Implication of probiotics with berry phenolic extracts against Avibacterium paragallinarum

Avibacterium paragallinarum (AP), the causative agent of infectious coryza, induces severe upper respiratory disease and major production losses in chickens of all ages. With increasing restrictions on antibiotic use and limited vaccine efficacy, alternative emerging strategies such as probiotics, prebiotics, and synbiotics are urgently needed to control this pathogen. This study evaluated the antagonistic activity of Lacticaseibacillus casei (LC) and a metabolically engineered LC strain overproducing conjugated linoleic acid (LC ^+ CLA), alone or combined with berry pomace polyphenol extract (BPE), against AP. Co-culture assays with LC or LC^CLA resulted in time-dependent inhibition and complete elimination of AP within 48 h. Cell-free culture supernatants from LC (CFCS1) and LC ^+ CLA (CFCS2) individually reduced AP by approximately 2 log CFU/mL at 48 h and completely inhibited growth by 72 h (p < 0.05). BPE at 0.2 mg GAE/mL fully suppressed AP within 24 h, while 0.1 mg GAE/mL reduced counts by 2.5 log CFU/mL at 24 h (p < 0.05). Combination of CFCS1 or CFCS2 with 0.1 mg GAE/mL BPE further enhanced AP inhibition within 24-48 h relative to untreated controls (p < 0.05). Gene expression analysis revealed modulation of AP stress response and survival-associated genes, and fluorescence microscopy using SYTO-9/propidium iodide confirmed increased membrane permeability and bacterial death. These integrated findings support probiotic and polyphenol-based interventions as promising, non-antibiotic approaches for controlling AP infections in poultry.