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Applied and Environmental Microbiology, July 2009, p. 4550-4556, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02625-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Response of Listeria monocytogenes to Disinfection Stress at the Single-Cell and Population Levels as Monitored by Intracellular pH Measurements and Viable-Cell Counts{triangledown}

Vicky G. Kastbjerg,1* Dennis S. Nielsen,2 Nils Arneborg,2 and Lone Gram1

National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads Bldg. 221, DK-2800 Kongens Lyngby, Denmark,1 Department of Food Science, Centre for Advanced Food Studies (LMC), Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1870 Frederiksberg C, Denmark2

Received 17 November 2008/ Accepted 26 April 2009

Listeria monocytogenes has a remarkable ability to survive and persist in food production environments. The purpose of the present study was to determine if cells in a population of L. monocytogenes differ in sensitivity to disinfection agents as this could be a factor explaining persistence of the bacterium. In situ analyses of Listeria monocytogenes single cells were performed during exposure to different concentrations of the disinfectant Incimaxx DES to study a possible population subdivision. Bacterial survival was quantified with plate counting and disinfection stress at the single-cell level by measuring intracellular pH (pHi) over time by fluorescence ratio imaging microscopy. pHi values were initially 7 to 7.5 and decreased in both attached and planktonic L. monocytogenes cells during exposure to sublethal and lethal concentrations of Incimaxx DES. The response of the bacterial population was homogenous; hence, subpopulations were not detected. However, pregrowth with NaCl protected the planktonic bacterial cells during disinfection with Incimaxx (0.0015%) since pHi was higher (6 to 6.5) for the bacterial population pregrown with NaCl than for cells grown without NaCl (pHi 5 to 5.5) (P < 0.05). The protective effect of NaCl was reflected by viable-cell counts at a higher concentration of Incimaxx (0.0031%), where the salt-grown population survived better than the population grown without NaCl (P < 0.05). NaCl protected attached cells through drying but not during disinfection. This study indicates that a population of L. monocytogenes cells, whether planktonic or attached, is homogenous with respect to sensitivity to an acidic disinfectant studied on the single-cell level. Hence a major subpopulation more tolerant to disinfectants, and hence more persistent, does not appear to be present.

* Corresponding author. Mailing address: National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads Bldg. 221, DK-2800 Kongens Lyngby, Denmark. Phone: 45 45 25 25 65. Fax: 45 45 88 47 74. E-mail: vgk{at}aqua.dtu.dk

{triangledown} Published ahead of print on 1 May 2009.

Applied and Environmental Microbiology, July 2009, p. 4550-4556, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02625-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Kastbjerg, V. G., Larsen, M. H., Gram, L., Ingmer, H. (2010). Influence of Sublethal Concentrations of Common Disinfectants on Expression of Virulence Genes in Listeria monocytogenes. Appl. Environ. Microbiol. 76: 303-309 [Abstract] [Full Text]  


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