High-Level Heat Resistance of Spores of and Results from the Presence of a Operon in a Tn Transposon.

Bacterial endospore formers can produce spores that are resistant to many food processing conditions, including heat. Some spores may survive heating processes aimed at production of commercially sterile foods. Recently, it was shown that a operon, designated , present on a Tn transposon in , leads to profoundly increased wet heat resistance of spores. Such Tn transposon elements including the operon were also found in several strains of and , and these strains were shown to produce spores with significantly higher resistances to wet heat than their counterparts lacking this transposon. In this study, the locations and compositions of Tn transposons encompassing the operons in and were analyzed. Introduction of these operons into 168 (producing spores that are not highly heat resistant) rendered mutant 168 strains that produced high-level heat resistant spores, demonstrating that these elements in and are responsible for high level heat resistance of spores. Assessment of growth of the nine strains of each species between 5.2°C and 57.7°C showed some differences between strains, especially at lower temperatures, but all strains were able to grow at 57.7°C. Strains of and that contain the Tn elements (and produce high-level heat resistant spores) grew at temperatures similar to those of their Tn-negative counterparts that produce low-level heat resistant spores. The findings presented in this study allow for detection of and strains that produce highly heat resistant spores in the food chain.