title: Effect of environmental stresses on the mean and distribution of individual cell lag times of Escherichia coli O157:H7.
abstract: The effect of starvation, heat or acid stress on duration of individual cell lag time (tau) and standard deviation (SD) of tau was investigated using Escherichia coli O157:H7. Cells were stressed by exposure to acid (pH 3.5), heat (50 degrees C), or starvation in either glucose-free mineral medium (MOPS), tryptic soy broth (TSB) or Luria broth (LB). Stressed cells were then diluted into wells of a Bioscreen plate to obtain single cells per well. Replicate time to detection (td) values were obtained using the Bioscreen and used to calculate the tau and SD. Significant (P< or =0.05) increases in tau over untreated controls were found for the following treatments: 14 days in acid; 2 h of heating; 3 days starvation in MOPS; and 2 days starvation in either TSB or LB. The largest increase in tau was >2-fold from 2.5 to 5.6 h observed with the heat treatment. MOPS starvation was more detrimental to the cells than was acid treatment over the same time period. A significant increase in SD was found with 21 days acid treatment, and 2 days starvation in either TSB or LB. No significant increase in SD was found for MOPS starvation or heat treatment. Lognormal, Gamma, ExtremeValue and Weibull distributions were fitted to the tau data using BestFit. The results suggest that the Lognormal distribution is suitable for fitting tau data from either stressed or unstressed cells.
authors.affiliation: Laboratory Service Division, University of Guelph, 95 Stone Road West, Guelph, Ontario, Canada.
authors.forename: Yaqin
authors.initials: Y
authors.lastname: Li
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Odumeru
authors.forename: Mansel
authors.initials: M
authors.lastname: Griffiths
authors.forename: Robin C
authors.initials: RC
authors.lastname: McKellar
mesh_terms: D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry*; D004777:Environment; D019453:Escherichia coli O157 / Q000254:growth & development*; D005516:Food Microbiology; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D015233:Models, Statistical; D011237:Predictive Value of Tests
chemical_list: D003470:Culture Media