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Evaluation of dietary supplements containing viable bacteria by cultivation/MALDI-TOF mass spectrometry and PCR identification
ID Mohar Lorbeg, Petra (Author), ID Golob, Majda (Author), ID Kramer, Mateja (Author), ID Treven, Primož (Author), ID Bogovič Matijašić, Bojana (Author)

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Abstract
The insufficient quality of products containing beneficial live bacteria in terms of content and viability of labelled microorganisms is an often-reported problem. The aim of this work was to evaluate the quality of dietary supplements containing viable bacteria available in Slovenian pharmacies using plate counting, matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and species- or subspecies-specific PCR with DNA isolated from consortia of viable bacteria, from individual isolates, or directly from the products. Twelve percent of the products (3 of 26) contained insufficient numbers of viable bacteria. Eighty-three of the labelled species (111 in total) were confirmed by PCR with DNA from the product; 74% of these were confirmed by PCR with DNA from viable consortium, and 65% of these were confirmed by MALDI-TOF MS analysis of colonies. Certain species in multi-strain products were confirmed by PCR with DNA from viable consortia but not by MALDI-TOF MS, suggesting that the number of isolates examined (three per labelled strain) was too low. With the exception of Lacticaseibacillus casei and closely related species (Lacticaseibacillus rhamnosus and Lacticaseibacillus zeae), PCR and MALDI-TOF identification results agreed for 99% of the isolates examined, although several MALDI-TOF results had lower score values (1.700–1.999), indicating that the species identification was not reliable. The species L. zeae, which appeared in 20 matches of the Biotyper analysis, was identified as L. rhamnosus by PCR. The MALDI-TOF MS analysis was also unsuccessful in detecting Lactobacillus acidophilus La-5 and Bacillus coagulans due to missing peaks and unreliable identification, respectively. Mislabelling was detected by both methods for two putative L. casei strains that turned out to belong to the species Lacticaseibacillus paracasei. PCR remains more successful in subspecies-level identification as long as the database of MALDI-TOF MS spectra is not expanded by building in-house databases. The lack of positive PCR results with viable consortia or colonies, but positive PCR results with DNA isolated directly from the products observed in 10% (11/112) of the labelled strains, suggests the presence of non-culturable bacteria in the products. MALDI-TOF MS is a faster and simpler alternative to PCR identification, provided that a sufficient number of colonies are examined. Generation of in-house library may further improve the identification accuracy at the species and sub-species level.

Language:English
Keywords:lactobacilli, bifidobacteria, dietary supplements, MALDI-TOF MS, identification, probiotic, PCR, viability, dietary supplements
Work type:Article
Typology:1.01 - Original Scientific Article
Organization:BF - Biotechnical Faculty
VF - Veterinary Faculty
Publication status:Published
Publication version:Version of Record
Year:2021
Number of pages:14 str.
Numbering:Vol. 12, art. 700138
PID:20.500.12556/RUL-132100 This link opens in a new window
UDC:579
ISSN on article:1664-302X
DOI:10.3389/fmicb.2021.700138 This link opens in a new window
COBISS.SI-ID:67936003 This link opens in a new window
Publication date in RUL:12.10.2021
Views:822
Downloads:161
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Record is a part of a journal

Title:Frontiers in microbiology
Shortened title:Front. microbiol.
Publisher:Frontiers Media
ISSN:1664-302X
COBISS.SI-ID:4146296 This link opens in a new window

Licences

License:CC BY 4.0, Creative Commons Attribution 4.0 International
Link:http://creativecommons.org/licenses/by/4.0/
Description:This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

Language:Slovenian
Keywords:mikrobiologija, probiotiki, prehranska dopolnila

Projects

Funder:ARRS - Slovenian Research Agency
Project number:P4-0097
Name:Prehrana in mikrobna ekologija prebavil

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