Molecular identification, whole-cell protein profiling, antibiotics sensitivity and pathogenicity of Chryseobacterium gleum recovered from diseased fishes of freshwater wetlands in India

Abstract

Globally, bacterial gill disease is one of the most prominent bacterial diseases affecting both marine and freshwater fishes. This study aimed to investigate diseased Labeo rohita, Labeo catla and Oreochromis niloticus with gill discoloration, tail rot and skin ulcer that resembles the typical sign of bacterial gill disease from East Kolkata Wetlands, India. The results revealed that four isolates of Chryseobacterium gleum were the responsible pathogens. The isolates CIFRI-RRM3, CIFRI-BFG2, CIFRI-SRM4 and CIFRI-TRM5 were identified using bacterial colony morphology, biochemical test, whole-cell protein profiling, 16S rRNA gene amplification and nucleotide sequence analysis. The antibiotic susceptibility assay showed that all the isolates were completely resistant to ampicillin, amoxyclav, cefalexin, cephalothin, ceftriaxone, ceftazidime, cefotaxime, cefuroxime, cefadroxil, chloramphenicol, kanamycin, netilmicin, penicillin-G, ticarcillin, tobramycin, erythromycin and tetracycline. A challenge experiment was also conducted for four isolates with intraperitoneal injection at a dose of 2.5 × 1010 CFU mL−1 to 4.2 × 1010 CFU mL−1in respective fish hosts. Only three isolates (CIFRI-BFG2, CIFRI-RRM3 and CIFRI-TRM5) proved their virulence by producing diseases with mild symptoms of skin lesions, gill disease and cumulative mortality of 10–20%. To the best of our knowledge, this is the first description of the phenotypic, molecular and whole-cell protein profiling of C. gleum derived from freshwater fishes in India.