**2. Probiotics**

Probiotics are defined as "live strains of strictly selected microorganisms which, when administered in adequate amounts, confer a health benefit on the host" [28]. The most common microorganisms used as probiotics in livestock production are lactic acid bacteria (LAB) from the genus *Lactobacillus*, *Pediococcus*, *Lactococcus*, *Enterococcus*, *Streptococcus*, and *Leuconostoc*. Nevertheless, only the genera *Lactobacillus*, *Streptococcus*, *Pediococcus*, *Enterococcus*, and *Weissella* are the most frequently used in poultry production [29]. Although the efficacy of probiotics reducing enteric pathogens is evident, one of the disadvantages is that they require refrigeration or lyophilization to survive for long storage periods or can be encapsulated to increase their stability/viability when included in the feed, which would increase the cost of production at the industrial level, making it unprofitable [30]. Unlike LAB, direct-fed microbials (DFM) as *Bacillus* spores, other types of probiotics, have several potential applications since they can be included as feed additives in poultry diets, due to their remarkable heat stability and long shelf life [31, 32]. Bacteria of the genus *Bacillus* are Gram-positive, frequently found in the soil. However, several studies have shown that *Bacillus* spores can also be present, germinate, and survive

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**Figure 1.**

*Mechanism of action of probiotics.*

*The Use of Probiotics in Poultry Production for the Control of Bacterial Infections and Aflatoxins*

in the gastrointestinal tract (GIT) of different animal species [25]. The survival rate and persistence of some *Bacillus* strains in the GIT could be related to their capacity to synthesize biofilms, thus protecting themselves against the different conditions present in the gut [33]. Furthermore, another advantage of *Bacillus* strains is that they are frequently used by biotechnology companies for the production of enzymes and antibiotics. Therefore, these multifunctional microorganisms have different

Although a large number of studies have shown the possible mechanisms by which probiotics have a beneficial action in inhibiting of pathogens, more studies

The possible modes of action of probiotics for the inhibition of pathogens include two basic mechanisms [29, 36, 37]: competitive exclusion and modulation of the host immune system (**Figure 1**). Competitive exclusion involves mechanisms such as (1) production of inhibitory compounds, that is, hydrogen peroxide, bacteriocins, and defensins [38, 39], (2) prevention of the pathogen adhesion [38], (3) competition for nutrients [40], and (4) reduction of toxin bioavailability [36]. Meanwhile, in the modulation of the host immune system, both innate and adaptive immune responses are involved [29]. The adaptive immune response depends on B and T lymphocytes to induce an antigen-specific response and produce antibodies [29, 41]. In contrast, physical and chemical barriers (innate immunity), such as intestinal epithelial cells (IEC), are the first line of defense to prevent the spread of pathogens and subsequent infections. Furthermore, IEC are the target cells for probiotics, which can improve the function of the intestinal barrier by stimulating the production of mucus and antimicrobial peptides such as defensins [42, 43].

applications, since they are useful inside or outside a host [34, 35].

*DOI: http://dx.doi.org/10.5772/intechopen.88817*

**2.1 Mechanisms of action probiotics**

*2.1.1 Pathogenic bacteria*

are needed to elucidate them.

*The Use of Probiotics in Poultry Production for the Control of Bacterial Infections and Aflatoxins DOI: http://dx.doi.org/10.5772/intechopen.88817*

in the gastrointestinal tract (GIT) of different animal species [25]. The survival rate and persistence of some *Bacillus* strains in the GIT could be related to their capacity to synthesize biofilms, thus protecting themselves against the different conditions present in the gut [33]. Furthermore, another advantage of *Bacillus* strains is that they are frequently used by biotechnology companies for the production of enzymes and antibiotics. Therefore, these multifunctional microorganisms have different applications, since they are useful inside or outside a host [34, 35].
