First Isolation and Characterization of Chryseobacterium cucumeris SKNUCL01, Isolated from Diseased Pond loach ( Misgurnus anguillicaudatus) in Korea

Abstract

Loaches are widely distributed throughout the natural environment and are consumed for medicinal purposes in East Asia. Usually, loaches are cultured in ponds where the water conditions can easily cause bacterial infections. Infections due to bacterial pathogens such as Aeromonas have been well described in cultured loaches; however, there is no report regarding Chryseobacterium infection. This study focused on the elucidation of the pathogenic and antibiotic resistance characteristics of C. cucumeris, SKNUCL01, isolated from diseased loaches ( Misgurnus anguillicaudatus). SKNUCL01 forms a biofilm, which is associated with its virulence. Koch’s postulates were satisfied with a lethal dose 50 (LD ₅₀) of 8.52 × 10 ⁷ colony-forming units (CFU)/ml. Abrasion facilitates the mortality of the fish, which makes it a possible infection route for C. cucumeris. The strain showed resistance to nearly all tested antibiotics, such as trimethoprim/sulfamethoxazole, levofloxacin, and ciprofloxacin, formerly considered effective treatments. Phenotypic analyses for antibiotic resistance—the combined disk test, double-disk synergy test, modified Hodge test, and efflux pump inhibition test—revealed that the resistance of SKNUCL01 originated from metallo-beta lactamases (MBLs) and efflux pumps. Our findings provide evidence that could result in a breakthrough against multidrug-resistant Chryseobacterium infection in the aquaculture industry; the antibiotic resistance-related genes can be elucidated through future study.