GROWTH OF ESCHERICHIA-COLI O157 H7 AT FLUCTUATING INCUBATION TEMPERATURES/

Temperature abuse of foods is often transitory and little information is available describing the response of the foodborne pathogen, Escher ichia coli O157:H7, to nonisothermal and/or fluctuating temperature st orage. Growth responses were determined for a mixture of three E. coli O157:H7 strains in brain heart infusion (BHI) broth as a function of temperature (static and fluctuating), initial pH (5, 6, and 7), and Na CL content(0.5, 1, 2, and 3%). Five 6-h ''square-wave'' fluctuating te mperature regimes were used: 4 to 12, 4 to 19, 4 to 28, 8 to 19, and 1 2 to 28 degrees C and compared with growth at 8, 10, 12, 19, and 28 de grees C. The growth curves obtained from fitting the Gompertz equation for the fluctuating temperatures were compared to those obtained for the static temperatures. Increased NaCl concentration decreased growth temperature both for the fluctuating temperature growth curves and th e static growth data. The cells grew or remained viable for up to 21 d ays under all conditions and fluctuating temperatures. Growth kinetics at fluctuating temperatures more closely approximated the higher temp erature than the midpoint temperature of each cyclic range. The result s indicate that transitory abuse could lead to more rapid growth than expected of E. call O157:H7 in foods and that given sufficient time E. coli O157:H7 can grow at as low as 8 degrees C.