THERMAL-RESISTANCE OF AEROMONAS-HYDROPHILA IN LIQUID WHOLE EGG

Aeromonas hydrophila (AH) is a psychrotrophic spoilage bacterium and p otential pathogen which has been isolated from a variety of refrigerat ed foods of animal origin, including raw milk, red meat, poultry, and commercially broken raw liquid whole egg (LWE). Decimal reduction time s (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 immerse d 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 degre es C) to 0.026 to 0.040 min (at 60 degrees C). Both processing plant i solates were more heat resistant than the ATCC strain. Decimal reducti on time curves (r(2) greater than or equal to 0.98) yielded z(D) value s of 5.02 to 5.59 degrees C, similar to those for other non-spore-form ing 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 cap ped test tube procedure (10 ml/tube). Cells heated in test tubes yield ed nonlinear (tailing) survivor curves and larger (P less than or equa l to 0.05) apparent D values at each temperature than those obtained u sing the ISCT method. This study provides the first thermal resistance data for AH in LWE and the first evidence that straight-line semiloga rithmic thermal inactivation kinetics may be demonstrated for Aeromona s using the ISCT procedure.