Bacillus licheniformis (B. licheniformis) is a probiotic known for its ability to enhance host resistance against pathogenic infections. This study aimed to evaluate the protective effects and underlying mechanisms of B. licheniformis in a mouse model challenged with Clostridium perfringens (C. perfringens). C57BL/6J mice were pretreated with B. licheniformis for 21 days before oral infection with C. perfringens. The probiotic administration significantly prevented infection-induced weight loss and immune organ enlargement. Serum cytokine analysis revealed that B. licheniformis increased anti-inflammatory IL-4 and IL-10 levels while reducing pro-inflammatory IL-1β, IL-6, and TNF-α levels. Histological analysis showed that B. licheniformis preserved intestinal morphology and inhibited epithelial cell apoptosis. Moreover, the probiotic mitigated the infection-induced decline in volatile fatty acid (VFA) production. 16S rRNA gene sequencing revealed that B. licheniformis reshaped the cecal microbiota, characterized by the increased abundance of Lachnospiraceae_NK4A136_group, Muribaculaceae, and Parabacteroides, and reduced abundance of Alistipes. Untargeted metabolomic profiling identified differential metabolites—including D-glucono-1,5-lactone, D-erythrose 4-phosphate, and D-sedoheptulose 7-phosphate—enriched in the pentose phosphate pathway, suggesting a regulatory role in redox homeostasis and host response. Collectively, these results indicate that B. licheniformis exerts protective effects against C. perfringens infection by modulating inflammation, apoptosis, microbial composition, and metabolic pathways. This work provides new insights into the application of B. licheniformis as a functional microbial feed additive in livestock disease prevention.

With 80% of bacterial infections occurring as biofilms, biofilm-related infections have evolved into a critical public health concern. Probiotics such as Bacillus licheniformis have emerged as promising alternatives, offering new avenues for effective treatment. This study aimed to evaluate the activity of licheniformis against the growth, biofilm formation, motility, and quorum sensing (QS) of Salmonella typhimurium. Several experiments were conducted: The minimum inhibitory concentration (MIC) of Bacillus licheniformis against Salmonella typhimurium was determined to be 0.5 mg/mL using the broth microdilution method. The inhibition zone of 100 mg/mL of B. licheniformis against Salmonella typhimurium was 19.98 ± 1.38 mm; the time-growth curve showed that B. licheniformis can effectively inhibit the growth of Salmonella typhimurium. In biofilm experiments, at the MIC of B. licheniformis, the inhibition rate of immature biofilm of Salmonella typhimurium was 86.9%, and it significantly reduced the production of biofilm components (EPS, e-DNA, and extracellular proteases) (p < 0.05). The disruption rate of mature biofilm by B. licheniformis at the MIC was 66.89%, and it significantly decreased the levels of biofilm components (EPS and e-DNA) (p < 0.5). Microscopic observation showed that both the MIC and 1/2 MIC of B. licheniformis could reduce the number of bacteria in the Salmonella typhimurium biofilm, which was not conducive to the formation and maintenance of the biofilm structure. Swimming/Swarming assays and QS experiments confirmed that B. licheniformis inhibits the motility of Salmonella typhimurium and the secretion of AI-1-type quorum sensing molecules and downregulates the AI-2 quorum sensing system by upregulating lsr gene expression. These findings suggest that B. licheniformis could be a potential antimicrobial agent and biofilm inhibitor.

In recent years, as the number of cats has increased, the intestinal health of cats has receied increasing amounts of attention. Probiotics have positive effects on maintaining intestinal homeostasis. This study was conducted to investigate the effects of probiotics Bacillus licheniformis (B. licheniformis) and Bacillus subtilis (B. subtilis) on cat immunity, inflammation, antioxidants, intestinal barrier and microbiota, and serum metabolites. Thirty-six cats (over one year old, 3.48 ± 0.71 kg) were randomly divided into 3 groups and fed with a basal diet (CON group), a basal diet + B. licheniformis (BL group), and a basal diet + B. subtilis (BS Group). The experiment lasted 35 days. Fecal scoring indicates that B. licheniformis and B. subtilis can improve fecal scores. Serum analysis indicated that the addition of both substances increased levels of IgA, IgM, T-AOC, and SOD, while reducing levels of the pro-inflammatory factor TNF-α. Moreover, 16S rRNA gene sequencing revealed that B. licheniformis and B. subtilis altered the fecal microbiota composition, characterized by the elevated abundance of Bacillus. Adding B. licheniformis to the diet increased the level of Faecalibacterium and decreased the level of Mogibacterium. Serum metabolomics revealed that levels of L-Glycine and Sn-Glycero-3-phosphocholine exhibited marked elevation in both the BL and BS groups, respectively. Furthermore, the study demonstrated that differential metabolites in the BL group were mainly enriched in amino acid metabolism pathways, while those in the BS group were chiefly concentrated in lipid metabolism pathways. However, this study acknowledges the limitations of its exclusive use of Ragdoll cats and its 35-day intervention period. It highlights the need for future research involving diverse breeds and longer durations. Overall, the data highlight B. licheniformis and B. subtilis as cat nutritional supplements that improve immunity and maintain intestinal health.