The effect of inoculum size and sublethal injury on the ability of Listeria monocytogenes to initiate growth under suboptimal conditions
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Date
2001-08-22
Authors
Pascual, C.
Robinson, T. P.
Ocio, M. J.
Aboaba, O.O.
Mackey, B. M.
Journal Title
Journal ISSN
Volume Title
Publisher
Letters in Applied Microbiology
Abstract
Aims: To investigate the effect of inoculum size and physiological state on the ability of Listeria monocytogenes cells to initiate growth under suboptimal conditions of salt concentration and pH.
Methods and Results: Cell suspensions were serially diluted in media of different salt concentration or pH and replicate inocula distributed into 96-well microplates. The proportion of wells showing growth at each dilution level was determined after incubation for 6 weeks for each set of conditions. Growth occurred from single cells up to a concentration of 1á2 mol l)1 NaCl; above this threshold, the inoculum size needed to initiate growth became progressively larger. A similar effect was seen with decreasing pH but only very close to the growth/no growth boundary. The threshold for inoculum-dependent growth was lower in exponential phase cells than in stationary phase ones and sublethal injury greatly decreased the probability of growth from small inocula.
Conclusions: The growth/no growth boundary for L. monocytogenes is not an absolute cut-off point but represents a region where the probability of growth rapidly decreases as conditions become more extreme. We interpret the requirement for a critical inoculum size for growth as being due to death of a proportion of cells in the inoculum rather than to co-operative population effects.
Signi®cance and Impact of the Study: Physiological heterogeneity within the cell population and inoculum size will affect the risk of L. monocytogenes growing in food.
Description
Scholarly article
Keywords
Listeria monocytogenes cells , Salt concentration , Cell suspension , Research Subject Categories::NATURAL SCIENCES
Citation
Pascual, C., Robinson, T. P., Ocio, M. J., Aboaba, O. O., & Mackey, B. M. (2001). The effect of inoculum size and sublethal injury on the ability of Listeria monocytogenes to initiate growth under suboptimal conditions. Letters in Applied Microbiology, 33(5), 357-361.