The Opportunistic Pathogen Chryseobacterium balustinum WLT: Pathogenicity and Antibiotic Resistance

Abstract

This study aimed to re-evaluate the pathogenic characteristics of Chryseobacterium balustinum, generally known as a food spoilage bacterium. We observed mass mortality in a rainbow trout farm in Jeonbuk province, Republic of Korea. Fewer studies have reported on rainbow trout mortality or infections in Korea than in other countries; among these, few studies have reported cases of Chryseobacterium infections. Sequencing analysis revealed that this bacterium is closely related (99.24%) to Chryseobacterium balustinum. Bacterial identification assays, including the API test, sequencing, and phylogenetic analysis, found the 24 isolates to be C. balustinum. The strain showed multiple resistance to 18 of 25 antibiotics tested. Primary clinical symptoms of its infection are damage to the fins, necrosis, and cytoplasmic vacuolation in hepatocytes. The pathogenicity of the strain was determined following Koch’s postulates and the challenge test. The present results suggest that C. balustinum WLT can be considered a multidrug-resistant zoonotic pathogen responsible for mortality and economic losses.

Pathological analysis and antimicrobial susceptibility of Chryseobacterium balustinum RTFCP 298 isolated from diseased rainbow trout, Oncorhynchus mykiss

“…C. balustinum RTFCP 298 was identified based on the colony morphology, physiological and biochemical characteristics 20 . It was further confirmed by the PCR amplification of the 16S rRNA gene and phylogenetic analysis.…”

“…Other Chryseobacterium spp., isolated from various clinical and environmental sources, include C. indologenes 9 and C. gleum 1 . In animals, chryseobacteria have been detected in the midgut of mosquitoes, the gut of cockroaches, millipede faeces, penguin guano, gut homogenates of freshwater copepods, bird feathers, cow's milk, raw meats, and chicken 10 – 20 . The genus Chryseobacterium has also been identified as a pathogen in various fish species, with Chryseobacterium species being considered potential emerging pathogens in both freshwater and marine fish globally 4 , 21 – 25 .…”

“…In recent years, several Chryseobacterium species have been identified from various sources, including teleosts, and have been associated with bacterial gill diseases and systemic hemorrhagic septicemia in turbot, Scophthalmus maximus L, pufferfish, rainbow trout ( Oncorhynchus mykiss) , Atlantic salmon ( Salmo salar) , and golden mahseer ( Tor putitora) 21 – 24 , 27 – 29 . The incidence of Chryseobacterium infection in animals has been increasing in South Korea, emphasizing the importance of ongoing monitoring and research on this emerging pathogen 20 . Additionally, Chryseobacterium species have demonstrated elevated levels of antibiotic resistance, including resistance to last-resort antibiotics, leading to concerns about their clinical implications and potential for zoonotic transmission 30 , 31 .…”

Atypical flavobacteria recovered from diseased fish in the Western United States

“…However, the majority are linked to disease by nature of their isolation from the external or internal tissues of clinically affected fish. Infected fish often display signs mimicking those caused by established etiologic agents, including skin ulceration, fin erosion, and gill necrosis (Loch and Faisal, 2016b;Jung et al, 2022;Malick et al, 2022). Additionally, fish may be concurrently infected by more than one species, and atypical flavobacteria may not be easily distinguished by conventional diagnostic methods (Bernardet et al, 2005;Bruce et al, 2020).…”

“…To address these knowledge gaps, international efforts in surveillance and characterization of fish associated Flavobacterium and Chryseobacterium strains are gaining in momentum. Methods to identify isolates more conclusively through biochemical or molecular means continue to be improved, and the advent of next generation sequencing has aided the discovery of genetic factors related to virulence, immunogenicity, and antimicrobial resistance, together supporting development of new tools for disease treatment and prevention (Garcıá-Loṕez et al, 2019;Saticioglu et al, 2021c;Jung et al, 2022;Malick et al, 2022). Antimicrobial resistance is a particularly notorious issue for both human and animal flavobacterial infections, as high intrinsic resistance to multiple classes of antimicrobials is archetypal of some genera (Verner-Jeffreys et al, 2017).…”