Applied Genetics and Molecular Biotechnology

Applied Microbiology and Biotechnology

, Volume 84, Issue 6, pp 1137-1147

First online:

Quantification of live and dead probiotic bacteria in lyophilised product by real-time PCR and by flow cytometry

  • Mateja KramerAffiliated withLek Pharmaceuticals d.d., Quality Control Email author 
  • , Nataša ObermajerAffiliated withDepartment of Biotechnology, Jožef Stefan Institute
  • , Bojana Bogovič MatijašićAffiliated withBiotechnical Faculty, Zootechnical Department, Dairy Science, University of Ljubljana
  • , Irena RogeljAffiliated withBiotechnical Faculty, Zootechnical Department, Dairy Science, University of Ljubljana
  • , Vojko KmetecAffiliated withFaculty of Pharmacy, Department of Biopharmaceutics and Pharmacokinetics, University of Ljubljana

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The basic requirement for probiotic bacteria to be able to exert expected positive effects is to be alive; therefore, appropriate quantification methods are crucial. Due to disadvantages of conventional microbiological methods, the bacterial quantification based on the nucleic acid detection is increasingly used. The objective of this study was to evaluate the possibility to use propidium monoazide (PMA) in combination with real-time polymerase chain reaction (PCR) method or LIVE/DEAD BacLight viability kit in combination with flow cytometry (FCM) for determination of probiotic bacteria in a lyophilised product containing Lactobacillus acidophilus LA-5 and Bifidobacterium animalis ssp. lactis BB-12. In addition, the viability of probiotic bacteria in lyophilised product during 3 months storage was investigated. In the product, the results of real-time PCR quantification of PMA-treated cells did not differ significantly from those of non-treated cells, which indicate that most of the bacterial cells retained the membrane integrity although they have lost the culturability. The results obtained by FCM analysis were comparable with those by PMA real-time PCR. In conclusion, the PMA real-time PCR and FCM determination of the viability of probiotic bacteria could complement the plate count method which considers only the culturable part of the population.


Quantification Real-time PCR Propidium monoazide Probiotic bacteria Flow cytometry