For seventeen dietary supplements containing viable bacteria sold in Slovenian pharmacies, we checked the consistency of the information on the label with the actual microbiological compositions. The number of live bacteria in the products was determined by the standard method of colony counting on selective media, and the presence of the labeled bacterial species by the PCR and MALDI-TOF MS methods. PCR was performed on total DNA from the product and on DNA from a consortium of colonies, and MALDI-TOF MS on individual colonies. We found several labeled irregularities. In eight cases, the labeled of the product mentioned the word "probiotic", which is not allowed for food supplements in the EU. In most cases, the labels only included the total number of all microorganisms in the product, but not the number of individual strains (incorrect in 15 out of 17 samples). In five products only the type of bacteria was indicated, the strain was not labeled. The total number of colony units per product unit (KE) was appropriate for fourteen products and too low for three products (18 %). The MALDI-TOF MS method and identification with the MALDI Biotyper (Bruker Daltonics) proved to be a rapid and simple method, reliable enough to identify most species, with the exception of the species Lacticaseibacillus (L. casei, L. zeae, L. rhamnosus). Sixteen of the 292 colonies examined (5 %) could not be identified due to missing spectrum (11 colonies) or unrecognized spectrum (5 colonies). Using the PCR method, we successfully identified all bacterial species listed on the product labeled for eleven products. The advantage of the PCR method is the ability to identify at the subspecies level: Bif. animalis subsp. lactis, Streptococcus salivarius subsp. thermophilus, Bif. longum subsp. longum, Bif. longum subsp. infantis.
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