Modelling time to growth of Escherichia coli as a function of water activity and undissociated lactic acid.
OBJECTIVE
To model the effect of water activity (a(w)) and concentration of undissociated lactic acid (HLac) on the time to growth (TTG) and the growth/no growth boundary of acid-adapted generic Escherichia coli, used as model organisms for Shiga toxin-producing E. coli (STEC).


RESULTS
For each of two E. coli strains, the TTG in brain heart infusion broth at 27 degrees C was estimated at 30 combinations of a(w) (range 0.945-0.995) and concentration of HLac (range 0-6.9 mol m(-3)) by using an automated turbidity reader. Survival analysis was used to develop a model predicting the TTG and the growth/no growth boundary.


CONCLUSIONS
The present model can be used to predict the TTG and to indicate the growth/no growth boundary of acid-adapted E. coli strains as a function of a(w) and concentration of HLac.


CONCLUSIONS
Fermented food products have been implicated as sources of STEC in several outbreaks. The study results are relevant for modelling of growth of STEC in fermented food and can be used in microbiological risk assessments or in the design and validation of food-production processes.
Lindblad
M
M
National Food Administration, Uppsala, Sweden. mali@slv.se
Lindqvist
R
R
D001686:Biological Phenomena; D003470:Culture Media; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development*; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000494:pharmacology*; D008954:Models, Biological; D054323:Shiga-Toxigenic Escherichia coli / Q000254:growth & development; D016019:Survival Analysis; D014867:Water
D003470:Culture Media; D014867:Water; D019344:Lactic Acid