# Iodobacter fluviatilis, a New Potential Opportunistic Pathogen Associated with Skin Lesions, First Report in Hypophthalmichthys nobilis in China

## TL;DR

A new potential opportunistic pathogen, Iodobacter fluviatilis, was found to be associated with skin lesions in H. nobilis fish in China.

## Contribution

This is the first report of Iodobacter fluviatilis causing disease in Hypophthalmichthys nobilis.

## Key findings

- Iodobacter fluviatilis was isolated from diseased H. nobilis and identified through 16S rRNA sequencing.
- The bacteria caused localized abscesses in experimentally infected fish.
- The isolate showed resistance to sulfonamides but susceptibility to other antibiotics like aminoglycosides and quinolones.

## Abstract

In the spring of 2023, a disease outbreak occurred in Lake Taihu in China, which caused a large number of deaths of H. nobilis. In order to investigate the cause of morbidity and mortality of the H. nobilis, the diseased fish were collected for histopathological and etiological studies. Histopathological observation revealed that substantial inflammatory cell infiltration was observed around skin lesion in diseased fish, extensive degeneration and necrosis were observed in the hepatic parenchymal cells, the spleen exhibited congestion, and the kidney showed congestion. A bacterial strain, C1, isolated from diseased H. nobilis was identified as Iodobacter fluviatilis through 16S rRNA gene sequencing and biochemical phenotypic characterization. Experimental infection of the fish via intramuscular injection induced a localized abscess in a subset of fish. Antimicrobial susceptibility testing revealed that the isolate was susceptible to aminoglycosides, tetracyclines, quinolones and amphenicols, but resistant to sulfonamides commonly used in aquaculture. Here, we describe an association between I. fluviatilis and skin lesions in H. nobilis. Furthermore, we report the biochemical characteristics and drug resistance profile of the isolated bacteria. These findings also facilitate further investigations into the role of I. fluviatilis associated with skin diseases of H. nobilis and other freshwater fish.