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Type of publication: Journal Article
Type of document: Full Paper

Year: 2009

Authors: Reichert-Schwillinsky, F; Pin, C; Dzieciol, M; Wagner, M; Hein, I

Title: Stress- and growth rate-related differences between plate count and real-time PCR data during growth of Listeria monocytogenes.

Source: Appl Environ Microbiol. 2009; 75(7):2132-2138



Authors Vetmeduni Vienna:

Dzieciol Monika
Hein Ingeborg
Wagner Martin

Vetmed Research Units
Institute of Food Safety, Food Technology and Veterinary Public Health, Unit of Food Microbiology


Abstract:
To assess the overestimation of bacterial cell counts in real-time PCR in relation to stress and growth phase, four different strains of L. monocytogenes were exposed to combinations of osmotic stress (0.5 to 8% [vol/vol] NaCl) and acid stress (pH 5 to 7) in a culture model at a growth temperature of 10 degrees C or were grown under optimal conditions. Growth curves obtained from real-time PCR, optical density, and viable count data were compared. As expected, optical density data revealed entirely different growth curves. Good to moderate growth conditions yielded good correlation of real-time PCR data and plate count data (r(2) = 0.96 and 0.99) with similar cell counts. When growth conditions became worse, the numbers of CFU decreased during the stationary phase, whereas real-time-PCR-derived bacterial cell equivalents differed in this regard; the correlation worsened (r(2) = 0.84). However, fitted growth curves revealed that maximum growth rates calculated from real-time PCR data were not significantly different from those derived from plate count data. The overestimation of bacterial cell counts by real-time PCR observed in the stationary phase under higher-stress conditions might be explained by the accumulation of viable but nonculturable bacteria or dead bacteria and extracellular DNA. Considering these results, real-time PCR data collected from naturally contaminated samples should be viewed with caution.

Keywords Pubmed: Acids/pharmacology
Anti-Bacterial Agents/pharmacology
Colony Count, Microbial/methods*
Listeria monocytogenes/drug effects
Listeria monocytogenes/growth & development*
Microbial Viability
Osmotic Pressure
Polymerase Chain Reaction/methods*
Statistics as Topic
Stress, Physiological


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