title: Responses of Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus to simulated food processing treatments, determined using fluorescence-activated cell sorting and plate counting.
abstract: Three common food pathogenic microorganisms were exposed to treatments simulating those used in food processing. Treated cell suspensions were then analyzed for reduction in growth by plate counting. Flow cytometry (FCM) and fluorescence-activated cell sorting (FACS) were carried out on treated cells stained for membrane integrity (Syto 9/propidium iodide) or the presence of membrane potential [DiOC2(3)]. For each microbial species, representative cells from various subpopulations detected by FCM were sorted onto selective and nonselective agar and evaluated for growth and recovery rates. In general, treatments giving rise to the highest reductions in counts also had the greatest effects on cell membrane integrity and membrane potential. Overall, treatments that impacted cell membrane permeability did not necessarily have a comparable effect on membrane potential. In addition, some bacterial species with extensively damaged membranes, as detected by FCM, appeared to be able to replicate and grow after sorting. Growth of sorted cells from various subpopulations was not always reflected in plate counts, and in some cases the staining protocol may have rendered cells unculturable. Optimized FCM protocols generated a greater insight into the extent of the heterogeneous bacterial population responses to food control measures than did plate counts. This study underlined the requirement to use FACS to relate various cytometric profiles generated by various staining protocols with the ability of cells to grow on microbial agar plates. Such information is a prerequisite for more-widespread adoption of FCM as a routine microbiological analytical technique.
authors: Food Science Research Centre, Department of Life Sciences, University of Limerick, Limerick, Ireland.
authors: Deirdre
authors: D
authors: Kennedy
authors: Ultan P
authors: UP
authors: Cronin
authors: Martin G
authors: MG
authors: Wilkinson
references: J Microbiol Methods. 2000 Sep;42(1):97-114
references: 11000436
references: Int J Food Microbiol. 2009 Oct 31;135(2):144-51
references: 19733929
references: Int J Food Microbiol. 1999 Sep 15;50(1-2):1-17
references: 10488839
references: Cytometry A. 2007 Aug;71(8):592-8
references: 17421025
references: Antimicrob Agents Chemother. 2000 Apr;44(4):827-34
references: 10722477
references: Cytometry A. 2004 Oct;61(2):189-95
references: 15382024
references: Water Res. 2005 Jan-Feb;39(2-3):478-86
references: 15644256
references: Food Microbiol. 2010 Sep;27(6):710-30
references: 20630313
references: Int J Parasitol. 1996 Jun;26(6):637-46
references: 8875309
references: Food Microbiol. 2008 Apr;25(2):235-43
references: 18206765
references: Cytometry A. 2007 Mar;71(3):143-53
references: 17200957
references: Int J Food Microbiol. 2008 Oct 31;127(3):252-60
references: 18765166
references: Appl Environ Microbiol. 2010 Aug;76(15):5088-96
references: 20543046
references: Int J Food Microbiol. 2007 Nov 30;120(1-2):51-70
references: 17614151
references: Appl Environ Microbiol. 2004 Aug;70(8):4449-57
references: 15294772
references: Methods Mol Med. 2008;142:175-86
references: 18437314
references: J Food Prot. 2008 Nov;71(11):2168-76
references: 19044257
references: Food Microbiol. 2009 Aug;26(5):542-6
references: 19465252
references: Food Microbiol. 2008 Feb;25(1):183-9
references: 17993393
references: Methods Cell Biol. 2001;64:511-37
references: 11070853
references: Int J Food Microbiol. 1995 Dec;28(2):317-26
references: 8750676