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Applied and Environmental Microbiology, April 2006, p. 2533-2538, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2533-2538.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Indirect Measurement of the Lag Time Distribution of Single Cells of Listeria innocua in Food

M. D'Arrigo,1 G. D. García de Fernando,1 R. Velasco de Diego,1 J. A. Ordóñez,1 S. M. George,2 and C. Pin2*

Departamento de Nutrición, Bromatología y Tecnología de los Alimentos, Facultad de Veterinaria, Universidad Complutense, 28040 Madrid, Spain,1 Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, United Kingdom2

Received 12 August 2005/ Accepted 24 January 2006

The distribution of log counts at a given time during the exponential growth phase of Listeria innocua measured in food samples inoculated with one cell each was applied to estimate the distribution of the single-cell lag times. Three replicate experiments in broth showed that the distribution of the log counts is a linear mapping of the distribution of the detection times measured by optical density. The detection time distribution reflects the lag time distribution but is shifted in time. The log count distribution was applied to estimate the distributions of the lag times in a liquid dairy product and in liver paté after different heat treatments. Two batches of ca. 100 samples of the dairy product were inoculated and heated at 55°C for 45 min or at 62°C for 2 min, and an unheated batch was incubated at 4°C. The final concentration of surviving bacteria was ca. 1 cell per sample. The unheated cells showed the shortest lag times with the smallest variance. The mean and the variance of the lag times of the surviving cells at 62°C were greater than those of the cells treated at 55°C. Three batches of paté samples were heated at 55°C for 25 min, 62°C for 81 s, or 65°C for 20 s. A control batch was inoculated but not heated. All paté samples were incubated at 15°C. The distribution of the lag times of the cells heated at 55°C was not significantly different from that of the unheated cells. However, at the higher temperatures, 62°C and 65°C, the lag duration was longer and its variance greater.

* Corresponding author. Mailing address: Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, United Kingdom. Phone: 44 1603 255021. Fax: 44 1603 255288. E-mail: carmen.pin{at}bbsrc.ac.uk.

Applied and Environmental Microbiology, April 2006, p. 2533-2538, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2533-2538.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Aguirre, J. S., Pin, C., Rodriguez, M. R., Garcia de Fernando, G. D. (2009). Analysis of the Variability in the Number of Viable Bacteria after Mild Heat Treatment of Food. Appl. Environ. Microbiol. 75: 6992-6997 [Abstract] [Full Text]  
  • Reichert-Schwillinsky, F., Pin, C., Dzieciol, M., Wagner, M., Hein, I. (2009). Stress- and Growth Rate-Related Differences between Plate Count and Real-Time PCR Data during Growth of Listeria monocytogenes. Appl. Environ. Microbiol. 75: 2132-2138 [Abstract] [Full Text]  
  • Metris, A., George, S. M., Mackey, B. M., Baranyi, J. (2008). Modeling the Variability of Single-Cell Lag Times for Listeria innocua Populations after Sublethal and Lethal Heat Treatments. Appl. Environ. Microbiol. 74: 6949-6955 [Abstract] [Full Text]  
  • Pin, C., Baranyi, J. (2008). Single-Cell and Population Lag Times as a Function of Cell Age. Appl. Environ. Microbiol. 74: 2534-2536 [Abstract] [Full Text]  
  • Metris, A., George, S. M., Baranyi, J. (2006). Use of Optical Density Detection Times To Assess the Effect of Acetic Acid on Single-Cell Kinetics. Appl. Environ. Microbiol. 72: 6674-6679 [Abstract] [Full Text]  


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