Gallibacterium anatis as an emerging pathogen in pet birds: biofilm formation contributes to treatment challenges and persistence.

BACKGROUND

Gallibacterium anatis (G. anatis), a microorganism of the Pasteurellaceae family, is an emerging avian pathogen associated with reproductive and respiratory diseases in poultry. However, its role in ornamental birds is still poorly understood. The aim of the present study was to conduct the first comprehensive survey of the prevalence of G. anatis in pet birds, to investigate its antimicrobial resistance (AMR) profile and to assess its ability to form biofilms using cultural, biochemical, molecular and histopathological methods.

METHODS

In this study, 191 fecal and tissue samples were collected from various companion birds. Clinical samples were cultured on 5% sheep blood agar and MacConkey agar plates to isolate bacterial pathogens. After incubation, colonies were evaluated based on their macroscopic characteristics such as size, color, and hemolytic properties on blood agar-and a Gram stain was performed as an essential preliminary step for bacterial identification. The 16-23 S rRNA gene region of G. anatis was amplified by PCR method. The disc diffusion method was used to assess microbial susceptibility and resistance. Biofilm formation was analyzed using a microtiter plate assay. Tissue samples were routinely processed, embedded in paraffin, sectioned and stained with common haematoxylin-eosin (H&E).

RESULTS

In this study, 20 G. anatis strains were isolated from 191 clinical samples of pet birds, representing a prevalence of 10.5%. Isolates were identified by colony morphology, Gram staining, biochemical testing and PCR for the -intergenic spacer region of 16-23 S rRNA, which yielded diagnostic amplicons of 790 bp and 1080 bp. Antimicrobial susceptibility testing showed complete susceptibility to ciprofloxacin (100%) and remarkable resistance to erythromycin (80%). β-lactam resistance was prevalent, with 70% and 75% of isolates resistant to ampicillin and amoxicillin, respectively. Biofilm formation tests showed that 80% of isolates had moderate biofilm formation. Gross and histopathological examinations of infected birds revealed severe respiratory and systemic lesions, including tracheitis, bronchopneumonia with focal necrosis, multifocal hepatic necrosis, and vascular congestion in multiple organs.

CONCLUSIONS

These results support the idea that G. anatis is a potentially important pathogen, with a biofilm-forming ability that contributes to treatment failure and environmental persistence. The 45% prevalence of multidrug resistance (MDR) highlights the pressing need for antimicrobial stewardship in avian veterinary medicine. Given the zoonotic potential of G. anatis, our study underscores the importance of One Health surveillance efforts in mitigating risk to both poultry and humans.