagic septicemia, fin rot, soft tissue rot and furunculosis resulting in major die-offs and fish kills. Aim: This study reports the occurrence of potential pathogenic Aeromonas sp. in tropical seafood (Squids, Prawns and Mussels), aquafarms and mangroves of Cochin, Kerala, South India. Materials and Methods :Tropical seafood (Squid, Prawn and Mussel), sediment and water samples from aquafarms and associated mangroves were screened for Aeromonas contamination. The isolates were identified by 16S rDNA sequence analysis and subjected to morphological and biochemical characterization. Haemolytic assay was used for determining pathogenicity of the organisms. Antibiotic susceptibility against 12 antibiotics were performed and the MAR index was calculated. Results: Atotal of 134 isolates were recovered from the samples of which 15 were identified as Aeromonas species by 16S rDNAsequence analysis and were assigned to 5 species namely, A. hydrophila, A. enteropelogenes, A. caviae, A. punctataand A. aquarorium. Morphological, biochemical and phylogenetic analyses revealed relatedness and variability among the strains. All the isolates were haemolytic on blood agar indicating their pathogenicity. The isolates exhibited varying degrees of resistance to vancomycin (86.66%), ampicillin (46.66%), nalidixic acid (20%), tetracycline (6.66%), co-trimaxozole (6.66%) and rifampicin (6.66%) and were susceptible to antibiotics like gentamycin, streptomycin, trimethoprim, azithromycin, cefixime and chloramphenicol. 20% of Aeromonas sp. showed MAR index ≥ 0.2 indicative of the high risk environment. Conclusion: The presence of Aeromonas sp. has been recognised as a potential health risk and surveillance of this pathogen is crucial for successful disease management and control.