Outbreaks of Elizabethkingia miricola Caused Fatal Meningitis-Like Disease in Cultured Bullfrogs

Elizabethkingia miricola is an emerging nosocomial pathogen responsible for meningitis, sepsis, urinary tract infection, pneumonia, and joint infection in humans. These pathogens were also reported to be causal agents for meningitis-like disease in cultured frogs, which displayed high infectivity, mortality, and significant loss. In July 2023, 10 outbreaks of infectious meningitis-like disease in bullfrogs occurred in Tangshan area. To determine the causal agent, 70 diseased frogs from 10 farms were collected for etiological identification. Gram-negative bacilli were isolated from the brain and liver of sick bullfrogs and identified as members of E. miricola by biochemical characterization and 16S rRNA sequencing analysis. A total of 42 strains of E. miricola were isolated and further determined as the etiological agent by reproducing neurological symptoms and deaths in an artificial infection test. A representative isolate, HBTS-1, was picked up for the pathogenicity test, and the data showed that this stain was highly pathogenic to bullfrogs with an LD₅₀ of 3.7 × 10⁵ CFU. Notably, the isolate also showed high pathogenicity to 5-day-old suckling mice, with an LD₅₀ of 3.1 × 10⁶ CFU, indicating its potential threat to mammals. Moreover, all the 42 E. miricola isolates showed resistance to multiple antibotics without an apparent inhibition zone observed in the test, making the choice of antimicrobial therapy challenging. These novel findings prioritized E. miricola as an important zoonotic agent, which may provide a reference for human medicine.