Survival of Escherichia albertii Following Exposure to Various Food Preservation Processes

Abstract

The enteric pathogen Escherichia albertii represents an emerging food safety challenge. It has been mistakenly identified as Hafnia alvei, Shigella, or as a member of the Enteropathogenic E. coli (EPEC). Isolates of certain strains of the organism are known to possess genes encoding pathogenesis factors capable of inducing attaching/effacing (A/E) lesions, cytolethal distending toxin and a variant Shiga toxin. The pathogen has been isolated from infants and adults and has been identified as a causative agent from an outbreak of foodborne disease occurring in an industrialized nation. Recent reports have detailed the ability of this pathogen to survive on ground beef and to resist several classes of therapeutic antibiotics. The objectives of this study were to: (i) determine the efficacy of E. albertii isolates to survive lactic acid exposure as a function of solution pH, and (ii) verify its inactivation in ground beef according to the USDA recommendations for in-home preparation.

Rifampicin resistant (RifR) isolates of E. albertii (ATCC 9194, 19982, 10457) were obtained according to published methods. Thermal resistance of parent and RifR isolates were compared in vitro at 55 °C to confirm no significant differences in tolerance to heat as a result of antibiotic resistance capacity. Tolerance to food grade lactic acid (Purac, Olathe, KS) (3.0% w/v) at differing pH levels (3.0, 4.0, 5.0, 7.0) was examined in physiological saline at 35 °C. Finally, ground beef patties (80% lean) inoculated with individual RifR isolates were cooked to internal temperatures of 62, 71, or 76 °C to determine resistance of different internal temperatures.

Experiments comparing the in vitro tolerances of parent and RifR E. albertii isolates indicated no differences between parent and mutant with regards to heat and lactic acid challenge. E. albertii inactivation in lactic acid increased as the pH of the solution was decreased; maximum reduction at pH 3.0 was at 30 min and maximum reduction for pH 4.0 at 2.5 hours. Changes in populations of E. albertii at pH 5.0 were not different than that at pH 7.0. Cooking of beef to 62 °C internal temperature produced reductions of all RifR isolates to non-detectable levels.