# A Multidrug-Resistant Escherichia coli Caused the Death of the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

## TL;DR

A multidrug-resistant E. coli strain caused severe illness and death in Chinese soft-shelled turtles, highlighting risks to aquaculture and public health.

## Contribution

Identification of a multidrug-resistant E. coli strain (HD-593) with high pathogenicity in Chinese soft-shelled turtles.

## Key findings

- The E. coli strain HD-593 showed resistance to 14 antibiotics and carried multiple resistance genes.
- Infected turtles exhibited organ damage and altered serum biochemistry, with a median lethal dose of 6.53 × 10⁵ CFU/g.
- Histopathological analysis revealed severe intestinal and hepatic damage in infected turtles.

## Abstract

Disease outbreaks caused by bacterial pathogens, particularly antimicrobial-resistant strains, represent a critical challenge in Chinese soft-shelled turtle (Pelodiscus sinensis) aquaculture. In this investigation, researchers characterized a multidrug-resistant Escherichia coli strain (HD-593) isolated from moribund specimens. Antimicrobial susceptibility profiling revealed resistance to 14 clinically relevant antibiotics and had several resistance genes. Experimental challenge trials demonstrated significant pathogenicity, with a median lethal dose of 6.53 × 105 CFU/g. Infected turtles had damaged organs and changes in serum levels. This study shows that this multidrug-resistant E. coli is a threat to aquaculture. It is important to use antibiotics carefully and find alternatives which can help protect animal and public health.

The rapid increase in drug resistance in recent years has become a significant global public health concern. Escherichia coli are ubiquitous bacteria, widely distributed in various environments. This study isolated a bacterial strain (HD-593) from diseased Chinese soft-shelled turtles (Pelodiscus sinensis). The bacterium was identified based on morphology, biochemical tests, and 16S rRNA sequencing, confirming it as E. coli. Drug susceptibility tests revealed that the HD-593 strain was highly resistant to ceftriaxone, enrofloxacin, doxycycline, sulfadiazine, gentamicin, neomycin, florfenicol, carbenicillin, cefradine, erythromycin, penicillin, ampicillin, midecamycin, and streptomycin. Resistance gene analysis confirmed the presence of quinolone resistance genes (oqxA and oqxB), aminoglycoside resistance genes (aac(3)-II and aphA1), a β-lactam resistance gene (blaTEM), and an acylaminol resistance gene (floR) in HD-593. The median lethal dose (LD50) of HD-593 for P. sinensis was 6.53 × 105 CFU/g. Biochemical analysis of serum revealed that HD-593 infection caused a significant reduction in total protein, albumin, and globulin levels, while markedly increasing the levels of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase. Histopathological analysis revealed severe intestinal damage characterized by villi detachment and muscle cell necrosis. Additionally, extensive splenocyte necrosis with nuclear marginalization, glomerular swelling, and pronounced hepatic steatosis accompanied by distended sinusoids were observed. This study identified a multidrug-resistant E. coli strain from deceased P. sinensis, suggesting that drug resistance genes may circulate in aquaculture ecosystems, posing potential risks to aquaculture.