A comparison of the Bioscreen method and microscopy for the determination of lag times of individual cells of Listeria monocytogenes

doi:10.1046/j.1472-765x.2000.00748.x

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Wiley InterScience

Letters in Applied Microbiology

Volume 30 Issue 6, Pages 468 - 472

Published Online: 20 Apr 2002

Published on behalf of the Society for Applied Microbiology

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A comparison of the Bioscreen method and microscopy for the determination of lag times of individual cells of Listeria monocytogenes

Y. Wu ¹ , M.W. Griffiths ¹ and R.C. McKellar ²

¹ Department of Food Science, University of Guelph and ² Food Research Program, Agriculture and Agri-Food Canada, Guelph, Ontario, Canada

Correspondence to: M.W. Griffiths, Department of Food Science, University of Guelph, Guelph, Ont., Canada, N1G 2W1 (e-mail: mgriffit@uoguelph.ca).

y. wu, m.w. griffiths and r.c. mckellar. 2000.

ABSTRACT

Lag phase durations (t_Lag) of individual Listeria monocytogenes cells were analysed using the NightOwl Molecular Imaging System, and results were compared with mean individual cell lag times (t_L) obtained from the detection time (t_d) method using Bioscreen. With Bioscreen, an average t_L of 6·39 ± 0·89 h was obtained from five separate experiments. With the NightOwl method, an average t_Lag of 2·73 ± 0·06 h was obtained from three experiments consisting of eight total replicates. Lag values from the NightOwl and Bioscreen are related by the equation: t_Lag=t_L + DT, where DT is the doubling time. The equivalent t_Lag mean value for the Bioscreen method was 7·11 ± 0·84 h. Individual lag times measured by both methods were normally distributed (r² for Bioscreen and NightOwl ranged from 0·951 to 0·999 and from 0·884 to 0·982, respectively). The results suggest that the NightOwl method can provide accurate estimates of individual cell lag times, which will facilitate the development of combined discrete continuous models for bacterial growth.