Staphylococcus xylosus Infection in Rainbow Trout (Oncorhynchus mykiss) As a Primary Pathogenic Cause of Eye Protrusion and Mortality.

Staphylococcal infections are extensively investigated in humans owing to the resistance of staphylococci to diverse antibiotics commonly used in hospitals. The resistance mechanism of methicillin-resistant Staphylococcus aureus has garnered the interest of researchers due to its risk to the global public health. Furthermore, the zoonotic potential of staphylococci has led to increased interest in their transmission mechanism via food, livestock, as well as domestic and wild animals. Although fish are globally consumed, there are only few studies on the potential threat of staphylococcal infection in aquatic animals. In this study, we present the first description of Staphylococcus xylosus infection and its pathogenicity in rainbow trout, which resulted in fish mortality and economic losses in trout fisheries. We focused on the pathogenic role of the bacterium and its influence on rainbow trout based on the clinical symptoms in the eyes. Staphylococcus xylosus infection induced exophthalmia and disrupted the primary immune barrier, which increased the possibility of other secondary bacterial infections in fish under poor conditions, resulting in continuous mortality.