Thermal resistance of Aeromonas hydrophila in liquid whole egg

Aeromonas hydrophila (AH) is a psychrotrophic spoilage bacterium and potential pathogen which has been isolated from a variety of refrigerated foods of animal origin, including raw milk, red meat, poultry, and commercially broken raw liquid whole egg (LWE). Decimal reduction times (D values) of 4 strains of AH (1 egg isolate, 2 egg processing plant isolates, 1 ATCC type strain) were determined in LWE using an immersed sealed capillary tube (ISCT) procedure. Initial populations (7.0 to 8.3 log CFU/tube in 0.05 ml LWE) were heated at 48, 51, 54, 57, and 60 degrees C, and survivors were plated onto starch ampicillin agar (48 h at 28 degrees C). D values ranged from 3.62 to 9.43 min (at 48 degrees C) to 0.026 to 0.040 min (at 60 degrees C). Both processing plant isolates were more heat resistant than the ATCC strain. Decimal reduction time curves (r(2) greater than or equal to 0.98) yielded z(D) values of 5.02 to 5.59 degrees C, similar to those for other non-spore-forming bacteria. D values of the most heat resistant AH strain were also determined in LWE at 48, 51, and 54 degrees C using a conventional capped test tube procedure (10 ml/tube). Cells heated in test tubes yielded nonlinear (tailing) survivor curves and larger (P less than or equal to 0.05) apparent D values at each temperature than those obtained using the ISCT method. This study provides the first thermal resistance data for AH in LWE and the first evidence that straight-line semilogarithmic thermal inactivation kinetics may be demonstrated for Aeromonas using the ISCT procedure.