Bacterial infections are common among pet birds and represent a significant threat, particularly to nestlings and individuals with compromised immune systems, frequently leading to substantial mortality within the initial days post-hatching. This research aimed to characterize the pathological alterations associated with a spontaneous bacterial co-infection involving Klebsiella pneumoniae and Pseudomonas aeruginosa in nestling European goldfinches (Carduelis carduelis), identified as the cause of early post-hatch deaths. Eight chicks housed in a breeding colony exhibited immobility, anorexia, and respiratory distress and were discovered dead between days 1 and 4 of life. Gross lesions revealed diffuse pulmonary edema and hemorrhagic pneumonia, along with occasional hepatic necrosis. Histologically, all examined specimens showed severe, subacute bronchopneumonia and necrotizing hepatitis. Gram-negative bacilli were detected in the parabronchial walls, pulmonary arteries, and surrounding necrotic hepatocellular areas. Bacteriological cultures from lungs, liver, and kidneys yielded two Gram-negative isolates. Species identification was achieved by amplification and sequencing of four housekeeping genes (16S rRNA, rpoB, khe, ecfX). Although K. pneumoniae and P. aeruginosa are well-recognized Gram-negative agents frequently co-isolated in human pneumonia, this combination has not previously been reported in nestling goldfinches. Correct pathogen identification is vital for accurate etiological diagnosis and to inform appropriate therapeutic intervention.
