Isolation of Aeromonas salmonicida subspecies salmonicida from aquaculture environment in India: Polyphasic identification, virulence characterization, and antibiotic susceptibility

• Published in: Microbial pathogenesis 2023-06, Vol.179, p.106100-106100, Article 106100
• Main Authors: Pradhan, Subham Kumar, Devi, Rajashree, Khan, Md Idrish Raja, Kamilya, Dibyendu, Gon Choudhury, Tanmoy, Parhi, Janmejay
• Format: Article
• Language: English
• Subjects: Aeromonas; Aeromonas salmonicida; Aeromonas salmonicida - genetics; ampicillin; Animals; Anti-Bacterial Agents - pharmacology; antibiotic resistance; Antibiotics susceptibility; Aquaculture; bacteria; biofilm; carp; casein; chloramphenicol; ciprofloxacin; Cirrhinus mrigala; edema; erythema; Fish Diseases - microbiology; gelatin; genes; hydrolysis; In vivo pathogenicity; India; Indian major carps; Labeo rohita; lipids; mortality; nalidixic acid; pathogenesis; rifampicin; RNA, Ribosomal, 16S - genetics; species; starch; surface proteins; tetracycline; vancomycin; virulence; Virulence - genetics; Virulence genes
• ISSN: 0882-4010; 1096-1208
• DOI: 10.1016/j.micpath.2023.106100

This study reports the polyphasic identification, characterization of virulence potential, and antibiotic susceptibility of Aeromonas salmonicida subspecies salmonicida COFCAU_AS, isolated from an aquaculture system in India. The physiological, biochemical, 16s rRNA gene sequencing and PAAS PCR test identified the strain as Aeromonas salmonicida. The MIY PCR tests established the subspecies as ‘salmonicida’. The in vitro tests showed the isolated bacterium as haemolytic with casein, lipid, starch, and gelatin hydrolysis activity, indicating its pathogenic attributes. It also showed the ability to produce slime and biofilm, and additionally, it possessed an A-layer surface protein. In vivo pathogenicity test was performed to determine the LD50 dose of the bacterium in Labeo rohita fingerlings (14.42 ± 1.01 g), which was found to be 106.9 cells fish−1. The bacteria-challenged fingerlings showed skin lesions, erythema at the base of the fins, dropsy, and ulcer. Almost identical clinical signs and mortalities were observed when the same LD50 dose was injected into other Indian major carp species, L. catla and Cirrhinus mrigala. Out of the twelve virulent genes screened, the presence of nine genes viz., aerA, act, ast, alt, hlyA, vapA, exsA, fstA, and lip were detected, whereas ascV, ascC, and ela genes were absent. The A. salmonicida subsp. salmonicida COFCAU_AS was resistant to antibiotics such as penicillin G, rifampicin, ampicillin, and vancomycin while highly sensitive to amoxiclav, nalidixic acid, chloramphenicol, ciprofloxacin, and tetracycline. In summary, we have isolated a virulent A. salmonicida subsp. salmonicida from a tropical aquaculture pond which can cause significant mortality and morbidity in Indian major carp species. •Isolation of A. salmonicida subsp. salmonicida strain COFCAU_AS form India.•In vitro and in vivo tests confirmed the virulent nature of COFCAU_AS.•COFCAU_AS possess 9 tested virulent genes: aerA, act, ast, alt, hlyA, vapA, exsA, fstA lip.•COFCAU_AS was resistant to penicillin G, rifampicin, ampicillin, and vancomycin.