Probiotic Lactocaseibacillus casei NK1 Enhances Growth and Gut Microbiota in Avian Pathogenic Escherichia coli Challenged Broilers

The present study was conducted to assess the efficacy of Laboratory-Isolated <i>Lactocaseibacillus casei</i> NK1 (Lc. NK1) in broilers hypothesizing that, Lc. NK1 supplementation will enhance growth performance, modulate the gut microbiome, and reduce fecal pathogenic <i>Escherichia coli</i> in broilers. The experiment spanned 35 days where 60 one-day-old broiler chicks were randomly assigned to four treatment groups (<i>n</i> = 15); control-group with no treatment (NC), APEC (challenged with <i>E. coli</i> only), CProb (received commercial probiotics), and LNK1 (treated with Lc. NK1). The APEC, CProb, and LNK1 groups were infected with <i>E. coli</i> O78 strain at 11 days of age. Growth performance analysis revealed that the LNK1 group by day 35 gained body weight similar to the CProb group, with both groups significantly outperforming the APEC group (<i>p</i> < 0.001). Both the LNK1 and CProp groups exhibited similar reduction in <i>E. coli</i> while increasing <i>Lactobacillus</i> colorizations in the cloacal swabs from day 21 to 35 of age (<i>p</i> > 0.05). Metagenomic analysis using 16S rRNA sequencing showed that the LNK1 group maintained a diverse and balanced gut microbiota, characterized by increased Firmicutes and reduced Proteobacteria. In contrast, the APEC group exhibited reduced diversity and dominance of <i>Escherichia-Shigella</i> (<i>p</i> < 0.001). These findings suggest Lc. NK1 could be a promising probiotic for enhancing gut health and growth performance in broilers, even under pathogenic challenges, offering a potential alternative to antibiotics in poultry production.