AAAP: Pathogenic Castellaniella in broiler breeders
Breeders exhibited signs of fowl cholera, but testing revealed Castellaniella
11 February 2026
1 minute read
By: Editor's note: The following is from a poster presentation at the 2025 annual meeting of the American Association of Avian Pathologists.
Is Castellaniella ginsengisoli an emerging pathogen in chickens? Since 2018, uncommon bacterial infections have been identified in broiler breeders at the Poultry Diagnostic and Research Center (PDRC), University of Georgia, USA. Birds from 22 cases exhibited increased mortality, lameness, and swollen wattles, resembling fowl cholera. However, gene sequencing revealed 99% homology with Castellaniella spp., suggesting a different causative agent.
Historically regarded as non-pathogenic environmental bacteria, Castellaniella lacked characterization as animal pathogens. A study by Yi Chen Luo and colleagues at the Athens Veterinary Diagnostic Laboratory, Georgia, and the PDRC addressed this research gap by providing the first comprehensive genomic and phenotypic characterization of chicken-origin Castellaniella isolates. All the isolates exhibited genome sizes of approximately 2.9 million base pairs and were phylogenetically closest to C. ginsengisoli.
Antimicrobial susceptibility testing revealed low minimum inhibitory concentrations (MICs) for tetracycline, oxytetracycline, enrofloxacin, neomycin, and gentamicin, suggesting these as potential treatment options. Conversely, high MICs were observed for β-lactams and macrolides, indicating that they should be avoided for clinical use. Elevated MICs for sulfonamides and aminoglycosides were linked to the detection of the sul2 and aph antimicrobial resistance (AMR) genes, respectively. Despite high MICs for β-lactams, no acquired resistance genes or resistance-associated mutations were found, suggesting an intrinsic resistance mechanism may exist.
Virulence factor analysis revealed that C. ginsengisoli possesses genes involved in several pathogenic mechanisms, including secretion systems, fimbriae, flagella, biofilm, and capsule formation. This study provides a vital foundation for advancing diagnostics, guiding treatments, and driving future Castellaniella research.
