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There are regular debates over whether or not probiotics should be used with antibiotics or not. There are a lot of misperceptions on the antagonisms between probiotics and antibiotics.

Yes, probiotics are bacteria that are sensitive to antibiotics but in the animal body, the situation is more complex than in vitro.

One MYTH is that antibiotics provide a performance-enhancing effect by their pure antimicrobial action. Thus, no additional benefit can be achieved with the combined usage of a probiotic and an antibiotic. The misconception is that the mode of action for each of the products is similar and probiotics aren't necessary when an antibiotic is used.

A second MYTH is that the simultaneous use of the two products will result in the destruction of the probiotic by the antimicrobial activity of the antibiotic. This also is a misperception or over simplification as to the susceptibility of the probiotic bacteria to the antibiotic. In particular, the spore-forming bacteria probiotics are naturally protected against aggressors. The non-spore forming probiotics, such as the Lactobocillus-based probiotics, could be sensitive but spore forming ones will be sufficiently protected.

Even once germinated, these categories of bacteria will resist to antibiotics to MIC (Minimum Inhibition Concentration) much above the recommended dose in the feed. In the table below, we are listing the level of sensitivity of germinated spore forming probiotics in term of MIC (Minimum Inhibition Concentration) value.

Moreover, the vegetative Bacillus likes to stick to the mucus layer near the villi, whereas the digesta, including the antibiotics, is floating in the lumen of the intestine and will be moved forward by peristalsis. Therefore, their contact is limited which will increase the survival and effectiveness of the vegetative form of the probiotics.

The ‘serious’ supplier of probiotics have conducted many research studies analyzing the additive value of the combined usage of a Bacillus-based probiotic with a feed additive antibiotic, Those results consistently demonstrate that effective probiotics deliver performance benefits with or without concurrent usage of a feed additive antibiotic, regardless of the type of antibiotic fed.

The explanation behind this ‘collaboration’ resides in the different and unique modes of action of both antibiotics and probiotics. The main mechanisms of action that support the contribution of effective probiotics are: Competitive exclusion, immuno-modulation, bacteriosin production and enzyme production.

Competitive Exclusion: Competitive exclusion is a probiotic mode of action that can occur via several different mechanisms. The direct mechanism is the basic space-occupying effect of the probiotic on intestinal cells. The result is less space for pathogenic bacteria to populate the gut. The indirect mechanism is through the production of secondary metabolites which affect the immediate environment of the probiotic. These metabolites result in the proliferation of lactic acid-producing bacteria, which benefit the intestine.

Bacteriocin or antimicrobial peptide production: Effective Bacillus-based probiotics produce antimicrobial substances that inhibit the growth of pathogens. As illustration, effective Bacillus licheniformis will produce lichenysin (antimicrobial peptide). Growth inhibitory and/or bactericidal effects against certain poultry pathogens have been described based on in vitro analysis of a number of probiotic bacteria. Probiotic strains of Bacillus spp. are shown to be especially effective (Svetoch et all, 2005; Teo and Tan, 2005; Latorre et al , 2016; Poormontaseri eI al 2017). It is known as well that other Bacillus species produce bacteriocins or bacteriocin-like substances, such as subtilin and coagulin.

Enzyme production: Bacillus-based probiotics can be a factory of digestive enzymes Those enzymes are released in the intestinal content by the germinated probiotics. Once released, they will continue to act locally, transforming the indigestible nutrients into digestible nutrients. Many of these enzymes are summarized in the table below.

The mode of action of some probiotics as described above are very additive to the standard mode of action of antibiotics that target either bacteria cell wall, cellular protein synthesis and DNA synthesis. The simultaneous use of both antibiotics and probiotics will enlarge the spectrum of action on the bacteria but it could add as well some positive effects on the feed digestibility.

Moreover, it seems that effective probiotics do not show signs of bacterial resistance. It may be more difficult for bacteria to find a resistance when attacked from several fronts. The most professional suppliers of probiotics are closely monitoring the efficacy of their strains through pathogen inhibition assays. So far, these suppliers did not find any development of resistance by pathogenic bacteria in relation to a probiotic being used as a feed additive. When you select the proper strain of probiotics, the rotation is not needed as it could often be for antibiotics.

But it would be dangerous to generalize. The bacillus subtilis or bacillus licheniformis are very large families of genotypes and all the information above could not apply to all the genotypes. As you know, there could be more genetic differences between 2 bacillus subtilis than there is between a fish and a pig. To identify properly the source of the probiotic to use, you need to ask the supplier to confirm the identity of his genotype (ex: Bacillus subtilis number 17299 or 5750) and ask scientific confirmation about that genotype mode of action. It is critical as well to ask the supplier to demonstrate the purity of the strain. Many probiotics on the market are a mix of different strains as consequences of contamination during storage and production.


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