Berberine Hydrochloride Attenuates Growth, Biofilm Formation, and Virulence Associated Phenotypes of Actinobacillus pleuropneumoniae Strain APP-2023.

Actinobacillus pleuropneumoniae (A. pleuropneumoniae), the causative agent of porcine contagious pleuropneumonia, poses significant economic threats to the global swine industry, further compounded by increasing antimicrobial resistance. This study investigated the antibacterial and antivirulence effects of berberine hydrochloride (BBH) against A. pleuropneumoniae strain APP-2023 using in vitro assays and a murine infection model. BBH exhibited measurable antibacterial activity against the tested strain, with a minimum inhibitory concentration (MIC) of 312.5 µg/mL, indicating relatively modest growth-inhibitory potency. At subinhibitory concentrations, BBH reduced crystal violet-stained surface-associated biofilm biomass and increased bacterial susceptibility to oxidative and osmotic stress. Treated bacteria displayed marked morphological alterations including cell elongation, accompanied by reduced transcription of cell division genes ftsZ and ftsA. In the murine challenge model, infection with BBH-pretreated bacteria resulted in improved survival and reduced pulmonary bacterial burden. These findings provide preliminary evidence that BBH attenuates several virulence-associated phenotypes of A. pleuropneumoniae strain APP-2023 and warrant further mechanistic and translational studies in multiple strains and natural porcine infection models.