THE EFFECT OF TRANSIENT TEMPERATURES ON THE GROWTH OF SALMONELLA-TYPHIMURIUM LT2 IN GELATIN GEL

The growth of colonies of Salmonella typhimurium derived from single i mmobilised cells was studied while subjected to constant and sinusoida lly-varying temperatures. The bacteria grew in microbiological culture media adjusted to different pH and sodium chloride (NaCl) concentrati on and solidified with gelatin that was contained within a cassette fo rmed between sheets of PVC film that allowed gaseous exchange. At pH 7 .0 and 0.5% (w/v) NaCl and either 12 degrees C or 20 degrees C, S. typ himurium grew at a rate similar to that in liquid medium. The decrease in growth rate at 20 degrees C at a lower pH or higher NaCl concentra tion was greater in the case of immobilised cells than for cells in li quid medium. The change in the numbers of viable bacteria was measured with time under sinusoidally-varying temperatures between 4 and 22 de grees C and between 12 and 22 degrees C of period in the range 12 to 4 80 min. The experimental growth curves were compared with predictions based on isothermal growth in liquid medium. The discrepancies between experiment and prediction were greater for gels stressed by NaCl or p H than for gels at pH 7.0 and containing 0.5% (w/v) NaCl, consistent w ith the isothermal observations.