Thermal Resistance of Francisella tularensis in Infant Formula and Fruit Juices

Abstract

Francisella tularensis is a gram-negative bacterium that can cause gastrointestinal or oropharyngeal tularemia from ingestion of contaminated food or water. Despite the potential for accidental or intentional contamination of foods with F. tularensis, little information exists on the thermal stability of this organism in food matrices. In the present study, the thermal resistance of the live vaccine strain of F. tularensis in four food products (liquid infant formula, apple juice, mango juice, and orange juice) was investigated. D-values ranged from 12 s (57.5°C) to 580 s (50°C) in infant formula with a z-value of 4.37°C. D-values in apple juice ranged from 8 s (57.5°C) to 59 s (50°C) with a z-value of 9.17°C. The live vaccine strain did not survive at temperatures above 55°C in mango juice and orange juice (>6-log inactivation). D-values at 55 to 47.5°C were 15 to 59 s in mango juice and 16 to 105 s in orange juice with z-values of 9.28 and 12.30°C, respectively. These results indicate that current pasteurization parameters used for destroying common foodborne bacterial pathogens are adequate for eliminating F. tularensis in the four foods tested. This study is the first to determine thermal inactivation of F. tularensis in specific foods and will permit comparisons with the thermal inactivation data of other more traditional foodborne pathogens.