The in vitro efficacy of oxytetracycline against re-isolated pathogenicAeromonas hydrophilacarrying the cytolytic enterotoxin gene through hybrid catfish,Clarias macrocephalus(Günther, 1864) ×Clarias gariepinus(Burchell, 1822) in Thailand

Abstract

Aeromonas hydrophila is a pathogen infecting farmed hybrid catfish, Clarias macrocephalus (Günther, 1864) × Clarias gariepinus (Burchell, 1822) which incurs substantial economic losses in Thailand. The study aimed at a genetic tracking of A. hydrophila infection and the in vitro assessment of the efficacy of antibiotics against its virulent strains. Five clinical strains from catfishes and Nile tilapia were employed. They were 3‐passage re‐isolated through healthy hybrid catfish and the cytolytic enterotoxin gene (AHCYTOEN) of individuals was traced. Each of the re‐isolates at a dose of ~6.67 × 105 CFU/g was intraperitoneally injected into ~15 g‐healthy hybrid catfish and their pathogenicity were observed for 7 days. It was found that AHCYTOEN was carried over whereas typical signs of motile aeromonas septicaemia were found in the specimens. The bacterial strains of Nile tilapia origin did not induce mortality but those of catfish origins (80%–100% rate of mortality). The strains were susceptible to the tetracycline antibiotics, and oxytetracycline produced MIC50 and MBC as low as 0.007–0.031 μg/ml and 1–8 μg/ml respectively. As oxytetracycline specifically inhibited pathogenic A. hydrophila in vitro, it is recommended that an appropriate dosage regimen of the drug should be established.

Potensi Ekstrak Makroalga Watercress sebagai Anti Bakteri Aeromonas hydrophila secara in vitro

“…Uji diameter zona hambatan terhadap antibiotik juga dilakukan untuk membandingkan antara uji efektivitas senyawa bioaktif watercress dengan antibiotik. Uji diameter zona hambatan yakni dengan menggunakan antiobiotik Oxytetracycline 1-8 μg/ml (Juntarut et al, 2018). Cakram antiobiotik diletakkan di atas permukaan media bakteri dengan pinset dan ditekan sedikit kemudian diinkubasikan selama 24 jam pada suhu 25 o C dalam inkubator.…”