A number of studies have confirmed the beneficial effect of the use of probiotics on the host, both in humans and in animals. The use of probiotics worldwide is rising. Lately, scientists have begun to warn that even deliberately ingested microorganisms can present a potential source of antibiotic resistance genes that can be transmitted among bacteria of various species. The European Food Safety Authority (EFSA), within the framework of the Qualified Presumption of Safety (QPS) concept, ensures that only those species of bacteria that are safe are used in foods and dietary supplements, and beside this, also the absence of transferable antibiotic resistance genes is mentioned. This can be assured only by determination of the presence of the genes associated with antibiotic resistance in the entire genomes of individual strains. Nowadays, the detection of the nucleotide sequences of total bacterial genomes has become available, and in the past phenotypic testing was only performed. Apart from intrinsic or natural resistance, the acquired resistance genes were found in many strains of bacteria from Lactobacillus and Bifidobacterium genera, among which those for erythromycin, tetracycline and aminoglycoside resistances predominate. The transfer of some antibiotic resistance genes, for example the transfer of the vancomycin resistance gene between enterococci and lactobacilli, have also been observed in vitro and in vivo in mice. The transmission of antibiotic resistance genes from lactic acid bacteria or bifidobacteria to pathogens in vivo has not been demonstrated yet, and potential risks can not be ruled out. For this reason regular control of probiotic bacteria on the market is very important, which also includes the identification of phenotypic and genotypic resistance to antibiotics.
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