ISSUE FOCUS FEED & ADDITIVE MAGAZINE May 2025 33 microbial substance’s uptake, modifying the drug target, inactivating the drug, or facilitating its discharge with efflux pumps. There are two types of resistance: natural resistance, which is further divided into intrinsic and induced resistance, and acquired resistance. Intrinsic resistance is a “characteristic” of a bacterial species and is not dependent on antibiotic exposure. An example is the reduced permeability of the outer membrane of gram-negative bacteria, which prevents certain antibiotics from entering. Induced resistance, however, needs to be initiated by antibiotics. Here, multidrug-efflux pumps can be mentioned. The third one, acquired resistance, refers to the process by which bacteria acquire genetic material, the resistance genes, from other bacteria that are resistant. The mechanisms include vertical transfer to daughter cells and horizontal transfer, such as the transfer from dead bacteria to living ones, by viruses, or the transfer of plasmids (Reygaert, 2018). DEOXYNIVALENOL (DON) PROMOTES RESISTANCE IN GUT MICROBIOTA A Chinese group of researchers (Deng et al., 2025) examined for the first time the influence of DON on the intestinal microbiota of chickens. One of the most alarming findings is DON’s ability to enhance antibiotic resistance. It contributes to this issue in several ways: 1. Encouraging resistant bacteria – By disrupting microbial balance, DON provides a survival advantage to bacteria that carry resistance genes. 2. Activating resistance genes – Studies suggest that DON can increase the expression of genes that help bacteria withstand antibiotics. 3. Enhancing gene transfer – Bacteria can share resistance genes through horizontal gene transfer. DON appears to promote this process, making antibiotic-resistant strains spread more rapidly. 4. Weakening antibiotic effectiveness – DON-induced changes in the gut environment can reduce the effectiveness of antibiotics, making treatments less successful. A further indication that mycotoxins can enhance resistance is the significant overlap in the geographical distribution of antimicrobial-resistant bacteria and genes with that of mycotoxins, as noted by Deng et al. WHICH PROTECTION MECHANISMS DO BACTERIA HAVE AGAINST MYCOTOXINS? In the case of mycotoxins, bacteria employ similar molecular mechanisms to those used against antibiotics. In an in vitro experiment, Hassan et al. (2019) challenged Devosia mutans, a gram-negative bacterium, with DON in the growth medium. DON inhibits protein synthesis, induces oxidative stress, and compromises cell membrane integrity in eucaryotic cells. Hassan et al. asserted three adaptive mechanisms as the response to the challenge: 1. Activation of cellular membrane proteins (adenosine 5’-triphosphate-binding cassette -ABC- transporters) responsible for the unidirectional transport Resistance Gene Transfer of free DNA Dead Bacterium Gene goes to plasmid or to chromosome Chromosomal DNA Bacterium infected by a virus Plasmid Virus Plasmid Transfer Figure 1. Different possibilities of transfer of resistance genes
RkJQdWJsaXNoZXIy MTUxNjkxNQ==