**3. Mode of action**

There is no one method via which probiotics exert their benefits; nevertheless, they are essential to the health of the host immune system and the interaction involving the gut microbiota and the immune system of the host. Probiotic microorganisms used in poultry production should fulfill several requirements to be considered effective, including being indigenous to the host, adhering to the intestinal epithelium, surviving gastric juices and mucous, engaging in competition for colonization within the gastrointestinal tract alongside other microorganisms, and exhibiting high viability under storage conditions [15].

Probiotics have been shown to improve digestion, increase the production of digestive enzymes, and even detoxify substances in the diet, resulting in improved growth and performance in poultry. Next possible action is: by prevention of pathogens via competition for adhesion sites; producing organic acids which can alter gut pH (predominantly probiotics containing *Lactobacillus* strains), which can promote absorption of minerals and protein, volatile fatty acids and antibacterial substances like bacteriocins, hydrogen peroxide, defensins, etc.; and physiological effect by regenerating intestinal mucosa, and immunological effects by modulating antigen presenting cells, regulatory T and B cells, and regulation of pro-inflammatory cytokines [16].

Furthermore, probiotics might alter the development and composition of the microbiota in the gut by restraining the impact of harmful bacteria, as well as bolster the body's natural defense mechanism through the synthesis of inhibitory substances. The adhesion of specific probiotics to the gut mucin, a glycoprotein, suggested the competitive suppression or colonization resistance of infectious pathogens adhering

**Figure 1.** *Mode of action and impact of probiotics in poultry.*

to the shared route/site [17]. Thus, it out competes the proliferation of opportunistic pathogenic microbes. Lastly, increasing the resistance of poultry animals against stress caused by temperature as a potent environmental factor.

The aforementioned mechanism of action provided foundational data for understanding the positive benefits on the poultry animals (**Figure 1**). However, transcriptome and proteomic analyses are needed in future studies of probiotic and host interaction to better understand probiotic activity.
